MANUAL OF TEMPORAL BONE DISSECTION by 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:
[email protected] 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
57 59 61 62 64
Abbreviations Glossary Surgical applications Instrumentation
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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1
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 get rapidly in focus, using macro- and micromovements, it is better first to select the highest magnification (usually 40x). Once focused on an object, magnification can be reduced and the focus will be maintained or be adjustable with minimal micromovements (Fig. 5).
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Fig. 4. Dissection bench.
Fig. 5. Operating microscope.
The drilling system can be threaded, electrical, or pneumatic (Fig. 6). In general, only electric drills allow the burr to rotate both clockwise and anticlockwise. You must be familiar with mounting and dismounting the burrs of all the systems at your disposal, since familiarity with the technology and instruments helps to enrich the cultural baggage of the otologist, as well as increasing his profile in the operating theatre. Two main types of burr are generally used: cutting (Fig. 7a) or diamond (Fig. 7b).
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Fig. 6. Pneumatic drill.
Fig. 7a. Cutting burr.
Fig. 7b. Diamond burr.
A cutting burr is made of multiple blades, more or less close to each other: the greater the number of blades, the more stable the burr, but the less well it cuts. Diamond burrs work by saucerising and thinning the contacted surface. They are generally used in proximity to or in contact with soft tissues (dura, sigmoid sinus or jugular bulb, facial nerve (FN)), or when a bony bleeding point has to be stopped (only in live bones!), closing the vascular channel with the bone dust produced (momentarily stopping irrigation). Although diamonds last forever, the glue which binds them to the steel ball does not. Hence the need for continuous irrigation to avoid overheating. When using an electric drill, in some cases it is necessary to make the burr rotate anticlockwise for a two-fold purpose: a. to reduce the cutting power (better to select a diamond burr); b. to avoid uncontrolled movements which make the burr hit an im-
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Fig. 8a-c. The hand piece of the drill as well as instruments have to be handled like a pen.
portant structure (e.g., during antrotomy, in a right ear, the short process of the incus). The handpiece of the drill should be handled like a pen with obvious individual differences (Fig. 8a-c), using continuous, regular strokes. When a cutting burr is used, it must be used in the opposite direction to the rotation, in order to increase the friction (and hence the cutting power) of the blade on the bone. The movements must be slow, repetitive, ho-mogeneous, not fast or jumpy. Apart from a few exceptions (blockage of a bleeding point, cochleostomy, platinotomy, part of internal auditory canal (IAC) skeletonisation), the lateral face (shoulder) of the burrs must always be used, NEVER THE TIP! which is unstable. Suction-irrigation must be adjusted from the start: its perfect combination will ease the dissection work, by avoiding accumulation of bone dust between the blades (for cutting burrs only), thus reducing efficacy. Whenever possible, it is preferable to position the suction medially (deeper) to the working site, in order not to have vision impeded by the collecting fluids. The continuous flow of water across the area of dissection will serve both to cool the drill burr and to wash away blood and bone debris. Finally, remember to use the largest burr at your disposal in relation to the region to be dissected.
7 LATERAL (TRANSMASTOID) APPROACH
The temporal bone (TB) must be placed in a bone-holder in the surgical position (Fig. 9). Orientation of the TB specimen is achieved by using surface land-
Fig. 9. Bone-holder.
Fig. 10. A right temporal bone placed in a bone-holder in the surgical position.
8 marks: the zygomatic process (ZP) of the TB, located superior to the external auditory canal (EAC), and the mastoid tip (T), located inferiorly (Fig. 10). All the soft tissues covering the lateral surface of the mastoid process must be removed with a knife periosteal elevator, a scalpel or even by drilling. The following landmarks appear: • the EAC; • Henle’s spine, a small bony crest, more or less pronounced, visible on the surface at the level of the postero-superior wall of the EAC; • Chipault’s cribriform area, a multiply-holed region posterior to Henle’s spine; • the mastoid emissary vein (EV) orifice, situated in the most posterior area of the mastoid process; • the mastoid tip (T), with its muscular attachments. Steps in the dissection The steps described below aim to follow the dissection as close as possible to surgical reality (also including phases that are not routinely carried out). They will progress from a dissection centred on a ‘closed’ technique (enlarged mastoidectomy, posterior tympanotomy, epitympanectomy), to an ‘open’ technique (lowering of the EAC), aimed at visualising the surface anatomy of the medial wall of the middle ear as well as at carrying out a classical radical mastoidectomy, an operation which today is only rarely performed in otosurgery. Only at this point will the dissection – up to this point adhering to the options of the surgical technique – deal with the identification of structures embedded within the TB, which only pathological processes or neurootological approaches need to expose in practice (cochlea, vertical intrapetrous segment of the internal carotid artery (ICA), jugular bulb). The dissection will then continue with clinical applications, ending with the translabyrinthine identification of the IAC: although conceptually far from this phase of surgical application, it is always exciting, for those who are learning, to know how to reach the nerves within the IAC! At the end of this manual, there is a rapid guide to: 1. Abbreviations 2. Glossary
9 3. Surgical applications of the dissection 4. Instrumentation Moreover, in the text it is possible to find: • surgical applications in bold • cell groups in blue • microsurgical instruments in red • anatomical structures and otological nomenclature in italics
10 Phase 1: Removal of the mastoid cortex This phase implies the removal of all the cortical bone on the lateral surface of the TB, which covers the various superficial cell groups. In simple mastoidectomy, this is carried out within a triangular area (MacEwen’s triangle) delimited by (Fig. 11a-b): • The temporal line (linea temporalis) (A), demarcated by a subtle ridge formed by the inferior edge of the temporal muscle, as a line that is prolonged posteriorly from the zygomatic process of the TB, roughly corresponding to the tegmen, the bone separating mastoid and middle ear cavities from the middle cranial fossa (MCF) dura. Hence, the tegmen is specifically defined as t. mastoidei, t. antri, and t. epitympani. • A line perpendicular to the linea temporalis (B), which runs vertically, parallel to the posterior wall of the EAC, from the temporal line in the direction of the mastoid tip. • An oblique line (C) which unites the previous two and which corresponds roughly with the projection and direction of the sigmoid sinus (SS). In enlarged mastoidectomy, the bony removal has to be extended posteriorly, behind the SS, as well as anterolaterally, to the ZP (taking as its anterior limit the anterior wall of the EAC); and inferiorly, to the mastoid tip. Start the dissection with a large (8-mm) cutting burr and profuse irrigation with a large-calibre suction tip, since a large amount of bone dust is produced during this step of the dissection.
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a
b
Fig. 11a, b. A triangular area (McEwen’s triangle) on the lateral mastoid aspect is traced with a cutting burr.
Fig. 12. The dark area marks the cortical mastoidectomy.
12 Phase 2: Opening of the superficial mastoid cell system Before starting this step, the distribution of cell groups within the mastoid cavity must be remembered. Mastoid cells While in the newborn the mastoid is a single cavity (antrum) which lies rather superficially (beware of the retroauricular incision as the facial nerve (FN) is very superficial at this age!), after the first few months and in adults, it can be pneumatic, diploic, or sclerotic, the latter two with a few cells limited to the antrum and the central cell tracts. Two main areas can be distinguished: • anterolateral (pars squamosa) • posteromedial, including the tip (pars petrosa) These two portions are separated by the petrosquamous septum (Koerner’s), a bony lamina which is usually reabsorbed, but at times can remain imperforate. In order to memorise the nomenclature of the different cell groups more easily, without relying on personal mnemonic capabilities, simply refer to the constant presence of some anatomical landmarks, such as tegmen, SS, FN, antrum, labyrinthine block, and mastoid tip (Fig. 13). Three areas can be distinguished in the mastoid region: 1. Antrum: a large space which communicates – through the aditus – with the posterior epitympanum, and is laterally delimited by the squamous portion; 2. Central area: extending inferior to the antrum, as a single cavity or a group of cells, partly divided by Koerner’s septum; 3. Peripheral area: including five groups of cells: a. tegmental: close to the tegmen, located superiorly; b. sinodural: occupying the posterosuperior corner of the mastoid, superiorly limited by the tegmen, and postero-inferiorly by the SS; c. perisinus: subdivided into lateral, medial, retrosinus (superior and inferior) and presinus; d. perifacial;
13
Fig. 13. Sagittal drawing of the mastoid cavity.
Fig. 14. Removal of the mastoid cortex.
Fig. 15. A cutting burr should always work with its lateral face (shoulder).
14 e. retrofacial: often as an isolated individual cavity, situated medially and inferiorly to the vertical (mastoid) segment of the FN; f. mastoid tip: separated by the posterior belly of the digastric muscle into medial and lateral cells; g. perilabyrinthine: – superior prelabyrinthine – translabyrinthine or infralabyrinthine – supralabyrinthine or petrous crest – retrolabyrinthine superior or retrolabyrinthine; h. infralabyrinthine; i. precochlear or inferior prelabyrinthine. Once the mastoid cortex has been exenterated (Fig. 14), the bone becomes more fragile and the burr works more effectively, especially in the pneumatic (cellular) mastoid. In fact, when more than one group of adjacent cells is opened, a larger cavity is created, in which the burr can work more easily in contact with its shoulder (Fig. 15). Drilling can continue with a slightly smaller cutting burr (6 mm) and with a suitable suction tip. When approaching the tegmen or the SS, it is advisable to use a diamond burr of the same size, remembering that the sound of the working burr may change, i.e., become metallic. At this point, the most important anatomical landmark, before reaching the deeper ones, is represented by the tegmen, i.e., the bony lamina that separates the mastoid cavity from the dura of the MCF. By identifying the tegmen (roughly corresponding to the linea temporalis) and isolating it in its postero-anterior course, this will definitely mark the upper limit of the dissection in TBs of any type, including malformed TBs, as in congenital aural atresia. Once removal of the superficial mastoid cells has been completed, a space may be encountered that is limited medially by a bony lamina, which is either continuous or has a narrow passage, which can be confused with the compact bone of the lateral semicircular canal (LSC). This is the petrosquamosal septum, known as Koerner’s septum, which, in the early stages of mastoid development, separates the lateral (squamosal) from the medial (petrosal) part of the mastoid, each with its
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Fig. 16. An incompletely reabsorbed Koerner’s septum (KS).
Lateral cells
Fig. 17. Cortical and lateral mastoid cells have been exenterated.
own cell groups and communicating independently with the antrum (Fig. 16). Verification of the close anatomical relationship between antrum and LSC helps the novice to find his or her way, considering how superficial the dissection still is. After finishing Phase 2, the following cell groups have been opened (Fig. 17): superficial supra- and infra-antral lateral pre- and retrosinus lateral tegmental lateral tip
16 Phase 3: Opening of the deep mastoid cell system and antrotomy After having opened Koerner’s septum, the dissection continues by drilling the anterolateral and superolateral cells, in order to better visualise the antral cavity. Obviously, a smaller-sized burr should be selected (4-5 mm or less). Care should be taken, especially in sclerotic bones, not to open the LSC, the dome of which may be violated by mistake, causing what American authors call ‘snake’s eyes’: two small holes on the dome of the LSC (Fig. 18). In order to complete antrotomy, the second landmark to be exposed, after the LSC, is the body with the short process of the incus. It is of the utmost importance to drill the most medial portion of the EAC, between the posterior and superior walls. Stagnation of the irrigation fluid during drilling often causes this structure to be visualised
Fig. 18. ‘Snake’s eyes’ as a result of the opening the dome of the LSC.
Fig. 19. The short process of the incus is first visualised (b) by refractive effect of the irrigation liquid, before being visible in the surgical cavity (a).
17 (b) – by light refraction – before it is in fact visible in the surgical cavity (a) (Fig. 19). This phase, erroneously considered to be the end of hurried dissection sessions, can be considered finished when the following are visible: • the short process of the incus and fossa incudis, occupied by whitish tissue resembling cholesteatoma or epidermisation (this is the posterior ligament of the incus); • the dome of the LSC, a compact, mat bone, which is brighter than the surrounding bone; • the superior aspect (roof) of the antrum, exposing the tegmen antri, which must be at the same level as the tegmen mastoidei, posteriorly and superiorly. Both superficial and deep cell groups will thus be drilled out (Fig. 20).
Fig. 20. All the mastoid cells have been exenterated.
18 Phase 4: Skeletonisation of the sigmoid sinus, opening of the retrofacial and medial tip cells, and exposure of the jugular bulb Retaining some of the perisinus cells already drilled during the previous phases for reference, the dissection continues by opening the cells placed posteriorly and laterally to the SS. Working with a cutting burr (6 mm), the orientation of the vertical course of the SS will be recognisable by the bluish colour of the laboratory as well as the live bones (more intense blue in live bones). This is the first delicate step of the dissection and needs particular care. Skeletonisation of the posterior wall of the SS consists of the removal of retrosinus cell groups, performed by alternating cutting and diamond burrs in order to optimise time and quality of the dissection. In the central part of the SS, posteriorly, in some bones, it is possible to visualise the channel of the posterior/mastoid emissary veins or the vein itself (remember the superficial landmark in the lateral aspect of the TB!), at the posterior cranial fossa dura level. One important landmark is represented by the opening of the superoanterior part of the SS, where the SS meets the MCF dura, thus obtaining exposure of the sinodural angle (Citelli’s) (SDA) after drilling out the lateral and medial sinodural angle cells (Fig. 21).
Fig. 21. The sigmoid sinus (SS) has been skeletonised, reaching the jugular bulb (JB). SDA= Sino-dural angle (Citelli’s).
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Fig. 22. The insertion of the posterior belly of the digastric muscle (DM) at the mastoid tip level.
Fig. 23. Isolation of the jugular bulb (JB). SS= Sigmoid sinus.
Fig. 24. The retrofacial cells (RFC) give access to the jugular foramen area. CT= Chorda tympani; FN= Facial nerve.
Once all the lateral, medial, superior, and inferior retrosinus cells have been opened, the dissection continues towards the mastoid tip. At this level, lateral and medial tip cell groups are delimited by a tangential line passing through the posterior belly of the digastric muscle (DM), which forms another important landmark anteriorly in TB surgery: the stylomastoid foramen as the exit for the FN (third to extracranial parotid segment) from the TB (Fig. 22). Careful dissection of the medial tip cells will also allow the most inferior portion of the SS and its ascending tract towards the jugular bulb (JB), located at different heights with respect to the inferior wall of the EAC, to be isolated (Fig. 23). This step is also very delicate
20 since, in the majority of TBs, the venous wall is very fragile (more fragile than in live bones!), while the bony tissue around the JB is brownish in colour (due to the bone marrow). Only diamond burrs, of smaller and smaller calibre (from 5 to 3 mm) should be used. At this point, medial and inferior to the third vertical segment of the FN, it is possible to visualise a group of cells, often fused in one cavity only: the retrofacial cells (RFC), which are of the utmost importance during the approach to the inferior and posterior walls of the tympanic cavity and, subsequently, to the petrous apex (Fig. 24).
21 Phase 5: Posterior and anterior epitympanectomy This step, which is of extreme importance, concludes – in its initial part limited to the posterior epitympanum – the surgical approach in a closed (canal wall up; CWU) tympanoplasty (TPL) which, in the absence of cholesteatoma, does not usually have to be completed with a posterior tympanotomy. It consists of progressive widening of the superoposterior access to the tympanic cavity already started with the antrotomy, and finishes up by visualising (remember the refractory effect with irrigation liquid) the short process of the incus and its insertion into the fossa incudis. It is very important to carry out a complete removal of the mastoid cortex: this will allow the antrotomy to be widened progressively mediolaterally, i.e., passing from the more fragile to the more resistant bony parts. It must be remembered that, while at the upper and lateral levels of the dissection, it is possible to expose the MCF dura – with a change in the sound of the burr or the onset of bleeding (another cue in live bones!) – the inferior level corresponds to the postero-superior EAC wall, which it is preferable not to perforate. If this occurs, but the skin of the ear canal remains intact, no complications should be expected; if, on the other hand, the skin is missing or has been elevated as a flap, or if pathological processes such as cholesteatoma have eroded it, it is absolutely essential to carry out a corrective osteo-(chondro)plasty. It is wise to carry out the most delicate opening of the posterior epitympanum with smallsized diamond burrs. Opening of the posterior epitympanum will allow the following to be visualised (Fig. 25): a. the short process, body, and superior ligament of the incus; b. the incudomalleolar (diarthrodial) joint; c. part of the head of the malleus with its superior ligament; d. the superior surface of the posterior aspect of the COG, the main element that separates the posterior epitympanum from the anterior one. Sometimes, by opening the epitympanic space, it is possible to visualise membranes around the ossicles or the bony epitympanic walls. These are not, as one might think, fibrotic reactions to in vivo inflammatory processes, but rather mucosal folds (anterior malleal fold, posterior
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Fig. 25. Posterior epitympanectomy is completed. M= Malleus; I= Incus; LSC= Lateral semicircular canal.
Fig. 26. Mucosal folds around the ossicles in the posterior epitympanum. M= Malleus; I= Incus.
malleal fold, incudal fold, stapedial fold (Proctor)) that delimit and direct air flows and mesotympanic and mastoid ventilation, as well as influence the development and extension of cholesteatoma. They are particularly visible in well-preserved bones (Fig. 26). The dissection continues with an extension of a closed TPL, a conservative approach to the middle ear. Opening of the anterior epitympanum is generally needed when a pathological process has invaded it, as in the case of a cholesteatoma which may already have induced local damage, such as tegmen or incus erosion, as well as COG demolition. Removal of the incus and head of the malleus and demolition
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Fig. 27a-b. After removal of the ossicles from the posterior epitympanum, COG becomes visualised. TT: Tensor Tympani tendon.
of the COG (if still intact) by drilling, are essential steps in order to gain access to the anterior epitympanum. Both ossicles are firmly anchored, and their removal should be carried out cautiously. The incus has to be separated from the stapes head, through the posterior tympanotomy; this manoeuvre can also be performed through the EAC after the creation of a tympanomeatal flap and is mandatory every time an ossicular manipulation is foreseen, in order to avoid involuntary luxation or fracture of the stapes crura or footplate, with possible bad functional consequences. The head of the malleus can be removed alone by using a special instrument (malleus nipper) placed medially to the malleus neck in order to separate the head from the handle. Disconnection of the upper ligaments of both ossicles is rather easy to perform using small hooks. Once the posterior epitympanum has been freed from this part of the ossicular chain, the posterior aspect and inferior edge of the COG are visible (Fig. 27a-b). The COG is a bony crest, generally half-moon shaped, inserted into the tegmen with an irregular inferior concavity. Its removal must be carried out with a small (0.5-1.0 mm) diamond burr, drilling it inferosuperiorly, towards the tegmen, in order not to damage the neighbouring structures. Once the COG has been eliminated, the whole epitympanum is opened, thus giving sight of the protympanum or supratubaric recess, located superiorly to the tubal orifice. The close relationship between the supratubaric recess, tubal orifice, and semicanal of the tensor tympani muscle should be taken into consideration.
24 Phase 6: Posterior tympanotomy (facial recess) Learning this step gives the otosurgeon (or, at least, the middle-ear otosurgeon) his/her identity card and driving licence: when correctly performed, his/her effective capabilities are clearly visible, while the inability to perform it should be reason enough for stopping that particular surgeon from cruising the otological highway. The aim of this approach is to allow visual (and instrumental) access to the tympanic cavity through the mastoidectomy cavity. Its application ranges from closed TPL (in which the posterior wall of the EAC remains intact) to cochlear implant surgery, FN decompression, insertion of some types of semi-implantable hearing aids. For its proper performance, first of all, progressive, latero-medial thinning of the posterior wall of the EAC should be carried out, until the mastoid cavity and middle ear cleft are separated by only a very thin bone (Fig. 28). This thinning out must be performed by first using cutting burrs (6 mm), which – under continuous irrigation – must work homogeneously supero-inferiorly or vice versa, using wide movements. Thinning of the posterior EAC wall can be controlled visually – after removal of the overlying skin – putting the suction tube in the EAC, which should be visible (by transparency) first laterally and later medially.
Fig. 28. Thinning out the posterior canal wall (EAC) is the first step in posterior tympanotomy.
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Fig. 29a. Drawing showing the relationship between posterior canal (EAC), chorda tympani (CT) and facial nerve (FN) when performing posterior tympanotomy.
Fig. 29b. Chorda tympani (CT) and facial nerve (FN) represent two sides of the triangle which forms the facial recess area.
Fig. 29c. The space between CT and FN has been entered and posterior tympanotomy completed.
It will be appreciated that, after a simple mastoidectomy, greater thinning of the lateral part of the posterior EAC wall has already been carried out, while the most medial part (where the facial recess is located) is still very thick. With this procedure, after uniform thinning of the posterior EAC wall, it will be possible to open a triangular bony space, delimited antero-laterally by the chorda tympani (CT), posteromedially by the vertical segment of the FN, and superiorly by a bony lamina (buttress) that separates it from the fossa incudis, which supports the short process of the incus (Fig. 29a-b-c). This fossa is always occupied by a whitish tissue (the posterior incudal ligament) which can be confused with epidermisation. It is important to bear in mind that the lateral limit of posterior tympanotomy – the chorda tympani – coincides anteriorly with the fibrous annulus and,
26 hence, with the tympanic membrane: if the posterior EAC wall is opened more laterally, the EAC itself will inevitably be entered and not the tympanic cavity. Nevertheless, the novice should choose a lateral rather than a medial (close to the FN!) approach. Once the drilling area of the posterior tympanotomy has been delineated, the calibre of the burrs (always diamond) must become smaller and smaller, remembering that the distance between the FN and the CT at that level is only 2-3 mm, or less where the CT emerges from the FN. Often, the facial recess region contains more or less large cell groups, located in the middle ear rather than in the mastoid area; so that, at times, these cells can erroneously mislead the surgeon into believing that the tympanic cavity has already been reached, while this will only be true after further cell removal. If a posterior tympanotomy is properly performed and the surgeon tilts the TB anteriorly, it should be possible to visualise the following structures: • incudo-stapedial joint • stapedius tendon • promontory and Jacobson’s nerve • round window niche • hypotympanic cells • medial aspect of the tympanic membrane with handle of the malleus • tubal orifice • fallopian canal (second segment-tympanic) • cochleariform process (CP) • semicanal of the tensor tympani muscle
27 Phase 7: Lowering of the posterior wall of the external auditory canal This step marks the passage from a ‘closed’ to a so-called ‘open’ technique. This latter technique also has different variants over and above classical or modified radical mastoidectomy. In fact, some otologists call a technique ‘closed’ even when, during the operation, the posterior EAC wall has been removed and is later reconstructed. In such cases, it should better be mentioned as a re-closed technique. In the TB, this step must be preceded by elevation or removal of the EAC skin together with the tympanic membrane, and the attached handle of the malleus also has to be removed: this step is facilitated by cutting (Bellucci’s scissors) the tensor tympani tendon at the level of the CP, proceeding tangentially to the medial aspect of the handle itself, so as not to damage the nearby tympanic segment of the FN. The posterior EAC wall may be lowered by choosing either of the two procedures, depending upon the proposed subsequent surgical sequence. However, whatever the procedure, any technique of lowering the posterior EAC wall during an ‘open’ technique must correctly reach the level of the vertical or third segment of the FN. Since a posterior tympanotomy has already been carried out during the previous step, this procedure can now be performed quite safely. The first option is to section the posterior wall temporarily, in order to achieve a larger and more comfortable approach to the tympanic cavity whilst aiming to remove pathology (cholesteatoma) and thereafter planning to put it back again. For this purpose, a small circular saw can be used, superiorly (at the epitympanic level) and inferiorly (at the level where the CT emerges from the FN). Instead of using a circular saw, the resection can also be performed by a small cutting burr, but this will lead to a larger defect when the wall has to be put back in place. The second procedure implies the use of a mid-sized (5-6 mm) cutting burr, to be used from lateral to medial along the whole length of the EAC posterior wall (Fig. 30). When the lowering of the posterior EAC wall has been completed, it will be possible to make a note of what portion of the posterior mesotympanum it is possible to visualise with an open technique. Remembering (or better still, recording) what it was possible to visualise
28
Fig. 30. The ‘open’ technique implies lowering of the posterior canal wall (PW). TM= Tympanic membrane.
through the posterior tympanotomy, it can be concluded that the ‘open’ technique: a. does not permit to see more than a ‘closed’ technique, but perhaps allows a more comfortable use of the instruments; b. does not allow to see the posterior mesotympanum, a region which cannot anyway be explored unless otoendoscopes are used. Posterior mesotympanum As mentioned above, this is the most hidden area of the TB, which can only be exposed after destructive steps have been taken. In fact, this region lies medial to the FN canal (vertical or mastoid segment) and anterior to the posterior semicircular canal (PSC). Other than the two major depressions in the posteromedial wall of the tympanic cavity, namely the round and oval window niches, the posterior mesotympanum is often named after only one part of it, the so-called sinus tympani. It lies between the ponticulus, which bridges the gap between the pyramidal eminence and the promontory superiorly, and the subiculum, a ridge stretching inferiorly between the styloid eminence to the posterior lip of the round window niche. The posterior depth of the sinus tympani is variable, reaching several millimetres in the direction of the ampullary arm of the PSC (Fig. 31).
29
Fig. 31. (Modified, with permission, from Schuknecht and Gulya (1986): Anatomy of the temporal bone with surgical implications.)
30 Phase 8: Classical radical mastoidectomy If it is true that the clinical indications for a ‘radical’ mastoidectomy are becoming fewer and fewer nowadays, it is also true that parts of this surgical technique may be included as steps in other, mostly neurootological approaches, and must therefore be part of the technical armamentarium of an otologist. At the end of Phase 7, we have a cavity mimicking a modified radical, namely a technique that requires lowering of the posterior EAC wall, at the same time sparing the existing middle ear structures (eardrum remnants, ossicles). However, a classical radical mastoidectomy implies the elimination of all middle ear structures (stapes or footplate excluded). Moreover, in order to carry out the main steps of this dissection, all EAC walls must be freed of skin, especially in the anterior part, with laterally-based flaps that may be difficult to perform in a cadaver bone. For an optimal ‘radical’, the following surgical steps have to be carried out: a. Lowering of the posterior EAC wall (already obtained after the previous phase); b. Drilling of the anterior EAC wall (AW), according to the Mickey Mouse technique popularised by the House Ear Institute in Los An-
Fig. 32. Drilling of the anterior canal wall (AW) is an important step during classic radical mastoidectomy. TMJ= Temporo-mandibular joint.
31
Fig. 33. Drawing showing the Mickey-Mouse technique for drilling of the anterior canal wall.
geles, which aims at avoiding direct penetration of the glenoid fossa and, therefore, of the temporomandibular joint (TMJ) (Fig. 32). This technique – preferably to be carried out with small-sized (1.52 mm) diamond burrs – first schedules drilling of the superior and inferior parts of the wall (Mickey Mouse’s auricles), since they are not directly contiguous with the TMJ, and afterwards uniting them in the middle, by drilling the central part (Mickey Mouse’s head) (Fig. 33). The purpose is to obtain a unique plan without any bulging of the anterior EAC wall, until the marginal bony annulus is exposed medially, and, if necessary, to remove any periannular skin remnants. As already mentioned, it is possible to open the anterior wall in its central portion adjacent to the TMJ, but it should be remembered that, in vivo, opening this part does not necessarily involve exposure of the TMJ, but only of the pericapsular fibrous tissue, usually without any symptom being experienced by the patient. c. Union of the anterior EAC wall with the overlying epitympanic anterior wall, at the expense of a solid, hard, bony ridge lying laterally to the tensor tympani muscle (anterior buttress). d. Removal of other bony ridges, especially at the level of the anterior aspect of the posterior EAC wall and of the inferior EAC wall.
32 Before leaving the ‘radical’ phase, it is important to remember that an essential non-osseous surgical step is represented by meatoplasty, namely widening of the outer orifice of the EAC, some of which has to be done by removal of the conchal cartilage. The next phase is the first of three, which are not generally included in the dissection steps of basic courses. However, since the dissection is medial to the promontory wall, it is propitious that otosurgeons obtain knowledge of it for at least two reasons: 1. to be able to deal with unusual pathological (cholesteatoma eroding the medial wall of the tympanic cavity) or anatomical (e.g., a high jugular bulb) situations; 2. to be familiar with the three-dimensional orientation of the cochlea for cochlear implant surgery, with both normal and malformed or ossified cochleas.
33 Phase 9: Opening of the petrous apex The apex of the petrous bone is routinely opened in a transmastoid approach to the IAC or to deal with local pathologies related to hyperpneumatisation and hypoventilation of the petrous apex cells (e.g., cholesterol granuloma). This step may be carried out by using an alternative, transcanal approach where the antero-infero-posterior EAC walls have to be saucerised after making a superiorly-based tympanomeatal flap. It is perhaps one of the most delicate steps, since drilling in the region of the medial wall of the tympanic cavity is delimited anteriorly by the vertical tract of the ICA, postero-inferiorly by the JB, and superiorly by the inferior border of the basal turn of the cochlea (BCT) (Fig. 34). Preferably with a diamond 1.5-2.0-mm burr, a triangularly-shaped area is delimited, in which a deeper dissection should be continued cautiously, by isolating the ‘blue lines’ of the ICA and the JB.
Fig. 34. The petrous apex (PA) is entered between the internal carotid artery (ICA) and the basal turn of the cochlea (BCT). FN= Facial nerve.
34 Phase 10: Cochleostomy and cochlear visualisation This phase of the dissection contains anatomical and practical elements with respect to cochlear implant surgery. Looking at the medial wall of the tympanic cavity, everyone knows that the promontory (a convex area) corresponds to part of the basal turn of the cochlea. The surgical landmarks for the identification of the deep projection of the cochlea are: • round window (RW) niche • stapes (S) and oval window (OW) • cochleariform process (CP) • semicanal of the tensor tympani muscle (STTM) • tubal orifice (TO) • vertical trait of the ICA • Jacobson’s nerve (J) It is important to remember that the baso-apical direction of the cochlear turn is opposite to the side operated: left direction in a right cochlea and vice versa. The initial step consists of cochleostomy, in accordance with the modalities of cochlear implant surgery. A small (2 mm) diamond burr is placed 1 mm up and 2 mm anterior to the lip of the RW niche, and kept in place while slight pressure is exerted. At that level, the bone of the otic capsule is very compact and hard to penetrate. After having created a niche, a smaller (also cutting) burr is chosen and drilling continues, always keeping the tip of the drill pushing slightly on the bone (remember that this is one of the few exceptions when the burr is not working as usual, i.e., with the shoulder and with oscillating strokes). Carrying on, with the burr working perpendicularly to the promontory wall, the endocochlear cavity is finally entered at the level of the scala tympani (in laboratory bones, no perilymph leakage will be observed) (Fig. 35a-b). At times, before entering the cavity, the endosteum may first be exposed, in accordance with the ‘soft surgery’ procedure advised to minimise cochlear trauma. At this point, it is possible to widen the hole, being careful not to hit the bony spiral lamina and the basilar membrane located in the posterosuperior pole of the cochleostomy, since their damage could interfere with the outcome of cochlear implant function. If a dummy is available, it is possible to try to simu-
35
J
Fig. 35a. With a small (1.8 mm) diamond Fig. 35b. The arrow shows the direction burr, cochleostomy is performed. of the basal turn of the cochlea.
late its insertion, ending with the application, before starting with the anatomical dissection of the cochlea. This step is carried out by using a diamond burr, and removal of the superficial part of the cochlear wall is continued anteriorly up to the projecting area of the ICA, and then superiorly in the region which is medial to the pathway between the CP and the semicanal of the tensor tympani muscle. At this level, care should be taken not to penetrate the MCF dura, remembering the strict relationship between the anterosuperior margin of the apical cochlear area, the geniculate ganglion, and the semicanal itself. In order to dissect and visualise the entire cochlea, it is also necessary to remove the stapes and to widen the drilling posterosuperiorly: it is important to acknowledge the central bearing axis (the modiolus), obliquely oriented from bottom to top, posteroanteriorly and mediolaterally (Fig. 36). If magnification is
Fig. 36. The lateral aspect of the cochlea has been removed and the cochlear turns are shown around the modiolus (MA). STTM= Semicanal of the tensor tympani muscle; CP= Cochleariform process; OW= Oval window; RW: Round window.
36 increased to the maximum (40x), unimaginable cochlear structures can be recognised (basilar membrane, scala tympani and vestibuli, pigmentation of the inner ear structures). Eustachian tube orifice This is located in the anterosuperior portion of the middle ear cavity, 4-6 mm superior to the inferior wall of the hypotympanum and just beneath the semicanal of the tensor tympani muscle (TTM) (Fig. 37). Its lumen is triangular, 3-5 mm in diameter, and surrounded by various degrees of pneumatisation. The bony part lies lateral to the ICA, with only a thin bone separating them, and small dehiscences for the passage of the caroticotympanic arteries. The tubal isthmus marks the transition, with cartilage occupying the anterolateral and superior walls.
Fig. 37. The entrance of the Eustachian tube orifice (TO) and the tensor tympani muscle (TTM) are shown.
Although proposed by some authors, tubal surgery is rarely necessary, except for removing a bony obstruction (always use small diamond burrs!; remember the closeness of the ICA and the possibility of bony dehiscences!).
37 Phase 11: Identification and skeletonisation of the vertical intrapetrous tract of the internal carotid artery, jugular bulb (subfacial approach) and petrous apex In the first part of this phase, drilling is concentrated in the anteroinferior part of the medial wall of the tympanic cavity and should be carried out – with a small diamond burr – superoinferiorly or vice versa, without movements that are too wide, provided the burr is never stopped. An important superior landmark is represented by the eustachian tube orifice, since inferomedial to it (by a few mm), the vertical ICA tract bends and proceeds anteriorly in its horizontal portion. By thinning out this area progressively and uniformly, due to the constant position of the intrapetrous ICA, colour variations can first be seen, and also a soft consistency (Fig. 38). The JB represents one of those structures that can have an extremely variable position, as far as height and postero-anterior position are concerned. Its identification and exposure are generally carried out through a transmastoid subfacial (medial to the third segment of the FN) approach, as described at the end of Phase 4. At this point, the dissection previously performed arrives at the exposure and opening of the retrofacial cells, often united in a single, large cavity. The dis-
BCT
Fig. 38. A needle is touching the posterior wall of the vertical, intra-petrous tract of the internal carotid artery (ICA), which has been exposed. TO= Tubal orifice; BCT= Basal turn of the cochlea; FN= Facial nerve.
38 section will then proceed anteromedially, having as its lateral limit the third portion of the FN, and as its upper limit, the labyrinthine block, and more specifically, the ampullary arm of the PSC. In order to optimise visualisation of the region to be opened, it is appropriate to tilt the specimen (in surgery, the operating bed) anteriorly. This manoeuvre will depend upon the degree of dissection of the retrosinus mastoidectomy, the posterior margin of which should not hamper visibility of the anterior regions. When necessary, at this point, further drilling of the posterior margin of the cavity should be carried out until this goal has been achieved. Once the JB has been identified, it is possible to go deeper, using smaller calibre (1-2 mm) diamond burrs, always being careful not to open the labyrinth (PSC). Apart from being smaller, the burrs should also have a longer shaft. It is thus possible to reach and open the petrous apex cells, finding an extreme variability of pneumatisation at this level.
39 Phase 12: Facial nerve decompression (second and third portions) As shown so far, the FN represents the structure around which the whole TB dissection rotates. It is important not to forget that the best method for preventing damage to the FN is always to keep looking for it. Apart from the monitoring systems performed during live surgery, one sign that should alert the surgeon and make him realise that he/she is close to the FN is the mild, sometimes annoying, bleeding along its course (obviously, never coagulate! Await its spontaneous remission!). Another important concept is not to fear facial palsy if, when looking for the nerve, it is uncovered: on the contrary, this can be useful to avoid damaging it. It is noticeable that, at this stage of the dissection, the FN is visible in its second (tympanic), and can be anticipated in its third (mastoid), segment. Before carrying out FN decompression, the nerve must be uncovered all along the vertical segment, drilling with a 5-mm diamond burr under continuous irrigation (facial palsy can also occur when the FN is overheated) (Fig. 39). In the superior segment of the mastoid portion, posterior to the fallopian canal, a soft structure can be seen, in close contact with the FN, but definitely separated from it,
Fig. 39. Isolation of the vertical (mastoid) segment of the FN. CP= Cochleariform process; LSC= Lateral semicircular canal.
40
Fig. 40. The stapedial muscle (SM) is found behind the vertical segment of the FN.
which may cause bleeding (Fig. 40). This is the stapedius muscle, which should not be confused with a damaged FN. Inferiorly, the dissection allows the emerging point of the CT to be identified, and, more inferiorly, the segment which precedes the exit of the FN from the temporal bone through the stylomastoid foramen; it should be borne in mind that at this level the nerve becomes more superficial. The landmark for the anterior deviation of the FN and its exit from the TB is the anterior margin of the posterior belly of the digastric muscle (which separates the lateral from the medial mastoid tip cells); this should not be sought at the level of the mastoid tip, but 1 cm higher. In order to ensure that drilling is being performed on the digastric belly, it is opportune to expose the entire belly (medial insertion to the mastoid process), which will appear as a half-moon structure directed posteroanteriorly. Once the fallopian canal of the third segment has been identified and decompressed, a similar decompression should be performed at the level of the second genu and in the tympanic segment, up to the geniculate ganglion. The region of the second genu is quite delicate, since the angle of curvature is not always the same (sometimes it is less than 90°), while it has a constant relationship with the superolateral dome of the LSC. In decompression of the tympanic segment of the FN, a sickle knife or dental excavator can be used, breaking the bone into pieces by putting either instrument under it. Once the most poste-
41 rior part has been decompressed, it is easier to carry out the more anterior part. After isolation of the second and third segments of the FN from the bony canal, the next step is to open the mid-lateral portion of the epineurial sheath (with a sickle knife or No. 11 scalpel), like an open book, leaving the most medial portion intact. Osteo-epineurial decompression of the most anterior second segment will allow the strict relationship between two soft tissue components to be visualised: the exposed FN and the underlying tensor tympani muscle. At this point, after setting the medial adherences in the fallopian canal free with a sickle knife or Rosen needle, it will be possible to raise both the second and third segments altogether, thus mimicking anterior rerouting of the FN, which is carried out, for example, in glomus tumour surgery or cholesteatoma surgery, when removing cholesteatoma that extend medially to the fallopian canal.
42 Phase 13: Identification of the endolymphatic sac This is an exciting phase of the dissection, during which the surgeon returns to large spaces, even mimicking a surgical procedure that is still in use today for treatment of Ménière’s disease, such as endolymphatic sac decompression or shunt. The endolymphatic sac (ES) is the membranous appendage of the posterior labyrinth that is a duplicate of the dura of the posterior cranial fossa (PCF). It is thus logical that the preliminary step for its identification is the exposure of the PCF dura situated anterior to the SS, almost up to the JB. The need for such a wide exposure is justified by the extreme variability of position and course of the ES itself. In this regard, one of the suggested surgical landmarks is represented by Donaldson’s line (arrow), an imaginary line which proceeds, tangentially to the dome of the LSC, towards the SS: this line marks the upper limit of the area within which the ES can lie, and which extends inferiorly up to the JB (always remember the not infrequent possibility of a high JB!) (Fig. 41). After exposure of the entire PCF dura, it is necessary to search for a thicker or darker (due to its rich vascularisation) area, surrounded upwards and downwards by a lighter or light blue colour. Particular
Fig. 41. The endolymphatic sac (ES) is isolated as dural duplicature. The arrow indicates Donaldson’s line. LSC= Lateral semicircular canal; PSC= Posterior semicircular canal; SS= Sigmoid sinus.
43 attention must be paid to not penetrating the PSC which, in some TB, may be close to an anteriorly located SS. Once the presumed ES area has been identified, it is necessary to follow it cautiously anteriorly, using a small curette or a small diamond burr on the posteromedial aspect of the PSC. The ES will certainly have been found when – depressing the corresponding dura – the surgeon can see the anterior prolongation medially to the labyrinthine block (PSC), which is still the ES and not yet the duct (ED).
44 Phase 14: Isolation of the labyrinthine block Drilling of the pre-sinus cells, performed to expose the PCF dura above Donaldson’s line as well, enables the posterior edge of the posterior labyrinthine block to be reached; this is represented by the three semicircular canals (SCs). At this point, their spatial orientation can be estimated, taking into account the dome of the LSC, visualised with the antral opening. Isolation of the three SCs is therefore obtained by delineating their tridimensional projection. As already noted, both colour and compactness of the otic capsule bone differ from that of the surrounding cellular or acellular bone, being glossy yellow and harder (Fig. 42). It is important to remember that the three SCs are located in the three spatial planes, perpendicular to one another, and that their name refers to the orientation of their dome. Hence, they are not at the same level, but rather at a different depth: the most superficial is the LSC, while the level of the PSC lies halfway to the non-ampullary arm of the LSC. The common crus of the PSC is much deeper, while the level of the superior semicircular canal (SSC) is the deepest of the three. During drilling of the central part of the SSC, a small channel
Fig. 42. The labyrinthine block. LSC= Lateral semicircular canal; SSC= Superior semicircular canal; PSC= Posterior semicircular canal.
45 containing the subarcuate artery (SA), a branch of the anterio-inferior cerebellar artery (AICA), will be encountered, which is a useful landmark for subsequent drilling, since it is equidistant from the course of the SSC, being situated in its centre. Before isolating the SSC, it is very important to skeletonise the tegmental line thoroughly (at that level, the tegmen antri). It must be remembered that each SC is surrounded by pneumatised or sclerotic bone, which covers the bony otic capsule. Isolation of the three SCs will be improved after exenterating the perilabyrinthine cell groups.
46 Phase 15: Labyrinthectomy and identification of the intraosseous endolymphatic sac and duct Labyrinthectomy consists of the total destruction of all SCs and should be associated with the removal of saccular and utricular receptors. Already exposed, the SCs must be drilled away in the same order, which can start from either the LSC or the PSC. The PSC can also represent the starting point for a surgical approach recently popularised in those rare cases of benign paroxysmal positional vertigo (BPPV) that cannot be controlled with classical positional manoeuvres: occlusion of the PSC, which consists of drilling the dome of the PSC and progressive intraluminal blockage with a gelfoam-type material. Thus, by performing careful opening of the PSC, a disputable but codified surgical procedure is being carried out. The LSC may also be the first canal to be opened, since it is clearly evident in the antral cavity since the first steps of the dissection. In principle, the opening of the SCs must proceed by highlighting – over its entire length – the groove containing the membranous labyrinth. The strict anatomical relationship between the LSC and the FN, which always lies inferomedial to it, must be borne in mind. In order to prevent a cutting burr from damaging the FN, three main rules should be adhered to: a. in a right ear, change the rotation of the burr, so that if it should inadvertently slip, it is directed away from the nerve; b. drill on its superior side, because drilling laterally may jeopardise the FN; c. move the burr on the main axis of the canal. After having exposed the groove of the LSC and PSC, it will be noted that the non-ampullary arm of the latter (common crus with SSC) lies on a deeper plane than the ampullary one. At this point, drilling of the SSC should be continued, with attention being paid that the MCF dura, which is in close contact with its dome, does not get torn (arcuate eminence (AE) in the MCF approach) (Fig. 43). It is only after having exposed the internal part of the three SCs in this way, that the dissection should proceed by their total removal. From an anatomical point of view, as labyrinthectomy proceeds, it will be possible to see, medially to the PSC, the anterior prolongation of the ES (intra-osseous portion), as a thin whitish channel which
47
Fig. 43. The three semicircular canals have been opened. SSC= Superior semicircular canal; LSC= Lateral semicircular canal; PSC= Posterior semicircular canal; SA= Subarcuate artery.
Fig. 44. The subarcuate artery (SA) is a landmark for the dissection of the SSC.
courses anterosuperiorly, then becoming the thinner ED, which passes medially to the common crus, at which level it turns inferiorly to enter the vestibule. There are two other important points regarding drilling of the SSC: a. remember to use the channel of the subarcuate artery (SA) as landmark in order to facilitate SSC dissection (Fig. 44); b. avoid drilling on the antero-inferior portion (ampullary arm) of the SSC: the presence of an intact ampulla is, in fact, an important landmark for future IAC isolation.
48 Phase 16: Opening of the vestibule Drilling on the base of the LSC, taking particular care to thin it out close and parallel to the FN, as well as to tilt the bone-holder (or the operating bed) anteriorly, will allow the vestibule cavity to be opened and visualised (Fig. 45). This cavity has four small openings: 1. for the ampullary ends of the LSC and SSC, located anterosuperiorly; 2. for the ampullary end of the PSC; 3. for the cochlear duct; 4. for the stapes footplate (if a needle is inserted through the oval window, it is possible to see it where it enters the vestibule). and two depressions: 1. elliptical recess, accommodating part of the utricular macula, lying posterosuperiorly; 2. spherical recess, accommodating the saccular macula, lying anteroinferiorly. Between these two recesses the vestibular crest is located, which bifurcates posteriorly into two wings, delimiting the cochlear recess for the vestibular caecum of the cochlear duct.
Fig. 45. Visualisation of the vestibule (V), with the ampullary arm of the LSC (ALSC).
49 Phase 17: Identification of the labyrinthine segment of the facial nerve After the previous steps of the dissection, the FN is decompressed osteo-epineurially and is lifted from the fallopian canal, thus having only two anchoring points: • its exit at the stylomastoid foramen; • at the level of the geniculate ganglion (GG). In order to allow its complete mobilisation (re-routing), not only anteriorly, but also posteriorly, the following dissection exercises must be performed: 1. identify the GG with its anterior prolongation, the greater superficial petrosal nerve (GSPN), which has to be severed; 2. decompress the labyrinthine segment (the shortest one, 3-4 mm, but also the most delicate), up to the entrance in the IAC. The first aim is reached by decompressing the most anterior part of the tympanic segment (12-13 mm long), above the cochleariform process (CP), opening the space delimited inferolaterally by the tympanic FN, superolaterally by the MCF dura, and posteriorly by the superior prelabyrinthine cells and the SSC. Dissection of the labyrinthine FN should not be hurried, since the nerve can easily be avulsed (Fig. 46).
Fig. 46. Isolation of the labyrinthine segment of the FN (LFN). GG= Geniculate ganglion; SSC= Superior semicircular canal; CP= Cochleariform process; TFN= Tympanic segment of the facial nerve.
50 In fact, in this segment, the FN is embedded in a very compact bony block which does not facilitate a gradual isolation, as is possible in the mastoid segment (15-20 mm long), for example. Light, but continuous irrigation will enable visualisation to be improved, as long as the dissection carries on. At the end of this task, after sectioning the GSPN anteriorly to the GG with a sickle knife or small hook, it will be possible to grasp it with a Hartmann cup forceps, and pull it posteriorly, setting it free from the bony canal, and to carry out a posterior dislocation (re-routing). The dissection should then continue medially to the various segments of the FN.
51 Phase 18: Identification and opening of the internal auditory canal This is the final dissection on a TB approached from its lateral aspect. It is one of the most delicate and difficult steps, in which smaller and smaller diamond burrs have to be used on a more and more compact bone. The dissection aims at isolating the IAC for 270° or more, in its posterior, superior, and inferior aspects. While the posterior limit is delineated by the dural reflection of the PCF with the IAC dura, the two other well-codified landmarks for extension and facilitation of the dissection are: a. superiorly, the ampulla of SSC, which should not be sacrificed during labyrinthectomy because it is important for identification of the entrance of the FN in the IAC; b. inferiorly, the orifice of the cochlear aqueduct; if the dissection is brought below this point, there may be damage to the pars nervosa of the jugular foramen (IX, X and XI cranial nerves). However, the dissection must start posteriorly, in the area corresponding to the posterior labyrinth (SCs), remembering that the position of the IAC is always more anterior than may be realised. To make it easier to visualise, remember the definition in Gray’s* English-language anatomical textbook, which states: “If you put a pencil in the EAC, and push it medially, you will find it in the IAC.” Basically, the roof of the IAC is represented by the medial wall of the vestibule, where the posterior edge will delimit the posterosuperior border of the IAC superficially (laterally). A diamond, mid-calibre (8-10 mm) burr may be used, as well as analogous cutting ones. At this point, the bone is very thick and compact, and gentle pressure should also be exerted during drilling: a diamond burr will avoid tearing the underlying dura, which has to be completely uncovered. A cutting burr cannot avoid this. The following consideration should be borne in mind during all phases of the dissection: to hurry a dissection, especially in the case of an inexperienced surgeon, is never without danger.
* Anatomist at St George’s Hospital Medical School, London (1821-1865).
52
Fig. 47. Bill’s bar (BB) divides the facial nerve (FN) from the superior vestibular (SV) nerve.
Fig. 48. Removal of the two vestibular nerves allows visualisation of the anterior IAC compartment which includes the cochlear (CN) and the facial (FN) nerves.
Superior and inferior dissections of the IAC are the most difficult stages in a TB dissection due to: • working with a small-sized diamond burr; • increasing postero-anterior thickness; • the closeness of the soft tissues with possible minor (tearing of PCF or MCF dura) or major (IAC penetration, with neural or vessel involvement) damage. During this step, the suction-irrigation tip can also be used as an instrument since it helps to move the acoustic-facial package away from the drilling zone. As has been pointed out above, when drilling on the IAC, the burr does not work in the usual (uniform and continuous strokes) way, but rather by means of a contact-and-pressure action, and sometimes with the tip as well. When the bone has been thinned out, a ‘blue-line’ may also have been produced, this colour being due to the underlying fluid-immersed tissue. Once isolation of the IAC dural surface is complete, the entrance of the labyrinthine FN into the IAC – in its superolateral part – can be identified. The dural layer of the IAC is then opened with a small hook, and the following four neural elements can be seen (Fig. 4748): • facial nerve (FN), antero-superiorly; • cochlear nerve (CN), antero-inferiorly; • superior vestibular nerve (SVN), postero-superiorly; and • inferior vestibular nerve (IVN) postero-inferiorly.
53 It is also possible to visualise the vertical crest – also known as Bill’s bar (B) after William House – which separates the FN from the SVN, as well as the transverse crest (TC), which separates the SVN from the IVN. When this final part of the dissection has been achieved, the lateral approach to the TB is completed. The various steps of the dissection have been interspersed with true surgical approaches in order to render the dissection more stimulating and interesting, in the view of the author.
54
SUPRATEMPORAL OR MIDDLE FOSSA APPROACH
For this approach, correct placement of the TB in the bone-holder may present some initial problems. In order to make it easier, it is a good idea to rotate the TB in the hands, bearing in mind that the surgical position of the otologist is that of looking down from above. For example, in a right ear, the mastoid tip should point inferiorly; for a right ear it must then be rotated to the left, and then upwards, so that it will be possible to have direct visualisation of the floor of the MCF itself (roof of the TB) (Fig. 49). Once fixed in this position, the dural lining should be removed by lifting it up to the passage from the MCF to the PCF, where the superior petrosal sinus (SPS) runs. This will be more or less hard, depending on the quality of bone preservation. The surface anatomy of the MCF is quite difficult, especially when landmarks are not clearly evident. These landmarks are identifiable as: a. arcuate eminence (AE), located posteromedially, corresponding to the dome of the SSC; b. the GSPN, a branch of the FN, which leaves anteriorly from the GG;
Fig. 49. The floor of the middle cranial fossa. AE: Arcuate eminence; SPS= Superior petrosal sinus.
55 c. the GG, sometimes devoid of bone covering, which occupies a central position on the floor of the MCF; d. the middle meningeal artery (MMA), a branch of the external carotid artery, which exits from the foramen spinosum positioned in the most anterior part of the surgical field. In cases of difficult orientation, it may be necessary to find the way by drilling regions not directly correlated with the surgical objective. The most inferior part, covered by more or less compact bone, is occupied by the tegmen, which lines the superior epitympanic wall (and posteriorly the mastoid part). Anteriorly, in a medial projection, the eustachian tube can be found. The following phases will be presented: • opening of the epitympanic cavity and of the petrous apex cells; • identification of the FN and GG; • exposure of the IAC; • isolation of the cochlea.
56 Phase 19: Opening of the epitympanic cavity and of the petrous apex cells This step can be used for the extirpation of local pathological processes, which cannot be removed by a transmastoid approach without violating the labyrinth, or it may represent a preliminary step in the identification of MCF landmarks. Due to the complex surface and deep
Fig. 50. The roof of the epitympanum has been removed and some middle ear structures appear. HM= Head of the malleus; LSC= Lateral semicircular canal; MAS= Mastoid cavity; GG= Geniculate ganglion; GSPN= Greater superficial petrosal nerve; AE= Arcuate eminence, corresponding to the SSC (Superior semicircular canal).
Fig. 51. Opening of the epitympanum from above allows visualisation of the incudomalleolar joint (IMJ), cochleariform process (CP), stapes (S), and tympanic segment of the facial nerve (TFN).
57 anatomy of the MCF, it is always preferable to use diamond, midcalibre (5-mm) burrs, with continuous irrigation. The aperture of the epitympanum enables the head of the malleus (HM) with the body of the incus and the malleo-incudal joint to be seen (Fig. 50-51). By widening the opening with smaller (2-3 mm) diamond burrs, it is then possible to visualise the stapes and CP. This also enables the prelabyrinthine, apical cells, to be entered, with care being taken not to penetrate the SSC.
58 Phase 20: Identification of the facial nerve and geniculate ganglion The previous step is of great value, since opening the epitympanum makes the following possible: • to use the tympanic FN as a landmark; • to follow the FN superiorly up to the GG. At the level of the GG, the FN, either covered by a thin layer of bone or exposed, bends medially towards the tympanic segment, superiorly towards the labyrinthine segment, and anteriorly gives rise to the GSPN. Isolation of the FN labyrinthine segment (LFN) must be carried out cautiously, gradually thinning out the very compact bone, under continuous irrigation. As well as any possible damage to the FN, care should be taken not to fenestrate the SSC. Identification of the GSPN, at times discovered after the dura has been lifted, represents the key to the following MCF step (Fig. 52).
Fig. 52. Isolation of the labyrinthine segment of the facial nerve (LFN). GG= Geniculate ganglion; GSPN= Greater superficial petrosal nerve; AE= Arcuate eminence.
59 Phase 21: Exposure of the internal auditory canal This is the most important part of this approach due to its surgical implications (vestibular neurectomy, acoustic tumour removal with hearing preservation). The methods of approach depend on the anatomical landmarks used, i.e.: • arcuate eminence (dome of the SSC), posteriorly; • GG, inferiorly; • GSPN, anterior to the GG. The projection of the IAC in the MCF is in a broadly triangular area with its base on the course of the superior petrosal sinus (SPS), and with its posterior side on the dome of the SSC. Conversely, the anterior side is not well defined, but coincides with a large, ‘mute’ area that extends anteriorly up to the exit of the MMA. Approach 1 Drilling starts directly at the presumed IAC level, using as a landmark the bisectrix passing through the obtuse angle formed between the course of the GSPN and the line of the arcuate eminence. Considering the major anatomical complexity of the inferolateral part in relation to the superomedial, the latter will first be drilled close to the reflection zone between the MCF and the PCF, and hence to the SPS.
Fig. 53. The roof and superior wall of the internal auditory canal have been opened, exposing the neural content: cochlear nerve (CN), facial nerve (FN) and vestibular nerves (VN).
60 Approach 2 In this approach, the initial landmark is represented by the arcuate eminence, the dome of the SSC, which must be carefully drilled in order to expose the ‘blue-line’ and then to proceed postero-anteriorly to delimit the anterior IAC border. Approach 3 This final approach, particularly recommended in an enlarged MCF approach, takes into account the ‘mute’, anteromedial area, the posterior edge of which will coincide with the anterior IAC wall. Whatever the approach, when proceeding with drilling, the surgeon must be aware that, at the level of the antero-inferior IAC wall, he/she will find the cochlear projection which, similarly to the SSC, must not be fenestrated, in order to avoid a functional impairment that should be avoided when choosing a MCF approach. Drilling has to go deeper superomedially until precise identification of the IAC can be made. Thereafter, drilling can continue towards the fundus of the IAC. Once the IAC dura has been exposed along its entire course, it will be opened by means of a small hook in order to identify its internal content with (Fig. 53): • the FN, anterolaterally; • the superior vestibular nerve, posterolaterally; • the cochlear nerve (CN), anteromedially; and • the inferior vestibular nerve, posteromedially. At the level of the fundus of the IAC, drilling will allow the vertical crest or Bill’s bar, which separates the FN from the SVN, to be exposed.
61 Phase 22: Isolation of the cochlea For complete knowledge of the supratemporal bone anatomy, the dissection can continue by isolating and exposing the cochlea. This is accomplished by progressive drilling of the postero-superior part of the IAC, until the contiguity of the cochlear basal wall and CN are evident (Fig. 54). It should also be remembered that an MCF approach to the cochlea has also been proposed for cochlear implant surgery.
Fig. 54. Drilling anterior to the internal auditory canal, the cochlea is exposed. CN= Cochlear nerve; FN= facial nerve.
62
POSTERIOR CRANIAL FOSSA APPROACH
The anatomy of the posterior aspect of the TB, although not complex, presents difficulties because it uses a route which is unfamiliar to most otosurgeons. Bearing in mind the advances in modern neurootosurgery and the frequent contact with neurosurgeons, it is obvious that good experience is also necessary with this type of dissection. The major indication is for the IAC approach, which usually follows cerebellar retraction, a step that cannot be reproduced unless the entire head is available. Before treating IAC landmarks, it is advisable to reflect on some aspects of the topographic anatomy of the posterior aspect of the TB, a combination of grooves, prominences, and foramina (Fig. 55). The posterior aspect of the TB forms a vertical wall, higher laterally than medially. The IAC orifice is located between the medial and the central third of the posterior aspect of the TB. Five or 6 mm, laterally, an irregular depression, the subarcuate fossa (SF), can be seen, which accommodates the cerebellar flocculum. More laterally, 10 mm from the IAC orifice, a fissure is located, the operculum (Op), at the exit of
Fig. 55. Posterior aspect of the temporal bone. SS= Sigmoid sinus groove; SF= Subarcuate fossa; IAC= Internal auditory canal; JF= Jugular fossa.
63
Fig. 56. The internal auditory canal (IAC) has been opened, exposing its neural content. PSC= Posterior semicircular canal; ES= Endolymphatic sac region; Op= Operculum; JF= Jugular foramen.
the vestibular aqueduct, which contains the ED and the intraosseus ES, and from which the extraosseus ES emerges. Posterolaterally to this, the groove of the SS is visible, 1 cm wide, with the mastoid region anteriorly. More medially, close to the jugular foramen (JF), the cochlear aqueduct orifice is located (Fig. 56).
64 Phase 23: Identification of the internal auditory canal Drilling is usually carried out with the acoustic-facial package (vestibular neurectomy) or tumour (acoustic neuroma, meningioma) arising from the vestibular nerve as the posteromedial landmark. Before starting drilling, the overlying dura has to be cut with a sickle knife and then lifted anteriorly and posteriorly. With small diamond burrs and under continuous irrigation, the dissection is started in a lateroanterior direction. It is extremely important to be cautious in posterior dissections, since it is possible to injure the ES or ED, or even worse functionally, to fenestrate the PSC. However, since this type of approach is generally selected as a last resort, this aim would not be relevant in such a case. At this same level, care must be taken regarding a possible high JB. Once the posterior wall of the IAC has been identified, drilling should go deeper both superiorly and inferiorly, in order to expose about two-thirds of its circumference (Fig. 57). Once this step has been completed, a longitudinal cut will be carried out with a No. 11 scalpel or Bellucci’s scissors, in order to open it and visualise its content. It is generally possible only to expose the medial two-thirds of the IAC, without running the risk of violating the vestibule or the PSC.
Fig. 57. The opened IAC. FN= Facial nerve; CN= Cochlear nerve; VNs= Vestibular nerves; VC= Vertical crest.
65
ABBREVIATIONS
A AE ALSC AICA ACT AW BB BCT CN CP CT DM EAC ED ES EV FN GSPN HM IAC ICA IMJ IVN JB LFN LSC MA MAS MCF Op OW PA PCF PSC
antrum arcuate eminence ampulla of the lateral semicircular canal antero-inferior cerebellar artery apical turn of the cochlea anterior wall of the EAC Bill’s bar basal turn of the cochlea cochlear nerve cochleariform process chorda tympani digastric muscle external auditory canal endolymphatic duct endolymphatic sac emissary vein facial nerve greater superficial petrosal nerve head of the malleus internal auditory canal internal carotid artery incudomalleolar joint inferior vestibular nerve jugular bulb labyrinthine segment of the FN lateral semicircular canal modiolar axis mastoid cavity middle cranial fossa operculum oval window petrous apex posterior cranial fossa posterior semicircular canal
66 PW RFC RW S SA SC SDA SM SPS SS SSC STTM SVN T TB TFN TO TL TM TMJ TT TTM V ZP
posterior wall of the EAC retrofacial cells round window stapes subarcuate artery semicircular canals sinodural angle stapedius muscle superior petrosal sinus sigmoid sinus superior semicircular canal semicanal of the tensor tympani muscle superior vestibular nerve tip of the mastoid temporal bone tympanic segment of the FN tubal orifice temporal line tympanic membrane temporomandibular joint tensor tympani tendon tensor tympani muscle vestibule zygomatic process
67
GLOSSARY
Arcuate eminence: bony overhang of the middle cranial fossa that corresponds to the dome of the SSC, anatomical landmark for the identification of the IAC. Bill’s bar: crest of the IAC that separates the FN from the SV nerve. Blue line: optical effect obtained when bony walls contain, or are close to, liquid (or when they are already thin anatomically, such as normal stapes footplate) as a result of light resorption, not reflection. Buttress: thin bony wall inferior to the fossa incudis, representing the base of the triangular zone of attack in posterior tympanotomy (facial recess). Chipault’s cribriform area: a multiply-holed area situated posterior to Henle’s spine for the passage of small vessels, which explains the exteriorisation of antral infection to the overlying subcutaneous tissue in early childhood. COG: a half-moon shaped bony septum located just anteriorly to the head of the malleus,which proceeds vertically from the tegmen to the direction of the CP, without reaching it. Some authors believe that it is the outmastoid part of Koerner’s septum. Donaldson’s line: the posterior prolongation of a line passing over the dome of the LSC, marking the upper dural limit where the ES can be localised. Facial recess: the space, delimited by the CT, FN, and fossa incudis, which has to be opened in order to gain access to the middle ear through the mastoid cavity (posterior tympanotomy). Koerner’s septum: or petrous-squamosal suture, a bony septum that, during mastoid development, divides the petrous (medial) from the squamous (lateral) cells. In general, when development is complete, this septum is reabsorbed more or less completely but, in a conspicuous number of TBs, it may persist as a bony lamina parallel to the lateral aspect of the mastoid process. Novices may be misled and confuse its smooth and compact aspect with the LSC. Light refraction of the short process of the incus: an optic phenomenon due to irrigation fluid that makes this structure visible before it actually appears in the surgical field.
68 Linea temporalis: an imaginary line that corresponds with the subtle ridge of the inferior edge of the temporal muscle. MacEwen’s triangle: a triangular area on the lateral aspect of the TB which corresponds medially to the antral region. Metallic sound of the burr: a sound variation when a burr – especially a cutting burr – works in close proximity to soft tissue, such as dura. Mickey Mouse technique: a dissection technique of the anterior wall of the EAC (in radical mastoidectomy) which implies first drilling the upper and lower parts of the wall, in order initially to avoid the central part of it – the closest to glenoid fossa, hence ATM – which is drilled afterwards, causing the anterior wall to be flat and uniform. Posterior tympanotomy: see Facial recess. Sinodural angle-Citelli’s: a mastoid space occupied by cells (lateral and medial) which is found between the mastoid tegmen and the SS. Sinus tympani: a depression of the posterior mesotympanum, often identified by its name, delimited between the ponticulus and subiculum. Snake’s eye: the way – as similitude – appears a flat opened dome of the LSC. Subarcuate fossa: a depression of the posterior aspect of the TB, accommodating the cerebellar flocculum. Tegmen: the bony plate that separates the mastoid and middle ear cavity from the middle cranial fossa dura. Transverse crest: in the IAC, this separates the superior (FN and SVN) from the inferior (CN and IVN) compartment. Vertical crest: see Bill’s bar.
69
SURGICAL APPLICATIONS
1 2 3 4 5. 6 7 8 9 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23.
Antrotomy Enlarged mastoidectomy Simple mastoidectomy Isolation of the sigmoid sinus Closed tympanoplasty Closed tympanoplasty with mastoidectomy and posterior tympanotomy Open tympanoplasty (modified radical mastoidectomy) Open tympanoplasty (classic radical mastoidectomy) Petrous apicotomy Cochlear implant Tubal surgery Facial nerve decompression (second and third segments) Facial nerve re-routing Subfacial approach Endolymphatic sac surgery Occlusion of the posterior semicircular canal Labyrinthectomy Transmastoid decompression of the labyrinthine segment of the facial nerve TLB internal auditory canal isolation and exposure Middle cranial fossa epitympanectomy and mastoidectomy Middle cranial fossa decompression of the labyrinthine segment of the facial nerve Middle cranial fossa neurectomy Posterior cranial fossa internal auditory canal exposure
70
INSTRUMENTATION
knife periosteal elevator burrs (diamond, cutting; from 0.8-0.2 mm) suction tip (0.2, 0.4, 0.6, 0.8, 1 cm) malleus nipper Bellucci’s scissors circular saw sickle knife dental excavator No. 11 scalpel Rosen needle curette hooks Hartmann cup forceps
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. This Manual of Temporal Bone Dissection is highly useful 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, informative didactic sessions, and anatomical dissection proctored by expert microsurgeons.
Kugler Publications/ The Hague/The Netherlands
