Endoscopic Lateral Skull Base Surgery E-Book

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

Veröffentlichungsjahr: 2022

Beschreibung

The quintessential state-of-the-art atlas on endoscopic approaches to the lateral skull base

The endoscope has become a highly effective tool in the arsenal of ear and skull base surgeons. Endoscopic Lateral Skull Base Surgery: Principles, Anatomy, Approaches by endoscopic surgery masters Daniele Marchioni and Livio Presutti, reflects their development of innovative transcanalar approaches to the lateral cranial base using the external auditory canal as a surgical corridor. This unique atlas is designed to teach and clarify current and emerging endoscopic-assisted surgery approaches to the lateral skull base.

The common goal of these cutting-edge procedures is to access and treat tumors located in the lateral cranial base via the most minimally-invasive endoscopic approach possible, thereby bypassing delicate cranial nerves, dural, cerebral, and vascular structures. Throughout 14 chapters, an impressive group of skull base surgeons share firsthand insights and expertise in areas vital to endoscopic skull base surgery.

Key Features

• Featuring contributions from the who's who of global experts who continue to innovate by using the endoscope beyond its traditional use in middle ear surgery
• Opening chapters cover anatomy, microscopic approaches, endoscopic dissection, instrumentation, OR set-up, and radiologic assessments
• Procedural chapters detail endoscopic approaches including transtemporal combined, retrosigmoid, and transcanalar techniques such as suprageniculate, transpromontorial, and infracochlear
• Patient cases, clinical applications, and step-by-step guidance enhance understanding of diverse endoscopic approaches
• High-quality preoperative, intraoperative, and postoperative illustrations are selected from thousands of surgeries performed by the authors

This remarkable book provides the most comprehensive and elucidating information written to date on endoscopic approaches to the lateral skull base, making it essential reading for novice and expert surgeons alike.

This print 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.

Endoscopic Lateral Skull Base Surgery

Principles, Anatomy, Approaches

Daniele Marchioni, MDProfessor of Otorhinolaryngology and Head & Neck SurgeryHead, Department of OtorhinolaryngologyUniversity Hospital PolyclinicModena, Italy

Livio Presutti, MDProfessor of Otorhinolaryngology and Head & Neck SurgeryDepartment of OtorhinolaryngologySant’orsola Malpighi Polyclinic IRCCSAzienda Ospedaliera UniversityBologna, Italy

2005 illustrations

ThiemeStuttgart • New York • Delhi • Rio de Janeiro

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

© 2022 Thieme. All rights reserved.

Georg Thieme Verlag KG

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www.thieme.de

+49 [0]711 8931 421, [email protected]

Cover design: © Thieme

Cover image source: © Daniele Marchioni

Typesetting by DiTech, India

Printed in Germany by Beltz Grafische Betriebe 5 4 3 2 1

ISBN 978-3-13-241277-4

Also available as an e-book:

eISBN (PDF): 978-3-13-241435-8

eISBN (epub): 978-3-13-258236-1

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Contents

Videos

Foreword

Preface

Contributors

1Anatomy of the Lateral Skull Base

Mustafa Kapadia, Livio Presutti, Alejandro Rivas, and Daniele Marchioni

1.1Introduction

1.2The Temporal Bone

1.3Internal Auditory Canal

1.4Facial Nerve

1.5Jugular Foramen

1.6Infratemporal Fossa

1.7Cerebellopontine Angle

1.7.1Relevant Nervous Contents

1.8Internal Carotid Artery

1.9Basilar Artery

1.10Venous Drainage from the Skull Base

1.10.1Cavernous Sinus

1.11Neck at the Base of Skull

1.12MedialWall of Tympanic Cavity: The Transcanal Door to the Fundus of the IAC

2Microscopic Approaches to Lateral Skull Base: Overview

Daniele Marchioni, Mohamed Badr El Dine, Luca Bianconi, and Daniele Bernardeschi

2.1Introduction

2.2Translabyrinthine Approach

2.2.1Indications

2.2.2Advantages

2.2.3Limitations

2.2.4The Use of the Endoscope

2.2.5Surgical Approach

2.2.6Hints and Pitfalls

2.3Translabyrinthine Approach and Cochlear Implant

2.3.1Indications

2.3.2Surgical Steps

2.4Translabyrinthine Approach and Brainstem Implant

2.5Indications

2.5.1Surgical Steps

2.5.2Postoperative Care

2.5.3Complications

2.6Retrolabyrinthine Approach

2.6.1Rationale

2.6.2Indications

2.6.3Advantages

2.6.4Limitations

2.6.5Use of the Endoscope

2.6.6Surgical Technique

2.6.7Endoscopic-Assisted Surgery

2.6.8Final Steps

2.6.9Vestibular Nerve Resection

2.6.10Hints and Pitfalls

2.6.11Postoperative Care and Complications

2.7Different Infratempoaral Fossa Approaches

2.7.1Infratemporal Fossa Type A

2.7.2Infratemporal Fossa Types B and C

3Transcanal Endoscopic Dissection of Lateral Skull Base

Noritaka Komune

3.1Introduction

3.2Overview of the Temporal Bone: Microscopic Dissection from Lateral and Above

3.3Transcanal Endoscopic Dissection to the Lateral Skull Base

3.4Endoscopic Approaches to the Lateral Skull Base

4Instruments and Operating Room Setup

Daniele Marchioni, Alessia Rubini, Stefano De Rossi, Muaaz Tarabichi, and Gabriele Molteni

4.1Introduction

4.2Operating Room Setup

4.2.1Setting for Microscopic and Endoscopic Lateral Skull Base Surgery

4.2.2Setting for Microscopic and Endoscopic Middle Cranial Fossa Surgery

4.2.3Setting for Exoscopic Lateral Skull Base Surgery

4.3The Operative Microscope

4.4The Rigid Endoscopes

4.53D Exoscope

4.6Xenon Light Sources for Endoscopic Surgery

4.7Nerve Integrity Monitor

4.8Instruments

4.9Retractor for Lateral Skull Base

4.10Bone Rongeur

4.11Special Instruments for Endoscopic/Microscopic Lateral Skull Base Surgery

4.12Drill and Microdrill

4.13Piezosurgery

4.14Bipolar

4.15Dissectors

4.16Suction Tubes

5Radiologic Assessment in Lateral Skull Base Surgery

Davide Soloperto, Elisa Ciceri, and Daniele Marchioni

5.1Introduction

5.1.1Anatomy of Lateral Skull Base

5.2General Considerations about CT and MRI in Lateral Skull Base

5.3Lateral Skull Base Lesions

5.3.1Lesions Involving External Auditory Canal (EAC), Middle Ear, and Mastoid

5.3.2Internal Auditory Canal (IAC) and Cerebellopontine Angle (CPA) Lesions

5.3.3Lesions Involving Jugular Foramen

6Transcochlear and Transotic Endoscopic Assisted Approaches

Daniele Marchioni, George Wanna, Mustafa Kapadia, Nicola Bisi, and Luca Bianconi

6.1Introduction

6.2Transcochlear Approach

6.2.1Indications

6.2.2Advantages

6.2.3Limits

6.2.4Use of the Endoscope

6.2.5Surgical Approach

6.2.6Endoscopic Assisted Surgery

6.2.7Extradural Lesions

6.2.8Intradural Lesions

6.2.9Final Steps

6.3Transotic Approach

6.3.1Indications

6.3.2Use of the Endoscope

6.3.3Surgical Approach

6.3.4Endoscopic Assisted Surgery

6.3.5Final Steps

6.4Postoperative Care

7Endoscopic Assisted Retrosigmoid Approach

Daniele Marchioni, Marco Bonali, Matteo Fermi, Barbara Masotto, Gianpietro Pinna, Matteo Alicandri Ciufelli, Giacomo Pavesi, and Livio Presutti

7.1Surgical Anatomy

7.2Retrosigmoid Endoscopic Assisted Surgery

7.3Indications

7.4Contraindications

7.5Advantages

7.6Surgical Approach for Acoustic Neuroma Removal

7.7Surgical Approach for Neurovascular Conflicts

7.7.1Trigeminal Neuralgia

7.7.2Hemifacial Spasm

7.7.3Glossopharyngeal Neuralgia

7.8Surgical Approach

7.9Complications

8Middle Cranial Fossa Approaches: Traditional Surgery and Endoscopic Assisted Procedure

Daniele Marchioni, Raphaelle A. Chemtob, Elliott D. Kozin, Daniel J. Lee, and Davide Soloperto

8.1Introduction

8.2Surgical Anatomy

8.3The Middle Cranial Fossa and the Anterior Petrosectomy Approaches

8.3.1Indications

8.3.2Advantages

8.3.3Limitations

8.3.4Use of the Endoscope

8.4Middle Fossa Approach for IAC Lesions

8.4.1Surgical Steps

8.4.2Identification of the IAC for Acoustic Neuroma Resection

8.4.3Dural Opening and Tumor Dissection

8.4.4Endoscopic Assisted Surgery

8.4.5Closure

8.4.6Postoperative Care

8.4.7Complications

8.4.8Endoscopic Middle Fossa Approach to Repair Superior Semicircular Canal Dehiscence

8.5Anterior Petrosectomy or Extended Middle Fossa Approach

8.5.1Rationale

8.5.2Surgical Steps

8.5.3Endoscopic Assisted Anterior Petrosectomy

8.5.4Lesions with Intradural Extension

8.5.5Postoperative Care

9Classification and Indications of Transcanal Lateral Skull Base Surgery

Daniele Marchioni, Brandon Isaacson, Alessia Rubini, Antonio Gulino, and Livio Presutti

9.1Introduction

9.2The Group of Transcanal Approaches

9.3Transcanal Suprageniculate Corridor

9.3.1Indications

9.3.2Advantages

9.3.3Limitations

9.4Transcanal Transpromontorial Corridor

9.4.1Exclusive Endoscopic Transcanal Transpromontorial Approach

9.4.2Expanded Transcanal Transpromontorial Approach

9.5Transcanal Infracochlear Corridor

9.5.1Indications

9.5.2Advantages

9.5.3Limitations

10Endoscopic Transcanal Suprageniculate Approach

Daniele Marchioni, Nirmal Patel, Nicholas Jufas, Alexander J. Saxby, and Jonathan H.K. Kong

10.1Introduction

10.2Surgical Anatomy

10.2.1Precochleariform Segment of the Tympanic Portion of the Facial Nerve

10.2.2Geniculate Ganglion

10.2.3Greater Superficial Petrosal Nerve

10.3Endoscopic Transcanal Suprageniculate Approach

10.3.1Indications

10.3.2Contraindications

10.3.3Advantages

10.3.4Disadvantages

10.3.5Preoperative Assessment

10.4ETSA for Tumors of the Geniculate Ganglion

10.4.1Reconstruction of the Facial Nerve

10.4.2Surgical Technique

10.5ETSA for Cholesteatoma Involving the Suprageniculate Ganglion Area

10.5.1Surgical Steps

10.5.2Inner Ear Involvement

10.6ETSA for Decompression of the Geniculate Ganglion and of the Tympanic Facial Nerve

10.6.1Surgical Steps

10.6.2Postoperative Care and Follow-up

11Transcanal Transpromontorial Approaches to the Internal Auditory Canal and the Cerebellopontine Angle

Daniele Marchioni, Barbara Masotto, Alejandro Rivas, Lukas Anschütz, and Livio Presutti

11.1Introduction

11.2Exclusively Endoscopic Transcanal Transpromontorial Approach

11.2.1Indications

11.2.2Contraindications

11.2.3Advantages

11.2.4Disadvantages

11.2.5Preoperative Assessment

11.2.6Surgical Technique

11.2.7Hints and Pitfalls

11.2.8Postoperative Care

11.3Enlarged Transcanal Transpromontorial Approach

11.3.1Indications

11.3.2Contraindications

11.3.3Advantages

11.3.4Disadvantages

11.3.5Preoperative Assessment

11.3.6First Step: Exposition of EAC Bone

11.3.7Shambaugh Skin Incision

11.3.8Retroauricolar Incision

11.3.9Second Step: Calibration of the Promontorial Access

11.3.10Third Step: Middle Ear Dissection

11.3.11Fourth Step: Transpromontorial Approach to the IAC

11.3.12Fifth Step: Tumor Dissection

11.3.13Sixth Step: Closure

11.3.14Hints and Pitfalls

11.3.15Postoperative Care

12Endoscopic Assisted and Transcanal Procedures in Cochlear Implant

Daniele Marchioni, Davide Soloperto, Luca Bianconi, Joao Flavio Nogueira, Domenico Villari, and Marco Carner

12.1Introduction

12.2Trans-attic Endoscopic Assisted Cochlear Implantation

12.2.1Endoscopic Anatomy of the Round Window

12.2.2General Considerations on Cochlear Implants

12.2.3Indications

12.2.4Cochlear Implant in Otosclerosis

12.2.5Cochlear Implantation in CHARGE Syndrome

12.2.6Surgical Steps

12.2.7Endoscopic Step

12.2.8Microscopic Step

12.3Transcanal Infrapromontorial Approach with Simultaneous Coclear Implant

12.3.1Indications

12.3.2Limitations

12.3.3Surgical Steps

12.3.4Preservation of the Cochlea and the Cochlear Nerve

12.3.5Postoperative Care

13Endoscopic Transcanal Infracochlear Approach

Seiji Kakeatha, Daniele Marchioni, and Brandon Isaacson

13.1Introduction

13.2Rationale

13.3Advantages

13.4Disadvantages and Limitations

13.5Indications

13.6Contraindications

13.7Surgical Considerations about the Round Window Chamber and the Hypotympanum

13.8Surgical Procedure

13.8.1Cholesterol Granuloma

13.8.2Cholesteatoma

13.9Postoperative Care

13.10Intraoperative Complications

14Complications and Management in Lateral Skull Base Surgery

Daniele Marchioni, Andrea Martone, and Matteo Alicandri Ciufelli

14.1Cranial Nerves Deficit

14.1.1Facial Nerve Reparation

14.1.2Primary Nerve Grafting

14.1.3Cable Nerve Grafting

14.1.4Nerve Substitution

14.1.5Cross-Facial Nerve Graft

14.2CSF Leak

14.3Bleeding

14.3.1Intraoperative Bleeding

14.3.2Postoperative Bleeding

Index

Videos

Video 1 Retrolabyrinthine approach

Video 2 Translabyrinthine approach

Video 3 Endoscopic dissection of internal auditory canal (IAC)

Video 4 Transotic endoscopic-assisted approach to petrous bone cholesteatoma

Video 5 Middle cranial fossa approach

Video 6 Endoscopic transcanal transpromontorial approach for a vestibular schwanomma limited to the internal auditory canal (IAC)

Video 7 Enlarged transcanal transpromontorial approach

Video 8 Endoscopic transcanal transpromontorial approach to intralabyrinthine schwanomma

Video 9 Trans-attic endoscopic assisted cochlear implant

Video 10 Transcanal infrapromontorial approach for simultaneous acoustic tumor removal and cochlear implant (clinical case 5)

Video 11 Translabyrinthine approach with simultaneous cochlear implant

Foreword

The use of endoscopes in ear surgery has become a great tool in the arsenal of the ear and skull base surgeon. This big leap toward accepting this technology is twofold: on one hand, it is mainly due to the advancement of the quality of the images; on the other hand, it is due to the innovation by the pioneers of this field.

Professors Marchioni and Presutti edited a state-of-the-art book entitled Endoscopic Lateral Skull Base Surgery. Their book includes 14 chapters that thoroughly cover all aspects of skull base surgery, including anatomy, principles, and approaches.

The editors feel fortunate to have assembled a cadre of worldrenowned experts to share their clinical insights and expertise in several areas that are vital to endoscopic skull base surgery. This book is substantively edited by two pioneers of endoscopic ear surgery who continue to push the boundaries by using the endoscope beyond its traditional use in middle ear surgery. They continue to expand the use of the endoscope by applying their endoscopic techniques to inner ear and skull base surgeries. In my opinion, this book is the holy grail of endoscopic skull base surgery. Each chapter elucidates a great deal of information for novices, as well as experts in the field of skull base surgery.

On behalf of the editors, Iwould like to extend sincere gratitude to each contributing author for dedicating a significant amount of time and effort toward the completion of this comprehensive book.

George Wanna, MD, FACS

Site Chair

Department of Otolaryngology

New York Eye and Ear Infirmary of Mount Sinai

Mount Sinai Hospital

New York, New York, USA

Preface

After finishing our book Endoscopic Ear Surgery (Thieme, 2015),we realized the need for a book that would extend the description of endoscopic anatomy and endoscopic techniques to the inner ear and lateral skull base.

In the last decade, endoscopic ear surgery has taken a step further: The discovery of new approaches and anatomical structures made it possible to treat pathologies of the inner ear and the petrous apex. Although surgery of the lateral cranial base relies mainly on microscopic approaches, the introduction of endoscopic surgery to the otological community has enabled the surgeon to use the endoscope in combination with the microscope to produce more effective approaches to the lateral skull base, with a lower morbidity.

In 2011, we started to investigate a possible transcanal treatment for lesions located in the lateral skull base. Our aim was exploring the possibility of using the external auditory canal as a natural surgical corridor to reach some anatomical areas located in the lateral skull base.We began to develop anatomical and surgical concepts by following the same rationale that was used for the development of the transnasal endoscopic approaches to the anterior skull base. The principlewas to develop the surgical possibility of directly and endoscopically reaching the tumors located in the lateral cranial base in order to avoid dural, cerebral, and vascular manipulation and to work only on the tumor itself, through a minimally invasive procedure. These surgical principles led to the first scientific publication on the topic, centeringon the endoscopic transcanal dissection to reach the internal auditory canal. At the end of 2012, this technique was for the first time successfully applied in a patient suffering from cochlear schwannoma. Following this, thefirst transcanal approaches using the external auditory canal as a surgical corridor to the lateral cranial base were performed.

This book contains our latest experiences on lateral skull base surgery. We are describing traditional surgical approaches combined with endoscopic steps but have also included the most upto- date fully endoscopic transcanal approaches to the lateral skull base, with a focus on the anatomical details and surgical strategies.

We created the illustrations in this book by ourselves. We also used the collection of images from our surgical procedures to share our recent experiences with the readers.

We hope that this book will be a starting point to develop endoscopic lateral skull base surgery in the future and that it will help the next generation of surgeons to improve the anatomical and surgical knowledge of the lateral skull base for the benefit of our patients.

Daniele Marchioni, MD

Livio Presutti, MD

Contributors

Lukas Anschütz, MD

Department of Otorhinolaryngology – Head and Neck Surgery

Inselspital, Bern University Hospital

University of Bern

Bern, Switzerland

Mohamed Badr-El-Dine, MD

Senior Consultant Otology Neurotology & Skull Base Surgery

Sultan Qaboos University Hospital Muscat, Oman;

Professor of Otolaryngology Faculty of Medicine

University of Alexandria

Alexandria, Egypt

Daniele Bernardeschi, MD, PhD

Otolaryngologist

ENT Department

Pitié-Salpêtrière Hospital

Paris, France

Luca Bianconi, MD

Otolaryngologist

Polyclinic Hospital of Borgo Trento

University of Verona

Verona, Italy

Nicola Bisi, MD

Department of Otorhinolaryngology

University Hospital of Verona

Verona, Italy

Marco Bonali, MD

ENT specialist

Department of Otorhinolarynogology – Head and Neck surgery

University Hospital of Modena

Modena, Italy

Marco Carner, MD

Professor

University of Verona

Verona, Italy

Raphaelle A. Chemtob, MD

Resident Physician

Cleveland Clinic Foundation

Cleveland, Ohio, USA

Elisa Ciceri, MD

Department of Neuroradiology

IRCCS Fondazione Istitute Neurologico “C.Besta”

Milan, Italy

Matteo Alicandri Ciufelli, MD

Associate Professor

Department of Maternal-Child and Adult Medical and Surgical Sciences

University of Modena and Reggio Emilia

Modena, Italy

Matteo Fermi, MD

Otorhinolaryngologist

Research Assistant

IRCCS Policlinico Sant’Orsola Malpighi

Alma Mater Studiorum – University of Bologna

Bologna, Emilia-Romagna, Italy

Antonio Gulino, MD

ENT Surgeon

Department of Otolaryngology

Verona University Hospital

Syracuse, Sicily, Italy

Brandon Isaacson, MD

Professor

Department of Otolaryngology – Head and Neck Surgery

UT Southwestern Medical Center

Dallas, Texas, USA

Nicholas Jufas, FRACS, MBBS (Hons), MS, BSc (Med)

Clinical Associate Professor

Department of Otolaryngology,

Head and Neck Surgery

Sydney University;

Macquarie University;

Sydney Endoscopic Ear Surgery Research Group

Royal North Shore Hospital

Sydney, Australia

Seiji Kakeatha, MD

Professor of Otolaryngology – Head and Neck Surgery

Faculty of Medicine

Yamagata University

Yamagata, Japan

Mustafa Kapadia MD

ENT Specialist;

Director of Education

Tarabichi Stammberger Ear Sinus Institute

Dubai, UAE

Noritaka Komune, MD, PhD

Assistant Professor

Department of Otorhinolaryngology – Head and Neck Surgery

Kyushu University Hospital

Fukuoka, Japan

Jonathan H.K. Kong, FRACS, FRCS, MS, MBBS (Syd), AMusA

Clinical Associate Professor

Department of Otolaryngology,

Head and Neck Surgery

Sydney University;

Macquarie University;

Sydney Endoscopic Ear Surgery Research Group

Royal Prince Alfred Hospital

Sydney, Australia

Elliott D. Kozin, MD

Assistant Professor

Harvard Medical School

Massachusetts Eye and Ear

Boston, Massachusetts, USA

Daniel J. Lee, MD, FACS

Associate Professor

Harvard Medical School

Massachusetts Eye and Ear

Boston, Massachusetts, USA

Daniele Marchioni, MD

Professor of Otorhinolaryngology and Head & Neck Surgery

Head, Department of Otorhinolaryngology

University Hospital Polyclinic

Modena, Italy

Andrea Martone, MD

Resident Physician

Department of Otorhinolaryngology – Head and Neck surgery

University Hospital Policlinico Modena

Modena, Italy

Barbara Masotto, MD

Head of Posterior Cranial Fossa Unit

Department of Neurosurgery

University Hospital of Verona

Verona, Italy

Gabriele Molteni, MD, PhD, FEBORL-HNS

Associate Professor of Otolaryngology

Section of Otorhinolaryngology – Head and Neck Surgery

Deparment of Surgery, Odontosomatology, and Pediatrics

University of Verona

Verona, Italy

Joao Flavio Nogueira, MD

Professor

Department of Otolaryngology – Head and Neck Surgery

Sinus & Oto Center

Hospital São Carlos

Fortaleza, Brazil

Nirmal Patel MBBS (Hons) FRACS (OHNS) MS (Research)

Clinical Professor of Surgery, Macquarie University;

Clinical Associate Professor,

Department of Otolaryngology,

Head and Neck Surgery

University of Sydney

Royal North Shore Hospital

Sydney Endoscopic Ear Surgery Research Group

Sydney, Australia

Giacomo Pavesi, MD

Head

Department of Neurosurgery

Modena Polyclinic University Hospital

Modena, Italy

Giampietro Pinna, MD

Head

Department of Neurosurgery

University Hospital of Verona

Verona, Italy

Livio Presutti, MD

Professor of Otorhinolaryngology and Head & Neck Surgery

Department of Otorhinolaryngology

Sant’orsola Malpighi Polyclinic IRCCS

Azienda Ospedaliera University

Bologna, Italy

Alejandro Rivas, MD

Division Chief of Otology/Neurotology

Department of Otolaryngology – Head and Neck Surgery

Vanderbilt University Medical Center

Nashville, Tennessee, USA

Stefano De Rossi, MD

Department of Otorhinolaryngology and Head & Neck surgery

Mater Salutis Hospital

Legnago, Verona, Italy

Alessia Rubini, MD

Consultant ENT Surgeon

Section of Otorhinolaryngology

Head and Neck Surgery

Deparment of Surgery, Odontosomatology, and Pediatrics

University of Verona

Verona, Italy

Alexander J. Saxby, MB, BChir, MA (Cantab.) FRACS

Clinical Associate Professor

Department of Otolaryngology,

Head and Neck Surgery

University of Sydney;

Royal Prince Alfred Hospital

Sydney Endoscopic Ear Surgery Research Group

Sydney, Australia

Davide Soloperto, MD PhD

Consultant

Azienda Ospedaliera Universitaria Integrata

Verona Italy

Muaz Tarabichi, MD

Co-Founder

Tarabichi Stammberger Ear and Sinus Institute

Dubai, United Arab Emirates

Domenico Villari, MD

ENT Specialist

University Hospital Policlinico di Modena

Modena, Emilia Romagna, Italy

George Wanna, MD, FACS

Professor of Otolaryngology – Head and Neck Surgery;

Professor of Neurosurgery

Icahn School of Medicine at Mount Sinai;

Chair, Department of Otolaryngology

New York Eye and Ear Infirmary

of Mount Sinai and Mount Sinai Beth Israel

New York, New York, USA

Chapter 1

Anatomy of the Lateral Skull Base

1.1Introduction

1.2The Temporal Bone

1.3Internal Auditory Canal

1.4Facial Nerve

1.5Jugular Foramen

1.6Infratemporal Fossa

1.7Cerebellopontine Angle

1.8Internal Carotid Artery

1.9Basilar Artery

1.10Venous Drainage from Skull Base

1.11Neck at the Base of Skull

1.12Medial Wall of Tympanic Cavity: The Transcanal Door to the Fundus of the IAC

1 Anatomy of the Lateral Skull Base

Mustafa Kapadia, Livio Presutti, Alejandro Rivas, and Marchioni Daniele

Abstract

The lateral skull base is a very complex anatomical region separating the brain from the ear and the upper neck. It is composed by the temporal, sphenoid, and occipital bones, and contains vital neurovascular structures. An advanced understanding of its threedimensional architecture is therefore mandatory for the surgeon approaching this area. In particular, a detailed knowledge of the anatomy of the temporal bone is the cornerstone to correctly perform lateral skull base surgery. In fact, it occupies a central position in the lateral skull base and contains several noble structures having a winding course such as the internal carotid artery, the sigmoid sinus with the internal jugular vein, the internal auditory canal with the acoustic-facial bundle, and the facial nerve. In the same way, the knowledge of the anatomical entities located in close relationship with the temporal bone plays a key role: (1) the jugular foramen, anterolaterally bounded by the petrous temporal bone and posteromedially by the basioccipital bone, transmitting the sigmoid sinus, the jugular bulb, the inferior petrosal sinus, the lower cranial nerves (IX, X, XI) with their ganglia, and the meningeal branches of the occipital artery and the ascending pharyngeal artery; (2) the infratemporal fossa, a complex three-dimensional nonfascial bound space located inferomedial to the zygomatic arch and the ramus of the mandible, acting as a conduit for the neurovascular structure entering and leaving the skull base; and (3) the cerebellopontine angle, the anatomic space between the petrous bone and the petrosal cerebellar surface folding around the pons and the middle cerebellar peduncle, containing the posterior cranial fossa nerves.

Keywords: lateral skull base anatomy, temporal bone, jugular foramen, infratemporal fossa, cerebellopontine angle, petrous apex

1.1 Introduction

The skull base forms the floor of the cranial cavity and separates the brain from the ear, the paranasal sinuses, and the upper neck. This anatomic region is complex and poses surgical challenges for otolaryngologists and neurosurgeons alike. In the skull base, there are numerous foramina that transmit cranial nerves, blood vessels, and other structures. The skull base foramina are openings located in the inferior portion of the cranium. They allow for the passage of several vascular and nervous structures. From an inferior view, there are 10 conventionally described skull base foramina: the greater palatine, lesser palatine, lacerum, ovale, spinosum, external opening of the carotid canal, stylomastoid, jugular, mastoid, and the external opening of the hypoglossal canal (see ▶ Fig. 1.1, ▶ Fig. 1.2, ▶ Fig. 1.3, ▶ Fig. 1.4). Working knowledge of the anatomy of the skull base is essential for effective surgical treatment of diseases in this area.

Fig. 1.1 Skull base foramina: exocranial and endocranial surfaces.

Fig. 1.2 Left exocranial surfaces of the skull base: the skull foramina are shown.

Fig. 1.3 Cranial nerves and vascular structures in the left exocranial surfaces of the skull base. ica: internal carotid artery; ijv: internal jugular vein; mma: middle meningeal artery.

Fig. 1.4 Cranial nerves and vascular structures in the endocranial surfaces of the skull base. afb: acoustic-facial bundle; ica(h): horizontal portion of internal carotid artery; ica: internal carotid artery; ips: inferior petrosal sinus; jb: jugular bulb; mma: middle meningeal artery; sps: superior petrosal sinus.

The five bones that make up the skull base are the ethmoid, sphenoid, occipital, frontal, and temporal bones. The skull base can be subdivided into three regions: the anterior, middle, and posterior cranial fossae (see ▶ Fig. 1.1).

The anterior cranial fossa is formed by the anterior and cribriform plate of the ethmoid bone, the lesser wings of the sphenoid, and the jugum sphenoidale. The middle cranial fossa is composed of the body and the greater wing of the sphenoid, the anterior surface of the temporal pyramid, and parts of the temporal squama. The posterior cranial fossa is bordered by the clivus, the pyramid of the temporal bone, and the occipital bone.

Irish and coworkers in 1994 reviewed 77 skull base malignancies from a clinical point of view. From this work, they developed a classification system of three regions based upon anatomic boundaries and tumor growth patterns. Region I is composed of the anterior cranial fossa. Tumors of this region are commonly resected via an anterior approach. Region II includes the infratemporal and pterygopalatine fossae, with a possible tumor extension into the middle cranial fossa. Region III involves the temporal bone with a possible tumor extension into the posterior or middle cranial fossa. From a clinical point of view, the “lateral skull base” is defined as the anatomical compartments resulting from the combination of Regions II and III. Anatomically, Region II extends from the posterior wall of the orbit to the petrous temporal bone and it is formed by the infratemporal and pterygopalatine fossae and the overlying part of the middle cranial fossa. In this region, there are several important neurovascular structures which include the internal carotid artery (ICA), the facial nerve, the vestibulocochlear nerve, and the maxillary (V2) and the mandibular (V3) divisions of the trigeminal nerve. Region III is located mainly in the posterior cranial fossa and also includes the posterior segment of the middle cranial fossa. Vital structures located in this region include the internal jugular vein and the vagus, the glossopharyngeal, the spinal accessory, and the hypoglossal nerves.

The lateral skull base has very noble and complex anatomical structures (see ▶ Fig. 1.5 and ▶ Fig. 1.6). Lateral skull base surgery demands an advanced anatomical knowledge of the temporal bone and a three-dimensional animated perception of the related surrounding structures. The surgical procedures are technically challenging because the pathological site is concealed deep within, which requires extensive bone drilling and tissue retraction, and because vital neurovascular structures are located in a relatively small area.

Fig. 1.5 Skull base bones. cc: carotid canal; eac: external auditory canal; fla: foramen lacerum; fo: foramen ovale ; fs: foramen spinosum; hyp: hypoglossal canal; jf: jugular foramen; petrous a: petrous apex; sty: styloid process.

Fig. 1.6 Endocranial view of skull base bones.

1.2 The Temporal Bone

The temporal bone occupies the central position in the lateral skull base and is anteriorly bounded by the zygomatic bone, and the greater wing and pterygoid plate of the sphenoid bone, superiorly bythe parietal bone, posteriorly and posteromedially by the occipital bone, and medially by the clivus (see ▶ Fig. 1.7). There are various vital structures related to the lateral skull base like the acoustic-facial bundle, trigeminal nerve, cochlea, semicircular canals, ICA, sigmoid sinus, internal jugular vein, lower cranial nerves, and brain parenchyma. Most of the times diseases in this area are benign, so we have to protect and preserve most of the vital structures.

Fig. 1.7 Temporal bone in the skull. Lateral view. Eac: external auditory canal.

The temporal bone has five different parts: the squamous, mastoid, tympanic, petrous, and styloid process (see ▶ Fig. 1.8). These parts are arranged the around external auditory canal and the tympanic cavity so that the tympanic part is directed downwards, the squamous part upwards and forwards, the mastoid part backwards, and the petrous part directed medially and inwards. The petrous temporal bone is a three-cornered pyramid with the base directed laterally and its long axis directed anteriorly and medially forming an angle of about 45 degrees with the median plane of the skull. The petrous apex is rough and uneven, having an anterior opening for the carotid canal, and it forms the posterolateral boundary of the foramen lacerum along with the greater wing of the sphenoid and the basioccipital bone. The labyrinth and the internal auditory canal (IAC) are located within the petrous temporal part. The petrous part of the ICA enters temporal bone through the carotid canal situated on its inferior surface. The other important structure related to the temporal bone is the jugular foramen (JF), which is located in the petro-occipital region.

Fig. 1.8 Temporal bone: (a) posterior fossa surface of the temporal bone; (b) base view of the temporal bone.

Fig. 1.9 Left ear. Drawing showing the acoustic-facial nerves from behind inside the internal auditory canal (IAC). The eighth nerve, upon passing into the IAC under the facial nerve, divides into two branches: the cochlear nerve and the vestibular nerve. The cochlear nerve runs into the fundus of the IAC, attaching to the foraminous tract of the fundus, forming the tractus spiralis foraminosus. The vestibular nerve divides into two branches: the upper branch which divides into the utricular nerve (which attaches on the elliptical recess) and the superior ampullary nerve (for the superior membranous ampulla), and the lower branch which divides into the saccular nerve (which attaches on the spherical recess) and the posterior ampullary nerve, which passes into the singular foramen. ivn: inferior vestibular nerve; lsc: lateral semicircular canal; psc: posterior semicircular canal; ssc: superior semicircular canal; svn: superior vestibular nerve.

1.3 Internal Auditory Canal

The IAC is a bony, 8 to 10 mm long neurovascular channel which runs from the posterior cranial fossa to the petrous temporal bone. It transmits the facial nerve, the cochlear-vestibular nerve, the nervus intermedius, and the labyrinthine artery (see ▶ Fig. 1.9 and ▶ Fig. 1.10). It has three distinguishable parts, namely, the porus (medial end) located on the posterior surface of the petrous bone, the canal itself and the fundus (lateral end), which is formed by a thin cribriform plate of bone separating the cochlea and the vestibule from the IAC. The fundus also constitutes the medial wall of the vestibule and its height and width are 2.5 to 4.0 mm and 2 to 3 mm, respectively. The fundus is divided by a transverse crest into a superior and an inferior quadrant. The superior quadrant is further divided into an antero-superior area for the facial nerve and a posterosuperior area for the superior vestibular nerve by a vertical crest/Bill’s bar. The inferior quadrant contains the cochlear nerve anteriorly, and the inferior vestibular nerve and the singular nerve posteriorly (see ▶ Fig. 1.11). The dura and arachnoid membranes extend up to the fundus and are attached to the transverse crest.

Fig. 1.10 Left ear. Anatomical relationships between the vestibule and the fundus of the internal auditory canal (IAC) from behind. The inner facial nerve is represented in yellow; the labyrinthine facial nerve is descending from the geniculate ganglion to the fundus of the IAC; the intrameatal facial nerve runs from laterally to medially, from anteriorly to posteriorly. bb: Bill’s bar; cho: cochlea; fn: facial nerve; fn*: labyrinthine facial nerve; fn**: intrameatal facial nerve; gg: geniculate ganglion; lsc: lateral semicircular canal; ow: oval window; psc: posterior semicircular canal; rw: round window; ssc: superior semicircular canal.

Fig. 1.11 Left side. (a, b) Anatomy of the fundus of the internal auditory canal (IAC); the nerves are separated by a transverse crest into a lower and an upper compartment. In the lower compartment, the inferior vestibular nerve and the singular nerve lie posteriorly while the cochlear nerve lies anteriorly. In the upper compartment, a vertical crest separates two nerves: the facial nerve lying anteriorly and the superior vestibular nerve lying posteriorly. coc: cochlea; cocn: cochlear nerve; fn**: labyrinthine segment of facial nerve; gg: geniculate ganglion; ivn: inferior vestibular nerve; lsc: lateral semicircular canal; psc: posterior semicircular canal; ssc: superior semicircular canal; svn: superior vestibular nerve.

The petrous ICA enters the temporal bone through the carotid canal anterior to the JF, being separated from it by the carotid ridge. It ascends upward and laterally as a vertical segment, then it turns medially under the bony eustachian tube acutely bending and continuing forward and medially as a horizontal segment. It gets out of the temporal bone through the petrous apex, passes through the foramen lacerum, and it becomes the cavernous segment of the ICA. The average length of the petrous ICA is 30 mm; the horizontal segment is twice the length of the vertical segment (see ▶ Fig. 1.12). The petrous part is often covered by very thick periosteum and its average diameter ranges between 3 and 5 mm. The first intrapetrous bend under the eustachian tube is an acute bend measuring approximately between 80 and 85 degrees. The petrous carotid is separated from the most anterior basal turn of the cochlea by a 2- to 3-mm-thick bone. The greater superficial petrosal nerve (GSPN) serves as an important landmark to identify the petrous carotid during a middle fossa approach as it runs superior and parallel to it (see ▶ Fig. 1.13). The carotid artery is surrounded in its canal by a venous plexus and by the pericarotid sympathetic plexus derived from the ascending branch of the superior cervical ganglion of the sympathetic trunk.

Fig. 1.12 Right side. The internal carotid artery at the base of the skull (a) and its subdivision (Bouthillier classification) (b).

Fig. 1.13 Right side. Anatomy of the facial nerve, in relation to the surrounding anatomical structures, from a middle fossa approach. coc: cochlea; cocn: cochlear nerve; cp: cochleariform process; fn**: intrameatal facial nerve; gg: geniculate ganglion; gspn: greater superficial petrosal nerve; ica(h): horizontal portion of internal carotid artery; imlf: incudomalleolar lateral fold; in: incus; ivn: inferior vestibular nerve; jf: jugular foramen; lsc: lateral semicircular canal; ma: malleus; mma: middle meningeal artery; psc: posterior semicircular canal; ssc: superior semicircular canal; svn: superior vestibular nerve; tf: tensor fold; ttm: tensor tympani muscle.

1.4 Facial Nerve

The facial nerve is one of the most important structures to be encountered during lateral skull base surgery, and its damage leads to significant functional and psycho-social morbidity for the patient. The facial nerve is a mixed nerve (motor root and sensory root/nervus intermedius) and innervates the second branchial arch derivatives. It contains five different populations of fibers (see ▶ Fig. 1.14):

●Special sensory fibers for taste sensation from anterior two-thirds of the tongue via the chorda tympani nerve (see ▶ Fig. 1.15).

●Somatic sensory fibers supplying the skin of the external auditory canal and the adjacent conchal region along with the auricular branch of the vagus nerve.

●Special visceral efferent fibers supplying the stapedius muscle, the posterior belly of digastric, the stylohyoid, and the muscles connected to the facial expression (see ▶ Fig. 1.14).

●General visceral efferent fibers for the lacrimal gland and the mucous secreting glands of the nasal cavity via the GSPN and for the submandibular and sublingual glands via the chorda tympani nerve (see ▶ Fig. 1.15 and ▶ Fig. 1.16).

●Visceral afferent fibers supplying the mucosa of the palate, pharynx, and nose.

Fig. 1.14 Left side. Fibers and nucleus of the facial nerve.

Fig. 1.15 Facial nerve and trigeminal nerve fibers' anastomosis. The anatomical relationship between the chorda tympany and lingual nerve is shown. eca: external carotid artery; fn: facial nerve; gg: geniculate ganglion; max: maxillary artery; mma: middle meningeal artery.

Fig. 1.16 Anatomy of the nerves on the medial wall of the tympanic cavity and anastomosis between the facial nerve and the trigeminal nerve. ct: chorda tympani; fn: facial nerve; gg: geniculate ganglion; gspn: greater superficial petrosal nerve; ica: internal carotid artery; in: incus; lpsn: lesser petrosal superficial nerve; lsc: lateral semicircular canal; ma: malleus; mcf: middle cranial fossa; pe: pyramidal eminence; rw: round window; sis: sigmoid sinus; sty: styloid process.

The facial nerve nucleus is located in the pons, ventrolateral to the abducens nucleus, and it is represented in the precentral gyrus of the cerebral cortex. The facial nerve course is broadly divided into three parts: intracranial (cisternal), intratemporal, and extratemporal part. The facial nerve emerges from the lower border of the pons between the olive and the restiform body as a motor and sensory root (nervus intermedius) and continues as an intracranial segment till the porus of the IAC (see ▶ Fig. 1.17). The total length of the intracranial segment is around 22 to 25 mm. It is cradled in a groove on the superior surface of the cochlear nerve. The sensory root runs parallel to it and joins it in spiraling fashion in the fundus of the IAC.

Fig. 1.17 (a, b) Topographic anatomy of the cranial nerves on the frontal surface of the brainstem and inside the cerebellopontine angle. (c) Acoustic-facial bundle inside the internal auditory canal (IAC). aica: anterior inferior cerebellar artery; coc: cochlea; cocn: cochlear nerve; flo: floccules; fn: tympanic segment of facial nerve; fn*: mastoid segment of facial nerve; fn**: intrameatal facial nerve; gg: geniculate ganglion;Fig. 1.18 gspn: greater superficial petrosal nerve; iac: internal auditory canal; in: incus; ivn: inferior vestibular nerve; lsc: lateral semicircular canal; ma: malleus; psc: posterior semicircular canal; sing: singular nerve; ssc: superior semicircular canal; svn: superior vestibular nerve.

The intratemporal part is further subdivided into four segments (see ▶ Fig. 1.18):

●The IAC segment is about 7 to 9 mm long and it extends from the porus till the fundus of IAC. It runs slightly anterior and superior to the cochlear nerve and it occupies the anterosuperior quadrant at the level of the fundus of the IAC.

●The labyrinthine segment is the smallest and the narrowest segment measuring around 3 to 5 mm in length and 0.68 mm in diameter. It extends from the fundus of the IAC heading anteriorly and laterally, running superior to the cochlea and vestibule until it reaches the geniculate ganglion. This segment is usually surrounded by very thick periosteum and can act as a strangulating tunnel in the presence of facial nerve edema leading to facial nerve palsy. At the level of the geniculate ganglion, it takes an acute bend of 75 degrees to form the first genu and then it continues as the tympanic segment. The first branch, the GSPN, arises from the anterior portion of the geniculate ganglion. It leaves the tympanic cavity and enters the middle cranial fossa through the facial hiatus and it runs forward toward to the foramen lacerum. At the level of the foramen lacerum, it is joined by the sympathetic fibers of the deep petrosal nerve and it forms the vidian nerve (nerve of the pterygoid canal). The vidian nerve passes through the pterygopalatine fossa to enter the sphenopalatine ganglion.

●The tympanic segment runs parallel to the long axis of the petrous pyramid and it is around 11 to 13 mm long. It passes posteriorly and laterally on the medial wall of the tympanic cavity between the oval window inferiorly and the lateral semicircular canal superiorly. At the level of the posterior wall of the tympanic cavity near the pyramidal eminence it turns 95 to 125 degrees forming the second genu and continuing as the mastoid segment. The tympanic segment doesn’t give any branches.

●The mastoid segment extends from the second genu to the stylomastoid foramen measuring 15 to 18 mm in length. It runs vertically downwards and slightly laterally on the posterior wall of the tympanic cavity in such a way that the nerve is more superficial at the stylomastoid foramen than at the level of the second genu. This segment gives off two branches, the nerve to the stapedius muscle and the chorda tympani nerve. The chorda tympani nerve usually arises about 4 mm superior to the stylomastoid foramen, but very rarely it may arise distal to it. During a posterior tympanotomy approach, the mastoid segment forms the medial limit and the chorda tympani the lateral limit for bone removal (see ▶ Fig. 1.19, ▶ Fig. 1.20, ▶ Fig. 1.21).

Fig. 1.18 Lateral view of the cerebellopontine angle. The relationship between the cranial nerves and the temporal bone is shown. afb: acoustic-facial bundle; aica: anterior inferior cerebellar artery; baa: basilar artery; flo: floccules; fn(exit): facial nerve at the exit zone; fn: tympanic segment of facial nerve; fn*: mastoid segment of facial nerve; gg: geniculate ganglion; gspn: greater superficial petrosal nerve; iac: internal auditory canal; ica(h): horizontal segment of internal carotid artery; ica(v): vertical segment of internal carotid artery; jb: jugular bulb; lsc: lateral semicircular canal; mma: middle meningeal artery; pcf: posterior cranial fossa (dura layer); pr: promontory; psc: posterior semicircular canal; rw: round window; sca: superior cerebellar artery; sis: sigmoid sinus; sps: superior petrosal sinus; ssc: superior semicircular canal; va: vertebral artery; ve: vestibule.

Fig. 1.19 Temporal bone dissection (right side): (a) A mastoidectomy with canal wall down procedure is performed exposing the tympanic cavity. The facial nerve is skeletonized in the mastoid. The retrofacial cells are removed connecting the mastoid to the hypotympanum (b). ct: chorda tympani; ed: eardrum; fn*: mastoid segment of facial nerve; in: incus; jb: jugular bulb; lsc: lateral semicircular canal; ma: malleus; mcf: middle cranial fossa; sis: sigmoid sinus.

Fig. 1.20 Temporal bone dissection (right side): (a) The labyrinthectomy is performed. The semicircular canals are opened. (b) The vestibule is exposed. ed: eardrum; fn: tympanic segment of facial nerve; fn*: mastoid segment of facial nerve; gg: geniculate ganglion; in: incus; jb: jugular bulb; lsc: lateral semicircular canal; ma: malleus; mcf: middle cranial fossa; pr: promontory; psc: posterior semicircular canal; rw: round window; sis: sigmoid sinus; ssc: superior semicircular canal; ve: vestibule.

Fig. 1.21 Temporal bone dissection (right side): (a) The internal auditory canal (IAC) is skeletonized. (b) The transmastoid anatomy of the facial nerve inside the temporal bone is noted after the ossicular chain is removed. cp: cochleariform process; ed: eardrum; fn: tympanic segment of facial nerve; fn*: mastoid segment of facial nerve; gg: geniculate ganglion; ica(v): vertical portion of internal carotid artery; in: incus; jb: jugular bulb; ma: malleus; mcf: middle cranial fossa; rw: round window; s: stapes; sis: sigmoid sinus.

The facial nerve emerges from the stylomastoid foramen and it continues as the extratemporal segment running anteriorly through the parotid gland. It divides at the posterior border of the ramus of the mandible into two main branches, namely, the superior temporofacial branch and the the inferior cervicofacial branch. From this, a plexiform arrangement of nerves forms known as the pes anserinus, which is eventually distributed over the muscles of the head, face, and upper part of neck (see ▶ Fig. 1.14).

Blood supply of the facial nerve:

●Intracranial part: anterior inferior cerebellar artery (AICA).

●IAC segment: labyrinthine artery (branch of AICA).

●Intratemporal segment: anastomosing branches of the superficial petrosal artery (branch of middle meningeal artery) and the stylomastoid artery (branch of posterior auricular artery). These branches form a rich arterial plexus between the fallopian canal periosteum and the epineurium of the facial nerve.

1.5 Jugular Foramen

The JF is a deeply located bony channel that transmits neurovascular structures from the posterior cranial fossa to the superior laterocervical area. A safe surgical access to this foramen is hindered by the important surrounding structures (see ▶ Fig. 1.22, ▶ Fig. 1.23). It is located in the posterior portion of the petro-occipital fissure, it is bounded anterolaterally by the petrous temporal bone and posteromedially by the basioccipital bone. In about 68% of the cases, the right foramen is larger than the left one, equal to the left in 12%, and smaller than the left in 20% of the patients.

Fig. 1.22 Lateral view of lateral skull base: The anatomical relationship between the vascular and nervous structures is shown. et: eustachian tube; fn: facial nerve; gg: geniculate ganglion; ica(h): horizontal portion of internal carotid artery; ica(v): vertical portion of internal carotid artery; ips: inferior petrosal sinus; jb: jugular bulb; lsc: lateral semicircular canal; mcf: middle cranial fossa; mma: middle meningeal artery; pr: promontory; psc: posterior semicircular canal; sis: sigmoid sinus; sph: sphenoid; sps: superior petrosal sinus; ssc: superior semicircular canal; tmj: temporal mandibular joint; zyg: zygomatic arch.

Fig. 1.23 (a) The jugular foramen anatomy (right side). (b) The lateral wall of the jugular bulb has been removed to expose the lumen of the vein. The opening of the inferior petrosal sinus into the lumen of the jugular bulb is noted. The lower cranial nerve runs from the brainstem to the upper neck through the jugular foramen passing medially to the jugular bulb. eca: external carotid artery; ica: internal carotid artery; ijv: internal jugular vein; imax: internal maxillary artery; ips: inferior petrosal sinus; sta: superficial temporal artery; tp: transverse process of atlas; va: vertebral artery.

The long axis of the JF is directed from the posterolateral wide part to the anteromedial narrow part. The structures passing through the JF are the sigmoid sinus, jugular bulb, inferior petrosal sinus, lower cranial nerves (IX, X, XI) with their ganglia, and meningeal branches of the occipital artery and ascending pharyngeal artery.

There are two different ways of dividing the JF into anatomical compartments. The first classification system divides the JF into an anteromedial (pars nervosa) smaller compartment containing the inferior petrosal sinus and the glossopharyngeal nerve and a posterolateral (pars vascularis) larger compartment containing the superior section of the jugular bulb, the vagus nerve, the spinal accessory nerve, and the meningeal branches of the occipital and the ascending pharyngeal artery (see ▶ Fig. 1.24).

Fig. 1.24 (a, b) Anatomy of the jugular foramen: the anteromedial (pars nervosa) compartment and the posterolateral (pars vascularis) compartment are noted. (c, d) Venous drainage through the jugular foramen. In the majority of cases the transverse sinuses are equal in size (c); asymmetric size of transverse sinuses with the dominant size and the narrow size in the contralateral portion (d). ips: inferior petrosal sinus; JB: jugular bulb.

In the second description the JF is divided into three compartments by the dura mater, namely, a large posterolateral venous compartment containing the sigmoid sinus, an intermediate neural compartment containing lower cranial nerves IX, X, and XI, and a small anteromedial venous compartment containing the inferior petrosal sinus. The sigmoid sinus drains into the posterior portion of the jugular bulb. The height of the jugular bulb varies a lot and it can be as high as the IAC. It is very important to note that the wall of the jugular bulb is very thin and fragile as it lacks an adventitia layer. As it gets out of the JF and it becomes the internal jugular vein, it is reinforced by the periosteal ring and it acquires a normal venous structure. Most often the inferior petrosal sinus (IPS) enters the JF passing between cranial nerves IX and X. IPS has a variable course and drainage pattern, terminating into the anterior portion of the jugular bulb in 90% of cases but it rarely might have multiple openings in both the jugular bulb and the internal jugular vein (see ▶ Fig. 1.25).

Fig. 1.25 Endocranial anatomy of petrosal sinus (Right side). afb: acoustic-facial bundle; cav: cavernous sinus; gag: gasserian ganglion; gg: geniculate ganglion; gspn: greater superficial petrosal nerve; ica: internal carotid artery; IJV: internal jugular vein; ips: inferior petrosal sinus; jb: jugular bulb; sps: superior petrosal sinus; ve: vestibule.

At the level of the external orifice of the JF, it gives rise to the tympanic branch (Jacobson’s nerve), which crosses the tympanic canaliculus to enter the tympanic cavity where it gives rise to the tympanic plexus. The auricular branch (Arnold’s nerve) arises at the level of the superior vagal ganglion and it is joined by a branch from the inferior glossopharyngeal ganglion (see ▶ Fig. 1.24). The auricular branch passes laterally in a shallow groove on the anterior wall of the jugular bulb to reach the lateral wall of the jugular fossa, where it enters the mastoid canaliculus and ascends toward the mastoid segment of the facial canal, giving off an ascending branch to the facial nerve as it crosses lateral to it before turning downward to exit the temporal bone through the tympanomastoid fissure (see ▶ Fig. 1.24).

1.6 Infratemporal Fossa

The infratemporal fossa (ITF) is a complex three-dimensional nonfascial bound space inferomedial to the zygomatic arch and the ramus of the mandible. It acts as a conduit for neurovascular structures entering and leaving the skull base (see ▶ Fig. 1.26). Due to its deep-seated location and important neurovascular structures, it is wise for neuro-otologists and skull base surgeons to have a thorough knowledge of its boundaries and adjacent structures. Fisch in 1977 first described different ITF approaches to surgically access and treat various lesions arising in and around this space.

Fig. 1.26 (a, b) Anatomy of the infratemporal fossa (right side). eac: external auditory canal; eca: external carotid artery; et: eustachian tube; fn: facial nerve; gg: geniculate ganglion; ica(h): horizontal portion of internal carotid artery; ica(v): vertical portion of internal carotid artery; ijv: internal jugular vein; jb: jugular bulb; lab: labyrinthine block; max: internal maxillary artery; mcf: middle cranial fossa; mma: middle meningeal artery; oc: occipital condyle; pr: promontory; sis: sigmoid sinus; sty: styloid process.

The ITF is an irregular space that can be described as an inverted square-shaped pyramid superiorly communicating with the temporal fossa under the zygomatic arch. It communicates medially through the pterygomaxillary fissure with the pterygopalatine fossa (see ▶ Fig. 1.31), anteriorly through the inferior orbital fissure with the orbit, and superomedially through the foramen ovale and spinosum with the middle cranial fossa (see ▶ Fig. 1.27, ▶ Fig. 1.28, ▶ Fig. 1.29, ▶ Fig. 1.30, ▶ Fig. 1.31). Due to the venous connections between the pterygoid venous plexus and the cavernous sinus, potentially life-threatening infections can spread from ITF to the cavernous sinus leading to cavernous sinus thrombosis.

Fig. 1.27 Infratemporal fossa anatomy; posterior view (left side). auric: auriculotemporal nerve; fosp: foramen spinosum; fova: foramen ovale; inal: inferior alveolar nerve; ling: lingual nerve; max: maxillary artery; mma: middle meningeal artery; sph: sphenoid.

Fig. 1.28 Infratemporal fossa anatomy; axial view (left side). auric: auriculotemporal nerve; et: eustachian tube; fn: facial nerve; ica: internal carotid artery; inal: inferior alveolar nerve; jb: jugular bulb; ling: lingual nerve; max: maxillary artery; mma: middle meningeal artery; sty: styloid process.

Fig. 1.29 Infratemporal fossa anatomy; lateral view (right side) (a); anatomy of the otic ganglion in relation to trigeminal nerve (b). eac: external auditory canal; eca: external carotid artery; et: eustachian tube; fn: facial nerve; ica: internal carotid artery; ijv: internal jugular vein; mma: middle meningeal artery.

The ITF is anteriorly bounded by the posterolateral surface of the maxillary sinus. Medially, it is bounded by the lateral pterygoid plate, the medial pterygoid and tensor veli palatini muscles, and the ramus of the mandible forms the lateral boundary (see ▶ Fig. 1.30, ▶ Fig. 1.31, ▶ Fig. 1.32). Superiorly, it is bounded by the infratemporal surface and the infratemporal crest of the greater wing of the sphenoid bone and inferiorly, it is closed by the insertion of the medial pterygoid muscle on the ramus of the mandible. The posterior boundary of the ITF is loosely defined and by the carotid sheath and the tympanic plate and the styloid process of the temporal bone.

Fig. 1.30 (a) Infratemporal fossa and pterygopalatine fossa anatomy (right side). (b) Temporomandibular joint and pterygoid muscles insertions. et: eustachian tube; fn: facial nerve; gg: geniculate ganglion; gspn: greater superficial petrosal nerve; ica(h): horizontal portion of internal carotid artery; ica(v): vertical portion of internal carotid artery; mma: middle meningeal artery; pr: promontory.

Fig. 1.31 Nervous content of the pterygopalatine (pterygomaxillary) fossa (lateral view; left side).

Fig. 1.32 (a, b) Temporomandibular joint and muscle contents in the infratemporal fossa (right side).

As mentioned earlier, the ITF acts as a passageway for neurovascular structures passing to and from the orbit, the middle cranial fossa, the pterygopalatine fossa, and the temporal fossa. It contains the following structures:

●Muscles:

-Medial pterygoid muscle.

-Lateral pterygoid muscle.

-Inferior part of temporalis muscle.

●Vascular structures:

-Maxillary artery and its branches.

-Maxillary vein.

-Pterygoid venous plexus.

●Nerves:

-Mandibular nerve and its branches.

-Chorda tympani nerve.

-Otic ganglion.

The muscles of mastication are associated with the ITF; the lateral pterygoid muscle occupies most of the superior ITF while the medial pterygoid muscle forms the inferior boundary. The masseter and temporalis muscles insert and originate from the borders of the fossa. The lateral pterygoid muscle arises from two heads (upper and lower) from the infratemporal surface of the greater wing of the sphenoid and lateral pterygoid plate, respectively, and inserts into the pterygoid fovea on the mandibular condyle (see ▶ Fig. 1.32). The lateral pterygoid is the only muscle of mastication that depresses the mandible and opens the jaw (see ▶ Fig. 1.32ba,b). The medial pterygoid muscle also has two heads of origin (deep and superficial), from the lateral pterygoid plate and the maxillary tuberosity, respectively, and inserts on the medial surface of the ramus of the mandible near its angle. All the muscles of mastication are supplied by the mandibular nerve.

The maxillary artery is the seventh (terminal) branch of the external carotid artery that originates at the neck of the mandible and runs through the ITF between the condylar process of the mandible and the sphenomandibular ligament to enter the pterygopalatine fossa. The maxillary artery is divided into three parts in relation to the lateral pterygoid muscle. The first part (mandibular) lies deep to the condyle of the mandible, the second part (pterygoid) lies on the lateral pterygoid muscle, and the third part (pterygopalatine) lies in the pterygopalatine fossa. All the three parts of the maxillary artery give several branches, described below:

●Branches from the first part:

-Deep auricular artery.

-Anterior tympanic artery.

-Middle meningeal artery.

-Accessory meningeal artery.

-Inferior alveolar artery.

●Branches from the second part:

-Anterior and posterior deep temporal arteries.

-Pterygoid branch.

-Masseteric branch.

-Buccinator branch.

●Branches from the third part:

-Posterior superior alveolar artery.

-Infraorbital artery.

-Descending palatine artery.

-Pharyngeal branch.

-Pterygoid canal artery.

-Sphenopalatine artery.

The pterygoid venous plexus has two parts—a superficial part between the temporalis and the lateral pterygoid muscles and a deep-lying part medial to the lateral pterygoid muscle. Most often, the deep-lying part of the pterygoid plexus is better developed. It receives tributaries corresponding to the branches of the maxillary artery. It mainly drains the orbit and the area in and around the ITF. The pterygoid venous plexus is drained by the maxillary vein which begins at its posterior border and it accompanies only the first part of the maxillary artery. Inside the parotid gland it joins the superficial temporal vein to form the retromandibular vein (see ▶ Fig. 1.33a).

Fig. 1.33 Venous drainage of the head and skull base. (a) Venous system of the infratemporal fossa. (b) Venous system of the brain.

The ITF is densely innervated and it provides a gateway for the mandibular nerve, the chorda tympani nerve, and the otic ganglion. These nerves grant sensory and motor functions to the lower face, the muscles of mastication, and the dura mater. The mandibular nerve is a mixed nerve which enters the ITF through the foramen ovale. It runs between the lateral pterygoid and the tensor veli palatini muscles and divides into smaller anterior and larger posterior branches. Just before its bifurcation, it gives motor branches to the tensor veli palatini, the tensor tympani, and the medial pterygoid muscles and a sensory meningeal branch to the dura mater (see ▶ Fig. 1.31). The anterior division gives four branches: one sensory buccal branch and three motor branches to the masseter, the temporalis, and the lateral pterygoid muscles. The posterior division is mainly sensory and gives three branches, namely, the auriculotemporal nerve, the lingual nerve, and the inferior alveolar nerve (see ▶ Fig. 1.29).

The chorda tympani nerve enters the ITF through the petrotympanic fissure and joins the lingual nerve. The chorda tympani nerve carries the taste sensation from the anterior two-thirds of the tongue and provides secretomotor fibers to the submandibular and sublingual salivary glands. The otic ganglion is located in the ITF on the medial side of the mandibular nerve inferior to the foramen ovale. The presynaptic parasympathetic fibers mainly stem from the lesser petrosal nerve (formed by the tympanic plexus). The postsynaptic parasympathetic secretomotor fibers supply the parotid gland via the auriculotemporal nerve.

1.7 Cerebellopontine Angle

The cerebellopontine angle (CPA) is the anatomic space between the petrous bone and the petrosal cerebellar surface folding around the pons and the middle cerebellar peduncle, containing the posterior cranial fossa nerves (see ▶ Fig. 1.17 and ▶ Fig. 1.34).

Fig. 1.34 Cerebellopontine angle anatomy (left side). afb: acoustic-facial bundle; aica: anterior inferior cerebellar artery; baa: basilar artery; flo: flocculus; ijv: internal jugular vein; ips: inferior petrosal sinus; jb: jugular bulb; pica: posterior inferior cerebellar artery; sca: superior cerebellar artery; sis: sigmoid sinus; va: vertebral artery.

Examining the anatomy of the CPA, we can define three neurovascular complexes:

●The upper complex (including the trigeminal, oculomotor, and trochlear nerves; the midbrain; the cerebellomesencephalic fissure; the superior cerebellar artery [SCA]; the superior cerebellar peduncle; and the tentorial surface of the cerebellum) (see ▶ Fig. 1.35).

●The middle complex (including the acoustic-facial nerve bundle and the abducent nerve; the pons; the cerebellopontine fissure; the AICA; the middle cerebellar peduncle; and the petrosal surface of the cerebellum) (see ▶ Fig. 1.17a,b).

●The lower complex (including the lower mixed cranial nerves; the hypoglossal nerve; the medulla; the cerebellomedullary fissure; the posterior inferior cerebellar artery [PICA]; the inferior cerebellar peduncle; and the suboccipital surface of the cerebellum) (see ▶ Fig. 1.17a,b).

Fig. 1.35 Relationships of the cranial nerves with the endocranial surface of the skull base and brainstem. baa: basilar artery; cocn: cochlear nerve; fn**: facial nerve in the cerebellopontine angle; gg: geniculate ganglion; gspn: greater superficial petrosal nerve; ica(h): horizontal portion of internal carotid artery; ivn: inferior vestibular nerve; ssc: superior semicircular canal; svn: superior vestibular nerve.

1.7.1 Relevant Nervous Contents

The trigeminal nerve emerges laterally from the pons, in proximity to its superior border, with a larger sensory root and a smaller motor root. The fibers of the sensory root have their somas in the trigeminal ganglion, in a dural duplication approximately 1.5 cm from the apex of the petrous ridge. Three roots arise from the trigeminal ganglion in Meckel’s cave: the ophthalmic nerve (V1), the maxillary nerve (V2), and the mandibular nerve (V3).

The acoustic-facial bundle arises from the brainstem close to the pontomedullary sulcus. The facial nerve exits at the level of the pontomedullary junction about 1 to 2 mm anteriorly to the vestibular nerve; after this level the facial nerve immediately meets the vestibulocochlear bundle. The eighth and the intermediate nerves join the facial nerve in the CPA. The gap between the vestibulocochlear bundle and the facial nerve is well visible at the level of the pontomedullary sulcus; these nerves get closer as they approach the meatus. The acoustic-facial bundle runs forward and lateral to the posterior surface of the petrous bone, entering the IAC. During its course in the CPA, the position of the facial nerve in relation to the other nerves is anterior and medial until the IAC is reached, while the vestibular nerve is located superiorly and the cochlear nerve inferiorly. In the porus of the IAC, the position of the nerves changes: the facial nerve runs superiorly with the vestibular nerve and the cochlear nerve is inferior.

The lower cranial nerves originate from the medulla oblongata and run superolaterally to enter the JF.

Topdown, the lower cranial nerves are located as follows:

●The glossopharyngeal nerve: This nerve is in the most superior position to the other lower cranial nerves and it is made up of by a single root.

●The vagus nerve: Located in the intermediate position, this nerve at the exit zone is close to the glossopharyngeal nerve and it is made up of by multiple roots.

●The spinal accessory nerve, located at the most inferior extremity, it is formed by two distinct roots: the cranial root and the spinal root. The exit zone of the cranial root is close to the fibers of the vagus nerve. This nerve is small if compared to the other root. The spinal root is larger and it is made up of multiple roots from the spinal cord; these roots merge into a single trunk that ascends the upper portion of the cervical canal and enters the posterior fossa through the foramen magnum.

The exit zone of the hypoglossal nerve is located medially on the ventral surface of medulla oblongata. The fibers of this nerve are grouped into two main trunks that usually merge inside the hypoglossal canal.

The PICA often runs in between the two roots of hypoglossal nerve.

1.8 Internal Carotid Artery

According to Bouthillier’s classification, the ICA is divided into seven segments according to the anatomical relationship of the artery with the adjacent structures and the anatomical compartments it crosses (see ▶ Fig. 1.12):

●Cervical segment (C1).

●Petrous segment (C2).

●Lacerum segment (C3).

●Cavernous segment (C4).

●Clinoid segment (C5).

●Ophthalmic segment (C6).

●Communicating segment (C7).

The C1 segment is the most inferior segment of the ICA, it is located in the neck. It starts from the carotid bulb where an enlargement of the artery is present. From the bulb, the vascular structure ascends at the base of skull, forming the ascending cervical segment. In this area a tortuosity of the artery may be present.