Seven Bypasses: Tenets and Techniques for Revascularization [1 ed.] 2017050463, 2017050740, 9781626234840, 9781626234833

Table of contents :
Seven Bypasses: Tenets and Techniques for Revascularization
IFC
Title Page
Copyright
Dedication
Contents
Foreword
Foreword
Preface
Acknowledgments
Section I: Three Anastomoses
1 End-to-Side Anastomosis
2 Side-to-Side Anastomosis
3 End-to-End Anastomosis
Section II: Ten Tenets
4 Dexterity
5 Donors and Recipients
6 In the Zone
7 Cross Clamp
8 Arteriotomy
9 SuturingTechnique
10 Tissue Handling
11 Tightening and Knotting
12 Bypass Patency
13 Aneurysm Occlusion
Section III: Seven Bypasses
14 Extracranial-Intracranial Bypass
15 Extracranial-lntracranial Bypass with Interposition Graft
16 Reimplantation
17 In-Situ Bypass
18 Reanastomosis
19 Intracranial-Intracranial Bypass with Interposition Graft
20 Combination Bypasses
Section IV: Bypass Strategy
21 MCA Bypass Strategy
22 ACA Bypass Strategy
23 Basilar Artery Bypass Strategy
24 PICA Bypass Strategy
Section V Conclusion
Sugested Readings
Index

Citation preview

'Thieme

Seven Bypasses Tenets and Techniques for Revascularization

Michael T. Lawton, MD Professor of Neurological Surgery, Barrow Neurological Institute President and Chief Executive Officer, Barrow Neurological Institute Chairman, Department of Neurological Surgery Chief of Vascular and Skull Base Neurosurgery Programs Robert F. Spetzler Endowed Chair in Neurosciences St. joseph's Hospital and Medical Center Phoenix, Arizona

Illustrated by Kenneth xavier Probst, MA, CMI Medical Illustrator Department of Neurological Surgery University of California, San Francisco

Thieme New York • Stuttgart • Delhi • Rio de janeiro

Executive Editor: Timothy Hiscock Managing Editor: Sarah Landis Director, Editorial Services: Mary jo Cil.sey Production Editor: Barbara A. Chernow International Production Director: Andreas Schabert Editorial Director: Sue Hodgson International Marketing Director: Fiona Henderson International Sales Director: Louisa Turrell Director of Institutional Sales: Adam Bernacki Senior Vice President and Chief Operating Officer: Sarah Vanderbilt President: Brian D. Scanlan Typesetting by Cil.rol Pierson, Chernow Editorial Services, Inc.

Ubrary of Congress cataloging-in-PubUcation Data Names: Lawton, Michael T., author. Title: Seven bypasses : tenets and techniques for revascularization f Michael T. Lawton ; illustrated by Kenneth Xavier Probst. Description: New York: Thieme, (2018)1 Includes index. Identifiers: LCCN 2017050463 (print) I LCCN 2017050740 (ebook) I ISBN 9781626234840 I ISBN 97816262348331 ISBN 9781626234840 (eiSBN) Subjects: I MESH: Cerebral Revascularization-methods I Neurosurgical Procedures-methods 1Vascular Surgical Procedures-methods I Anastomosis, Surgical-methods Classification: LCC RD594.2 (ebook) I LCC RD594.2 (print) I NLM WL 355 I DDC 617.4/81-dc23 LC record available at https:lflccn.Ioc.govf2017050463

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To Suzanne, for your unwavering support, generosity, and love.

Contents

Foreword 'by' Ro'bert F. Spetzler .............................--..............,.,_......................- ..............,.,_........................................--..............,.,_..............

ix

Foreword 'by' Rokuya Tanikawa ···················--···········-···············-···········-····························--···········-··········

xi

Preface·········-························································---···········-························································---···········-····

xHi

Ackltowleclg111ents ·············-···············-···········---·······································-···············-···········---··················· xxix Section 1: Three Anastomoses

1 End-to-Side Anastomosis........................................................................................................................................

3

2 Side-to-Side Anastomosis....................................................................................................................................... 15 3 End-to-End Anastomosis........................................................................................................................................ 31 Section II: Ten Tenets

4 Dexterity...................................................................................................................................................................... 49 5 Donors and Recipients............................................................................................................................................. 60 6 In the Zone .................................................................................................................................................................. 72 7 Cross Clamp................................................................................................................................................................. 80 8 Arteriotomy................................................................................................................................................................. 93 9 SuturingTechnique ................................................................................................................................................... 105 10 Tissue Handling.......................................................................................................................................................... 125

11 Tightening and Knotting ......................................................................................................................................... 137 12 Bypass Patency ........................................................................................................................................................... 149 13 Aneurysm Occlusion................................................................................................................................................. 163 Section Ill: Seven Bypasses

14 Extracranial-Intracranial Bypass .......................................................................................................................... 171 15 Extracranial-lntracranial Bypass with Interposition Graft........................................................................... 236 16 Reimplantation........................................................................................................................................................... 282 17 In-Situ Bypass ............................................................................................................................................................. 326 18 Reanastomosis ............................................................................................................................................................ 377 19 Intracranial-Intracranial Bypass with Interposition Graft ........................................................................... 423 20 Combination Bypasses............................................................................................................................................. 520

Contents

Section IV: Bypass Strategy

21

MCA Bypass Strategy................................................................................................................................................ 597

22 ACA Bypass Strategy................................................................................................................................................. 609 23 Basilar Artery Bypass Strategy .............................................................................................................................. 617 24 PICA Bypass Strategy ................................................................................................................................................ 632 SectionV

Conclusion................................................................................................................................................................... 641 SUgested Readings ·········································--···········-···············-·········································--···········-········ 647 Ind-ex ···········-························································---···········-························································---···········-···· 653

viii

Foreword

In this era of multiauthor textbooks compiled by expert editors but written by residents and fellows, it is rare to have a series of books written by a single senior author with one voice, many insights, and a refined message. It is even rarer for such a series of books to become a classic in the library of every neurosurgeon. The Seven series by Michael T. Lawton belongs on the shelf of every neurosurgeon right next to Yasargil's volumes of Microneurosurgery. As with Seven Aneurysms and Seven AVMs, Seven Bypasses is instructive and beautifully written with precise prose. These books are a testament to the author's motivation and dedication to his topics. The countless hours required to produce such a thoughtful and marvelously illustrated treaty on bypasses, while having one of the most demanding clinical cerebrovascular practices in the country and overseeing laboratory investigations, has to have been a labor of love. As a result, we have another classic added to the list of required reading for every surgeon whose passion it is to be their very best. Although of particular interest to the cerebrovascular specialists, the operative pearls will benefit all of us who have the privilege to practice this wonderful specialty. Having trained Michael as a resident, I could not help but notice his dedication from the very start. I saw him sacrifice

so many hours above and beyond what was demanded; I watched him eagerly absorb the subtleties ofoperative neurosurgery and nuances of delicate decision-making; I found in him the core ethics required to properly counsel and advise our patients; and I helped him mature into one of the finest neurosurgeons of this generation. If the mark of a teacher is that his pupil surpasses the master, then I applaud myself! Furthermore, I am particularly grateful that Michael Lawton has returned to the Barrow Neurological Institute to assume the leadership in my place, so that this hallowed neurosurgical center will ascend to new heights with further gains in technical excellence, patient care, academic productivity, scientific research, and resident and fellow education. This trilogy-Seven Aneurysms, SevenAVMs, and now Seven Bypasses-represents the very best in neurosurgical publications and should be studied by every resident, fellow and neurosurgeon aspiring to be a cerebrovascular surgeon. It is with the greatest paternal professional pride that I applaud Michael Lawton on this magnificent collection. Robert F. Spetzler, MD Phoenix, Arizona

Foreword

Some may say that the future of bypass surgery looks bleak. Microanastomosis of intracranial arteries for ischemic conditions has been questioned since the negative results of international cooperative study of extracranial-intracranial bypass in 1985. The results of the Carotid Occlusion Surgery Study (COSS) again challenged the efficacy of microsurgical revascularization for this ischemic lesion. However, microanastomosis of intracranial arteries remains an important procedure which can save the patient's brain from an ischemic complication by intentional or accidental occlusion of the parent artery during intracranial aneurysm or tumor surgery. Therefore, I believe the future of bypass surgery looks bright, and textbooks like Seven Bypasses are needed to cultivate proficiency with these essential procedures. A high-flow bypass between the external carotid artery and the middle cerebral artery with an interposed radial artery or saphenous vein graft is a standard surgical procedure for large and giant aneurysms involving the cavernous segment of the internal carotid artery, enabling the proximal ligation of the cervical internal carotid artery. However, the advent of flow diverters has and will continue to decrease the use of bypass for these lesions to a small fraction of selected patients, such as those with a tortuous parent artery in which the flow diverter cannot be deployed safely. In contrast, low-flow bypass or small arterial microanastomosis will become increasingly important in the surgical treatment of distal intracranial aneurysms, because these aneurysms are more difficult to treat by flow diverters. A low-flow bypass between the superficial temporal artery or occipital artery to an intracranial artery is not easy without a sufficient education and training, because the size of the donors and recipients are relatively smaller than the cervical carotid artery or radial artery. Failed anastomosis of these bypasses causes immediate ischemia in the patient's

brain with dire consequences, and therefore bypass surgeons must learn the correct procedure and achieve high rates of bypass patency. A true expert neurosurgeon like Michael Lawton knows the right way to perform the perfect microanastomosis. And he knows the more important thing, which is the way to recover when challenges or complications arise. Dealing with a failed bypass is extremely difficult because of the intima of redpient and donor arteries is injured, the coagulation pathway is activated, and the surgeon feels frustrated and stressed. The microanastomosis must be performed all over again to salvage the bypass, which takes more time and greater care, with a lower chance of patency. This unwelcome complication exhausts us, and when it occurs in the evening or late at night, tests our fortitude. Recovering from a bypass complication or a failed microanastomosis reveals our attitude toward the patient and our craft. I always think that I love neurosurgery and especially love microanastomosis, but an accidental bypass occlusion can make me feel sick of performing microanastomosis. Therefore, I must learn to control my internal emotional condition to perform bypass surgery at the highest level and deal with unwelcome complications during the surgery. Bypass surgeons must learn the correct technique, skills, and anatomy, as well as the right attitude towards bypass surgery and bypass patients. Seven Bypasses describes in great detail the technique, skills, and anatomy for microanastomosis, but more importantly captures that correct attitude towards bypass surgery and bypass patients. I am certain the readers of this book will feel the philosophy and spirit of Professor Michael Lawton between the lines and amongst the pages, which will make them become better bypass surgeons. Rokuya Thnikawa, MD Sapporo, japan

Preface

The driver grips the BV75-3 needle firmly and hovers over a once bright red and pulsating arterial wall, now colorless, translucent, and still after cross-clamping the artery, cutting it open, and clearing it with a heparin flush. The No. 5 microforceps maneuvers into the arterial lumen and gently lifts the wall with its fine tips, presenting a smooth tissue plane to the needle like an offering. After surveying distances from the edge of the arteriotomy and from the last bite, the needlepoint contacts the arterial wall with precision spacing to line up a bite that pulls enough tissue into the anastomosis, but not so much that the parent artery is narrowed. As infinitesimal forces drive the needle forward and the wall backward, the needlepoint pierces the tissue with a haptic "pop" that transmits through the instruments, fires the fingertips' sensory receptors, and stimulates the faintest perception of a bite. The needle glides through the tissue until the driver meets the microforceps to fully consume the bite. The microforceps then exits the arterial lumen, gently lifts the second wall with its fine tips, and the cycle repeats. Another collision of infinitesimal forces and another haptic pop as the needle pierces and glides and bites. With a squeeze of the microforceps and a release of the driver, the driver circles around to counter-sweep the tissue off the back end of the needle and the needle completes its bite. Micromovements are the essence of bypass surgery. A bypass is born from these delicate actions during 20 or so critical minutes. The tedious steps are already completed: the donor has been harvested, the craniotomy is done, the recipient has been prepared, and the surgical stage has been set. During the next 20 minutes, a cycle of bites, needle grabs, counter-sweeps, and reloads repeats in a steady rhythm. The microscope's magnification and light intensity are dialed to their maximum and still the eyes strain to define the transparent tissues and follow the needle through its arc. Tension permeates these 20 minutes, having opened an artery and passed a "point of no return," sensing the ongoing brain ischemia and wondering whether the bypass will work. Muscles tighten under the weight of these thoughts, but the hands fight to stay loose and fluid and calm. The intense concentration needed to execute these micromovements almost stops the breathing. Sewing a bypass is almost a battle against one's own physiology and the limitations of equipment. As that battle rages, a beautiful spiral of continuous suture lengthens from one end of the arteriotomy to the other. Tightening this looping spiral seals the tissues with a

snug seam, and a knot secures the victory. There is a thrill that comes from joining two arteries in an anastomosis with the simplest of tools: suture, a few microinstruments, and a microscope. There is a thrill that comes from applying skill, dexterity, and determination to complete a challenging bypass. There is a thrill that comes from constructing something, rather than deconstructing something, in a place already so magnificent. Years ago, when 1 reached Malcolm Gladwell's milestone of 10,000 hours of practice needed to magically achieve mastery, I decided to write a book. I recognized that in the midst of this ongoing endovascular revolution that was diminishing open vascular neurosurgery worldwide, my surgical experience was unique and I had pearls to pass on to posterity. I envisioned a trilogy on aneurysms, AVMs, and bypasses that captured what I had learned and conveyed my passion for my three favorite operations. Together with Seven Aneurysms and Seven AVMs, Seven Bypasses completes that trilogy. Each book has its metaphor. In Seven Aneurysms, I analogized aneurysm clipping to ballet with choreographed steps progressing from subarachnoid dissection to proximal and distal control to aneurysm neck dissection to dip application. In Seven AVMs, its "angry twin," AVM resection is like a war with AVM types and subtypes to classify the enemy, strategic battle plans for each AVM, and a stepwise campaign progressing from exposure to subarachnoid dissection to identification of draining veins and feeding arteries to pial, parenchymal, and ependymal dissection to finally AVM resection. Now, in Seven Bypasses, the metaphor is architecture. Whether erecting a cathedral or a skyscraper, the structure is envisioned, the design is drawn, blue prints and models are developed, construction progresses, and finally the building is brought to life with plumbing, electricity, interior decoration, art, people, and activity. When performing a bypass, the arterial connections are envisioned; a bypass is designed based on the individual's anatomy; blue prints lay out the anastomotic sites, techniques, and conduits; the anastomoses are constructed; and finally the bypass is brought to life with pulsations, flow, and reperfusion. Bypass surgery stands apart from aneurysm dipping and AVM resection because it is constructive rather than deconstructive. Aneurysms and AVMs are beasts to be exposed, controlled, and obliterated, whereas bypasses are unusual creations requiring imagination and meticulous assembly.

Preface Puncture deflation of a well-clipped aneurysm and coagulation of the draining vein of a blue nidus are sweet neurosurgical victories, but neither can compare to the first pulsations of blood flow through a newly sutured anastomosis as the temporary clips are released. With aneurysms and AVMs, success is having avoided an intraoperative rupture or ischemic complication; with bypasses, success is having built something that did not exist before. I drive across the Golden Gate Bridge on my commute to work, and run or mountain bike the trails of the Marin headlands for my morning exercise. I watch the rising sun illuminate the graceful curves of the bridge's cables, the soaring height of its towers, the gentle arc of its truss, and its magnificent setting between mountains, strait, and San Francisco skyline. Even after seeing this engineering marvel almost daily for twenty years, it still awes me. Inspired architecture has the power to move people. Architecture moves people because it embodies cherished beliefs and bold ambitions with beams and bolts and stones. David Childs' One World Trade Center, or "Freedom Tower," in New York City, is a statement of American resilience after hijackers affiliated with al-Qjieda crashed two commercial airplanes into the North and South Towers on September 11, 2001, collapsing both buildings and killing 2,753 people. The new tower was erected from the ashes of that terrorist attack to become the tallest skyscraper in the Western hemisphere with 104 stories. jsrn Utzon's Sydney Opera House is a modern expressionist design that stacks precast concrete sections of a sphere or "shells" onto a podium supported by concrete piers sunk deeply into Sydney Harbor, creating a performing arts center that mimics sailboats nearby. Antoni Gaudi's Basilica of the Sagrada Familia in Barcelona is a Gothic and Art Nouveau treasure that combines elaborate facades and the tallest church spires in the world with his unique use of intersecting geometric forms, like ever-changing columnar surfaces, branched columns mimicking trees, and hyperbolic vaults forming the roof of the nave, crossing, and apse. Frank Gehry produced a daring contemporary design in the Guggenheim Museum in Bilbao, Spain, that has exterior curves that undulate randomly, with a cloak of reflective titanium panels reminiscent of fish scales, and large windows that let in the estuary and hills of the surrounding Basque country. All of these architectural masterpieces combine function and unique fonn, creating the desired shelter or space but also expressing the ideas and philosophies of the architect in ways that inspire those who observe or inhabit the building. Bypass surgery can be viewed similarly. Bypasses function as conduits that replace lost flow, either from underlying disease or deliberate arterial sacrifice, and they restore vital circulation to the brain. However, their form varies widely from a simple STA-MCA bypass to a complex sideto-side anastomosis between two M2 segments of the MCA. As with architecture, the neurosurgeon's choices reflect an aesthetic or a philosophy. Bypasses fall into categories of

xiv

complexity ranging from extracranial-to-intracranial {EC-IC) bypasses with scalp arteries to combination bypasses, such as the double reimplantation technique that implants two branch arteries onto an interposition graft already connected to its donor artery (Table P.t). This book discusses the fundamentals of microsurgical anastomosis and the spectrum of bypass surgery, but highlights my aesthetic and preference for intracranial-to-intracranial (IC-IC) bypasses and arterial reconstruction. IC-IC bypasses are alternatives to traditional EC-IC bypasses that reanastomose parent arteries, reimplant efferent branches, revascularize efferent branches with insitu donor arteries, and reconstruct bifurcated anatomy with interposition grafts that are entirely intracranial. These newer bypasses represent an evolution in bypass surgery from using scalp arteries and remote donor sites in the neck toward a more local and reconstructive approach. The title Seven Bypasses comes from these categories of bypasses: (1) EC-IC bypass, (2) EC-IC interpositional bypass, (3) intracranial arterial reimplantation, {4) in-situ bypass, (5) arterial reanastomosis, (6) IC-IC interpositional bypass, and (7) combination bypasses. Since finding comparable bypass patency rates and patient outcomes in my IC-IC and EC-IC bypass patients, I have adopted a practice that seeks opportunities to utilize the IC-IC bypass and express my reconstructive aesthetic (Table P.2). The EC-IC bypass still comprises 70% of my bypass experience, largely because of the broad indications and versatility of STA-MCA bypass. However, I have come to favor the IC-IC bypass because of its beauty and utility, and because it makes bypass surgery less invasive by sparing the patient additional incision sites in the neck, extracranial harvests of donor arteries, and tunneled grafts. These IC-IC bypasses and reconstructive techniques are the modem state of the art. just as imaginative architects conceive unique designs for their next project, bypass surgeons innovate new reconstructions. Creative inspiration and daring anastomosis may join two arteries that have never been joined before. The azygos ACA bypass, the SCA-PCA bypass, and the ATA-SCA bypass are some of my innovations. I enjoy reading others' innovations that I never thought of, such as Robert Spetzler's "figure of 8" anastomosis, Peter Vajkoczy's STA-ACA bypass with Y-shaped radial artery interposition graft, and Tanikawa's combined pericallosal-pericallosal and callosomarginalcallosomarginal bypasses. I have conceived of dozens of new bypasses that I have yet to do because the right patient with the right lesion and the right indication has not presented. My laboratory busily explores new ways to reconnect arteries that shorten grafts, simplify exposures, or solve a difficult aneurysm. Detractors say that nothing is new in open vascular neurosurgery and that the specialty is fully matured, but bypass surgery debunks this notion. Vascular neurosurgery will expand in ways unchallenged by endovascular devices as bypass surgeons hone their skills and express artistry in their bypass designs. Therefore, bypass surgery is

Table P.1

Summary of Seven Bypasses and Their Characteristics Number

Generation

Donors

Recipients

Craft

No. of Anastomoses

Anastomosis 1

Anastomosis 2

Flow

Surgical Sites

Tunnel

EC-IC bypass

1

1st

Scalp arteries (STA, OA)

No

1

E·S

NA

Low

1

No

EC-IC interpositional bypass

2

2nd

Long

2

E·S, E-E

E-S, E-E

High

3

Yes

Rei mplantation

3

3rd

Cervical carotid artery (ECA, CCA, ICA) MCA, ACA, PCA/SCA, PICA/VA

MCA,ACA, PCAJSCA, PICA/AICA MCA,ICA, PCA/SCA

No

1

E-S

NA

Low

1

No

In-situ bypass

4

3rd

No

1

S-S

NA

Low

1

No

Rl!anastomosis

5

3rd

No

1

E-E

NA

Low

1

No

IC-IC interpositional bypass

6

3rd

MCA, ACA, PCA/SCA, PICA, ICA, IMA, VA

Short

2

E-S, E-E

E-S, E-E

Medium

2

No

Combination bypass

7

3rd

Scalp arteries, cervical carotid arteries, MICA, ACA, PCA/SCA, PICA, ICA, IMA, VA

MCA,ACA, PCAJSCA, PICA MCA,ACA, PCA/SCA, PICA MCA,ACA, PCA/SCA, PICA MCA,ICA, ACA, PCA/SCA, PICA/AICA MCA,ACA, PCA/SCA, PICA/AICA

Variable

:!:2

E-S, S-S, E-S

E-S, S-S, E-S

Mixed

Variable

Variable

Bypass

MCA, ACA, PCA/SCA, PICA/AICA -

MCA, ACA, PCA/SCA, PICA

""1:1

n;

,.,iit' ~

(1)

Preface Table P.2 Summary of Seven Bypass Types Performed by the Author During a 20..Year Experience Type EC-IC Bypass EC-IC interpositional bypass Reimplantation In-situ bypass Reanastomosis IC-IC interpositional bypass Combination bypass Total

MCA

313 56 6 4 11 14 46 450

PCAJSCA

ACA

96% 97% 29% 17% 31% 40% 87% 82%

1 0 3 7 2 5 3 21

0%

10

0% 14%

2

29%

2

6% 14% 6% 4%

3 14 2 34

an art not only because suturing arteries is a majestic performance, but also because established anastomoses can be applied in fresh ways to devise new bypasses. The first section of this book describes a stepwise approach to the three anastomoses that are the building blocks of all bypasses: ( 1) the end-to-side anastomosis, (2) the sideto-side anastomosis, and (3) the end-to-end anastomosis. Although most textbooks discuss the plumbing of bypass surgery, they skimp on the technical nuances that are covered here in the tenets in the second section: dexterity, preparing the donor and recipient arteries, establishing a working zone, temporary arterial occlusion, arteriotomy, suturing technique, tissue handling, knot tying, patency, and aneurysm occlusion. In architecture, the temple is built only if the design conceived in the architect's mind is captured on blue prints for the construction crew. Elaborate symbols for floor plans, windows and doors, kitchen appliances, plumbing fixtures, and electrical wiring translate the architect's vision into a working plan. Symbols for bypass surgery would be equally helpful in translating the surgeon's ideas to the operating room, yet surprisingly none exist. Therefore, Seven Bypasses introduces a system of symbols representing anastomosis techniques, interposition grafts, seven bypass types, and aneurysm occlusions (Fig. P.t). The seven bypasses are demonstrated in the third section, with case examples using these symbols and schematics to show the variety of reconstructions for a wide range of pathology in four main bypass locations: the middle cerebral artery ( MCA), anterior cerebral artery (ACA), posterior cerebral artery (PCA)/superior cerebellar artery {SCA), and posterior inferior cerebellar artery (PICA). In addition to symbols and schematics, in an effort to improve our current nomenclature and discourse, Seven Bypasses applies a more precise language or code for bypasses based on segmental anatomy of arteries. Arteries have abbreviations (Table P.3), their segments have alphanumerics (Table P.4), and their combination specifies anastomotic sites. For example, by adding the segmental address of the anastomosis in an STA-MCA bypass, language becomes more informative, and an STA-M2 MCA bypass to an efferent trunk

xvi

1

PICA

3% 3% 5% 8% 9% 40% 4% 6%

2 0 11 11 19 2 2

47

Total

1% 0% 52% 46% 54% 6% 4% 9%

326 58 21 24

35 35 53 552

59% 11% 4% 4% 6% 6% 10%

of a MCA aneurysm is differentiated from an STA-M4 MCA bypass to a cortical recipient in a moyamoya patient. Similarly, segmental descriptions of posterior circulation bypasses, like the STA-SCA bypass, clarify important technical nuances, such as whether the anastomosis is performed subtemporally on the lateral pontomesencephalic segment (STA-s2 SCA bypass) or pretemporally on the distal anterior pontomesencephalic segment (STA-sl SCA bypass). The PICA-PICA in-situ bypass is clarified when described as a left p3 PICA-right p3 PICA bypass, and so is the PICA reimplantation when described as a p2 PICA-V4 VA reimplantation. This alphanumeric code provides quick shorthand for more detailed schematics or bypass "blueprints." The case examples in the third section apply these segmental descriptions to sharpen the nomenclature of bypasses (Table P.5). With this expansive view of bypass surgery and so many EC-IC and lC-IC options, selecting the best bypass and treatment strategy can be challenging. In the fourth section, algorithms are presented to clarify bypass choices for aneurysms and other pathology in the four key anatomic locations: the MCA and the Sylvian cistern; the ACA and the interhemispheric cistern: the basilar artery and the basal cisterns (interpeduncular, ambient, and crural cisterns); and the PICA and the cisterna magna. Aneurysms are first classified based on regional or segmental anatomy, and these distinctions then guide decisions (Table P.S). For example, bypass selection for MCA aneurysms depends on their location relative to the MCA bifurcation (pre-bifurcation, bifurcation, or post-bifurcation), and similarly for ACA aneurysms {precommunicating, communicating, and post-communicating). As will be shown, bypass strategy is often dictated by these classifications. Abbreviations for veins and venous sinuses are defined in (Table P.&) and abbreviations for brain, nerves, and cisterns, as well as miscellaneous abbreviations are defined in (Table P.7). Bypass surgery is a sport that is difficult to capture with still photographs. However, Ken Probst's spectacular illustrations depict these elusive nuances and ideas with details and perspectives that are missed even by videos. Ken's illustrations are drawn from my photograph collection and crude

Preface LEGEND

...--= .,- ...

Anastomosis

Circulation

~""IIICJ

~I~

~

End-to-End

~ Skull base foramen c!:;>--- (EC-IC transition)

\

...

Side-to-Side

Extracranial (EC) --------{round end =vessel continues) lnterpositional Grafts

~G - Saph~o"'

\

Vel" G""'

{flat end = vessel transacted) (nigh flow arrow) Aneurysm Occlusion Scalp Artery (e.g., superficial temporal artery)

Aneurysm trapping

(low flow arrow)

~

RAG -Radial Artery Graft Proximal occlusion

Distal occlusion

Diagnoses Aneurysm {untreated)

Occluded Artery

.

-Blood flow-

,,......... --.,.

Optional dip placement Moyamoya Disease

Stenosis of IC Artery

' ... '

Dolichoectatic IC Artery

Occlusion of IC Artery

Ocdusion Devices

Fig. P.1

Excised aneurysm (flat end = vessel transacted)-------

Treatments Thrombectomy

\

Stent

Combined

\

\

\

\

\ \

\

'. Thromboendarterectomy

System of symbols for bypass schematics. (continued on page xvii1)

xvii

Preface Middle Cerebral Artery Bypass Schematic

rug~~~

Anterior Cerebral Artery Bypass Schematic Right

Left

MCA ~----­

Segments ACA (A2

~CA

(A2)

STA!

Carotid Canal

~ t

t

Blood flow

Blood flow Blojflow

Basilar Artery Bypass Schematic Right

Posterior Inferior Cerebellar Artery Bypass Schematic Right

Left

I

Left

s BA OA

·coA

Segments

~

I

t

Blood flow

Ag. P.l (continued} System of symbols for bypass schematics.

xviii

Foramen Magnum

t

Blood flow

Preface Table P.3 Abbreviations for Arteries Abbreviation

Artery

ACA AChA ACrJA AICA AI FA An AngA AntParA AntSpA AntThaP

Anterior cerebral Anterior choroidal Anterior communicating Anterior inferior cerebellar Anterior internal frontal Aneurysm Angular Anterior parietal Anterior spinal Anterior thalamoperforators

Ao

Aorta

ASA AscPharA ATA BA CalcA CenA CirP CmaA FrPoiA HippoA ICA IMA lnWarA lnfrr lnsP LingA ILSA IPChA MCA MidTempA MidTr MIFA mlSA mPChA OA

Anterior spinal Ascending pharyngeal Anterior temporal Basilar Calcarine Central Grcumflex perforators Callosomarginal Frontopolar Hippocampal Internal carotid Internal maxillary Inferior parietal Inferior trunk of MCA Insular perforators lingual lateral lenticulostriate lateral posterior choroidal Middle cerebral Middle temporal Middle trunk of MCA Middle internal frontal Medial lenticulostriate Medial posterior choroidal Occipital

sketches that emerged from our countless hours of weekly meetings, and consequently, they depict a left-handed surgeon. Although most neurosurgeons are right-handed, illustrations are consistent with the left-handed intraoperative photographs throughout the book. When I study photographs and images of right-handed surgeons, I find that the extra effort needed to reorient spatially in my mind helps me to learn better, and I expect this process might also benefit the right-handed readers. If right-banders disagree, I offer my apologies in advance. Some neurosurgeons say that bypass surgery is a niche practice relevant only to a vanishingly small group of vascular neurosurgeons, which might discourage the reader or deter him or her from reading this book. Some would argue that the negative results of the Carotid Occlusion Surgery Study (COSS) and the advent of flow diverters further di-

Abbreviation OphA OrbFrA OrbFrA PAA ParaCenA ParOccA PCA PcaA PCoA PedP PICA PI FA Pas ParA PosTempA PosTempA PosThaP PreCenA PreFrA PSA RAH SCA SciA SHA SplenA STA SupParA SupThyrA SupTr TempOccA TempPoiA ThaP ThGenP TPA VA VBJ

Artery Ophthalmic Orbitofrontal (ACA) Orbitofrontal (MCA) Posterior auricular Paracentral Parieto-occipital Posterior cerebral Pericallosal Posterior communicating Peduncular perforators Posterior inferior cerebellar Posterior internal frontal Posterior parietal Posterior temporal (MCA) Posterior temporal (PCA) Thai amoperforators Precentral Prefrontal Posterior spinal Recurrent of Heubner Superior cerebellar Subclavian Superior hypophyseal Splenial Superfi~;ial temporal Superior parietal Superior thyroid Superior trunk of MCA Temporo-occipital Temporopolar Thai amoperforators Thai amogeniculate perforators Temporopolar Vertebral Vertebrobasilar junction

minish the relevance of bypass surgery. However, I believe that proficiency in bypass surgery remains essential because when conventional clipping or coiling techniques fail, or even when the latest endovascular devices fail due to broadbased aneurysm anatomy, intraluminal thrombus, giant size, or a sidewall branch, arterial reconstruction usually offers a solution. Furthermore, the complications in the operating room that unnerve neurosurgeons are arterial injuries with uncontrolled bleeding. A tumor neurosurgeon might damage an artery that adheres to the backside of a meningioma hidden from view, or a spine neurosurgeon might injure the vertebral artery drilling laterally during a corpectomy. Agility in handling arteries and controlling bleeding with temporary clips helps manage the crisis, and repairing the arterial injury might require suturing the artery or performing a bypass. Bypass proficiency is the critical skill needed to

xix

Preface Table P.4 Abbreviations for Arterial Segments Abbreviation (1

(2 C3 (4 (5

(6 C7 A1

A2 A3 A4

A5 M1 M2 M3 M4

P1 P2 P2A P2P

P3 P4 s1 s2 53 s4

a1 a2 a3

a4

p1 p2 p3 p4 p5

V1 V2 V3 V4

XX

Arterial Segment ICA, cervical ICA, petrous ICA,Iacerum ICA, cavernous ICA, dinoidal ICA, ophthalmic ICA, communicating ACA, precommunicating or horizontal ACA, postcommunicating or infracallosal ACA, precallosal ACA, supracallosal ACA, postcallosal MCA, sphenoidal MCA, insular MCA, opercular MCA, cortical PCA, precommunicating PCA, postcommunicating PCA, crural PCA, ambient PCA, quadrigeminal PCA, calcarine SCA, anterior pontomesencephalic SCA, lateral pontomesencephalic SCA, cerebellomesencephalic SCA, cortical AICA, anterior pontine AICA,Iateral pontine AICA, flocculopeduncular AICA, cortical PICA, anterior medullary PICA, lateral medullary PICA, tonsillomedullary PICA, telovelotonsillar PICA, cortical VA, pre-foramina I VA, foramina! VA, extradural VA, Intradural

deal with these catastrophes and therefore it breeds confidence. Competencies that instill confidence in the operating room are worth developing, no matter what subspecialty one practices. Architectural critics hail new buildings for their inspired design and imaginative forms, and functionality is almost assumed. However, the building's inhabitants notice something more: the fine details, the finishing touches, the look and feel of the materials, the way the light fills the rooms, and the quality of the construction. More than form and function, craftsmanship transforms a dwelling into a home and imbues its ambiance. Similarly with bypass surgery, the regularity of the stitches, the precision spacing of bites, the pristine condition of the arterial walls, the fullness of the anastomosis, and the robust pulsations of the bypass all display the surgeon's craftsmanship. Seven Bypasses is meant to be more than just another book about arterial plumbing: it is about the many elements that give a bypass its aesthetic and the elements that make the bypass surgeon a true craftsman. This book analyzes the craft in exquisite detail to capture this high art and transmit it to the next generation of neurosurgeons. The golden era of bypass surgery is long gone and its masters are vanishing from the field. Few neurosurgeons have amassed the experience needed to become master craftsmen. Seven Bypasses is my distillation of over 500 bypass operations into lessons and pearls to prepare future generations of bypass surgeons. As with architecture, we cannot construct masterpieces that express our creativity and push boundaries without first becoming master craftsmen. This book is meant to develop craftsmen and also proclaim that creative innovation, manual dexterity, technical prowess, and attention to fine details still matter in vascular neurosurgery, even as it drifts further and further toward endovascular technology, radiosurgery, and minimally invasive alternatives. The master pianist Vladimir Horowitz once said to his pupil Murray Perahia, himself one of the greatest living pianists, "If you want to be more than a virtuoso, first be a virtuoso." Seven Bypasses is meant to first develop virtuoso bypass surgeons, and then encourage neurosurgical masterpieces.

Preface Table P.5 Alphanumeric codes for Bypasses In case Examples (Section Ill) case Number Case 14.1 Case 14.2 Case 14.3 Case 14.4 Case 14.5 Case 14.6

Case 14.7 Case 14.8

Diagnosis Left M2 MCA stenosis Left moyamoya disease Left MCA aneurysm (dolichoectatic) Right MCA aneurysm (giant serpentine) Left MCA aneurysms (dolichoectatic) Cerebral arteriopathy (ACTA2 gene mutation) Vertebrobasilar ischemia Left PCA aneurysm (giant)

Aneurysm Classification

Craniotomy/Approach

Alphanumeric Bypass Name

Bypass Type

NA NA

Frontotemporal craniotomy Frontotemporal craniotomy

LSTA-M4MCA LSTA-M4MCA

EC-IC EC-IC

MCA bifurcation

pterional craniotomy/ transsylvian approach pterional craniotomy/ transsylvian approach pterional craniotomy/ transsylvian approach Bifrontal craniotomy/ interhemispheric approach

LSTA-M2 MCA

EC-IC

RSTA-M4 MCA

EC-IC

L STA-M2 MCA+M2 MCAdouble barrel L STA-PM-AIFA

Combination

7

Combination

7

R STA-P2A PCA

EC-IC

L STA-P2P PCA

EC-IC

L OA-a3 AICA and R p3 PICA reanastomosis R OA-M4 MCA and R STA-M4 MCA ROA-a3AICA

Combination

7

Combination

7

EC-IC

LSTA-M4MCA

EC-IC

L ECA-RAG-M2 MCA

EC-IC interpositional Combination

MCA post-bifurcation (Sylvian) MCA post-bifurcation (insular) NA

NA Basilar postquadrifurcation (PCA) Basilar prequadrifurcation

Orbitozygomatic craniotomy/ transsylvian approach Orbitozygomatic craniotomy/ transsylvian-subtemporal approach Extended retrosigmoid craniotomyftranscerebellopontine approach Parietal and pterional craniotomies Extended retrosigmoid craniotomyftranscerebellopontine approach Pterional craniotomy

Case 14.9

Basilar trunk aneurysm (giant)

Case 14.10

Right moyamoya disease Vertebrobasilar ischemia

NA

Case 14.12

Left moyamoya disease

NA

Case 15.1

Left MCA ocd usion

NA

Case 15.2

Right cavernous ICA aneurysm (giant)

Cavernous ICA

Case 15.3

Basilar apex aneurysm and Takayasu's arteritis Left PCoA aneurysm (thrombotic) Left supraclinoid ICA aneurysm (giant) Vertebrobasilar ischemia

Basilar quadrifurcation

Orbltozygomatic craniotomy/ transsylvian approach

Supraclinoid ICA

Case 15.7

Obliterative arteritis

NA

pterional craniotomy/ transsylvian approach Orbitozygomatic craniotomy/ transsylvian approach Extended retrosigmoid craniotomyftranscerebellopontine approach Sternotomy

Case 16.1

Right MCA aneurysm (mycotic) Right MCA aneurysm (fusiform)

MCA bifurcation MCA post-bifurcation (Sylvian)

pterional craniotomy/ transsylvian approach Pterional craniotomy/ transsylvian approach

RightACA aneurysm (dolichoectatic)

ACA post-communieating (A3 ACA)

Bifrontal craniotomy/anterior interhemispheric approach

Case 14.11

Case 15.4 Case 15.5 Case 15.6

Case 16.2

Case 16.3

NA

Supraclinoid ICA NA

Pterional craniotomy/ transsylvian approach Pterional craniotomy/ transsylvian approach

R CCA-RAG-M2 MCA and RCCA-SVG-M2 MCA L subclavian-SVGM2MCA

Number

2 7

EC-IC Interpositional

2

EC-IC interpositional EC-IC interpositional EC-IC interpositional

2

L Ao-AIIoSVG-CCA

EC-EC interpositional

2

RM2MCA-ATA reimplantation R M2 MCA-M2 MCA reimplantation and R CCA-RAG-M2 MCA RA3 ACA-L AI FA reimplantation

Reimplantation

3

Combination

7

Combination

7

L CCA-AIIoSVG-C7 ICA L C1 ICA-RAG-C7 ICA L OA-RAG-a3 AICA

2 2

(continued)

xxi

Preface Table P.5 (continued) Alphanumeric codes for Bypasses in case Examples (Section Ill) Case Number Case 16.4

Aneurysm Classification

Craniotomy/Approach

Alphanumeric: Bypass Name

Bypass Type

Number

Rei mplantation

3

Combination

7

Reimplantation

3

R p1 PICA-V4 VA reimplantation

Reimplantation

3

L p1 PICA-V4 VA reimplantation and p1 PICA-p1 PICA reanastomosis R p1 PICA-L p3 PICA contralateral reimplantation

Combination

7

Reimplantation

3

RightACA aneurysm (dolichoectatic) Left SCA aneurysm (dolichoectatic)

ACA post-communieating (A3 ACA) Basilar postquadrifurcation (SCA)

Bifrontal craniotomy/anterior interhemispheric approach Orbitozygomatic craniotomy/ transsylvian approach

Case 16.6

Right VA/PICA aneurysm

PICA, anterior medullary

Case 16.7

Right VA/PICA aneurysm (dissection) Left VA/PICA aneurysm (dissection)

PICA, anterior medullary

Far lateral craniotomy/ transcerebellomed ullary approach Far lateral craniotomy/ transcerebellomed ullary approach Far lateral craniotomy/ transcerebellomed ullary approach

Case 16.9

Right VA/PICA aneurysm

PICA, anterior medullary

Far lateral craniotomy/ transcerebellomed ullary approach

Case17.1

Left MCA aneurysm (dolichoectatic) Right MCA aneurysm (thrombotic) Left ACA aneurysm (pseudoaneurysm) and meningioma

MCA post-bifurcation (Insular) MCA post-bifurcation (Insular) ACA post-communieating (A2 ACA)

L M3 MCA-MJ MCA in situ R M3 MCA-M3 MCA in situ RA3 ACA-L A3 ACA in situ

In situ

4

In situ

4

In situ

4

Case 17.4

ACoA aneurysm (serpentine)

RA3 ACA-L A3 ACA in situ

In situ

4

Case 17.5

Left ACA aneurysm (fusiform) Right PCA aneurysm (pseudoaneurysm) Left PICA aneurysm (fusiform)

ACA communicating (with unilateral A2 occlusion) ACA post-communieating (A4 ACA) Basilar post-quadrifurcation (PCA) PICA, anterior medullary

Pterional craniotomy/ transsylvian approach Pterional craniotomy/ transsylvian approach Extended bifrontal craniotomy/anterior interhemispherictranssylvian approach Bifrontal craniotomy/anterior interhemispheric approach

L CmaA-R CmaA in situ s1 SCA-P2 PCA in situ

In situ

4

In situ

4

R p3 PICA-l p3 PICA in situ

In situ

4

Case 17.8

Right PICA aneurysm (thrombotic)

PICA, anterior medullary

L p3 PICA-R p3 PICA in situ

In situ

4

Case 17.9

Left basilar trunk aneurysm

Basilar prequadrifurcation

Bifrontal craniotomy/anterior interhemispheric approach Orbitozygomatic craniotomy/ transsylvian approach Far lateral craniotomy/ transcerebellomed ullary approach Far lateral craniotomy/ transcerebellomed ullary approach Far lateral-retrosigmoid craniotomyftranscerebellomedullary approach

L V4 VA-a3 AICA in situ

Combination

7

Case 18.1

Right MCA aneurysm MCA pre-bifurcation (thrombotic) Left MCA aneurysm MCA bifurcation (giant, thrombotic) Right MCA aneurysm MCA post-bifurcation (thrombotic) (Sylvian) Right MCA aneurysm MCA post-bifurcation (dolichoectatic) (opercular) ACA post-communiLeft ACA aneurysm (pseudoaneurysm) eating (AJ ACA)

RM1 MCA reanastomosis L M1 MCA-M2 MCA reanastomosis RM2MCA reanastomosis RM3MCA reanastomosis LA3ACA reanastomosis

Reanastomosis

5

Reanastomosis

5

Reanastomosis

5

Reanastomosls

5

Reanastomosis

5

Case 16.5

Case 16.8

Case 17.2 Case 17.3

Case 17.6 Case 17.7

Case 18.2 Case 18.3 Case 18.4 Case 18.5

xxii

Diagnosis

PICA, anterior medullary

Pterional craniotomy/ transsylvian approach Pterional craniotomy/ transsylvian approach Pterional craniotomy/ transsylvian approach Pterional craniotomy/ transsylvian approach Bifrontal craniotomy/anterior interhemispheric approach

R PcaA-R CmaA reimplantation LATA-s1 SCA reimplantation and LATA reanastomosis R p1 PICA-V4 VA reimplantation

Preface

Diagnosis

Aneurysm Classification

Case 18.6

Left PICA aneurysm (dissection)

PICA, lateral medullary

Case 18.7

Left PICA aneurysm (dissection)

PICA, lateral medullary

Case 18.8

Left PICA aneurysm (dissection)

PICA, lateral medullary

Case 18.9

Right PICA aneurysm (dissection)

PICA, lateral medullary

Case 18.10

Left PICA aneurysm (dolichoectatic)

PICA, tonsillomedullary

Case 18.11

Right PICA aneurysm (dolichoectatic)

PICA, telovelotonsillar

Case 19.1

Left cavernous ICA aneurysm (giant)

Cavernous ICA

Case 19.2

Right supradinoid ICA aneurysm (Blister) RightMCA aneurysm (giant dolichoectatic) Right MCA aneurysm (giant thrombotic) Right MCA aneurysm (giant recurrent) Left MCA aneurysm (dolichoectatic recurrent) Right MCA aneurysm (mycotic) RightACA aneurysm (dissection)

Supradinoid ICA

case Number

Case 19.3

Case 19.4 Case 19.5 Case 19.6

Case 19.7 Case 19.8

Case 19.9 Case 19.10

Case 19.11

Case 19.12

Case 19.13

RightACA aneurysm (mycotic) Basilar trunk aneurysm (dolichoectatic) Basilar trunk aneurysm (dolichoectatic) Basilar trunk aneurysm (giant recurrent) Right VA aneurysm (dissection)

Craniotomy/Approach Far lateral craniotomy/ transcerebellomed ullary approach Far lateral craniotomy/ transcerebellomed ullary approach Far lateral craniotomy/ transcerebellomed ullary approach Far lateral craniotomy/ transcerebellomed ullary approach Far lateral craniotomy/ transcerebellomed ullary approach Far lateral craniotomy/ telovelar approach

Alphanumeric Bypass Name

Bypass Type

Number

Lp2 PICA reanastomosis

Reanastomosis

5

Lp2 PICA reanastomosis

Reanastomosis

5

Lp2 PICA reanastomosis

Reanastomosis

5

Rp2 PICA reanastomosis

Reanastomosis

5

Lp3 PICA reanastomosis

Reanastomosis

5

Rp4PICA reanastomosis

Reanastomosis

5

Orbitozygomatic craniotomy/ anterior transpetroustranssylvian approach Pterional craniotomy/ transsylvian approach

L C2 ICA-SVG-C6 ICA

IC-IC interpositional

6

R C6 ICA-RAG-M2 MCA

IC-IC interpositional

6

MCA pre-bifurcation

Orbitozygomatic craniotomy/ transsylvian approach

R M1 MCA-RAG-M1 MCA

IC-IC interpositional

6

MCA bifurcation

Orbital-pterional craniotomy/ transsylvian approach Orbltal-pterional craniotomy/ transsylvian approach Orbital-pterional craniotomy/ transsylvian approach

R M1 MCA-RAG-M2 MCA R M2 MCA-RAG-M4 MCA L A1 ACA-RAG-M2 MCA and STA-M2 MCA R IMA-RAG-M2 MCA

IC-IC interpositional IC-IC interpositional Combination

6

MCA post-bifurcation (Sylvian) MCA bifurcation

MCA bifurcation ACA pre-communicating ACA post-communieating (A2 ACA) Basilar pre-quadrifurcation Basilar prequadrifurcation Basilar prequadrifurcation

PICA, anterior medullary

Pterional craniotomy/ transsylvian approach Orbital-pterional craniotomy/ transsylvian approach

RATA-SVG-A1 ACA

6 7

IC-IC interpositional IC-IC interpositional

6 6

Bifrontal craniotomy/anterior interhemispheric approach Orbitozygomatic craniotomy/ transsylvian approach

RA2 ACA-RAG-A3 ACA R M2 MCA-RAG-P2 PCA

IC-IC interpositional IC-IC interpositional

6

Orbitozygomatic craniotomy/ transsylvian approach

R M2 MCA-SVG-P2 PCA

IC-IC interpositional

6

Orbitozygomatic-retrosigmold craniotomy/ transsylvian-cerebellopontine approach Far lateral craniotomy/ transcerebellomed ullary approach

R M2 MCA-SVG-P2 PCA

IC-IC interpositional

6

RV3 VA-RAG-p3 PICA

IC-IC interpositional

6

6

(continued)

xxiii

Preface Table P.5 (continued) Alphanumeric codes for Bypasses in case Examples (Section Ill) Case Number

Aneurysm Classification

Craniotomy/Approach

Case19.14

Vertebrobasilar ischemia

NA

Case 19.15

Basilar trunk aneurysm (dolichoectatic)

Basilar pre-quadrifurcation

Case 19.16

Left carotid occlusion and neck carcinoma

NA

Case 20.1

Left MCA aneurysm (giant thrombotic)

MCA bifurcation

Pterional craniotomy/ transsylvian approach

Case20.2

Right MCA aneurysm (dolichoectatic)

MCA bifurcation

Orbital-pterional craniotomy/ transsylvian approach

Case20.3

Right MCA aneurysm (recurrent)

MCA bifurcation

Orbital-pterional craniotomy/ transsylvian approach

Case 20.4

Right MCA aneurysm (giant)

MCA bifurcation

Orbital-pterional craniotomy/ transsylvian approach

Case20.5

RlghtACA aneurysm (giant mycotic)

ACA post-communieating (A3 ACA)

Blfrontal craniotomy/anterior interhemispheric approach

Case20.6

ACoA aneurysm (giant thrombotic)

ACA communicating (with unilateral A2 occlusion)

Case20.7

Right MCA aneurysm (thrombotic)

MCA post-bifurcation (Sylvian)

Orbital-pterional-bifrontal craniotomyftranssylvia nanterior interhemispheric approach Pterional craniotomy/ transsylvian approach

Case20.8

Left MCA aneurysm (dolichoectatic recurrent) Left MCA aneurysm (giant dolichoectatic) Basilar trunk aneurysm and right PICA aneurysm Left moyamoya disease Right supraclinoid ICA occlusion

MCA post-bifurcation (Sylvian)

Pterional craniotomy/ transsylvian approach

MCA pre-bifurcation

Orbltal-pterional craniotomy/ transsylvian approach

Basilar pre-quadrifurcation and PICA, tonsillomedullary

Extended retrosigmoid craniotomyftranscerebellopontine approach

NA

Frontotemporal craniotomy

NA

Frontotemporal craniotomy

Case20.9

Case 20.10

Case 20.11 Case 20.12

xxiv

Diagnosis

Extended retrosigmoid craniotomy/transcerebellopontine approach Far lateral-temporal craniotomyftranscerebellomedullary-subtemporal approach Pterional craniotomy with suboccipital exposure/ transsylvian approach

Alphanumeric: Bypass Name

Bypass Type

Number

L V3 VA-SVG-a3 AICA

IC-IC interpositional

6

RV3 VA-SVG-s2 SCA

IC-IC interpositional

6

L V3 VA-RAG-M2 MCA

IC-IC interpositional

6

L ECA-SVG-M2 MCA (lnfrr)+M2 MCA (SupTr) double reimplantation RA1 ACA-RAG-M2 MCA (SupTr)+M2 MCA (lnfTr) double reimplantation RA1 ACA-RAG-M2 MCA (SupTr)+M2 MCA (lnfTr) double reimplantation RA1 ACA-SVG-M2 MCA (SupTr)+M2 MCA (lnfTr) double reimplantation RAI FA-RAG-CmaA+ PcaAdouble reimplantation R PcaA-RAG-L PcaA+L CmaAdouble reimplantation (Azygos bypass) M2MCA-AngA reanastomosis and PosParA-M2 MCA reimplantation STA-M4 MCA and M2 MCA-M3 MCA reanastomosis L M1 MCA-RAG-M2 MCA and STA-M2 MCA L OA-a3 AICA and R p3 PICA reanastomosis

Combination

7

Combination

7

Combination

7

Combination

7

Combination

7

Combination

7

Combination

7

Combination

7

Combination

7

Combination

7

Combination

7

Combination

7

L STA reanastomosis and STA-M4 MCA R STA reanastomosis and STA-M3 MCA

Preface case Number

Diagnosis

Aneurysm Classification

Craniotomy/Approach

Case20.13

Bilateral cavernous ICA aneurysms

cavernous ICA

Pterional craniotomies/ transsylvian approach

Case20.14

Bilateral cavernous ICA aneurysms

Cavernous ICA

Pterional craniotomies/ transsylvian approach

Case 20.15

Left MCA occlusion

NA

Pterional craniotomy/ transsylvian approach

Case 20.16

Right PCoA aneurysm

Supraclinoid ICA

Pterional craniotomy/ transsylvian approach

Alphanumeric Bypass Name R CCA-RAG-M2 MCA and LCCARAG-M2 MCA R CCA-SVG-M2 MCA and L ICA-SVG-M2 MCA L STA-M4 MCA and thromboendarterectomy Thromboendarterectomy

Bypass Type

Number

Combination

7

Combination

7

Combination

7

Combination

7

Table P.6 Abbreviations for Veins and Sinuses Abbreviation AHemV AntCalcV AntFrV AntParV AntTempV AtrV BVR CauV CavS CenV ChorV DeepSylV FrPoiV FrSyiV HippoV ICV

IHemV IJV IPetrV IPS ISS IVerV Labbe LAMedV LAPonMesV LMedV LMesV MAMedV MAPonMesV MedFrV MedParV MedTempV MidFrV MidTempV MPMedV OccBasV

Vein

Type

Anterior hemispheric Anterior calcarine (internal occipital) Anterior frontal Anterior parietal Anterior temporal Atrial (medial, lateral) Basal of Rosenthal Caudate (anterior, posterior) Cavernous sinus Central Choroidal (superior, inferior) Deep Sylvian Frontopolar Frontosylvia n Anterior hippocampal Internal cerebral Inferior hemispheric Internal jugular Inferior petrosal Inferior petrosal sinus Inferior sagittal sinus Inferior vermian Vein of Labbe Lateral anterior medullary Lateral anterior pontomesencephalic Lateral medullary Lateral mesencephalic Median anterior medullary Median anterior pontomesencephalic Medial frontal (anterior, central, posterior) Medial parietal (anterior, posterior) Medial temporal Middle frontal Middle temporal Median posterior medullary Occipital basal

Cerebellum Parieto-occipitallobes Frontal lobe Parieto-occipitallobes Temporal lobe Deep Temporal lobe Deep Sinus Frontal lobe Deep Frontal lobe Frontal lobe Frontal lobe Temporal lobe Deep Cerebellum Cervical Cerebellum Sinus Sinus Cerebellum Temporal lobe Brainstem Brainstem Brainstem Bralnstem Brainstem Brainstem Frontal lobe Parieto-occipitallobes Temporal lobe Frontal lobe Temporal lobe Brainstem Parieto-occipitallobes

(continued)

XXV

Preface

Table P.6 (continued) Abbreviations for Veins and Sinuses Abbreviation OccV

OIN OrbFrV ParaCenV PcaV PcaV PComV PedV PosCalcV PosCenV PosFrV PosParV PosTempV PreCenCbiV PreCenV ReOivV ReTonsV SepV SHemV SigmS SPetrV SphBasS SphParS SphPetS SplenV SPS

sss StrS

STV SupSyiV SVerV TecV TempBasV TentS ThaStrV TonsV Tore TrMedV Trolard TrPonV TrvS UncV VCMedF VCMesF VCPonF VaG VPonMedS VPonMesS

xxvi

Vein

Type

Occipital Olfactory Orbitofrontal (anterior, posterior) Paracentral Pericallosal (anterior, posterior) Pericallosal (anterior, posterior) Posterior communicating Peduncular Posterior calcarine Postcentral Posterior frontal Posterior parietal Posterior temporal Precentral cerebellar Precentral Retro-olivary Retrotonsi liar Septal (anterior, posterior) Superior hemispheric (anterior, posterior)

Parieto-occipitallobes Frontal lobe Frontal lobe Parieto-occipitallobes Frontal lobe Parieto-occipitallobes Brainstem Brainstem Parieto-occipitallobes Parieto-occipitallobes Frontal lobe Parieto-occipitallobes Temporallol>e Cerebellum Frontal lobe Brainstem Cerebellum Deep Cerebellum

Sigmoid sinus Superior petrosal Sphenobasal sinus Sphenoparietal sinus Sphenopetrosal sinus Splenial Superior petrosal sinus Superior sagittal sinus Straight sinus Superficial temporal Superficial Sylvian Superior vermian TectaI Temporal basal (anterior, middle, posterior) Tentorial sinus Thalamostriate Tonsillar Torcular Transverse medullary Vein ofTrolard Transverse pontine Transverse sinus Uncal Vein of cerebellomedullary fissure Vein of cerebellomesencephalic fissure Vein of cerebellopontine fissure Vein of Galen Vein of the pontomedu llary sulcus Vein of the pontomesencephalic sulcus

Sinus Cerebellum Sinus Sinus Sinus Parieto-occipitallobes Sinus Sinus Sinus Scalp Frontal lobe Cerebellum Brainstem Temporallol>e Sinus Deep Cerebellum Sinus Brainstem Parieto-occipitallobes Brainstem Sinus Temporallol>e Cerebellum Cerebellum Cerebellum Deep Brainstem Brainstem

Preface Table P.7 Abbreviations for Brain, Nerves, Cisterns. and Miscellaneous Brain SFG MFG IFG STG MTG lTG SPL IPL

SOG lOG OTG LOG MOG POG AOG

cc Tha Cau Clau IC EC Put GPe GPi Lent

LGB Vent ChPI ChFis FoM Cbl SupCP MidCP lnfCP Cranial Nerves CN1,orl CNl, or II CN3, or Ill CN4,oriV CNS, orV CN6,oriX CN7,orVII CN8,orVIII CN9,oriX CN10,orX CN11,orXI CN12,orXII GSPN Cisterns Sy1C CarC

Superiorfrontal gyrus Middle frontal gyrus Inferior frontal gyrus Superior temporal gyrus Middle temporal gyrus Inferior temporal gyrus Superior parietal lobule Inferior parietal lobule Superior occipital gyrus Inferior occipital gyrus Occipitotemporal gyrus Lateral orbital gyrus Medial orbital gyrus Posterior orbital gyrus Anterior orbital gyrus Corpus callosum Thalamus Caudate nucleus Claustrum Internal capsule External capsule Putamen Globus pallid us, pars external Globus pallid us, pars internal Lentifonn nucleus Lateral geniculate body Ventricle Choroid plexus Choroidal fissure Foramen of Monro Cerebellum Superior cerebellar peduncle Middle cerebellar peduncle Inferior cerebellar peduncle Olfactory Optic Oculomotor Trochlear Trigeminal Abducens Facial Vestibulocochlear Glossopharyngeal Vagus Spinal accessory Hypoglossal Greater superficial petrosal Sylvian Carotid

ChiC LTC OlfC Calle CruC lpC AmbC Quade Pone CbPonC MedC CbMedC MagnC AntSpC PosSpC Miscellaneous

An ABC ACP AVM BTO CFD CSF CT DDR EAC EC-IC EEG

cos lAC ICG IHT L MEP Mol mRS PCP R RAG RCPM SAH SCM SHT SOF SPECT SSEP SVE Tent UDTF

Chiasmatic Lamina terminalis Olfactory Callosal Crural Interpeduncular Ambient Quadrigeminal Prepontine Cerebelloponti ne Premedullary Cerebellomedullary Magna Anterior spinal Posterior spinal Aneurysm Age, bleeding, and compactness in supplementary grading scale Anterior clinoid process Arteriovenous malformation Balloon test occlusion Computational Fluid Dynamics Cerebrospinal fluid Computed tomography Distal dural ring External auditory canal Extracrania 1-to-intracranial Electroencephalogram Glasgow Outcome Scale Internal auditory canal lndocyanine green Infra-hypoglossal triangle Left Motor evoked potentials Membrane of Liliequist modified Rankin Scale Posterior clinoid process Right Radial artery graft Rectus capitis posterior major Subarachnoid hemorrhage Sternocleidomastoid muscle Supra-hypoglossal triangle Superior orbital fissure Single photon emission computed tomography Somatosensory evoked potentials Size, venous drainage, eloquence in SpetzlerMartin grading scale Tentorium Upper dural transitional fold

xxvii

Acknowledgments

The author thanks Arnau Benet, Ali Tayebi Meybodi, and the many members of the Cerebrovascular and Skull Base Surgery Laboratory at the University of California-San Francisco for the anatomical dissections used to illustrate the anatomy in this book.

I

Three Anastomoses

1

End-to-Side Anastomosis

2

Side-to-Side Anastomosis

3

End-to-End Anastomosis

7 BYPASSES:

PARTS LIST;

-1.01 -1.02 -1.03

·1.04 -1.05 -1.06

-1.07 -1.08 -1.09

-1.10 -1.11 -1.12

-1.14 -1.15

TENETS AND TECHNIQUES FOR REVAStULARIZATIDN SECTION I: THREE

ANASTD~OSIS

I

I Three Anastomoses

• End-to-Side Anastomosis Anastomoses are the connections that join arteries together to create a bypass. The Greek roots of the word translate to "furnish with a mouth," which in this case means creating an outlet in one tube that connects with an opening in another tube to form a branching network. Arterial bypasses, no matter their complexity, are all built with just three simpie anastomoses: end to side, side to side, and end to end. The application of these three anastomotic techniques in different locations, with different donor-recipient pairings, in unique combinations, and with subtle variations, yields the immensity and elegance of microsurgical bypasses. The end-to-side anastomosis is the convergence of donor and recipient arteries that redirects donor flow destined for another territory into the recipient. This anastomosis is the opposite of an arterial bifurcation: whereas bifurcations divide trunks into diverging branches that distribute blood flow peripherally, end-to-side bypasses unite separate branches into converging streams that augment or replace flow in the recipient. Arterial convergence is unusual in circulatory systems; it is seen intracranially only at the confluence of the vertebral arteries, on the exiting side of arterial fenestrations, and in leptomeningeal networks in watershed zones. Therefore, this Y-shaped anastomosis is a strikingly surgical construct. It is also an efficient construct because the connection between donor and redpient can exceed the diameter of each, unlike conventional end-to-end reanastomosis. A linear arteriotomy in the recipient can be made two to three times the diameter of the recipient to encourage flow through the anastomosis by lowering its resistance. Similarly, the donor artery can be widened with a "fish-mouth" arteriotomy, or an oblique transection at a 60-degree angle and a longitudinal linear incision in the sidewall equal to the length of the oblique transection. Fish-mouthing transforms the circular end of the donor artery into a quadrangular opening with four linear sides that enlarges the donor orifice. Poiseuille's law describes the relationship between flow (Q), perfusion pressure (P), radius of an artery (r), length of an artery (L), and viscosity (q): Q -nPr 4/1JL The only variable impacting flow through an anastomosis under the surgeon's direct control is the radius, and this dominant variable can be easily increased with well-crafted arteriotomies. A gen-

4

erous arteriotomy in the recipient artery and a fish-mouthed arteriotomy in the donor artery also create mostly linear tissues that are easily matched in length and caliber.

• Technique The sequence of steps in an end-to-side anastomosis is illustrated with a right-angled or T-anastomosis between a radial artery graft and PICA as part of a left V3 VA-RAG-p2 PICA bypass in a patient with vertebrobasilar ischemia (Fig. 1.1). Although much less common than a STA-MCA bypass, this IC-IC interpositional bypass does not require a fish-mouth arteriotomy in the donor and deploys a larger-caliber graft that displays its circular lumen better than the smallercaliber STA. The donor is harvested as a free graft and prepared by tying off leaky branches, stripping adventitia from the distal end, and making a fresh perpendicular transection at the distal end. The recipient PICA remains stationary in the cerebellomedullary dstem throughout the anastomosis because a RAG is easily transported to the recipient site. An accessible segment is selected that is reasonably sized, without brainstem perforators, and tolerant to temporary clipping (Fig. 1.1). Branches or perforators that lie at the redpient site within the temporary clips will back-bleed during the suturing and obscure the field. 1\v:igs at eloquent locations are vigorously protected, whereas those at non-eloquent sites might be temporarily clipped or cauterized safely. Circumferential dissection under the recipient artery enables passage of a protective rubber dam, or piece of background material, and a suction catheter as part of the surgical stage. Temporary clips are applied to the recipient artery, which interrupts cerebral blood flow and begins the ischemia time (Fig. 1.2). The smallest possible temporary clips are used (typically 3-mm straight clips) to lower the clip profile and keep its large shanks from snagging suture. Clips are applied at an oblique angle or laid down in the field to displace the shanks away from the anastomotic site. The trapped recipient segment should allow space for the arteriotomy and for the bites at the ends of the arteriotomy. The recipient artery is marked with ink to guide the arteriotomy and, more importantly, to visualize the edges of its incised walls, which otherwise become translucent after the arteriotomy.

1 End-to-Side Anastomosis

•

The sequence ofsteps in an end·to-side anastDmosis is illustrated with a right-angled or T-anastDmosis between a radial artery graft and PICA as part of a left V3 VA-RAG-p2 PICA bypass In a patient with vertebrobasilar isdlemia. The recipient artery is exposed (Sb!p 1) through a left far lateral craniotomy (inset) with the recipient artery Fig. 1.1

just above the vagoac:c:essory biangle (surgeon's view with the patient in the three-quarter prone position, the cranial vertex to the bottom rtght, the foramen magnum to the top lett. the posterior petrous face at the top right, and the retracted cerebellum at the bottom left).

Fig. 1.2 Sb!p 2. The recipient ilrtery is

temporary dipped, with inking of the lineilr artertotomy. Note that the surgical stage has been set with a blue rubber dilm, a soft rubber suction cathetEr beneath the dilm (not seen), a retractor tD secure the suction cathetEr, and Telfa strtps to protect the cerebellum.

5

Tnree Anastomoses

I

The artery is pierced parallel to its long axis with the beveled tip of a 25-gauge needle bent at a 45-degree angle (F.Ig. 1.3). The puncture site provides entry for one blade of a fine, right-angled microsdssors, which then extends the arteriotomy in both directions (flg. lA). Smooth cuts make a dean arteriotomy rather than a jagged, saw-toothed one, with a length three times that of the arterial diameter. Lifting the luminal blade of the microsdssors under the arterial wall visualizes its tip through the translucent tissues and keeps it from catching the bade wall. The lumen is flushed with heparinized saline to dear the lumen and identify badebleeding through clips or unrecognized branches. The first of two stay sutures joins the donor and recipient arteries (Fig. 1.5). There is little difference between the first and second stay sutures with this perpendicularly tran-

sected graft. However, a fish-mouthed donor artery takes the shape of a foot, with its toe at the distal tip at the end of the oblique angled cut and its heel at the proximal end of the longitudinal cut. The "heel stitch" is placed first with a fishmouthed donor, taking the first bite of the heel stitch from outside to inside the donor artery and flipping the donor foot to visualize the donor lumen. The donor artery is then rolled back into its downward-facing position for the remainder of the anastomosis, and the heel stitch is completed with a second bite from inside to outside the recipient artery. When the "toe stitch" is placed first, the donor lumen faces downward and the rest of the foot covers the heel, making the bite through the heel awkward. The toe stitch prevents flipping the donor foot to visualize the donor lumen during the first bite of the subsequent heel stitch. A surgeon's knot

Fig. 1.3 StEp 3. lhe recipient artery Is pierced with the beveled tip of a bent 25-gauge needle to initiate the

arteriotomy.

6

End-to-Side Anastomosis Flg. 1.4 Step 4. The arteriotomy Is exbmded In both dlrectlons with right-angled microarteriotomy scissors.

Fig. 1.5 Step 5. The first anchoring stitch joins the donor graft and recipient artery.

7

•

I

I Tnree Anastomoses

is used with stay sutures to keep the arteries together between the first and second throws of the knot (FJg. 1.6). The second of the two stay sutures is placed more easily because the donor and recipient are already joined and the donor lumen is easily visualized (Fig. 1.7). The second anchoring stitch is completed with a second bite from inside to outside the recipient artery, sometimes with a backhanded throw if necessary. A surgeon's knot is used again to tie the anchoring stitch and keep the arteries together between the first and second throws of the knot, even though the arteries are less likely to move after placing the first anchoring stitch. The first suture line is sewn with continuous sutures (Fig. 1.8). The sewing direction {toe-to-heel versus heel-to-toe) does not matter with aT-shaped anastomosis and a perpendicularly transected graft, but it does matter with obliquely transected and fish-mouthed donors. The most awkward bites are around the heel because the "ankle" of the foot can obscure the view, and therefore sewing toe-to-heel first puts these awkward bites in the middle of the suturing sequence.

when the donor is mobile and the anastomotic lumen is easier to visualize. In contrast, sewing heel-to-toe first puts these awkward bites at the very end of the suturing sequence, when the anastomosis is nearly completed and the anastomotic lumen is over-sewn. The first stitch of the first suture line is often taken as two separate bites. passing and reloading the needle after a bite through the donor graft. and then passing and reloading the needle after a bite through the recipient artery. The trajectory of the needle through the recipient can be modified with this second half-bite in order to place it right next to the stay suture, which is the site most prone to anastomotic leaks. Subsequent stitches are placed with one bite, without reloading the needle, spacing the depth and advance of each bite evenly for a tight suture line. The depth of a stitch is approximately two wall thicknesses and the advance should be approximately four wall thicknesses. The typical suture line has four to five stitches per millimeter oflength, or a dozen bites, plus or minus two. The last bite should lie immediately adjacent to the heel stitch and is another site prone to anastomotic leaks.

H

Ag. 1.6 Step 6. A surgeon's knot (two wraps of suture around the mlcroforceps) In the first anchoring

stitch keeps the arteries together between the first and second throws of the knot.

8

End-to-Side Anastomosis

11

RAG

Fig. 1.7 Step 7. The second and-loring stitch is much easier to place because the donor and recipient are already joined and the donor lumen is easily visualized.

Fig. 1.8 Step 8. The first suture line ls sewn with continuous sutures placed loosely in a spiral until all stltdles are placed.

9

•

I Tnree Anastomoses

I

Ag. 1.9 Step 9. The loose spiral of suture is tightened loop by loop, slilrting at the first anchoring stitch and progressing to the second anchoring stitcll.

Fig. 1.10 Step 10. The knot is tied between the running suture and the

tail of the knot on the second anchoring stitch.

10

1

End-to-Side Anastomosis

Fig. 1.11 Step 11. The donor graft is shifted over to the opposite side of the field to uncover the second suture line. Transposition of the donor graft opens a view into the anastomotic lumen to Inspect the suture line intraluminallyforb!chnical errors such as a through-stitch, a gap between bites, or a suture pullout.

The loose spiral of suture is tightened one loop at a time, starting at the first anchoring or toe stitch and progressing to the second anchoring or heel stitch (Fig. 1.9). Tightening the suture loop by loop aligns the loops properly, everts the donor and recipient edges, snugs the suture line, and removes all slack. After the last loop is pulled tight, the suture is tied to the tail of the anchoring stitch's knot and trimmed, securing the first suture line (Rg. 1.10). The donor graft covers the second suture line and must be moved to the opposite side of the field to uncover it (Fig.

1.11). A donor artery initially positioned to the right must now flip to the left, and a donor artery initially positioned superiorly must now flop inferiorly. Transposing the donor artery opens the anastomotic lumen for an inside view of the suture line, which is checked for rechnical errors such as through-stitches (a catch of the back wall with the suture), wide gaps between bites, and sutures that have pulled through the tissues. This precious intraluminal glimpse is fleeting, lost as soon as the second suture line is sewn. If the first suture line passes inspection, the needle from the heel

11

•

I

I

Tnree Anastomoses

stitch is passed around the donor artery to the other suture line, the microscope and chair position are shifted to optimize hand comfort and visualization, and the second suture line is sewn with continuous sutures (Fig. 1.12). The first stitch is again taken as two separate bites, passing andreloading the needle after a bite through the recipient artery, and then passing and reloading the needle after a bite through the donor graft, in order to modify the needle's trajectory for the second half-bite. Subsequent bites are taken in one pass, using the microforceps to carefully position the

wall of the donor graft for the second half of the bite without reloading the needle (Hg. 1.13). The same spacing of bites is used for the second suture line as was used for the first. The loose spiral of suture is tightened loop by loop, starting at the second anchoring or heel stitch and progressing to the first anchoring or toe stitch, snugging the suture line and removing slack. After the last loop is pulled tight and the suture line is snugged, the suture is tied to the tail of the knot on the anchoring suture and trimmed, securing the second suture line (Fig. 1.14).

Flg.1.12 Step 12. The second suture line is sewn wid! continuous sutures placed loosely In a spiral untll all stitches are pli!ced. Tne microforceps presents the ilrterial wall to the needlepoint with tfle spreading technique.

12

1

End-to-Side Anastomosis

Ag. 1.13 Continuous bites are taken in one pass, witfl the miaoforc:eps using tfle tenting technique to carefully position the wall of the graft for tile second half-bite witflout reloading tfle needle.

Rg. 1.14 Step 13. The loose spiral of suture Is tightened loopby-loop, starting at the second anchoring stitch and progressing to tile first anchoring stitdt. The suture is tied to the tail of tfle knot on the first anchoring stitch.

13

•

I Three Anastomoses

I

Ag. 1.15 Step 14. The temporary clip on the distal recipient artery is removed first to back-bleed the anastomosis. Bleeding points are oovered with fibrillar Nu-Knlt and gentle pressure Is applied. The tempo-

rary clip on the proximal recipient artery is removed next to restore cerebral blood flow. Then the temporary clip on the donor graft is removed to Initiate flow In the bypass.

Although not illustrated, the proximal end-to-side anastomosis of this V3 VA-RAG-p2 PICA bypass is performed in the same way to complete the bypass. The temporary clip on the distal recipient artery is removed first to back-bleed the anastomosis (Fig. 1.15). Bleeding points are covered with hemostatic material, and gentle pressure is applied with the microforceps and sucker. Next, the temporary clip on the proximal recipient artery is removed to restore the cerebral blood flow and end the ischemia time. Gentle bleeding from the suture line is expected and takes several minutes to stop, after which the temporary clip on the donor graft is removed to initiate Dow in the bypass. Patency is confirmed by inspecting the anastomosis, confirming pulsations in the donor artery, performing ICG videoangiography, and/or insonating the graft with a Doppler Dow probe. As illustrated, the right-angled end-to-side anastomosis is a variation that joins two arteries of unequal caliber in a T-shaped connection, typically when the donor vessel is at least two times larger than the recipient vessel. This right-

angled anastomosis is used with radial artery and saphenous vein grafts in interpositional bypasses, where an obliqueangled or fish-mouthed anastomosis of the donor graft would only exaggerate the caliber mismatch. The mismatch is rectified by transecting these donor grafts transversely, without fish-mouthing, and connecting them orthogonally to a long linear arteriotomy on the recipient. Fish-mouthed end-toside anastomoses are more commonly used than right-angled end-to-side anastomoses because they are part of the classic EC-IC bypasses like the STA-MCA bypass, which joins two arteries of equal caliber in a Y-shaped connection with an enlarged orifice in between them. A third variation of end-toside anastomosis is the patch anastDmosis, where the donor vessel has a branch or bifurcation that can be transected obliquely across the bifurcation to create a funnel shape incorporating the base of the branch artery into the section across the parent artery to enlarge the donor orifice (transection bifurcotomy). This preparation of the donor artery widens its connection without resorting to fish-mouthing.

14

7 BYPASSES;

PARTS LIST;

-2.01 -2.02 -2.03

·2.04 ·2.05 ·2.06

·2.07 -2.08 -2.09

-2.10 -2.11 -2.12

-2.111 -2.15 -2.16

-2.17 -2.18 -2.19

TENETS AND TECHNIQUES FOR REVAStULARIZATIDN SECTION I: THREE

ANASTD~OSIS

I

I Three Anastomoses

• Side-to-Side Anastomosis

• Technique

The side-to-side anastomosis is a communicating bypass between two arteries that mimics the brain's anterior and posterior communicating arteries. The anastomosis creates a connection between two separate arteries without compromising their individual inflow or outflow, and without governing flow across their connection. Flow across a sideto-side anastomosis is governed instead by demand created by a pressure gradient or arterial occlusion, which is often remote from and not intrinsic to the bypass. Therefore, unlike the end-to-side anastomosis, the side-to-side anastomosis does not have a structural donor limb with dedicated input of blood flow to the recipient, and like the communicating arteries in the circle of Willis, responds to hemodynamic changes in adjacent circulations. The side-to-side anastomosis is also a "kissing" bypass, with two arteries coming together, connecting, and coming apart. Therefore, one anatomic requirement is that the participating arteries run parallel and in dose proximity to one another. A technical requirement is that the anastomosis has a large and widely patent connection with low resistance that encourages cross-communicating flow. Performing two linear arteriotomies two to three times the diameter of the participating arteries minimizes resistance and maximizes flow according to Poiseuille's law. These two arteriotomies make the suture lines in this anastomosis completely linear, unlike those in the end-to-end anastomosis that are circular and those in the end-to-side anastomosis that are quadrangular. The unique feature of the side-to-side anastomosis is that it is a "one-way-up" anastomosis, and intraluminal suturing is needed to complete the first suture line. The bypass's endothelium is more vulnerable to injury with intraluminal suturing, necessitating extra-gentle handling of the tissues, careful awareness of all four arterial walls while sewing, and entrance and exit stitches.

The side-to-side anastomosis is used to construct an in-situ bypass because it joins two arteries with limited mobility in their natural position, without having to swing in or pull over a donor artery from afar. The sequence of steps in a side-to-side anastomosis is illustrated with an R p3 PICA-L p3 PICA in-situ bypass for a fusiform aneurysm on the left lateral medullary segment of PICA, exposed through a far lateral craniotomy (Fig. 2.1 ). Even though arteries involved with in-situ bypasses remain stationary, they are released thoroughly along their parallel segments and 1 to 2 em proximally and distally, thereby allowing them to approximate without tension (Fig. 2.2). The arteries in a side-to-side anastomosis may be parallel and separated by only a few millimeters, but arachnoid adhesions and branch arteries tether them and may keep them apart. When tying the first stay suture between inadequately prepared arteries, tension in the suture may tear through the arterial wall and damage the anastomosis. Even if the knot is tied successfully, tethered arteries can kink and occlude as they mobilize into the anastomosis. As a general rule, properly prepared arteries should touch or kiss each other naturally, without any manipulation or force. The anastomotic site should be a "twig-free" zone without perforators or branches. Temporary clips are applied to the first artery distally and proximally, spaced as far apart as possible to increase working space, and with this clip application ischemia time begins in this artery (Fig. 23). Small temporary clips are used for a low profile, and they are applied obliquely to move the shanks away from the anastomosis site. The artery is inked to better visualize the translucent walls later. An arteriotomy is begun by piercing the artery with a bent 25-gauge needle (Fig. 2A) and extended with a right-angle microscissors toward the temporary clips in both directions (Fig. 2.5). The lumen is flushed with heparinized saline

16

2

Side-to-Side Anastomosis

A

I

Mastoid tip

B

Fig. 2.1 The side-to-side anastomosis technique is illustrated with an R p3 PICA-L p3 PICA In-situ bypass for a fustfonn aneurysm on the left lateral medullary segment of the PICA. (A) The aneurysm is exposed through a far lateral craniotomy. (B) This fusiform aneurysm inwlves the left lateral medullary p2 segment of the PICA (surgeon's

view with the patient in the three-quarter prone or park bench positron, the cranial vertex at the bottom, the foramen magnum at the top, and the midline to the left; the surgeon is seated over the top of the patienfs head).

17

I

Three Anastomoses

Fig. 2.2 Step 1. The p3 segments are released bilaterally along their parallel segments to approximate them without t:ension over a 1- to 2-cm length.

I

Fig. 2.3 Step 2. Donor and redpient art:eries are occluded t:emporarilywith mini· clips applied to both artertes distally and proximally. Arteriotomy lines were marked In advance to reduce the Ischemia Ume.

18

Distal

temporary clips

2

Side-to-Side Anastomosis

Flg. 2.4 Step 3. (A) The arteriotomy in the right PICA Is Initiated by piercing It with a bent 25-guage needle. (B) Arteriotomies are skewed slightly toward each other In the 2 and 10 o'clock positions to bring the inner layers closer together and deepen the Inner suture line relative to the outer suture line, thereby optimizing approximation, visualization, and maneuverability.

A

Art

solution. These steps are repeated with the second artery, applying temporary clips distally and proximally, marking the artery, puncturing it with the beveled needle, and completing the arteriotomy. Using sequential arteriotomies shortens the ischemia time in the second artery, but synchronized arteriotomies can increase efficiency. With synchronized arteriotomies, four mini-clips are applied initially. Alternatively, applying two larger clips-one clip on both arteries proximally and one dip on both arteries distally--«) Anatomy of the SG!Ip arteries for EC-IC bypass. (A) The superficial temporal artery, posterior auricular artery, and occipital artery form the external carotid arterial system and are the major suppliers to the scalp. The STA is the main scalp supplier and the smaller of the ECA's two terminal branches, the other one being the Internal maxillary artery. The STA originates within the parotid gland deep to the fadal nerve and ascends over the zygomatic root, anterior to the external auditory canal. The STA gives rise to a small zygomaticoorbital branch at the level of the zygomatic root that courses anteriorly to the orbit, and then divides into frontal and parietal (anterior and posterior) branches. The PAA originates from the ECA distal to the OA and divides into auricular and stylomastoid branches, but its small caliber and unfavorable location limit its use in EC-IC bypasses. (B) The OA arises from the ECAjustopposite the or1gln of the facial artery and just proximal to the ECA's tenmination into the STA and IMA. The OA courses medial to the mastoid process of the temporal bone and medial to the posterior belly of the digastric muscle. It passes through the ocdpilill groove, a dedicated sulcus in tile temporal bone medial to the mastoid sulcus or groove for the digastric muscle, and lateral to the mastoid foramen for an emissary vein from the sigmoid sinus. It

continues lateral to the superior oblique muscle and medial to the longissimus capitis muscle, and then travels beneath the splenius capitis muscle laterally and over the semispinalis capitis muscle medially. The OA reilches the fascia of the cranial attachment of trapezius, just inferior to the superior nuchal line, and ascends to the scalp suboccipitally. (C) Superior view of the head showing four of the five arteries supplying the left scalp: supratrochlear, supraorbilill, superficial temporal, and occipital arteries (PAA nat shown). The supratrochlear and supraorbital arteries are part of the internal carotid arteriill system and originate as branches of the OphA to supply the skin, muscles, and pericranium of the midline and lateral forehead, respectively. The supraorbital artery arises from the OphA as it entErs the orbit. runs along the superior rectus and levator palpebrae superioris muscles, and exits the supraorbllill foramen. The supratrochlear artery Is a terminill branch of the OphA that exits from the medial orbit These two anterior scalp arteries are nat used In EC-IC bypasses because of their small caliber and unfavorable location. Tenminal branches of the STA anastomose freely with each other and with counterparts on tile contralateral side to supply the scalp over the frontal and parietal convexities, underiying muscles, and pericranium.

donor because is lies along the skin incision of the pterional craniotomy (Fig. 5.2). One simple reality is that if a donor artery is ha.Ivested and ready for use, the chances of performing a bypass increase significantly: one corollary is that if a donor artery is not harvested and ready, a bypass is not likely to be performed. Therefore, SfA should be mapped with the Doppler flow probe, harvested, and prepared in advance if the thought of performing a bypass even crosses the mind.

Harvesting the STA should take about 20 minutes. Keys to a quick harvest include incising the skin directly over the posterior or parietal branch, dissecting the donor under the microscope to see branches and tissue planes, applying upward traction on the scalp with a toothed forceps to separate the dermal layer and subcutaneous fat from the SfA (Fig. 5.3), and dialing the bipolar cautery high to control scalp bleeding and avoid using Raney clips. The initial cut-down

Extracranial Skin Dense connective tissue Muscular fllscia Temporalls muscle

Fig. 5.2 The SG!Ip has five lil)'ei"S, captllred in the mnemonic "SCALP:" skin, dense connective tissue, galea aponeurosis, loose connective tissue, and pericranium. These layers are appreciated best ilt the verb!x where the galea courses between the frontalis and occipitalis muscles, but are less relevant laterally and posteriorly In the regions of the STA

and OA. respectively (cross-sectionill view). Scalp arteries reside in the subcutaneous tissue beneath the skin and above the galea aponeurotica, and periostEum in these regions is replaced by musde ilnd muscular fasda.

63

II TenTenets

Scalp---...._ SlV'---.,_

Cortex--------

Ag. 5.3 Keys tD a quick harvest: incise the skin directly over STA; dissect under the microscope to see branches and tissue planes; apply upward traction on ttle scalp with a toothed forceps tD separate the

dennallayer and subcutaneous fat from the STA; and dial the bipolar cautery high tD control scalp bleeding.

to the artery exposes its 8-cm course from the zygoma to the superior temporal line. which is sufficient for all but the deep bypasses to the SCA/PCA Next, the artery is freed from its connective tissue attachments. The STA has a serpentine morphology; branches running anteriorly originate at the anterior-most point on the serpentine curve, and those running posteriorly originate at the posterior-most point on the curve (Fig. SA). There are few branches originating from the lateral wall and none from the medial wall. This anatomy makes it easy to find, cauterize, and cut branches 1 to 2 mm from the trunk. Leaving a protective cuff of connective tissue around the STA keeps the dissection away from the arterial wall and decreases the risk of donor injury. The superficial temporal vein typically parallels the STA and has larger caliber, thin-

ner walls, darker color, and no serpentine morphology (Fig. 5.5). The vein may need to be separated from the STA to clearly follow the artery's course. The STA is released from the scalp, but left in continuity with its distal connections beyond the superior temporal line to maintain flow until it is ready for anastomosis. When the anterior limb is also needed for a double-barrel bypass, the scalp incision is extended anteriorly and the artery is followed into the reflected scalp flap (Fig. 5.6). Again, with the division of small branches, 6 to 8 em of artery mobilizes from the scalp flap and allows its rerouting into the field. Even with only a linear incision along the parietal limb of STA, dissection under the flap with upward traction on the scalp will expose 3 to 5 em of artery, which may be enough fur a bypass to a temporal recipient artery on the cortical surface.

64

5

A

Donors and Recipients

t.

Anter1or

Posterior

l B

Fig. SA (A) lhe STA has a serpentine morphology; branches running

anteriorly originate at the anterior-most point on the serpentine curve, and those running postertorty originate at the posterior-most point on the curve. Branches occur on the outside wall of the curve

and not on the inside wall of the curve (x). In addition, few branches originate from the lateral STA wall and none from the medial wall. (B) This anatomy makes It easy to find, cauterize (C), and cut branches 1 to 2 mm from the trunk.

The superficial temporal vein typically parallels the STA and has larger caliber, thinner walls, darker color, and no serpentine morphology. The STA is released from the scalp, but left in continuity with Its distal connections to maintain flow untfllt Is ready for anastomosis. When the anterior limb is also needed for a double-banrel bypass, the scalp incision is extended anteriorly and the artery is followed into the reflected scle ncP/4

Transection

Oval

End

E-S, E-E

2.2x

ndl2

ncP/2

2nd

ncP

90degrees, nd/2 45-60 degrees,

ndJ-.12 Transection +incision Excision Transection Incision

E-S, E-E

60degrees, ndf,J3 + ndf,J3

3.6x

Oval Oval

End+ sidewall Sidewall Bifurcation

E-S, S-S E-S, E-E

3d 3d

3X

6d

3X

6d

Varial>le Variable

Crescent

Bifurcation

E-S

3d

Jx

6d

Variable

Quadrilateral

d, diameter; E-E, end to end; E-S, end to side; S-S, side to side.

Fig. 8.1 (opposite) The three basic cuts used to make an arteriotomy are incision, excision, and transection, and they generate arterial openings in five shapes: lines, circles, ovals, quadrilaterals, and crescents. Seven basic arteriotomies are used in bypass surgery: (A) lin-

94

ear incision arteriotomy; (B) perpendicular transection arteriotomy; _ ____,~ (C) oblique transection arteriotomy; (D) fish-mouth arteriotomy; (E) excision arteriotomy; (F) transection bifurcotomy; and (Ci) incision bifurcotomy.

8 Arteriotomy

A

Unear lndllon arteriotomy

B Perpendicular transection arteriotomy

C Oblique transection arteriotomy

D

Ash-mouth arteriotomy

E

Exc:ilion arteriotomy

F

Tran1ec:tlon blfurcotomy

G lndlfon blfurcotomy

95

II Ten Tenets

E

Ag. 8.2 Unear incision arteriotomy is the simplest and most common arteriotomy, used in end-to-side and side-to-side anastomoses. (A) The artery Is trapped with temporary dips and a line three times as long as the artery's width Is martced with blue ink. (B) The artery is pierced with a beveled 27-gauge needle whose shaft Is angled 45 degrees off the axis for tangential puncture. {C) The puncture hole Is created and (D) entered with one blade of a mlcrosclssors. (E) The arteriotomy Is extended with smooth, straight cuts along the marked line In both directions.

96

8 Arteliotomy is situated at the midpoint of the arteriotomy. and the arte- or the paired artery in the anastomosis, but may not open riotomy is then extended in the opposite dirertion by re- widely in thick, rigid arteries such as the ECA or CCA. versing the orientation of the micro-arteriotomy scissors. Smooth cuts in a straight line avoid a jagged. saw-toothed arteriotomy. The needle creates small transverse cuts in the arterial wall at the puncture site, which have the least im- • Fish-Mouth Arteriotomy pact in the middle of the suture line where the anastomosis The "fish-mouth" arteriotomy creates a quadrilateral-shaped opening that optimizes the area of the anastomotic lumen. is widest. Linear incision arteriotomies can be made alternatively getting the most bang for the buck, or most flow for the cuts. with a pointed scalpel blade, such as a No. 11 blade, or with Classically, this arteriotomy combines a perpendicular trancurved microscissors. A small snip in the artery with micro- section and a longitudinal linear incision in the sidewall, with scissors can initiate the arteriotomy instead of a needle its length equal to the artery's diameter (Fig. 83). These puncture. The linear arteriotomy fashions straight suture cuts transform a small circular transection into a flared. lines that are the easiest to suture because relationships quadrangular orifice described as a cobra head or spatula. between the hands, instruments, needles, and tissues are Mathematically, an artery with diameter d that is transected constant along the entire line. This arteriotomy conserves perpendicularly has an anastomotic circumference of m:l the arterial wall to maintain luminal size, unlike excision and an anastomotic area ofrccP/4. In contrast, the same artery arteriotomies that resect a piete of wall and can cause ste- with a fish-mouth arteriotomy (perpendicular transection nosis at the anastomosis. Linear arteriotomies are ideal with and longitudinal incision) has an anastomotic circumfercerebral arteries whose thins walls are easily splayed by flow ence of 2nd and an anastomotic area of mP. Therefore,

C

Circumference • nd./2

Perpendicular transection

r.g. 8.3 The fish·mouth arteriotomy creates a quadrilater.d·shaped opening that optimizes ttte area of ttte anastomotic lumen, combining a GO-degree oblique transection and a longitudinal linear Incision In the sidewall equal to the length of the oblique transection. {A) Matttematically, an artery wittt a diameter d that Is transected perpendicularly has an anastomotic circumfer· ence of Ted and an anastomotic area of ndZ/4. (B) The same artery transected obliquely at a 45-degree angle witftout fish-mouthing has an anastomotic circumference of ndf2 and an anastomotic area of mfl/2 (double that of perpendicular transection). (C) The same artery with a fish-moutft arteriotomy (perpendicular transection and longitudinal Incision} has an anastomotic circumference of 2nd and an anastomotic area of ndZ. Therefore, fish-mouttttng the artery doubles the anastomotic circumference and qua· druples ttte anastomotic area, relative to perpendicular transection. 97

II TenTenets fish-mouthing the artery doubles the anastomotic circumference and quadruples the anastomotic area, relative to perpendicular transection. For comparison. the same artery transected obliquely at a 45-degree angle without fishmouthing has an anastomotic circumference ofmN2 and an anastomotic area of 1fd2/2 (double that of perpendicular transection). These calculations are simplest with 45- and 90-degree angled cuts, but. in practice, the ideal fish-mouth arteriotomy combines a 60-degree angled arterial transection (60 degrees from the long axis of the artery) and a longitudinal linear incision in the sidewall equal to the length of that cut, or the hypotenuse of the GO-degree right-angled triangle (2d/..f3, or 1.2d) rather than the artery's diameter (Fig. 8.4). This geometry reduces slightly the anastomotic area but relaxes the angles of this quadrilateral, changing its shape

from a square to a kite shape with obtuse angles (120 degrees) in the middle of the suture lines and acute angles (60 degrees) at the ends of the arteriotomy. The fish-mouth arteriotomy is widely used in EC-IC end-to-side anastomoses such as the STA-MCA bypass to prepare and enlarge scalp arteries as donors. It is also used in IC-IC end-to-side reimplantations and in reanastomoses when the two ends can be aligned in alternating fashion. heel to toe and toe to heel (double fish mouth anastomosis). The increased anastomotic area in fish-mouthed donors augments bypass flow and prevents stenosis. The matching arteriotomy in the recipient artery must be lengthened to accommodate this more capacious anastomosis, increasing from 1.5d (or rrd/2) with the perpendicular transection arteriotomy, to 2.2d (or nd/..f2) with the oblique transection arteriotomy, and to 3.1d (or rrd) with the fish-mouth arteriotomy.

F'llh-mouth arteriotomy A

B

c

Fig. 8.4 (A} The ideal fish-mouth arteriotomy combines a 60-degree angled arterial transecUon (60 degrees from the long axis of the artery and length x) and (B) a longitudinallinear incision in the sidewall equal to the length of that cut (x). (C) These arts transfonn an oblique transection into a flared, quadrangular orifice like a cobra head or spatula. (D) This geometry relaxes tile angles of tills quadrilateral and forms a

98

kite with obtuse angles (120 degrees) in the middle of tile sub.tre lines and acute angles (60 degrees) at the ends of the arteriotomy. (E) The fish-mouth arteriotomy is widely used in end-to-side anastomoses such as tile STA-MCA bypass and IC-IC reimplantations. The matching arteriotomy in the recipient artery must be three times the diameter (d) of the donor artery, or 3d In length.

8 Arteriotomy

• Perpendicular Transection Arteriotomy End-to-side anastomoses in interpositional bypasses often use a perpendicular transection arteriotomy. According to the mathematics above, the perpendicularly transected artery has the smallest anastomotic area and might seem unfavorable, but one of an arteriotomy's functions is to adjust openings in two arteries with different calibers. The cross-sectional arteriotomy matches an oversized interposition graft with a smaller recipient. Caliber mismatches are seen occasionally between RAGs and their intracranial recipients, and frequently between SVGs and their intracranial redpients. In these cases, a fish-mouth arteriotomy would further enlarge the anastomotic area of the graft and exaggerate this disparity, whereas the cross-sectional arteriotomy minimizes the anastomotic area. of the graft and crafts a good connection. Perpendicular transection arteriotomy in a. graft creates a. right-angled or T-shaped anastomosis with the recipient, rather than the oblique-angled orY-sha.ped a.na.siDmosis with fish-mouthing (fil. 8.5). The diameter of oversized grafts is kept ID twice that of the recipient because larger mismatches might slow the Dow in the graft and precipitate thrombosis and occlusion. The perpendicular transection arteriotomy connects the graft orthogonally to a linear arteriotomy on the recipient. Transection arteriotomies are also used with cervical arteries (ECAand ICA) in the proximal ends ofEC-IC interpositional bypasses joined with end-to-end anastomoses, creating direct linear hemodynamics from the donor artery into the bypass graft.

Perpendicular tranHction arteriotomy A

B

Fig, 8.5 (A) Several millimeters of donor artery or SVG are needed to grasp the end of the vessel and strip back the connective tissue cuff. (B) Cleaning the donor vessel traumatizes this grasped tissue, which is removed with perpendicular transection. (C) A perpendicular transection arteriotomy In the donor Joins with a linear arteriotomy In the recipient to create a right-angled or T-shaped anastomosis, rather than the oblique-angled crY-shaped anilstomosis with fish-mouthing, which is useful for oversized interposition grafts that are much larger than the redpient.

99

II TenTenets

straight linear course. Obliquely sectioned arteries that are joined toe to toe and heel to heel will angulate like the An oblique transection arteriotomy enlarges the area of comers of a picture frame, producing unfavorable curves an end-to-side anastomosis above that of a perpendicu- and hemodynamics at the anastomosis. Obliquely seclar transection but less than with fish-mouthing. Oblique tioned arteries that are properly joined heel to toe gradutransection also enlarges the area of end-to-end anasto- ally change the diameter of the anastomosed arteries. The moses in intracranial reconstructions after aneurysm exci- reconstructed artery acquires a funnel shape with slanted sion and in interpositional bypasses. Oblique cuts adjust suture lines and gently transitioning caliber. In contrast, different calibers of donor and recipient arteries, with the arteries with different calibers that are joined after persmaller artery sectioned more obliquely than the larger pendicular transections have transverse suture lines and a one to equalize the lengths of their arteriotomies (Fig. stepped or purse-stringed shape with an abrupt, stenosing 8.6). Unlike perpendicular transections that have a uni- change in caliber. Oblique transection arteriotomies require form shape, oblique transections give arteries a heel and a forethought and planning before making the arteriotomy toe that must be oriented carefully in the anastomosis with cuts in order to achieve the correct orientations, particularly the initial stay sutures. The toe of one artery joins the heel with in-situ arteries that resist rotation or mobilization of of the other and vice versa, connecting the arteries in a their ends.

• Oblique Transection Arteriotomy

Oblique transection arteriotomy A

B

Toe

Perpendicular transection arteriotomy E

Stenosing change in caliber

---~--::!'!"'--

Fig. 8.6 (A} Oblique transectlons enlarge the anastomotic area relative to perpendiculartransections, but not as much as with fish-mouthing. (B) Oblique tr.msection gives the donor artery a heel proximally and a toe distally. (C) Oblique cuts can equalize the anastomotic areas of donor and recipient arteries of different sizes. The smaller artery is sectioned more obliquely (30 degrees off tne long axis of the artery and lengthx) to match the length of the arteriotomy of the larger one (45 degrees off tne long axis of the artery and length x). (D) The toe

100

of one artery joins the heel of tne other, connecting the arteries In a straight murse with a diameter that changes gradually from one artery to the other. The reconstructEd artery acquires a funnel shape with slanted suture lines and gently transiUonlng caliber. (E) Mismatched arteries that are joined after perpendicular transections have transverse suture lines and a stepped or purse-stringed snape, whicn creates a stenosis.

8 Arteriotomy

• Excision Arteriotomy The excision arteriotomy removes an elliptical piece of sidewall to create a hole in the artery for the anastomosis. On a small scale, this arteriotomy is made by grabbing a piece of the wall with microforceps, elevating or tenting it upward, and cutting smoothly along its base. A small stitch can also be placed in the center of this ellipse as a handle to raise and excise it (Fig. 8.7). On a larger scale, the arteriotomy is made in extracranial arteries like ECA and CCA with an aortic punch. After making a linear arteriotomy with a No. 11 scalpel blade and enlarging the opening with mosquito forceps, a flanged rod or anvil is inserted into the arterial lumen and a 4- or 5-mm plunger cuts a precise circular hole in the wall. A smooth disk of arterial wall is removed cleanly, or a larger elliptical piece is removed with two overlapping circular punches.

The punch arteriotomy is ideal with these muscular arteries in the neck with thick, sometimes atherosclerotic walls that may not open in the anastnmosis after just a linear arteriotomy. Excisional arteriotomies with larger arteries do not compromise the circumference or cross-sectional area of the parent artery. However, excisional arteriotomies can significantly decrease the circumference and cross-sectional area of smaller arteries and stenose the recipient, making incisional arteriotomies preferable. The punch arteriotomy used with cervical donors in end-to-side anastnmoses creates a right-angled junction with the interpositional graft with a wide-open orifice in the donor wall for optimal flow. The punch is superior to the linear arteriotomies in the ECA. ICA, CCA, and subclavian artery, and on intracranial donors such as the V3 VA.

Excision arteriotomy

A

B

D

E

Fig. 8.7 (A) The excision arteriotomy removes an elliptical piece of sidewall to create a hole in tlle artery for the anastomosis. With a small recipient such as an M4 MCA, this arteriotomy is made by grabbing a piece of the wall with mlaoforceps, tenting It upward, and cutting smoothly along its base. (B) With a larger recipient such as the cervical ECA. a linear arteriotomy is made with a No. 11 scalpel blade and (C) widened with mosquito forceps. (D) The excision arteriotomy

F

is made with an aortic punch, inserting the anvil into the arterial lumen and cutting a circular hole in the wall with the plunger. (E) A larger elliptical piece of arterial wall is removed witf1 two overlapping circular punches. (F) The punch arteriotomy Is Ideal with musrular arteries In the neck with thick, sometimes atherosderotic walls (e.g., ECA. ICA, CCA, subdavian artery, and V3 VA) that may not open in an end-to· side anastomosis after a linear arteriotomy.

101

II TenTenets

• Transection Bifurcotomy A bifurcation in an artery can be transected across its branches to fashion an outlet for anastomosis with a diameter wider than that of its parent artery (Fig. 8.8). The cut may be straight, oblique, or curved, preserving the base of both branches while removing the dividing crotch of their divergence. This transection creates a funnel-shaped or flanged enlargement of the artery that depends on the size of the branches, the obliquity of the cut, and the amount of arterial base incorporated into the arteriotomy. A generous incision that arcs across the arterial base can splay the branches and create a large anastomotic ellipse. Alternatively, a straight oblique transection across the arterial base can be fish-mouthed to widen the ellipse into a quadrilateral. Adonor prepared with transection bifurcotomy and joined to a linear incision arteriotomy on the recipient creates a "patch" anastomosis, used occasionally with the STA's bifurcation into frontal and parietal branches. Oblique transection through the both limbs increases the anastomotic area of the donor STA. Transection bifurcotnmy can also be used with interposition grafts that have branches along their course, as seen frequently with saphenous vein grafts.

TranHCI:ion bifurcotorny A

B

c

c

• Incision Bifurcotomy The incision bifurcotomy is almost the opposite of the transection bifurcotomy: an indsion is made in the redpient artery in the dividing inner wall of the bifurcation that extends along both branches and across their branch point Rather than removing the bifurcation's divider as with transection bifurcotomy, the bifurcation is opened to incorporate both branches into the anastomotic circumference. This arteriotomy is typically used with interpositional bypasses when the redpient artery is small and a T-shaped anastomosis would be mismatched. This crescent-shaped opening in the bifurcation can be adjusted to match the caliber of the graft In this case, indsion bifurcotomy enables an end-toside anastomosis that delivers flow in line with the redpient's parent artery, rather than perpendicular to one ofits smaller branch arteries, thereby enlarging the anastomotic area and supplying three arteries at once (Fig. 8.9). The suture lines associated with a crescent-shaped opening are more challenging to sew. Unlike the fish-mouthed

102

Fig. 8.1 (A) A bifurcation ln a donor artery can be transected across its br.~nches to fashion an outlet for anastomosis that is wider than its parent artery. The obilquity of the cut varies the size of the outlet: an oblique cut (a, gi"WI solid line) is longer than a straight OJt (c. black dashed line) and creates a larger anastomotic area. (B) Transection blfurcotomy creates a funnel-shaped or flanged enlargement of the donor artery, even with a straight tr.~nsection (c, black dashed line). (C) A donor prepared with transection bifurcotomy and joined to a linear lnclslon arteriotomy on the recipient creates a "patch" anasto· mosis, used occasionally with the STA's bifurcation irrto frontal and parietal br.~nches.

8 Arteriotomy Incision bifurcotomy

c

A

B

D

Fig. 8.9 {A) Incision bifurcotomy incises the dividing inner wall of a bifurcation along both branches and across their branch point. (B) Rather than removing the bifurcation's divider and branches as with transection bifurcotomy, a crescentshaped opening in the bifurcation incorporatEs both branches into the anastomotic drcumfenence. (C) Incision bifurcotomy is used with oversized SVGs in lnterposltional bypasses when the recipient artery Is small and aT-shaped anastomosis would be mismatdled. Row is delivered in line with the recipient's parent artery into three arteries at once. (D) lndsion bifurcotDmy creates a concave suture line that closes at its midpoint and may be more susceptible to through· stitches.

anastomosis that ftilll!s open at its midpoint, the crescentshaped anastomosis doses at its midpoint. Whereas the fishmouthing and transection bifurcotomy enlarge the donor arteries, incision bifurcotomy enlarges the recipient artery. This arteriotomy is useful with oversized saphenous vein grafts that connect to MCA recipients in a spacious Sylvian fissure that facilitates this more difficult anastomosis.

•

Throwing Your Hat Over the Wall

The arteriotomy is the point of no return. Donor harvest. zone preparations, and temporary clip application ilil! reversible steps easily undone if problems arise. However, incising the superior MCA trunk or transecting PICA from a VA aneu-

rysm is consequential. Arteriotomy requires a commitment to perform the bypass and a leap of faith that the deconstructive maneuver can be reconstructed. What if the PICA does not mobilize to the donor site on the VA because it is tethered by a medullary perforator? What if the ends of an artery cannot be reapproximated after excising the aneurysm? Uncertainties that cannot always be addressed in advance make this the most unsettling moment of the procedure. Arteriotomy is analogous to "throwing your hat over the wall." When you do this, you keep it from falling off during the climb, but importantly you commit to dimbing the wall. Throwing your hat over the wall forces you to accomplish something significant by making the consequences of failure painful. That commitment to performing the bypass can be

103

II Ten Tenets overwhelmed by concerns about ischemic complications, the strength of the bypass indications, technical competencies, the feasibility of simpler bypass options, and the readiness of the operative team. All of these factors bear down on the neurosurgeon at that critical moment and test one's resolve. Proceeding with arteriotomy comes from forethought and confidence. The list of concerns should be contemplated before entering the operating room, otherwise they will linger and lurk. Confidence also quiets one's halting thoughts. Confidence comes from a stepwise progression in operative experience that begins with simple, superficial bypasses such as the STA-M4 MCA bypass and advances to shallow bypasses such as high-flow EC-lC interpositional bypasses and the OA-p3 PICA bypass. Experience with these bypasses emboldens deeper bypasses in the interhemispheric fissure, as well as IC-IC bypasses with side-to-side and end-to-end

104

anastomoses. As one's confidence grows, the deepest and most difficult bypasses to the carotid and ambient cisterns with interposition grafts, caliber mismatches, and multiple anastomoses become a comfortable part of one's bypass repertoire. Confidence can be scarce early in one's bypass career while learning the technique, trying new bypasses, and discovering one's abilities, but it builds with the case progression over time. As one of the few constructive interventions in vascular neurosurgery, bypass surgery demands skill, creativity, and near-perfect execution. However, bypass surgery also demands a measure of daring to commit to a complex bypass that is difficult and risky. Bypass surgeons must conquer the inhibitions that make bypass surgery unnerving and summon the mettle to figuratively throw one's hat over the wall.

7 BYPASSES;

PARTS LIST;

-9.01 -9.02 -9.03

-9.04 -9.05 -9.06

-9.07 -9.08 -9.09

-9.10 -9.11 -9.12

-9.14 -9.15 -9.16

-9.17 -9.18 -9.19

-9.20

TENETS AND TECHNIQUES FOR REVASCULARIZATION SECTION II: TEN TENETS

II Ten Tenets

• Craftsmanship

Surgical Needle

Like pillars and buttresses that strengthen a building, sutures join arteries together and secure their connection. And as exposed brick and beams display the builder's craftsmanship, sutures display the surgeon's aesthetic. Smooth, snug approximation of everted endothelium on the artery's inside is what matters most, but the number, spacing, and regularity of stitches show outwardly in the suture lines like a fa~de making a statement about the surgeon's skill, standards, and pride.

• Anatomy of Sutures The needle has a body, a point, and a swage; the latter is the hollowed end that receives the nylon suture (Fig. 9.1). The body is rounded with a tapered tip for atraumatic penetration, although the points are also made with cutting and reverse cutting designs. The body curves in a % circle, but also comes in 1A, ~. and ~ circles. The circle has a radius (mm) and a chord length (mm), which is the distance from the needle's point to the swage. The diameter of the needle ranges between 50 and 100 )lm (Table 9.1). Manufacturers describe the needle with a code combining its diameter and chord length; for example, the BV75-3 needle used for most STA-MCA bypasses has a 75-JJm diameter and 3-mm chord length with 10-0 suture (Ethicon US, LLC, Somerville, Nj). Circle and radius are not in the descriptive code, but are printed on the package. Other manufacturers such as Davis & Geck and Xomed have other codes that may or may not incorporate these descriptors. Bypass suture is nonabsorbable, monofilament nylon defined by its size according to the United States Pharmacopeia (USP). USP nomenclature refers to suture diameter that originally ranged from No. 1 to No. 6, but as thinner sutures were manufactured with improved techniques, the range extended to No. 0, No. 00, and so on. A higher number of zeros indicates a smaller suture diameter with lower tensile strength. Neurosurgical bypasses use 10-0 and 9-0 suture, with diameters of 20 and 30 Jlffi, respectively. Associated needle size varies in proportion to the suture, with the 11-0

14 circle

1h circle

o/e circle

Fig. 9.1 Anatomy of surgical needles. The needle has a body, a point, and a swage that receives the nylon suture. The body is rounded with a tapered tip for atraumatic penetration. Curvature of the needle is defined by the fraction of a circle. Manufacturers describe the needle with a code combining its diameter in micrometers and chord length in millimeters, which is the distance from the needlepoint to the swage.

suture using the smallest BVS0-3 needle and the 9-0 suture using a larger BV1 00-4 needle. The smallest BVS0-3 is useful in small pediatric patients with fragile tissues, but size advantages must be weighed against the disadvantages of delicate suture more prone to breaks, particularly with the running suture technique. A 10-0 suture comes with both BV75-3 and BV100-4 needles. The BVl00-4 needle is preferred for radial artery and saphenous vein grafts with thick walls requiring greater forces to pass the needle, and stronger 9-0 suture is used for stay sutures that pull together the ends of two arteries separated by a wide gap when tying the first knot. Needle diameter always exceeds suture diameter, producing holes in the arterial walls that are only partially filled by

Summary of Suture Material

Table9.1

Needle Diameter (~o~m)

30-70 50-70 70-100 100 130 140-160

106

%circle

Suture Diameter

Ethicon Codes

USP

Metric

~o~m{min)

~o~m(max)

BVS0-3 BV75-3, BV100-4 BV100-4 BV130-5 BV-1

12-0 11-0 10-0 9-0 8-0 7-0

0.01 0.1 0.2 0.3 0.4 0.5

10 20 30 40

9 19 29 39 49 69

so

Length (em)

13 15 13

9 Suturing Technique Suture diameter

A

looking intraluminally before passing the needle all the way through the walls if there are concerns about a suturing error or through-stitch. The needle can be backed out easily if a problem is identified, or advanced if not.

• The Needle Driver

Needle hole diamater

Fig. 9.2 (A) Needle diameter always exceeds suture diameter, produdng holes (B) In the arterial walls that are only partially filled by the suture material and that will leak around the sub.Jre when temporary dips are removed.

the suture material and that leak around the suture when temporary clips are removed (Fig. 92). This bleeding is expected, stops quickly, and is a favorable sign of anastomosis patency. The difference between the needle and suture diameter secures a bite once the needle passes through the wall. A suture loaded on a donor artery will not back out when the donor is mobilized into the field. However, this size discrepancy makes it difficult to undo a bite after it is taken. Backing a needle out will damage the wall, and therefore stitches should be inspected by mobilizing arteries and

Titanium needle drivers are strong, lightweight. and preferred (FJg. 9.1). Curved tips translate wrist rotation into needle rotation with a motion arc that has a larger radius than straight tips. Curved tips also facilitate viewing the needle in deep surgical fields where tangential views down the shaft of the needle driver are obstructed A curved needle driver brings the needle forward into view and compensates for this angulation of the instrument. Curved needle drivers are less important in shallow surgical fields where hands and instruments lie flat with a good overview of the needle, but curved needle drivers are still preferred. Rounded handles are superior flat handles because the instrument can be rolled between the thumb and index finger to smooth the rotational motion. Knurled handles add friction to the handgrip, and diamond dusting on the inside surface of the tips adds friction to the needle grip. The tips of the needle driver are maximally tapered for a low profile (Lawton micro titanium needle holders. Mizuho America, Inc., Union City, CA). Locking mechanisms are not used because locking and unlocking requires extra movements that interrupt suturing mechanics and might injure the tissues with tweaks of the needle.

B

Fig. 9.3 (A) rrtanium needle drivers are preferred for their strength and light weight. Rounded handles allow the instrument to roll between tile tflumb and index fingersmootflly, and knurled handles add friction to the grip. (B) Curved tips translatE wrist rotation Into needle rotation with a motion art: that has a larger radius than straight tips.

Curved tips also improve viewing of the needle in deep surgical fields where tangential views down the shaft of the needle driver are obstructed. (C) Diamond dusting on the inside surface of the tips adds friction to the needle grip. (D) The tips of the needle driver are maximally tapered for a low profile.

107

II TenTenets

• Mechanics of a Bite A bite passes the needle through the arterial wall and transfers it to instruments on the opposite side in four steps; bite, grab, counter-sweep, and reload. The bite is the needle's

penetration through the wall (Fig. 9A). The needle's body is held in the needle driver between the one third closest to the swage and the two thirds closest to the needlepoint, which allows more than half of the needle to travel through the wall. The grasp is most stable when the needle and

B

.........---·---..."'..

F

,...·· / :'

Fig. 9A A bite passes the needle though arterial wall and transfers it to Instruments on the oppositE side In four steps: bite, grab, munt-

er-sweep, and reload. (A) The bite, or the needle's penetration through the wall, Is drtven by supination of the wrist and hand, which rotates the needle driver. (B) By holding the needle's body between the one third closest to the swage and the two thirds closest to the point, a bib! advances more than half of the needle through the wall. (C} The needle's point is positioned at the point of penetration on one side of the wall, and the microforceps' tips are positioned on the opposite side of the wall to present the tissue to the needle's point.

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(D) The bite begins with a faint push and rotation of the wrist and fingers, with tfle needle passing perpendicularly through the full lfllckness of the wall and all of its layers. While the needle driver powers the bite, the mlcroforceps applies munterpressure with equal and opposite force. (E) The curve of the needle filces downward and the driver is rolled between the thumb and index finger to align the needle perpendicular to the wall. (F) The bite follows tfle curvature of tfle needle and advances until the driver meets the wall and microforceps on the other side.

9 Suturing Technique

Frg. 9.5 (A) The grab transfers control of tfte needle to tfte microfor· ceps on the opposite side of the wall. With tfte spreading technique of presenting arterial wall to the needlepoint. the tips of tfte microforceps counter-resist tfte needle during the bite and lie waiting on either side of the needle as It passes through the wall. The body of the needle

is grasped between the one third closest to the needlepoint and the (B) With this grab, the needle driver can release its hold on the needle. These transfers take place on tfte needle's body with contact on metal