Vascular Challenges in Skull Base Surgery E-Book

Paul Gardner

• Herausgeber: Thieme Medical Publishers
• Kategorie: Fachliteratur
• Sprache: Englisch

Veröffentlichungsjahr: 2021

Beschreibung

The essential multidisciplinary guide for the prevention and management of vascular injury from master skull base surgeons

Vascular injury is the most significant source of morbidity or mortality during skull base surgery, regardless of the surgical approach. While skull base approaches always placed arteries and veins at risk, newer endoscopic endonasal approaches have introduced new challenges for the prevention and management of vascular injury. Greater anatomic knowledge, additional surgical options, improved instrumentation, advances in interventional neuroradiology, and enhanced training all contribute to successful outcomes. Vascular Challenges in Skull Base Surgery by renowned skull base experts Paul Gardner, Carl Snyderman, Brian Jankowitz, and distinguished contributors, fills a gap in the literature, with invaluable guidance on managing rare but potentially catastrophic surgical complications.

The full range of surgical approaches to the anterior, middle, and posterior cranial fossae are covered in 22 chapters. Diverse topics encompass open and endoscopic endonasal surgical approaches, endovascular techniques including balloon test occlusion and embolization, and standard and alternative bypass procedures. The last three chapters discuss venous considerations, neurophysiologic monitoring, and the role of training and simulation in vascular injury prevention. Key learning points, illustrated discussion of relevant anatomy, and tips and tricks are targeted at helping skull base surgeons leverage practical strategies to improve patient outcomes.

Key Highlights

• An impressive group of expert, highly-experienced surgeons share firsthand knowledge
• Insightful analyses of root causes and clinical pearls provide indispensable prevention tactics
• High-quality images and videos enhance visual understanding of surgical anatomy and techniques

Trainees and practicing skull base surgeons will greatly benefit from the collective knowledge and evidence-based injury avoidance strategies shared by authors who have learned to master the art of skull base surgery.

This book includes complimentary access to a digital copy on https://medone.thieme.com.

Leseprobe

To access the additional media content available with this e-book via Thieme MedOne, please use the code and follow the instructions provided at the back of the e-book.

Vascular Challenges in Skull Base Surgery

Paul A. Gardner, MD Professor and Peter J. Jannetta Endowed Chair Department of Neurological Surgery University of Pittsburgh School of Medicine; Co-Director, Center for Cranial Base Surgery University of Pittsburgh Medical Center Pittsburgh, Pennsylvania, USA

Carl H. Snyderman, MD, MBA Professor Department of Otolaryngology University of Pittsburgh School of Medicine; Co-Director, Center for Cranial Base Surgery University of Pittsburgh Medical Center Pittsburgh, Pennsylvania, USA

Brian T. Jankowitz, MDAssociate Professor Director, Cerebrovascular Surgery Department of Neurological Surgery Perelman School of Medicine at the University of Pennsylvania Philadelphia, Pennsylvania, USA

410 illustrations

ThiemeNew York • Stuttgart • Delhi • Rio de Janeiro

Library of Congress Cataloging-in-Publication Data is available with the publisher.

© 2022. Thieme. All rights reserved.

Thieme Publishers New York 333 Seventh Avenue, 18th Floor New York, NY 10001, USAwww.thieme.com [phone], [email protected]

Cover design: © Thieme Cover image source: © Penny Oliver Typesetting by TNQ Technologies, India

Printed in USA by King Printing Company, Inc.                       5 4 3 2 1

ISBN 978-1-68420-068-9

Also available as an e-book:eISBN (PDF): 978-1-68420-069-6eISBN (epub): 978-1-63853-646-8

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This book is dedicated to:

My greatest contributions to the future, my children, Emma and Ella.

Paul A. Gardner, MD

My family for their unwavering support.

Carl H. Snyderman, MD, MBA

My children, Kathleen, Liam, and Julian, all that's sacred comes from youth.

Brian T. Jankowitz, MD

Contents

Videos

Preface

Acknowledgment

Contributors

1Vascular Anatomy of the Head and Neck/Circle of Willis

Aneek Patel, Hussam Abou-Al-Shaar, Maximiliano A. Nuñez, Georgios A. Zenonos, Paul A. Gardner, and Juan C. Fernandez-Miranda

1.1Key Learning Points

1.2Introduction

1.3Anterior Circulation

1.3.1Cervical Carotid Artery

1.3.2Petrous and Lacerum Carotid Artery

1.3.3Paraclival and Cavernous Carotid Artery

1.3.4Supraclinoid Internal Carotid Artery

1.3.5Anterior Cerebral Artery (A1 and A2 Segments)

1.3.6Middle Cerebral Artery (M1 Segment)

1.4Posterior Circulation

1.4.1Vertebral and Basilar Arteries

1.4.2Posterior Cerebral Artery (P1 and P2 Segments)

1.4.3Extracranial-Intracranial Anastomoses

1.5Conclusion

References

2Evaluation of Tumor-Involved Vasculature (Including Balloon Test Occlusion)

Joao Alves Rosa, Becky Hunt, and Shelley Renowden

2.1Key Learning Points

2.2Introduction

2.3Arterial and Venous Anatomy

2.4Imaging of Skull Base Vascular Tumors

2.4.1Digital Subtraction Angiography (DSA)

2.5Balloon Test Occlusion (BTO)

2.5.1Balloon Test Occlusion Protocol

2.5.2Alternative Common Adjuncts

2.6Conclusion

References

3Embolization of Skull Base Tumors

Daniel A. Tonetti and Brian T. Jankowitz

3.1Key Learning Points

3.2Introduction

3.3Goal of Embolization and Injury Avoidance

3.4Available Embolysates

3.5Case Examples

3.6Management Strategy

3.7Potential Complications

3.8Venous Anatomy

3.9Conclusion

References

4Vascular Supply of Local-Regional Flaps in Skull Base Surgery

Philippe Lavigne and Eric W. Wang

4.1Key Learning Points

4.2Introduction

4.3Extranasal Reconstructive Flaps

4.3.1Anterior Pericranial Flap

4.3.2Temporoparietal Fascial Flap

4.3.3Temporalis Muscle Flap

4.3.4Occipital Pericranial Flap

4.3.5Facial Artery Musculomucosal (FAMM) Flap

4.4Endonasal Reconstructive Flaps

4.4.1Nasoseptal Flap

4.4.2Lateral NasalWall Flap

4.4.3Middle Turbinate Flap

4.5Conclusion

References

5Bypass in the Treatment of Skull Base Tumors

Laligam N. Sekhar, Ananth K. Vellimana, and Zeeshan Qazi

5.1Key Learning Points

5.2Introduction

5.3Vascular Challenge

5.4Injury Avoidance

5.5Related Pathologies

5.6Management Strategy

5.6.1Internal Carotid Artery

5.6.2Vertebral Artery (VA)

5.6.3Basilar Artery

5.6.4Middle Cerebral Artery

5.6.5Anterior Cerebral Artery

5.6.6Other Arteries

5.7Technical Considerations

5.7.1Technique of High-Flow Bypass

5.8Outcomes and Complications

5.9Case Examples

5.10Alternative Strategies

5.11Conclusion

References

6Alternatives to Standard Bypass Techniques for Skull Base Tumors (Including Direct IMax Bypass)

Kevin Kwan, Julia R. Schneider, Ivo Peto, and Amir R. Dehdashti

6.1Key Learning Points

6.2Indications

6.3Determination of Cerebrovascular Reserve

6.4Traditional High-Flow Cerebral Revascularization Methodology and Limitations

6.5Advantages of the Internal Maxillary (IMax) External Carotid-Internal Carotid (EC-IC) Bypass

6.6IMax Artery—Importance of Preoperative Angiography

6.7IMax Artery Anatomical Considerations

6.8Autograft Selection for High-Flow Bypass

6.9IMax Bypass Operative Technique

6.10Illustrative Case 1

6.11Illustrative Case 2

6.12Limitations of the IMax Bypass

6.13Advantages of IC-IC Bypass

6.14Advantages of the “Bonnet” Bypass

6.15Conclusion

References

7Skull Base Approaches for Aneurysm

Rokuya Tanikawa and Kosumo Noda

7.1Key Learning Points

7.2Introduction

7.3Transzygomatic Approach

7.4Transpetrosal Approach (lncludes Posterior Petrosectomy and Anterior Petrosectomy)

7.4.1Posterior Petrosectomy

7.4.2Anterior Petrosectomy

7.5Far Lateral Suboccipital Approach

7.5.1Suboccipital Layer-by-Layer Muscular Dissection

7.6Transcondylar (Fossa) Approach

7.7Vascular Challenges

7.7.1High-Riding Distal Basilar Aneurysm (Basilar Tip and Basilar-Superior Cerebellar Artery [SCA] Aneurysm)

7.7.2P2p or P2-P3 Junction Aneurysm

7.7.3VA-PICA Aneurysm

7.7.4VA-AICA Aneurysm (Midbasilar Aneurysm)

7.8Injury Avoidance

7.8.1Prevention of Frontalis Nerve and Temporomandibular Joint (TMJ) Injury

7.8.2Preservation of Orbital Fascia

7.8.3Avoiding Optic Nerve and Internal Carotid Artery (ICA) Injury

7.9Related Pathologies

7.10Case Examples

7.10.1Case 1

7.10.2Case 2

7.10.3Case 3

7.11Management Strategy

7.11.1Preoperative Management

7.12Potential Complications

7.13Conclusion

References

8Endoscopic Endonasal Aneurysm Treatment

Aneek Patel, Hussam Abou-Al-Shaar, Michael M. McDowell, Georgios A. Zenonos, Eric W. Wang, Carl H. Snyderman, and Paul A. Gardner

8.1Key Learning Points

8.2Introduction

8.3Vascular Challenge

8.4Injury Avoidance

8.4.1Case Selection

8.4.2Proximal and Distal Control

8.4.3Contingency Planning

8.4.4Reconstruction

8.5Related Pathologies

8.6Case Examples

8.6.1Case 1

8.6.2Case 2

8.7Management Strategy and Potential Complications

8.7.1Management of Intraoperative Rupture

8.7.2ICA Sacrifice

8.7.3Minimizing Postoperative Complications

8.8Management Algorithm

8.9Root Cause Analysis

8.10Conclusion

References

9Dealing with Major Intraoperative Vascular Injury During Endonasal Approaches to the Anterior Skull Base

Vincent Dodson, Neil Majmundar, Gurkirat Kohli, Wayne D. Hsueh, Jean Anderson Eloy, and James K. Liu

9.1Key Learning Points

9.2Introduction

9.3Relevant Anatomy

9.4Vascular Challenges

9.5Injury Avoidance

9.6Related Pathologies

9.7Case Example

9.8Management Strategy

9.8.1Initial Steps

9.8.2ICA Injury

9.8.3ACA Injury

9.9Potential Complications

9.10Management Algorithm

9.10.1ICA

9.10.2ACA

9.11Root Cause Analysis (Post Hoc Analysis)

9.12Conclusion

References

10Dealing with Major Intraoperative Vascular Injury

Sean P. Polster, Paul A. Gardner, and Juan C. Fernandez-Miranda

10.1Key Learning Points

10.2Introduction

10.3Vascular Challenge

10.3.1Anatomy of the Middle Fossa ICA

10.3.2Endoscopic Aspects/Challenges

10.4Injury Avoidance

10.4.1Preoperative

10.4.2Anatomical Risk

10.5Impact of Pathologies

10.5.1Operator/Intraoperative

10.6Case Example

10.7Management Strategy/Management Algorithm

10.7.1The Surgeons

10.7.2Cautery

10.7.3Suture/Clip Repair/Ligation

10.7.4Packing

10.7.5Anesthesia Team

10.7.6OR Staff (Technicians, Nurses, Neurophysiology, Blood Bank, and Additional Resources)

10.7.7Neurointerventional/Endovascular Assessment and Treatment

10.8Delayed Complications

10.8.1Vasospasm

10.8.2Pseudoaneurysm Formation/Carotid-Cavernous Fistula

10.9Root Cause Analysis and Lessons Learned

10.9.1Review of the Modern Literature (Search Strategy)

10.10Conclusion

References

11Dealing with Major Vascular Injuries During Endonasal Posterior Fossa Surgery

Pierre-Olivier Champagne, Thibault Passeri, Eduard Voormolen, Anne-Laure Bernat, Rosaria Abbritti, and Sébastien Froelich

11.1Key Learning Points

11.2Introduction

11.3Preoperative Considerations

11.4Surgical Avoidance of Injury

11.5Surgical Management

11.5.1Bleeding Localization and Control

11.5.2Extradural Bleeding

11.5.3Intradural Bleeding

11.6Closure and Reconstruction

11.7Postoperative Management

11.8Illustrative Case

11.8.1Management Analysis and Root Cause Analysis of the Presented Case

11.9Conclusion

References

12Vascular Challenges in Anterior Skull Base Open Surgery

Vinayak Narayan and Anil Nanda

12.1Key Learning Points

12.2Introduction

12.3Surgical Vascular Anatomy of Anterior Cranial Base

12.4Pathologies Involving Anterior Cranial Base, Surgical Approaches, and Associated Vascular Challenges

12.5Vascular Complications in Anterior Cranial Base Surgery

12.6How to Avoid Arterial and Venous Complications?

12.7Illustrative Case Example

12.7.1Case History and Examination

12.7.2Management Strategy and Complications

12.7.3Other Options to Control Intraoperative Severe Bleeding in This Case

12.7.4Root Cause Analysis of the Vascular Injury

12.8Conclusion

References

13Dealing with Vascular Injury During Middle Fossa Surgery

Rami O. Almefty, Michael Mooney, and Ossama Al-Mefty

13.1Key Learning Points

13.2Introduction

13.3Vascular Control and Injury Avoidance

13.4Related Pathologies

13.5Case Example

13.6Management Strategy

13.7Potential Complications

13.8Management Algorithm

13.9Root Cause Analysis—Common Factors Leading to Carotid Artery Injury

13.10Conclusion

References

14Posterior Fossa During Open Skull Base Surgery

David L. Penn, Marte Van Keulen, and Nicholas C. Bambakidis

14.1Key Learning Points

14.2Introduction

14.3Arterial Injury and Complications

14.3.1Arterial Anatomy of the Posterior Fossa

14.3.2Anatomical Variants

14.3.3Management Strategies for Arterial Injury

14.4Venous Injury and Complications

14.4.1Venous Anatomy of the Posterior Fossa

14.4.2Anatomical Variants

14.4.3Management Strategies for Venous Injury

14.4.4Dural Venous Sinus Thrombosis and Postoperative Management

14.5Conclusion

References

15Perforator Injury During Endoscopic Endonasal Skull Base Surgery

João Mangussi-Gomes, Matheus F. de Oliveira, Eduardo A. S. Vellutini, and Aldo C. Stamm

15.1Key Learning Points

15.2Introduction

15.3Compartmentalization of Skull Base Perforators—Related Pathologies and Potential Complications

15.3.1The Anterior Compartment

15.3.2The Posterior Compartment

15.3.3The Inferior Compartment

15.4Injury Avoidance and Management Strategies

15.5Case Example

15.5.1Case Vignette

15.5.2Discussion

15.5.3Root Cause Analysis

15.6Conclusion

References

16Perforator Injury During Open Skull Base Surgery

Nicholas T. Gamboa and William T. Couldwell

16.1Key Learning Points

16.2Introduction

16.3Vascular Challenges

16.4Perforator Injury Avoidance

16.4.1Fundamentals of Perforator Flow Monitoring and Injury Avoidance

16.4.2Technical Nuances

16.5Related Pathologies

16.5.1Open Skull Base Surgery for Pathology Near the Anterior Circulation

16.5.2Open Skull Base Surgery for Pathology Near the Posterior Circulation

16.6Case Examples

16.6.1Optic Tract Glioma Near the Posterior Clinoid

16.6.2Basilar Apex Aneurysm Clipping

16.7Management Algorithm

16.8Root Cause Analysis

16.9Conclusion

References

17Endovascular Options to Treat Iatrogenic Vascular Injury and Tumor Involvement of the Skull Base

Jacob F. Baranoski, Colin J. Przybylowski, Bradley A. Gross, Felipe C. Albuquerque, and Andrew F. Ducruet

17.1Key Learning Points

17.2Introduction

17.3Endovascular Treatment for Iatrogenic Skull Base Vascular Injuries Sustained during Skull Base Surgery

17.3.1Case Example

17.4Preoperative Evaluation, Endovascular Stenting or Vessel Sacrifice Prior to Resection of Skull Base Tumors

17.4.1Case Example

17.5Treatment Considerations for Concomitant ICA Aneurysms and Skull Base Tumors

17.6Conclusion

References

18Extracranial Anterior Cranial Base Surgery for Vascular Tumors

Carl H. Snyderman

18.1Key Learning Points

18.2Introduction

18.3Vascular Challenge

18.4Injury Avoidance

18.5Related Pathologies

18.5.1Fibro-osseous Tumors

18.5.2Angiofibroma

18.5.3Glomangiopericytoma

18.5.4Solitary Fibrous Tumor

18.5.5Sinonasal Malignancy

18.5.6Metastasis

18.6Case Examples

18.6.1Angiofibroma

18.6.2Chondrosarcoma

18.7Management Strategy

18.8Potential Complications

18.9Management Algorithm

18.10Root Cause Analysis

18.11Conclusion

References

19Extracranial Lateral Cranial Base Vascular Tumor Surgery

Sampath Chandra Prasad Rao and Ananth Chintapalli

19.1Key Learning Points

19.2Introduction

19.3Paragangliomas of the Head and Neck

19.4Tympanomastoid Paragangliomas

19.4.1Preoperative Assessment

19.4.2Surgical Approach

19.4.3Class A Tumors

19.4.4Class B Tumors

19.5Tympanojugular Paragangliomas

19.5.1Preoperative Assessment

19.5.2Permanent Balloon Occlusion (PBO)

19.5.3Intraluminal Stenting of the Internal Carotid Artery

19.5.4Facial and Hearing Rehabilitation

19.5.5Surgical Approach

19.6Carotid Body Tumors

19.7Vagal Paragangliomas

19.8Hemangiomas of the Temporal Bone

19.9Malignant Vascular Tumors

19.9.1Kaposi’s Sarcoma

19.9.2Hemangioendothelioma

19.9.3Angiosarcoma

19.9.4Hemangiopericytoma

References

20Venous Considerations in Skull Base Surgery

Chandranath Sen and Carolina Benjamin

20.1Key Learning Points

20.2Introduction

20.3Venous Anatomy

20.3.1Temporal Lobe Draining Veins

20.3.2The Petrosal Vein

20.3.3Torcula

20.3.4Sigmoid Sinuses and Jugular Bulb

20.4Avoidance of Injury

20.4.1Understanding the Relevant Anatomy

20.4.2Using Alternate Approaches

20.4.3Dissection and Preservation of Veins

20.4.4Working on Both Sides of the Sinus

20.4.5Planned Transection of the Sinus for Access to the Tumor and Reconstruction

20.4.6Planned Sacrifice of the Transverse Sinus for Tumor Removal

20.4.7Iatrogenic Thrombosis of the Sinus

20.5Injury to Venous Sinuses

20.6Conclusion

References

21Neurophysiologic Monitoring and Its Role During Cerebrovascular Injury

Carla J.A. Ferreira, Katherine Anetakis, Donald J. Crammond, Jeffrey R. Balzer, and Parthasarathy D. Thirumala

21.1Key Learning Points

21.2Introduction

21.3Cerebral Perfusion Principles and Neurophysiologic Tools for Measurement

21.4IONM Modalities: Technical Considerations

21.4.1SSEP

21.4.2EEG

21.4.3BAEP

21.4.4TcMEP

21.5Anesthetic Considerations

21.6Interpretation

21.7Case Examples

21.7.1Case 1: IONM as an Indicator of Adequate Brain Perfusion

21.7.2Case 2: IONM as an Indicator of Insufficient Brain Perfusion

21.7.3Case 3: IONM as a Predictor of a Large Postoperative Stroke

21.7.4Case 4: IONM as a Predictor of a Subcortical Stroke

21.8Conclusion

References

22Simulation and Training—Preparing for Vascular Injury

Rowan Valentine and Peter-John Wormald

22.1Key Learning Points

22.2Introduction

22.3Simulation Training

22.4Vascular Injury Simulation

22.5Cadaver Models of Endoscopic Vascular Injury

22.6The Sheep Model of Vascular Injury

22.7Surgical Field Visualization and Control

22.8Hemostatic Techniques in Simulated Vascular Injury

22.9Outcomes of Vascular Simulation Training

22.10Conclusion

References

Index

Videos

Video 6.1

Video showing an IMax to MCA interposition graft bypass for treatment of fusiform anterior choroidal artery aneurysm, including interposition graft thrombectomy.

Video 10.1

Video showing a right cavernous ICA injury during resection of a fibrous, invasive growth-hormonesecreting adenoma. Multiple maneuvers were attempted but control finally achieved through muscle packing which led to vessel occlusion requiring endovascular stenting to re-establish flow.

Video 12.1

Operative video showing the transnasal transsphenoidal microsurgical resection of sellar-suprasellar fibrosarcoma and the intraoperative complication of basilar artery injury.

Video 15.1

Video showing endoscopic endonasal resection of a craniopharyngioma with careful dissection and preservation of superior hypophyseal artery perforators.

Video 16.1

Left frontotemporal craniotomy for resection of optic tract glioma complicated by dissection of the posterior communicating artery and anterior choroidal artery vasospasm.

Video 18.1

Endoscopic endonasal/transmaxillary approach with lateral orbitotomy for stage V angiofibroma.

Video 22.1

Video showing a carotid artery injury animal simulation using an endoscopic endonasal model on a sheep cervical carotid artery.

Preface

The cranial base is one of the most inaccessible regions of the human body and consequently presents a complex surgical challenge. Every cranial nerve and intracranial artery and vein pass through foramina, concentrically splayed around the central skull base. Cranial nerve injury can impact quality of life, but injury to arteries or veins poses the greatest potential to devastate a patient. This makes vascular damage the most feared complication for both patients and surgeons. Outcomes range from headache to loss of senses or function to irreversible stroke, vegetative state, or even death.

The understanding of the anatomy, surgical techniques for avoidance and management of injury, and endovascular adjuncts have advanced dramatically over the past decade. These advances, in addition to new surgical techniques and approaches, from endoscopic and minimally invasive to creative bypass techniques, have revolutionized the practice of skull base surgery.

This book was designed to learn from masters of each of these facets with careful consideration of all possible vascular challenges. No single practitioner or specialty can develop all aspects of intra- and extracranial vascular control alone, but through a conglomeration of knowledge, the basic tenets for avoidance and management strategies for vascular injury can be set forth for all skull base surgeons to apply.

Many of the chapters and all of the authors were chosen to further our own practice and, not surprisingly, formulating and editing this text has dramatically advanced our understanding of the challenges facing our subspecialty as it relates to the management of these critical structures.

Paul A. Gardner, MD Carl H. Snyderman, MD, MBA Brian T. Jankowitz, MD

Acknowledgment

We extend our gratitude to Mary Jo Tutchko, without whom nothing would get done.

Paul A. Gardner, MD Carl H. Snyderman, MD, MBA Brian T. Jankowitz, MD

Contributors

Rosaria Abbritti, MD Department of Neurosurgery Lariboisière Hospital Paris, France

Hussam Abou-Al-Shaar, MD Department of Neurological Surgery University of Pittsburgh Pittsburgh, Pennsylvania, USA

Felipe C. Albuquerque, MD Department of Neurosurgery Barrow Neurological Institute Phoenix, Arizona, USA

Ossama Al-Mefty, MD Department of Neurosurgery Brigham andWomen’s Hospital Harvard Medical School Boston, Massachusetts, USA

Rami O. Almefty, MD Department of Neurosurgery Temple University Philadelphia, Pennsylvania, USA

Katherine Anetakis, MD Department of Neurological Surgery University of Pittsburgh Pittsburgh, Pennsylvania, USA

Jeffrey R. Balzer, PhD Department of Neurological Surgery University of Pittsburgh Pittsburgh, Pennsylvania, USA

Nicholas C. Bambakidis, MD Department of Neurological Surgery University Hospitals of Cleveland Cleveland, Ohio, USA

Jacob F. Baranoski, MD Department of Neurosurgery Barrow Neurological Institute Phoenix, Arizona, USA

Carolina Benjamin, MD Department of Neurosurgery University of Miami Miami, Florida, USA

Anne-Laure Bernat, MD Department of Neurosurgery Lariboisière Hospital Paris, France

Pierre-Olivier Champagne MD, PhD, Department of Neurosurgery Laval University Hospital Center Quebec, Canada

Ananth Chintapalli, MS Department of ENT- Head & Neck Surgery Kamineni Academy of Medical Sciences and Research Center Hyderabad, India

William T. Couldwell, MD, PhD Department of Neurosurgery University of Utah Salt Lake City, Utah, USA

Donald J. Crammond, PhD Department of Neurological Surgery University of Pittsburgh Pittsburgh, Pennsylvania, USA

Amir R. Dehdashti, MD Department of Neurosurgery North Shore University Hospital Zucker School of Medicine at Hofstra/Northwell Manhasset, New York, USA

Matheus F. de Oliveira, MD, PhD Department of Neurosurgery São Paulo Skull Base Center São Paulo, Brazil

Vincent Dodson, MD Department of Neurological Surgery Rutgers New Jersey Medical School Newark, New Jersey, USA

Andrew F. Ducruet, MD Department of Neurosurgery Barrow Neurological Institute Phoenix, Arizona, USA

Jean Anderson Eloy, MD Department of Otolaryngology Rutgers New Jersey Medical School Newark, New Jersey, USA

Juan C. Fernandez-Miranda, MD Department of Neurosurgery Stanford University Stanford, California, USA

Carla J.A. Ferreira, MD Department of Neurological Surgery University of Pittsburgh Pittsburgh, Pennsylvania, USA

Sébastien Froelich MD Department of Neurosurgery Lariboisière Hospital Paris, France

Nicholas T. Gamboa, MD Department of Neurosurgery University of Utah Salt Lake City, Utah, USA

Paul A. Gardner, MD Professor and Peter J. Jannetta Endowed Chair Department of Neurological Surgery University of Pittsburgh School of Medicine; Co-Director, Center for Cranial Base Surgery University of Pittsburgh Medical Center Pittsburgh, Pennsylvania, USA

Bradley A. Gross, MD Department of Neurological Surgery University of Pittsburgh Pittsburgh, Pennsylvania, USA

Wayne D. Hsueh, MD Department of Otolaryngology Rutgers New Jersey Medical School Newark, New Jersey, USA

Becky Hunt, MBChB, FRCR Department of Neuroradiology North Bristol NHS Trust Bristol, United Kingdom

Brian T. Jankowitz, MD Associate Professor Director, Cerebrovascular Surgery Department of Neurological Surgery Perelman School of Medicine at the University of Pennsylvania Philadelphia, Pennsylvania, USA

Gurkirat Kohli, MD Department of Neurological Surgery Rutgers New Jersey Medical School Newark, New Jersey, USA

Kevin Kwan, MD Department of Neurosurgery North Shore University Hospital Zucker School of Medicine at Hofstra/Northwell Manhasset, New York, USA

Philippe Lavigne, MD Department of Otolaryngology University of Montreal Montreal, Quebec, Canada

James K. Liu, MD Department of Neurological Surgery Rutgers New Jersey Medical School Newark, New Jersey, USA

Neil Majmundar, MD Department of Neurological Surgery Rutgers New Jersey Medical School Newark, New Jersey, USA

João Mangussi-Gomes, MD Department of Otolaryngology São Paulo Skull Base Center São Paulo, Brazil

Michael M. McDowell, MD Department of Neurological Surgery University of Pittsburgh Pittsburgh, Pennsylvania, USA

Michael A. Mooney, MD Department of Neurosurgery Brigham andWomen’s Hospital Harvard Medical School Boston, Massachusetts, USA

Anil Nanda, MD, MPH, FACS Department of Neurosurgery Rutgers-New Jersey Medical School and Rutgers-RobertWood Johnson Medical School Newark, New Jersey, USA

Vinayak Narayan, MD Department of Neurosurgery Rutgers-RobertWood Johnson Medical School and University Hospital New Brunswick, New Jersey, USA

Kosumo Noda, MD Department of Neurosurgery Sapporo Teishinkai Hospital Sapporo, Hokkaido, Japan

Maximiliano A. Nuñez, MD Department of Neurosurgery Stanford University Stanford, California, USA

Aneek Patel, BS School of Medicine New York University New York, New York, USA

Thibault Passeri, MD Department of Neurosurgery Lariboisière Hospital 2Paris, France

David L. Penn, MD, MS Department of Neurological Surgery University Hospitals of Cleveland Cleveland, Ohio, USA

Ivo Peto, MD Department of Neurosurgery North Shore University Hospital Zucker School of Medicine at Hofstra/Northwell Manhasset, New York, USA

Sean P. Polster, MD Department of Neurological Surgery University of Pittsburgh Pittsburgh, Pennsylvania, USA

Sampath Chandra Prasad Rao, MS, DNB, FEB-ORLHNS Department of ENT- Skull Base Surgery Manipal Hospital Bangalore, India

Colin J. Przybylowski, MD Department of Neurosurgery Barrow Neurological Institute Phoenix, Arizona, USA

Zeeshan Qazi, MBBS, MS, MCh Department of Neurological Surgery Mayo Clinic Phoenix, Arizona, USA

Shelley Renowden, BSc, MBChB, MRCP, FRCR Department of Neuroradiology North Bristol NHS Trust Bristol, United Kingdom

Joao Alves Rosa, MD, MRCP, FRCR Department of Neuroradiology North Bristol NHS Trust Bristol Bristol, United Kingdom

Julia R. Schneider, DO Department of Neurosurgery North Shore University Hospital Zucker School of Medicine at Hofstra/Northwell Manhasset, New York, USA

Laligam N. Sekhar, MD, FACS, FAANS Department of Neurological Surgery University ofWashington Seattle,Washington, USA

Chandranath Sen, MD Department of Neurosurgery NYU Langone Health New York, New York, USA

Carl H. Snyderman, MD, MBA Professor Department of Otolaryngology University of Pittsburgh School of Medicine; Co-Director, Center for Cranial Base Surgery University of Pittsburgh Medical Center Pittsburgh, Pennsylvania, USA

Aldo C. Stamm, MD Department of Otolaryngology São Paulo Skull Base Center São Paulo, Brazil

Rokuya Tanikawa, MD Department of Neurosurgery Sapporo Teishinkai Hospital Sapporo, Hokkaido, Japan

Parthasarathy D. Thirumala, MD, MS Department of Neurological Surgery University of Pittsburgh Pittsburgh, Pennsylvania, USA

Daniel A. Tonetti, MD Department of Neurological Surgery University of Pittsburgh Pittsburgh, Pennsylvania, USA

Rowan Valentine, MBBS, PhD Department of Surgery-Otorhinolaryngology, Head and Neck Surgery University of Adelaide Adelaide, Australia

Marte Van Keulen, MD Department of Neurological Surgery University Hospitals of Cleveland Cleveland, Ohio, USA

Ananth K. Vellimana, MD Department of Neurological Surgery Washington University St. Louis, Missouri, USA

Eduardo A.S. Vellutini, MD Department of Neurosurgery São Paulo Skull Base Center São Paulo, Brazil

Eduard Voormolen, PhD, MD Department of Neurosurgery Lariboisière Hospital Paris, France

Eric W.Wang, MD Department of Otolaryngology University of Pittsburgh Pittsburgh, Pennsylvania, USA

Peter-JohnWormald, MD Department of Surgery-Otorhinolaryngology, Head and Neck Surgery University of Adelaide Adelaide, Australia

Georgios A. Zenonos, MD Department of Neurological Surgery University of Pittsburgh School of Medicine Pittsburgh, Pennsylvania, USA

1 Vascular Anatomy of the Head and Neck/Circle of Willis*

Aneek Patel, Hussam Abou-Al-Shaar, Maximiliano A. Nuñez, Georgios A. Zenonos, Paul A. Gardner, and Juan C. Fernandez-Miranda

Summary

This chapter reviews the pertinent anatomy of head and neck vasculature as it relates to skull base and cerebrovascular surgery. Understanding this anatomy is a foundational step to selecting surgical approaches and treatment modalities, knowing the clinical consequences of intraoperative decisions, and avoiding complications. In this chapter, we will break down the head and neck circulatory system into anterior and posterior circulation and review the major branches, common variants, and their clinical significance.

Keywords: Internal carotid artery, vertebral artery, anterior cerebral artery, middle cerebral artery, basilar artery, posterior cerebral artery, posterior communicating artery

1.1 Key Learning Points

●The vasculature of the head and neck can have a considerable level of anatomic variability, including variations in origin points, origin vessels, collateralization, and trajectories in relation to other anatomical landmarks.

●An understanding of the origins, courses, and variants of head and neck vessels is essential for the successful planning of skull base and cerebrovascular surgery, including the selection of the optimal approach, visualization of vital structures, proximal and distal vascular control, and limitations.

●The cavernous internal carotid artery (ICA) has the following components: short vertical or ascending segment, posterior genu, horizontal segment, and anterior genu.

●The communicating segment of the ICA carries the largest numbers of perforators to the anterior perforated substance and optic tracts. Injury to these small vessels that lie posterior to the carotid bifurcation will cause a dense contralateral motor deficit.

●The second division of the anterior cerebral artery (A2) gives off the recurrent artery of Heubner after the anterior communicating artery, which is the most common site of intracranial aneurysms. It is critical to preserve this branch whose occlusion typically results in a caudate infarct.

●The M1 segment of the middle cerebral artery delivers the lateral lenticulostriate arteries as well as the anterior temporal artery. Temporary clipping of M1 should be done as distally as possible to avoid occluding these critical M1 perforators.

●The ophthalmic artery and other branches of the ICA commonly anastomose with extracranial vessels, including the internal maxillary artery and ethmoidal arteries.

●Access to the basilar apex often requires a posterior clinoidectomy and/or transcavernous corridor; for low-lying apical aneurysms, an endoscopic endonasal approach may be an option.

1.2 Introduction

The vasculature of the head and neck consists of an anterior and a posterior circulations that give off branches as they travel up the neck and partially anastomose at the circle of Willis to provide blood supply throughout the brain. The circle of Willis sits in the center of the cranial base and can be accessed through a variety of skull base and cerebrovascular surgical techniques, each one with its advantages and limitations. The circle of Willis plays a vital role in providing adequate collateral supply to both hemispheres through communicating arterial trees both anteriorly and posteriorly. A comprehensive understanding of head and neck vasculature is fundamental for the treatment of vascular and skull base lesions as well as for preventing complications and identifying surrounding critical structures. However, this anatomic understanding must also remain fluid, as head and neck vasculature can often include natural variations or distortions because of pathology which should be taken into account preoperatively and adapted to intraoperatively. In this chapter, we will review the anatomy of the head and neck vasculature, and discuss the major anatomical variants and clinical significance of the vasculature in the head and neck as they are pertinent to skull base and cerebrovascular surgery.

1.3 Anterior Circulation

1.3.1 Cervical Carotid Artery

The internal carotid artery (ICA) has seven segments: cervical (C1), petrous (C2), lacerum (C3), cavernous (C4), clinoid (C5), ophthalmic (C6), and communicating (C7) segments (Fig. 1.1).

Fig. 1.1(a–c) Left-sided lateral dissection demonstrating the circle of Willis and the relationship of the vasculature to surrounding neural structures. Note the segments of the internal carotid artery (ICA) as it courses superiorly through the skull base. A., artery; A. Com. A., anterior communicating artery; A.I.C.A., anterior inferior cerebellar artery; Bas. A., basilar artery; Br., branch; Cer. Mes. Fiss., cerebellomesencephalic fissure; Clin., clinoidal; CN., cranial nerve; Cran., cranial; I.C.A., internal carotid artery; Inf., inferior; L., left; Lac., lacrimal; Max., maxillary; Occip. A., occipital artery; Opth., ophthalmic; Par. Occ. Br. of P.C.A., parieto-occipital branches of the posterior cerebral artery; P.C.A., posterior cerebral artery; P. Com. A., posterior communicating artery; Pet., petrous; P.I.C.A., posterior inferior cerebellar artery; R., right; S.C.A., superior cerebellar artery; Seg., segment; Sphen., sphenoid; Tr., trunk; Tent., tentorium; Vent., ventricle; Vert., vertebral.

The common carotid artery (CCA) branches directly off the aortic arch on the left and the brachiocephalic artery on the right, which then becomes the right subclavian artery. This brachiocephalic bifurcation most commonly occurs posterior to the sternoclavicular joint.1 The most common anatomical variation is known as a “bovine aortic arch,” in which both the left and right CCAs originate from the brachiocephalic artery.2 Most often incidentally found, this variation has a prevalence of 11 to 27%.3 Bilaterally, the CCAs travel up the neck within the fibrous carotid sheath, which is made up of deep fascial layers and also contains the internal jugular vein (IJ) and vagus nerve (Fig. 1.2). Within the carotid sheath, the CCA runs medial to the IJ and anterior to the vagus nerve in most individuals.4 The CCA then bifurcates into the ICA and external carotid artery (ECA). The level of this bifurcation varies and is most commonly at the level of C3, approximately 1 to 2 cm above the superior border of the thyroid lamina, although it can also bifurcate as low as the level of the cricoid cartilage or as high as the hyoid cartilage.5,​6,​7 High-bifurcating CCAs become clinically important because they serve as cautionary surgical landmarks for a nearby hypoglossal nerve and marginal mandibular nerve.8,​9 For this reason, carotid stenting may be preferable over carotid endarterectomy in cases of high-bifurcating CCAs.10

After the carotid bifurcation, the ECA exits the carotid sheath and the ICA continues within the sheath. The origin of the superior thyroid artery (STA), the first branch of the ECA, varies widely between the CCA, the carotid bifurcation, and the ECA, and studies largely disagree on which variant is most prevalent.7,​8,​11 After potentially giving off the STA, the ECA then gives off the ascending pharyngeal artery, which supplies the larynx, after which it gives off the lingual artery.9 The other branches of the ECA in order include the facial, occipital, and posterior auricular arteries (Fig. 1.2). The ECA ends as the internal maxillary and superficial temporal artery, both of which are readily utilized during bypass surgery. After the bifurcation, the ICA continues within the carotid sheath toward the skull base, where it enters the carotid canal of the temporal bone.

It should be noted that the common classification system used for the segments of the ICA was made to describe the course of the ICA based on pertinent anatomical landmarks as they are encountered from an open, microsurgical perspective. However, with the increasing applications of endoscopic endonasal approaches to skull base lesions, the standard classification scheme for the ICA will also be compared to a classification scheme that is more suitable for endonasal surgery (Table 1.1). As such, what has been described microscopically as the cervical segment of the ICA, C1, can also be classified as the parapharyngeal segment of the ICA; through an endoscopic corridor, this segment is defined as the portion of ICA found behind the lateral cartilaginous eustachian tube spanning to the external opening of the carotid canal.12

Table 1.1 Correlating traditional ICA segments to their nearest anatomic counterparts from an endoscopic endonasal ICA classification scheme

Microscopic ICA segments

Endoscopic ICA segment correlates

Cervical (C1)

Parapharyngeal

Petrous (C2)

Petrous

Lacerum (C3)

Lacerum (Paraclival origin)

Cavernous (C4)

Paraclival/Parasellar

Clinoid (C5)

Parasellar

Ophthalmic (C6)

Intradural/Supraclinoidal

Communicating (C7)

Abbreviation: ICA, internal carotid artery.

Fig. 1.2(a–c) Left posterolateral dissection showing the course of the common carotid artery after its origin ascending in the carotid sheath until its bifurcation into the external and internal carotid arteries. Note the branches of the external carotid artery depicted in the figure including the facial and occipital arteries. The internal jugular vein lies lateral to the internal carotid artery (ICA) in the carotid sheath. A., artery; Bas.A., basilar artery; CN., cranial nerve; Common carotid A., common carotid artery; Ext., external; Facial A, facial artery; I.C.A., internal carotid artery; Int. Jug., internal jugular; Occip.A., occipital artery; P.I.C.A., posterior inferior cerebellar artery; Vert. A., vertebral artery; V3, 3rd segment vertebral artery.

1.3.2 Petrous and Lacerum Carotid Artery

The petrous segment of the ICA, C2, describes the portion of the ICA that courses first vertically and then horizontally through the carotid canal of the temporal bone, entirely encased in bone; however, the superior aspect of the canal may be dehiscent, placing the ICA at risk of inadvertent injury during middle fossa approaches. Within the carotid canal, the ICA is surrounded by periosteum and gives off no branches.13 While coursing anteromedially, C2 runs deep and medial to the greater and lesser superficial petrosal nerves and to the tensor tympani and eustachian tube.14

Upon exiting the petrous carotid canal, the ICA courses along the superior aspect of the foramen lacerum. This lacerum or C3 segment describes the stretch of ICA that bends and courses medial to the petrolingual ligament and lingual process to enter the cavernous sinus (Fig. 1.1 and Fig. 1.3). Throughout this segment, the ICA continues to be surrounded by periosteum and has a constant anatomic relationship with the pterygosphenoidal fissure and vidian nerve.14,​15 In fact, the pterygosphenoidal fissure represents a highly reliable landmark to identify and expose the lacerum ICA during endonasal endoscopic approaches.

Fig. 1.3 The left-sided petrous internal carotid artery (ICA) courses through the petrous bone to become the C3 segment after traversing the petrolingual ligament to enter the cavernous sinus. A., artery; A.I.C.A., anterior inferior cerebellar artery; Asc. Segm., ascending segment of cavernous ICA; CN., cranial nerve; I.C.A., internal carotid artery; Inf. Pet. Sin., inferior petrosal sinus; Lat. Rect.M., lateral rectus muscle; Max. A, internal maxillary artery; P.C.A., posterior cerebral artery; Petroling. Lig., petrolingual ligament; S.C.A., superior cerebellar artery; Seg(m)., segment; Tent. tentorium.

Fig. 1.4(a, b) Cadaveric dissection showing the right cavernous (C4), clinoidal (C5), and ophthalmic (C6) segments of the internal carotid artery (ICA). Note the different branches of the cavernous ICA segment. Additionally, note the course of the ICA as it traverses through the proximal and distal dural rings and the different turns that the cavernous ICA takes. A., artery; Ant. Lobe, anterior lobe of pituitary gland; CN., cranial nerve; Clin., clinoidal; Dors.Men.A., dorsal meningeal artery; Inf.Hyp.A., inferior hypophyseal artery; Inf.Lat.Tr., inferolateral trunk; Men.Hyp.Tr., meningohypophyseal trunk; Opth.A., ophthalmic artery; Petrosphen.Lig., petrosphenoid ligament; Post., posterior; Prox., proximal dural; Seg(m)., segment.

1.3.3 Paraclival and Cavernous Carotid Artery

After exiting the carotid canal of the petrous temporal bone and passing through foramen lacerum, the ICA courses parallel to the clivus before entering the cavernous sinus (Fig. 1.1 and Fig. 1.4). At this level, the ICA runs within the carotid sulcus or groove, which is located in the lateral aspect of the body of the sphenoid. In cases of well-pneumatized sphenoid sinuses, the carotid grooves are readily identified at the lateral aspect of the clival recess; that is why this ICA segment has been classically named “paraclival.” This ICA segment also courses medial to V2 and the inferior aspect of gasserian ganglion for which it has also been called “paratrigeminal.”16

The upper petroclival fissure runs just behind the ICA at the carotid groove, with the petrous apex laterally and the petrosal process of the sphenoid bone medially; the top of this process can be used as a reliable landmark to identify the floor of the cavernous sinus where the abducens nerve enters from Dorello’s canal.17,​18

The cavernous ICA has the following components: short vertical or ascending segment, posterior genu, horizontal segment, and anterior genu (Fig. 1.4). The posterior genu commonly serves as the origin of the meningohypophyseal trunk (or the inferior hypophyseal, tentorial, and dorsal meningeal arteries separately), which supplies the posterior pituitary gland, dorsum sella, clival dura, and tentorium, while the lateral aspect of the proximal horizontal segment is typically the origin of the inferolateral trunk that gives off branches to the lateral wall of the cavernous sinus and related cranial nerves (Fig. 1.4).19 The horizontal segment of the cavernous ICA delimits the venous compartments of the cavernous sinus into: superior, inferior, posterior, and lateral;20 each compartment has distinct boundaries and dural and neurovascular relationships: the superior compartment relates to the interclinoidal ligament and oculomotor nerve, the posterior compartment bears the gulfar segment of the abducens nerve and inferior hypophyseal artery, the inferior compartment contains the sympathetic nerve and distal cavernous abducens nerve, and the lateral compartment includes all cavernous cranial nerves and the inferolateral arterial trunk.

The ICA then ascends lateral to the medial wall of the cavernous sinus and medial to V1, trochlear, and oculomotor nerves as it continues superiorly until it reaches the proximal dural ring, which is formed ventrally by the carotido-clinoidal ligament and dorsally by the carotid-oculomotor membrane.21 Thus, cavernous ICA aneurysms are extradural and their rupture does not lead to subarachnoid hemorrhage but may lead to the formation of spontaneous carotid-cavernous fistulae.

The segment between the proximal and distal dural rings is known as the clinoid segment (Fig. 1.4). It is not uncommon to have bony dehiscence over the ventral aspect of the clinoid segment of the carotid artery, which is vital to identify during endoscopic endonasal surgery to avoid ICA injury. Identifying the clinoid segment is particularly important in the surgical management of paraclinoidal aneurysms because this segment is the site of proximal control. Microsurgically, it can be accessed by performing an anterior clinoidectomy and distal annulectomy. Endoscopically, this segment is entered by transecting the carotido-clinoidal ligament, which forms the ventral aspect of the proximal dural ring.17 This ligament can also be calcified, connecting the middle clinoid to the anterior clinoid, making its removal significantly more difficult. The aforementioned bony dehiscence and calcified rings make studying the preoperative imaging and computed tomography scans as well as meticulous dissection intraoperatively of paramount importance. After passing through the distal dural ring, the ICA enters the intradural space.

1.3.4 Supraclinoid Internal Carotid Artery

After passing through the distal dural ring, the ICA runs posteriorly and then superiorly until it bifurcates into the anterior cerebral artery (ACA) and middle cerebral artery (MCA) at the circle of Willis. Before this bifurcation, the ICA gives off several critical branches: the superior hypophyseal artery, the ophthalmic artery, the posterior communicating artery, and the anterior choroidal artery.

The first major branch of the ICA is the ophthalmic artery (OphA), which arises from the medial surface of the ICA (Fig. 1.5). The OphA is responsible for supplying the muscles of the orbit as well as several facial muscles. It runs inferior to the optic nerve to enter the optic canal in the lesser wing of the sphenoid bone. The OphA branches into the critical central retinal artery (usually medial to the ciliary ganglion), which supplies the retina.22 The OphA typically branches off the inferior surface of the ICA, near the distal dural ring, and therefore risk of OphA occlusion needs to be taken into account when deciding between flow diversion and clipping for proximal ICA aneurysms.23 However, it should be noted that the distal ophthalmic artery has significant collateral from the ethmoidal arteries, making occlusion of the proximal ophthalmic artery often asymptomatic.24

Fig. 1.5 The left ophthalmic artery branches anteromedially from the internal carotid artery (ICA) and courses anteriorly into the orbit along with and inferolaterally to the optic nerve in the optic canal. A., artery; CN., cranial nerve; Inf. Rec. M., inferior rectus muscle; Lac., lacrimal; Max. A., internal maxillary artery; Ophth. A., ophthalmic artery; Sphen., sphenoid; Tent. tentorium.

The medial aspect of the ophthalmic segment of the ICA may give off one or more superior hypophyseal arteries (SHAs) that supply the inferior and anterior aspects of the chiasm, stalk, and pituitary gland. A recent study, however, has shown that the origin of the SHA is often at the clinoidal ICA segment.25 The anatomy and potential displacement of the SHAs become particularly important during suprasellar surgery, as their displacement over the superolateral aspect of tumors such as meningiomas and craniopharyngiomas dispose them to a greater risk of injury from an “open,” lateral approach in comparison to an endonasal one. There are many variations in the branching pattern of the SHAs, but most commonly there are three branches: infundibular anastomotic, which supplies the stalk and universally anastomoses with its counterpart; optic or recurrent, which vascularizes the inferior and anterior aspects of the precanalicular optic nerve and chiasm; and the descending or diaphragmatic, which irrigates the dural diaphragm and/or the upper surface of the gland. The SHA branches supplying the chiasm and stalk should be preserved in every instance while SHA branches that supply the sellar diaphragm can be more readily sacrificed if necessary. It is important to note that craniopharyngiomas and other suprasellar lesions will often get vascular supply from the SHA branches, and selective cauterization is mandatory to preserve the critical main trunks.

The ICA next gives off the posterior communicating artery (PComA) either posteriorly or laterally. The PComA runs posteromedially to reach the posterior cerebral artery (PCA) above the oculomotor nerve, which is most commonly medial, although it can occasionally run lateral, to the nerve (Fig. 1.1c). Due to this proximity, PComA aneurysms can often present with third nerve palsies.26 Approximately 4 to 15 perforating vessels can be found throughout the length of the PComA, the largest of which is designated the anterior thalamoperforating artery. Perforator injury can be avoided closer to the PCA, where the frequency of PComA perforators decreases substantially.27,​28 Not uncommonly the PComA terminates as the PCA, without a distinct PCA originating from the basilar artery (BA), termed fetal PCA. Thus, aneurysms of a fetal PCA should be dealt with high caution as occlusion of the vessel can lead to catastrophic PCA stroke. The PComA or proximal PCA is frequently adherent to the posterior or lateral aspect of suprasellar lesions, especially craniopharyngiomas, and should be carefully identified and preserved.

The anterior choroidal artery (AChA) arises from the inferolateral aspect of the ICA and runs inferior to the optic chiasm, crossing the optic tract first medially and then laterally. Branches of the AChA supply the uncus of the temporal lobe (unco-hippocampal artery), optic tract, and choroid plexus of the temporal horn. They also go through the anterior perforated substance to supply the posterior limb of the internal capsule. Hence, injury to this artery may result in hemianopia and contralateral hemiparesis.29 After entering the choroid plexus via the anterior choroidal point, the AChA may still give off branches to the pulvinar of thalamus and other relevant areas of the central core.

The communicating segment of the ICA carries the largest numbers of perforators to the anterior perforated substance and optic tracts. Injury to these small vessels that lie posterior to the carotid bifurcation will cause a dense contralateral motor deficit. Importantly, AChA aneurysms commonly occur at the branch points between the parent AChA vessel and a perforator; these aneurysms are difficult to treat both endovascularly and microsurgically due to the proximity of perforating vessels and limited surgical corridor.30,​31

1.3.5 Anterior Cerebral Artery (A1 and A2 Segments)

The anterior branch of the ICA bifurcation is the ACA, which travels anterior, medial, and superior to the optic tract to reach the anterior communicating artery (AComA) (Fig. 1.1). The ACA is divided into five segments, the first two of which are important to understand their course and branches for skull base and cerebrovascular surgery. The most proximal segment, A1, is defined as the segment between the origin of the ACA from the ICA and the branching point of the AComA. The medial lenticulostriate arteries originate from the medial aspect of A1 to enter the anterior perforated substance. The AComA can also carry perforators to the superior aspect of the chiasm and hypothalamus. The subcallosal artery emerges from the posterior or posterosuperior surface of the AComA to supply the septal region and one or both fornices and is most commonly encountered inferior to the AComA through an endonasal approach.32 Damage to this vessel can result in acute, severe memory loss.33

The proximal segment of A2 gives off one or more recurrent arteries of Heubner (RAH), which run parallel and lateral to A1 in opposite directions and end anterior to the carotid bifurcation where they enter the anterior perforated substance. In approximately half of the patients, the RAH can run anterior to the A1, which is particularly salient during the surgical treatment of AComA aneurysms. Damage to the RAH, which supplies portions of the basal ganglia, caudate, and internal capsule, can lead to hemiparesis and/or aphasia.34

The A2 segment also gives rise more distally to the fronto-orbital artery (FOA), which runs along the inferior surface of the frontal lobe and supplies the olfactory bulb and olfactory tract along with adjacent fronto-basal gyri. It courses anteriorly along the frontal lobe, crossing the olfactory tract, and enters the olfactory sulcus. As such, it is commonly involved in olfactory groove meningiomas (OGMs) and must be carefully dissected away from the resected tumor.34

The AComA itself, a small anastomosis between the A1 segments of the ACAs bilaterally, is the most common intracranial site of aneurysms.35 Although endovascular treatment of these aneurysms is possible, it can be difficult in some instances due to the tortuosity of A1 and wide involvement of the A1/A2 bifurcation.36 In such instances, surgical clipping may be indicated; medially projecting aneurysms may be rarely considered for endoscopic endonasal surgery, but these are generally best treated with microsurgical clipping. The A3 and A4 segments correspond to the callosomarginal artery at the superior surface of the corpus callosum and the pericallosal artery, respectively, followed by A5 terminal branches of the ACA.

1.3.6 Middle Cerebral Artery (M1 Segment)

After giving off the ACA, the ICA becomes the MCA, which supplies the majority of the lateral cerebral cortex as well as parts of the basal temporal and occipital lobes, and insula (Fig. 1.1c). The origin of MCA is commonly found medial to the sylvian fissure and lateral to the chiasm.37 The MCA is made up of four segments; the first segment, M1, is most relevant to skull base and cerebrovascular surgery. The M1 segment courses within the sylvian vallecula along the proximal or sphenoidal sylvian fissure, running posterior and parallel to the lesser sphenoid wing, superior and medial to the uncus, and inferior to the anterior perforated substance to which it delivers the lateral lenticulostriate arteries before becoming M2. However, in instances of a short M1 segment that ends before traversing the vallecula of the sylvian fissure, the perforating branches can originate from the proximal M2 as well. The lateral lenticulostriate arteries supply deep structures of the basal ganglia (the lentiform nucleus, portions of the internal capsule, and caudate) as well as the insular cortex, and their occlusion can lead to motor, cognitive, and speech impairments. Infarcts in lateral lenticulostriate arteries tend to present with more severe motor deficits than those in anterior lenticulostriate arteries.38,​39

The M1 segment of the MCA also gives off the anterior temporal artery (ATA), which supplies the temporal pole and is responsible for semantic and social processing. The M1 segment ends at the limen insulae, where the MCA typically bifurcates into a superior and inferior division.

It is important to note that M1 perforators, predominantly branching off the dorsolateral surface of the M1 segment, are present throughout the length of the segment as it crosses through the sylvian fissure. Therefore, temporary proximal clipping of M1 risks occlusion of these critical perforators; if necessary, clipping should be done as distally and as close to the lesion as possible to minimize unnecessary vessel occlusion.40 The M2 starts after the bifurcation to enter the distal or opercular sylvian fissure and circular sulcus of the insula, followed by the opercular (M3) and cortical (M4) segments of the MCA.41 The cortical segments of the MCA are the common recipients of anastomosis in bypass surgery, given their ease of access, size match with donor and arterial interposition grafts, and avoidance of even transient M1 occlusion.

1.4 Posterior Circulation

1.4.1 Vertebral and Basilar Arteries

The vertebral arteries (VAs) provide posterior cerebral blood supply, ultimately anastomosing with the anterior carotid supply at the circle of Willis. The VA originates from the subclavian arteries bilaterally and has a short extraosseous segment before entering the transverse foramen of C6 (in 15–20% C7) as the V1 segment. As it travels in the transverse foramina, it becomes V2, giving off several muscular branches on its way. At the level of C3, V2 exits the transverse foramen and loops along the vertebral artery groove posterosuperiorly and then exits the C2 transverse foramen to become the V3 segment.46 V3 then enters the transverse foramen of C1 and exits, which gives off the posterior meningeal and sometimes the accessory meningeal arteries. It then turns medially in the sulcus arteriosus of C1 before heading anteriorly and superiorly to enter the dura as V4 (Fig. 1.2b, c).47

The V4 segment is divided by the preolivary sulcus into lateral and anterior medullary segments. Intracranially, V4 gives off the posterior inferior cerebellar artery (PICA), which is responsible for supplying part of the cerebellum as well as the lateral aspect of the medulla (Fig. 1.1a, b). The origin of PICA commonly occurs approximately 2 cm superior to the dural entrance of V4, although this origin can vary, occurring anywhere from the V3 segment to the BA.48 Occlusion of the PICA can lead to a lateral medullary syndrome, which is characterized by ipsilateral face and contralateral body hemisensory deficit, ipsilateral Horner’s syndrome, and cerebellar signs (ataxia, dysmetria, dysdiadokinesia, nystagmus, slurred speech, and intention tremor).49

Continuing superiorly, the VA then gives off the anterior spinal artery bilaterally and then courses between the lower cranial nerves to reach the contralateral VA and forms the BA. The anterior spinal artery most commonly originates approximately 5 to 10 mm proximal to the vertebrobasilar junction (VBJ).50 The VBJ occurs medial and most commonly immediately inferior to the origin of cranial nerve VI (CN VI) in the pontomedullary sulcus, although it can often occur superior to the sulcus as well.50,​51 As such, the VBJ is a good landmark for the origin of CN VI.

The first major branch of the BA, if the PICA has already originated from the VA, is the anterior inferior cerebellar artery (AICA), which originates from the more inferior half of the BA in over 90% of individuals (Fig. 1.1b, c). Rarely, as mentioned when discussing the PICA, the AICA can originate from a common AICA-PICA trunk stemming off the BA as well.52 The BA then gives off multiple pontine perforating vessels bilaterally before branching into the superior cerebellar artery (SCA) followed closely by the PCA.53 This bifurcation, known as the basilar apex, is significant because it is a relatively common site for aneurysms and can be difficult to access microsurgically; it can often require posterior clinoidectomy and/or a transcavernous corridor (for both open and endonasal approaches). For this reason, the position of the basilar apex is important; low-lying basilar apex aneurysms (as well as low-lying AICA aneurysms, which are less common but similarly challenging to access microsurgically) can be accessed through the endoscopic endonasal approach if clipping is indicated. The third cranial nerve courses between the PCA and SCA, a reliable and important localizing relationship.

1.4.2 Posterior Cerebral Artery (P1 and P2 Segments)

The PCA is the terminal branch of the BA, originating from the basilar apex (Fig. 1.1). The first segment, P1, runs from the basilar bifurcation up to the anastomosis with the PComA. Posterior thalamoperforators branch off the PCA and go into the interpeduncular cistern and the posterior perforated substance. Long and short circumflex arteries originate in this segment to supply the mesencephalon. The origins of these branches and the trunk of P1 can be accessed through a lateral frontotemporal or cranio-orbital approach with or without a posterior clinoidectomy, or endoscopically through a transclival (pituitary transposition) approach although endovascular intervention is often a first-line treatment modality for P1 aneurysms.54

The critical P2 segment begins after the anastomosis with the PComA, courses around the midbrain along the ambient cistern, and gives off one to three cortical branches or inferior temporal arteries (Fig. 1.1c and Fig. 1.3). The thalamogeniculate artery arises from this segment and enters the geniculate body to supply the thalamus and optic radiations. Occlusion of the thalamogeniculate artery moreover leads to thalamic symptoms, which are marked by severe pain and pure sensory loss in the face, arm, and legs.55 It then gives off the middle and lateral posterior choroidal arteries. While the middle posterior choroidal artery supplies the thalamus, pineal gland, and choroid plexus in the third ventricle, the lateral posterior choroidal artery enters the choroidal fissure to supply the choroid plexus in the posterior temporal horn and atrium. A PCA bifurcation was identified in 89% of hemispheres, typically at the middle segment of the medial temporal region, just before the quadrigeminal cistern. The most common pattern of bifurcation was by division into posteroinferior temporal and parieto-occipital arterial trunks.56 P3 originates distal to the inferior temporal arteries and ends at the beginning of the calcarine fissure, followed by P4 ending as the splenial artery.

1.4.3 Extracranial-Intracranial Anastomoses

Together, the ICA and vertebral artery supply the entire intracranial (IC) circulation, while the ECA is responsible for the entire extracranial (EC) circulation. Although predominantly two separate circulatory systems, the two circulations anastomose in several locations, commonly at the skull base. Branches of the OphA are often involved in EC-IC anastomoses. The proximal lacrimal branch commonly anastomoses with the middle meningeal artery (MMA), a major branch of the internal maxillary artery (IMax); this variant is found in approximately 40% of individuals. When present, this anastomosis typically occurs between the superior orbital fissure and the posterior wall of the orbit.24 The distal lacrimal branch of the OphA also commonly anastomoses extracranially, interfacing in many cases with the deep temporal artery within the orbit. Other frequently encountered OphA anastomoses include the anastomosis of the anterior and posterior ethmoidal arteries with the sphenopalatine, septal, greater palatine, or middle meningeal arteries within the ethmoid sinus, as well as potential connections between the supraorbital artery with the STA.42

Direct branches of the ICA also commonly anastomose with other branches of the IMax. The inferolateral trunk can connect with the IMax within the cavernous sinus, and the arteries of foramen ovale and lacerum (from the ICA) can anastomose with the accessory meningeal artery of the IMax and the ascending pharyngeal artery, respectively. The meningohypophyseal trunk and vertebral artery, too, can occasionally anastomose with clival branches of the ascending pharyngeal artery.42 In the neck, muscular branches of the ascending and deep cervical arteries can connect with vertebral arteries spanning from the level of C1 to C7.43

Several key collaterals between intracranial vessels are important to consider as well. Leptomeningeal collateralization has been observed in a majority of individuals and, through varying courses, comprises a network of leptomeningeal vessels that connect major vessels of the circle of Willis. These connections often go unnoticed, but can become critical during acute ischemic events.44 Much more rarely, an embryologically persistent trigeminal artery can remain and connect the intracavernous segment of the ICA to the BA, providing another anastomosis between anterior and posterior intracranial circulations.45

1.5 Conclusion

The vasculature of the head and neck consists of a system of circulation that centers on the collaterals of the circle of Willis at the skull base. Both the anterior and posterior circulations supply blood to the head and neck branch directly or indirectly from the aorta and travel superiorly. The CCA travels up the neck in the carotid sheath before giving off the ECA and entering the skull base as the ICA, which then gives off several major branches before splitting into the ACA and the MCA at the circle of Willis. The vertebral arteries also travel up the neck posteriorly, giving off branches and perforators, before merging to become the BA, which then also bifurcates as it enters the circle of Willis. The bilateral anterior circulations variably anastomose and collateralize via the AComA and the anterior and posterior circulations can have significant collateral supply via the PComA. However, other variants, including ECA-ICA anastomotic variants, can be equally or more important and should be carefully studied and understood in each individual.

Anterior and posterior circulation consists of a series of common variants that must be anticipated and accounted for in successful skull base surgery. For vascular surgeries, an anatomical and clinical understanding of the vasculature allows for approach planning as well as a dynamic understanding of what should and cannot be occluded or sacrificed based on the patient’s anatomy. For all other skull base surgeries, a strong understanding of the anatomy allows for the prevention of intraoperative complications and is useful in planning safe surgical corridors.

* The relevant venous anatomy is covered in depth in Chapter 20

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