Manual of Temporal Bone Dissection

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MANUAL OF TEMPORAL BONE DISSECTIONby Maurizio Barbara

Kugler Publications/ The Hague/The Netherlands

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MANUAL OF TEMPORAL BONE DISSECTION

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MANUAL OF TEMPORAL BONE DISSECTION

by

M. Barbara

Kugler Publications / The Hague / The Netherlands

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ISBN 90 6299 190 4

Distributors: For the USA and Canada: Pathway Book Service 4 White Brook Road Gilsum, NH 03448 USA Telefax (603) 357 2073 For all other countries: Kugler Publications P.O. Box 97747 2509 GC The Hague, The Netherlands Telefax (+31.70) 3300254 E-mail: info@kuglerpublications.com website: kuglerpublications.com

Copyright 2002 Kugler Publications All rights reserved. No part of this book may be translated or reproduced in any form by print, photoprint, microfilm, or any other means without prior written permission of the publisher. Kugler Publications is an imprint of SPB Academic Publishing bv, P.O. Box 97747, 2509 GC The Hague, The Netherlands

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TABLE OF CONTENTS

Foreword Preface Introduction Lateral (transmastoid) approach Phase 1: Removal of the mastoid cortex Phase 2: Opening of the superficial mastoid cell system Phase 3: Opening of the deep mastoid cell system and antrotomy Phase 4: Skeletonisation of the sigmoid sinus, opening of the retrofacial and medial tip cells, and exposure of the jugular bulb Phase 5: Posterior and anterior epitympanectomy Phase 6: Posterior tympanotomy (facial recess) Phase 7: Lowering of the posterior wall of the external auditory canal Phase 8: Classical radical mastoidectomy Phase 9: Opening of the petrous apex Phase 10: Cochleostomy and cochlear visualisation Phase 11: Identification and skeletonisation of the vertical intrapetrous tract of the internal carotid artery, jugular bulb (subfacial approach) and petrous apex Phase 12: Facial nerve decompression (second and third portions) Phase 13: Identification of the endolymphatic sac Phase 14: Isolation of the labyrinthine block Phase 15: Labyrinthectomy and identification of the intraosseous endolymphatic sac and duct Phase 16: Opening of the vestibule Phase 17: Identification of the labyrinthine segment of the facial nerve Phase 18: Identification and opening of the internal auditory canal Supratemporal or middle fossa approach Phase 19: Opening of the epitympanic cavity and of the petrous apex cells

vii ix 1 7 10 12 16

18 21 24 27 30 33 34

37 39 42 44 46 48 49 51 54 56

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Phase 20: Identification of the facial nerve and geniculate ganglion Phase 21: Exposure of the internal auditory canal Phase 22: Isolation of the cochlea Posterior cranial fossa approach Phase 23: Identification of the internal auditory canal Abbreviations Glossary Surgical applications Instrumentation

57 59 61 62 64 65 67 69 70

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FOREWORD

The temporal bone is an anatomical jewel box of extraordinary complexity. Both the minuscule scale of its vital structures and their convoluted three-dimensional relationships make microsurgery of this region one of the most technically demanding of all operative endeavours. Unravelling the mysteries of temporal bone anatomy is the foremost challenge faced by every otologist. The goal of achieving perfect knowledge and facility will never be achieved. No matter how experienced a surgeon becomes, ongoing study of the finer points of temporal bone anatomy (observed both in the operating room and dissection laboratory) serves to maintain and improve his or her skill. Dr Barbara has produced a highly useful Manual of Temporal Bone Dissection to guide exploration of the temporal bone. Its stepwise approach will prove useful for both the novice otologist and the experienced surgeon seeking to refresh his or her knowledge. Its orientation upon specific surgical procedures, rather than pure anatomy, enhances its utility for the practising surgeon. This written resource is an essential element of the three components needed for a high quality surgical dissection course: a lucid manual (such as that authored by Dr Barbara), informative didactic sessions, and anatomical dissection proctored by expert microsurgeons. The team at La Sapienza are to be congratulated for their efforts in producing an outstanding educational programme. Robert K. Jackler, MD San Francisco July, 2002

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PREFACE

When the Programme of the Permanent Educational Center in Otology at the University of Rome La Sapienza started its First Basic Course on the Temporal Bone in 1996, a long-standing dream of both my teacher, Professor Roberto Filipo, and myself was realised: to create a reference point for all colleagues who, in mid-southern Italy, wished to make a start in, or to improve their knowledge of, otology and otosurgery. The presence of a prestigious foreign guest of honour at each course, the use of advanced technology and, last but not least, the informal setup of the courses expressly desired by Professor Filipo, have been the winning weapons for the ever greater diffusion of our Center in Italy as well as abroad. Therefore, in the present manual, it was natural to bring together all the teaching and advice that are offered to participants during the laboratory sessions, in a formula that combines pure anatomy with surgical applications. Although simple and certainly not exhaustive, this manual has required a huge amount of effort, and its realisation has only been possible thanks to: Professor Roberto Filipo, my teacher, for all his advice and stimulating criticism; Professor Robert Jackler, from the University of San Francisco (UCSF), who followed my work with his particular expertise; Mr John Ballantyne, who revised the English version of the manual with his renowned professionalism; Drs Aleandro Harguindey, Daniele Bernardeschi and Francesco Ronchetti for their constant dedication and tirelessness; Dr Francesca Auriti for enriching the iconography; and, most of all, my beloved Simonetta for her support. Maurizio Barbara

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INTRODUCTION

This manual is for ENT specialists/residents wishing to deal with surgical dissection of the temporal bone, and thus to be initiated into ear surgery. However, it should only be taken as a guide and not as a substitute for the many obligatory laboratory dissections. It is also a stimulus for a deeper look at the surgical techniques in the major otosurgical textbooks. The major part of it will be dedicated to the lateral (transmastoid) approach through which the huge majority of otological approaches are performed but space will also be reserved for dissection of its superior (middle cranial fossa) and posterior (posterior cranial fossa) aspects. In fact, the progress in otosurgery as well as the more frequent cooperation with neurosurgeons, make this type of exercise very useful. The only difference lies in the lack of soft tissue, which is generally manipulated before working on the bone. Hints ! Before starting on the topic, it is important to devote a few words to some aspects which emerge during laboratory (or live) dissections: the dissection should always be carried out in a well-ventilated room, which allows for air exchange, since it will sooner or later become saturated with noxious agents (fixatives, bone dust, etc.);

Fig. 1. A proper sitting position is advised during the dissection.

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Fig. 2. The instruments should be handled correctly, with a firm point.

protect yourself against potentially infectious materials by dressing correctly (waterproof gown, mask, glasses, ear plugs!); before starting, familiarise yourself with the laboratory instruments: operating microscope, drill, suction-irrigation system, surgical microinstruments; maintain a proper sitting position, leaning against the back of the chair, with both feet (heels included) fully in contact with the floor, and both hands on a firm point (little finger, wrist) (Fig. 1-2);

Superior view

Lateral view

Fig. 3. Topographic terminology always has to be used in a proper way.

3 always follow the same steps during each dissection; use the biggest burr possible in every dissection region; think (and talk) in millimetres regarding the size of surgical instruments (hooks, burrs), prostheses, and middle ear anatomical structures; take into account the possible anatomical variations from one bone to another in different dissections; manoeuvre personally the drill pedal and do the same in the operating theatre; unintentional holes in specific parts of the temporal bone (dura, sinus) are possible, and should not prevent use of the specimen: this can also depend upon the poor fixation or storage of the bones. If you are responsible for bone collection, it is better to fix the bones by freezing. Remember that, in vivo, some delicate anatomical structures (dura, sigmoid sinus, jugular bulb, internal carotid artery) are more resistant than expected. topographic terminology is of the utmost importance and must always be used correctly, i.e., superior: towards the vertex; inferior: towards the feet; anterior: towards the nose; posterior: towards the nape; lateral (or external or superficial): towards the external meatus; medial (or internal or deep): towards the brainstem (Fig. 3). Clean the microscope (being careful with the lens), burrs, and any other instruments used. Leave your dissection position as clean as you found it (Fig. 4). When using a standard operating microscope, before looking through it, it must be checked for the motility of each arm, without overtightening it, since, over time, its mechanical characteristics could be altered. The focal lens should be 250 mm in the laboratory, but 300 or 350 mm are often used in neurotology and skull-base surgery. It is obviously important to correct for visual defects and interpupillary distance. In order to ge