Manual of Temporal Bone Exercises

Manual of Temporal Bone Exercises

 

Henning Hildmann • Holger Sudhoff Stefan Dazert • Rudolf Hagen

Manual of Temporal Bone Exercises

Prof. Dr. med. Henning Hildmann† Klinik für Hals-, Nasen- und Ohrenheilkunde, Kopf- und Halschirurgie der Ruhr-Universität Bochum St. Elisabeth-Hospital GmbH Bleichstr. 15 44787 Bochum Germany Prof. Dr. Holger Sudhoff Klinikum Bielefeld Klinik für HNO-Heilkunde Kopf- und Halschirurgie Plastische Operationen Teutoburger Str. 50 33604 Bielefeld Germany [email protected]

Prof. Dr. med. Stefan Dazert Klinik für Hals-, Nasen- und Ohrenheilkunde, Kopf- und Halschirurgie der Ruhr-Universität Bochum St. Elisabeth-Hospital GmbH Bleichstr. 15 44787 Bochum Germany [email protected] Prof. Dr. med. Rudolf Hagen Klinik und Poliklinik für HNO-Heilkunde Universitätsklinikum Würzburg Josef-Schneider-Str. 11 97080 Würzburg [email protected]

ISBN  978-3-642-19497-9     e-ISBN  978-3-642-19498-6 DOI 10.1007/978-3-642-19498-6 Springer Heidelberg Dordrecht London New York Library of Congress Control Number: 2011925946 © Springer-Verlag Berlin Heidelberg 2011 This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilm or in any other way, and storage in data banks. Duplication of this publication or parts thereof is permitted only under the provisions of the German Copyright Law of September 9, 1965, in its current version, and permission for use must always be obtained from Springer. Violations are liable to prosecution under the German Copyright Law. The use of general descriptive names, registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. Product liability: The publishers cannot guarantee the accuracy of any information about dosage and application contained in this book. In every individual case the user must check such information by consulting the relevant literature. Cover design: eStudioCalamar, Figures/Berlin Printed on acid-free paper Springer is part of Springer Science+Business Media (www.springer.com)

This book is dedicated to those who gave their temporal bones to the purpose of teaching and science in medicine. We are deeply indebted to Dr. Agnes Hildmann. She showed virtually endless patience and understanding for Henning’s work. The royalties of this book will be completely donated to Henning Hildmann’s project in Rwanda. It will support the training of young ear, nose and throat doctors.

 

Foreword

Attendees of a course on microsurgery of the ear are confronted with an unexpected large volume of information from the first minute on when watching live surgery. The special anatomy, biology of diseases, concepts of procedures and many of their technical details, preconditions, and consequences are discussed and transferred into surgical practice. The hands-on temporal bone exercises, however, introduce the beginner systematically into surgery of the ear. The benefit of such dissection activity depends on the knowledge of standard anatomy and the ability to adapt this background into the situation of the single temporal bone under preparation. This will remain an important concept in later-life surgery. The first aim is to remove bone of different hardness and to preserve safely all relevant structures. This needs adequate understanding of drilling and suction procedures and a sincere training. This manual, on the basis of Plester’s school of ear surgery, offers a comprehensive, systematic, and didactically frequently and successfully practiced system of guidelines. Developing ear surgeons should follow this advice as close as possible. They would in this way ensure a maximum of safety when later performing ear surgery on their patients. The experience of Henning Hildmann with innumerable national and international surgical courses on microsurgery of the ear since 1969 and the sincere cooperation over years of his younger partners finally led to the development of this remarkable and sincerely recommended manual. Tübingen, Germany

Jan Helms

vii

 

Contents

1

Introduction................................................................................................ 1.1  Drills................................................................................................... 1.2  Microscope......................................................................................... 1.3  Preparation and Planning.................................................................... 1.4  Identify the Following Structures Prior to the Surgical Exercises......

1 1 2 2 4



Basic Surgery of the Temporal Bone........................................................ 2.1 Mastoid............................................................................................... 2.2 Antrostomy......................................................................................... 2.3  Mastoidectomy................................................................................... 2.4 Identification of the Semicircular Canals........................................... 2.5  Posterior Tympanotomy...................................................................... 2.6  Identification of the Facial Nerve in Its Mastoidal Portion................ 2.7  Cochleostomy..................................................................................... 2.8  Endolymphatic Sac Surgery............................................................... 2.9  Epitympanotomy................................................................................. 2.10  Open Mastoid Cavity.......................................................................... 2.11 Facial Nerve Decompression.............................................................. 2.12 Labyrinthectomy................................................................................. 2.13  The Translabyrinthine Approach to the Internal Auditory Canal........... 2.14 Transtemporal Approach to the Internal Auditory Canal (IAC).............

5 5 5 9 11 12 15 15 17 19 20 21 23 25 27



Surgical Exercises in the Middle Ear....................................................... 3.1  Perforation of the Tympanic Membrane............................................. 3.2  Ossicular Chain Reconstruction......................................................... 3.3  Stapes Surgery.................................................................................... 3.4  Malleovestibulopexy...........................................................................

31 32 33 35 36

2

3

Recommended Reading.................................................................................... 37 Index................................................................................................................... 39

ix

1

Introduction

The same instruments used for middle ear surgery should be available for temporal bone preparation. A small set of instruments is advisable. This should contain different forceps, a sickle knife, straight and angled round elevator, needle, micro perforator, 0.6-mm angled-hook, curette, and different sizes of diamond and cutting burrs. More delicate instruments for special procedures should be provided on demand by the instructor. Suction and irrigation are mandatory.

1.1 Drills Prior to actual bone work, testing of the drill is required. The drill has to be securely fixed to the hand piece. It is important to select the burr according to anatomy, starting with a large-sized burr. Rotation should be directed to the cutting side of the burr. Approach the bone surface with a rotating burr. Sculpture the bone with decent pressure and 20,000–40,000 rpms. Touch the bone with a rotating burr and irrigate sufficiently, to avoid thermal damage. Sharp burrs are necessary in order to work precisely and to save time. Blunt burrs waste time and may jump and cause trauma to vulnerable structures. The use of a large burr is recommended at the beginning of the preparation for faster bone removal and to reduce the danger of perforating, the dura or damaging the facial nerve or the labyrinth. Continuous irrigation during drilling removes bone dust and connective ­tissues from the drill. Get a feeling for the differing resistance of the bone. During the drilling procedure, it is important to get accustomed to the changing density of the bone as well as the concomitant sound. Adjacent to vulnerable structures such as the labyrinth and the facial nerve, the use of diamond burrs is preferable. The direction of drilling should be parallel to important structures and not perpendicular. The hand holding the drill should rest on the specimen or the bowl holding it. Note that both sides of the drill can cause damage.

H. Hildmann et al., Manual of Temporal Bone Exercises, DOI:10.1007/978-3-642-19498-6_1, © Springer-Verlag Berlin Heidelberg 2011

1

2

1  Introduction

1.2 Microscope Make yourself comfortable with the microscope, check its mobility. It must be balanced and easily movable. Start with a lower magnification providing a better overview. Check for binocular stereoscopic vision and correct the position of the eyepieces.

1.3

Preparation and Planning

Make sure that you are sitting comfortably. Uncomfortable sitting positions result in unnecessary discomfort. Let your hands rest on the table or on the bowl holding the specimen. Your hands are more stable and delicate manipulations are easier. It is preferable to work with fresh or fresh-frozen, rather than air-dried or formalin-fixed specimens. Safety procedures, e.g., gloves, gowns, and eye protection are strongly recommended. Remove connective tissue from the temporal bone and fix the cleaned bone in the temporal bone holder. Position it similar to normal surgical orientation. Inspect the specimen and identify the anatomical structures and landmarks (Fig. 1.1).

Fig. 1.1 

1.3  Preparation and Planning

3

Mastoid preparation includes several steps, beginning with antrostomy, extending to a mastoidectomy. Subsequently the semicircular canals and the facial nerve in its descending portion can be identified. Facial nerve decompression and posterior tympanotomy with cochleostomy are usually the next steps, followed by a saccotomy, labyrinthectomy, and the approach to the internal auditory canal (IAC). If ossicular chain reconstruction is planned, the exercises should be performed prior to removal of the posterior meatal wall to create a mastoid cavity. The soft tissue of the ear canal is more rigid compared to in vivo. Therefore a large portion of the outer meatal skin should be taken out. Removed ossicles should be spared for later reconstruction exercises. The positions of the lateral sinus and the jugular bulb, and the extent of pneumatization are extremely variable (Fig. 1.2a, b). For the beginner, it is very ­difficult to a

b

Fig. 1.2 

4

1  Introduction

start with a sclerotic specimen. The landmarks may be not as obvious. If possible, try to obtain a different temporal bone.

1.4 Identify the Following Structures Prior to the Surgical Exercises Lateral surface (Fig.  1.3): Zygomatic process, mandibular fossa, temporal line, external auditory canal, tympanomastoid fissure, tympanosquamous fissure, Henle’s spine, mastoid tip Medial surface: Sigmoid sulcus, subarcuate fossa, external aperture of the vestibular aqueduct, internal auditory canal, superior petrosal sulcus, inferior petrosal sulcus, canaliculus cochlearis Superior surface: Arcuate eminence, sulcus of the greater petrosal nerve, sulcus of the middle meningeal artery, superior petrosal sinus Inferior surface: Mandibular fossa, zygomatic process, petrotympanic fissure, internal carotid artery, jugular fossa, styloid process, stylomastoid foramen

Temporal line landmark 2

* ** Petrotympanic fissure Zygomatic process * Henle‘s spine landmark 1

Mastoid tip Tympanomastoid fissure * * posterior wall of the external ear canal landmark 3

Fig. 1.3 

2

Basic Surgery of the Temporal Bone

2.1 Mastoid

2.2 Antrostomy 2.2.1 Partial Opening of the Mastoid and Antrum A wide access to the mastoid provides a good overview and reduces the danger of damaging important structures. Select the size of the burr according to actual anatomy. At the beginning of the procedure a large-sized burr is preferable. Irrigation is necessary to remove bone dust and soft tissue from the burr to keep it sharp. Test the drill for fixation, rotation and spinning prior to actual bone work. The bone should be securely fixed in a temporal bone holder and should not move when touched with a rotating burr, to avoid damage to important structures (Fig. 1.1). We recommend outlining a wide approach posterior to Henle’s spine (landmark 1), parallel to the temporal line (landmark 2), and posterior to the meatal wall ­(landmark 3). Start outlining the opening with a large cutting burr. Work parallel but inferior to the temporal line, along the supposed position of the lateral sinus and behind the posterior meatal wall (Fig. 2.1). Follow the mastoid air cells from lateral to medial, keeping the mastoid opening as wide as possible (Figs. 2.2 and 2.3), i.e., “saucerization.” The degree of pneumatization is very variable. Remember that the posterior meatal wall bends slightly forward medially. The sinus is more superficial in its upper portion and curves medially forming the jugular bulb (Fig.  2.4). The depth of the dissection can be controlled by inspecting the external ear canal. When approaching the antrum, a bony plate lateral to the antrum (Körner’s ­septum) may lead to confusion but may also facilitate anatomical orientation.

H. Hildmann et al., Manual of Temporal Bone Exercises, DOI:10.1007/978-3-642-19498-6_2, © Springer-Verlag Berlin Heidelberg 2011

5

6 Fig. 2.1 

Fig. 2.2 

Fig. 2.3 

2  Basic Surgery of the Temporal Bone

2.2  Antrostomy

7

Fig. 2.4 

Medially, the mastoid air cells are generally larger. Expose the lateral portion of the lateral semicircular canal (Fig. 2.4). The colour of the labyrinthine bone appears more yellow. Remember that the posterior meatal wall bends slightly forward. Keep the posterior wall evenly thin (Fig. 2.4). The beginner tends to drill in the wrong direction and his drill hole tends to become narrower the closer he approaches the antrum. This is dangerous because in a hole not much wider than the burr, the underlying structures, lateral canal or facial nerve, are harder to identify. The dura of the middle cranial fossa is a reliable landmark in a poorly pneumatized temporal bone. Some air cells may be safely opened with a House curette. The next landmark is the short process of the incus. It is exposed when the posterior wall is thinned out superiorly. The cranial extension of mastoid ­pneumatization toward the middle fossa varies. In a well-pneumatized mastoid, the head of the malleus and the epitympanum can be identified. If the bony plate of the middle fossa is low, access to the antrum is limited and the head of the malleus may not be visualized (Fig. 2.5). The approach to the antrum is more difficult in the case of a protruding sigmoid sinus, especially in a temporal bone with little pneumatization. Extensive removal of bone lateral to the sinus must be undertaken to obtain a better view. In cases of extreme protrusion, the bony coverage of the sinus should be removed and the sinus compressed. A wide opening of the antrum is recommended not only in temporal bone preparation but also in surgery. It provides a sufficient overview of the relevant landmarks and does not compromise the patient or further surgery. Lateral to the horizontal semicircular canal, the incus and the facial nerve are usually not in danger except in extremely rare abnormalities. Be careful not to touch the incus or the malleus with the rotating burr. This would cause noise-induced trauma in real surgery.

8

2  Basic Surgery of the Temporal Bone

Fig. 2.5 

2.2.2 Clinical Application This procedure is indicated in a coalescent mastoiditis. Depending upon the extension of the disease, the antrostomy may be extended into a mastoidectomy. In these cases, we follow the disease. This surgical approach may be also used to access the tympanic cavity via a posterior tympanotomy to position implantable hearing devices (e.g., cochlear implant, implantable hearing aids).

Landmarks

Middle fossa Lateral or sigmoid sinus Lateral semicircular canal Short process of the incus

2.3  Mastoidectomy

9

2.3 Mastoidectomy Follow the same steps described above for the antrostomy procedure starting from a saucer-shaped wide triangular opening, limited by the bony cover of the medial fossa, the sigmoid sinus, and the posterior meatal wall. Extend the cavity by removing all air cells toward the sino-dural angle, the dura of posterior cranial fossa and the tip of the mastoid. Here, identify the digastric ridge after removing the air cells medially and laterally. The bony covering of the sigmoid sinus and the dura to the middle and posterior fossa remains as a compact bone layer after completely removing the mastoid cells. Identify and delineate the sino-dural angle. Follow the sigmoid sinus downward as far as possible to identify the jugular bulb. If you are not sure if you have exposed the facial nerve or a mastoid cell, drill around the structure. If the exposed tissue is limited to a cavity, it is a cell. If the exposed tissue extends into a longitudinal structure, the facial nerve must be anticipated. Rarely the facial nerve may lay dehiscent in a cell. Abnormal courses of the facial nerve are exceptional but possible, especially with craniofacial malformation. The facial nerve is found more laterally in its mastoid than in its tympanic portion. As in surgery for extensive cholesteatoma, identify the nerve under its bony cover by drilling parallel to the its course using a large diamond burr. Slowly remove the surrounding cells under continuous irrigation. A thin layer of bone should remain on the nerve before decompressing it later. The chorda tympani branching off the facial nerve must be identified and preserved (Fig. 2.6). Even in young children, the inner ear structures and the ossicles are more or less completely developed at the time of birth. The tympanic bone is still a ring and the mastoid cavity and the mastoid tip are small. Therefore, the facial nerve is positioned more laterally and will be met earlier compared to the adult temporal bone. Care must be taken even when making the skin incision because the facial nerve is not yet protected by the developing mastoid process in a child.

Fig. 2.6 

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2  Basic Surgery of the Temporal Bone

Fig. 2.7 

At the end of the procedure, you should have outlined the sigmoid sinus, the sino-dural angle, and the thin bone covering the middle and posterior fossa. The yellow shining bone of the lateral and posterior canals should be visible. The facial nerve should be covered by a thin layer of bone and appear white in the temporal bone specimen. The chorda tympani is branching off the facial nerve. The body of the incus should be partially visible. In a well-pneumatized mastoid, the head of the malleus may also be exposed (Fig. 2.7). The air cells might extend beyond the sigmoid sinus. Posteriorly and anteriorly, they may continue into the zygomatic process and around the labyrinth and the cochlea.

2.3.1 Clinical Application In coalescent mastoiditis the affected bone is often softened due to inflammation. If involvement of the dura or the sinus is suspected, these structures should be exposed and assessed for pathologic alterations (e.g., granulation tissue, pus, thrombosis). The mastoidectomy is the fundamental approach to several procedures described below.

Landmarks

Outline your field of surgery: Temporal line, Henle’s spine, posterior meatal wall Tegmen of the middle fossa Sigmoid sinus Lateral semicircular canal Body of incus Facial nerve Digastric ridge

2.4  Identification of the Semicircular Canals

11

2.4 Identification of the Semicircular Canals Remove the cells behind and around the lateral semicircular canal (Fig. 2.8). The bone of the canals is always solid and yellow. The subarcuate fossa is located behind the lateral canal and under the superior canal. In ita centre, the subarcuate artery may be seen (Fig. 2.9, arrow). Progress with your bone work until the posterior canal is identified. It is more medial than the lateral canal and is often separated from the posterior fossa bone by a narrow tract of air cells. The inferior end may be close to the facial nerve. To clearly identify the semicircular canals, the blue lines should be exposed without opening the perilymphatic space. Identify the superior semicircular canal. The ampullae of the lateral and superior canal are situated close to each other, below the body of the incus. They should be left intact. The superior semicircular canal arches deep medially toward the ­posterior

Fig. 2.8 

Fig. 2.9 

(

A. subarcuata)

12

2  Basic Surgery of the Temporal Bone

Fig. 2.10 

(

A. subarcuata)

fossa where it meets the posterior canal to form a common crus (Fig. 2.10). The beginner often has difficulties following the superior semicircular canal backward because a large amount of cellular bone has to be removed lateral to the posterior and inferior part. At the end of this step, the canals should be sculptured clearly and the subarcuate fossa be partly excavated. Identify the sino-dural angle and Trautmann’s triangle. This is a triangular area of the bony plate covering the posterior fossa between the sigmoid sinus, the superior petrosal sinus and the bony labyrinth.

2.4.1 Clinical Application In the clinical context, this step may be necessary in a more extensive mastoiditis, in extensive cholesteatoma, and as a first step to labyrinthectomy, or on the way to the internal auditory canal for translabyrinthine vestibular nerve section or acoustic neuroma surgery.

Landmarks

Facial nerve Lateral semicircular canal Subarcuate fossa Posterior semicircular canal Superior semicircular canal

2.5 Posterior Tympanotomy The intent in this approach is to expose the posterior portion of the middle ear cavity.

2.5  Posterior Tympanotomy

13

Fig. 2.11 

Thin out the posterior meatal wall and identify the posterior incudal ligament. The chorda tympani can be seen and preserved in the majority of cases. The space between the facial nerve, chorda tympani, and the short process of the incus should be opened until there is sufficient room to identify the long process of the incus, the pyramidal eminence, the posterior part of the stapes with its tendon, and the posterior part of the promontory. The niche of the round window can be visualized but cannot necessarily be exposed completely due to the position of the facial nerve (Fig. 2.11). The facial nerve is generally positioned further medially than the lateral semicircular canal. According to Anson and Donaldson, the median distance between the lateral semicircular canal and the facial nerve is 1.77 mm (range 0.98–2.29 mm) and the median distance between the lateral semicircular canal and the short process of the incus is 1.25 mm (range 0.92–1.70 mm) (Fig. 2.12).

2.5.1 Clinical Application This procedure is used for excision of small cholesteatomas (combined approach technique according to Jansen) and is the most common approach to insert a cochlear implant electrode into the cochlea or to couple an implantable hearing aid to the ossicular chain.

Landmarks

Facial nerve Short process of the incus Chorda tympani

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2  Basic Surgery of the Temporal Bone

Median, 1.77 mm Range, 2.29−0.98 mm

Median, 1.25 mm Range, 1.70−0.92 mm

Median, 2.36 mm Range, 3.02−.1.38 mm

Fig. 2.12 

2.7  Cochleostomy

15

2.6 Identification of the Facial Nerve in Its Mastoid Portion This exercise is practically part of the previous exercise. The mastoidectomy has been completed. Find the facial nerve in front of the lateral semicircular canal, slightly medial (median 1.77 mm, Donaldson), and arching down toward the stylomastoid foramen. It is slightly more lateral in its inferior course. Use a large diamond burr to remove bone until the nerve can be identified as a white structure under the bone. Drilling should be performed parallel to the expected course of the nerve. The soft tissue (origin of the stapedius muscle) in an air cell may be wrongly identified to be the nerve. Drill carefully around the structures and see if they extend up ward and downward. You may also probe with an instrument to see if you have exposed a continuous structure, which would be the facial nerve. In live surgery, facial nerve monitoring may help to follow the course of the nerve. Identify the Chorda tympani branching from the facial nerve. For decompression, the thin bone can be carefully elevated exposing the perineurium. To achieve complete nerve decompression the perineurium may be incised (Fig. 2.13).

2.7 Cochleostomy After performing a posterior tympanotomy, a pillar of bone caudal to the short process of the incus was originally preserved (the so-called buttress). Note the projection of the cochlea (Fig. 2.14). The buttress may protect the incus from damage whilst drilling (important to prevent noise damage when positioning implantable hearing aids) and is also used by some surgeons to fix a cohlear implant electrode to prevent extrusion. A posterior tympanotomy may be performed as described above. Identify the head of the stapes and the edge of the round window niche. The site of the cochleostomy is determined by doubling the width of the stapes footplate in

Fig. 2.13 

16

2  Basic Surgery of the Temporal Bone

Fig. 2.14 

Fig. 2.15 

a inferior direction, to locate the round window niche. Drill with a diamond burr slightly in front of the edge of the round window niche (Helms) or straight into the round window (Fig.  2.15). No bone dust should enter the cochlea, as this might induce ossification in a patient and complicate or hinder reimplantation. The front edge of the opening into the cochlea must be smoothened to prevent kinking of the electrode during insertion. The electrode can be inserted with a narrow forceps or a manufacturer approved “claw like” instrument (Fig. 2.16). Practice also the approach drilling forward from the round window niche to expose the Scala tympani. This directly leads to the Scala tympani via the round window but may be difficult if the facial nerve is located too far ventrally. Take care that the shaft of your drill does not touch the nerve while performing the cochleostomy, as this may cause thermal or mechanical damage to the facial nerve. The size of the mastoid is smaller in young children, the tympanic bone is still developing, and the facial nerve appears more laterally. The cochlea and the ossicles have already reached adult size.

2.8  Endolymphatic Sac Surgery

17

Fig. 2.16 

2.7.1 Clinical Application Severe hearing loss, when hearing aids cannot achieve sufficient hearing.

Landmarks

Facial nerve Chorda tympani Handle of malleus Incus, long process and body Stapedius tendon Round window niche Round window Scala tympani

2.8 Endolymphatic Sac Surgery The endolymphatic sac is a space within the dural sheets of the posterior cranial fossa. It is connected with the inner ear by the endolymphatic duct, leading to the vestibule. As it is part of the dura of the posterior fossa, it is usually removed with the dura when the temporal bone specimen is cleaned for preparation. However, the site of the duct, and the external aperture of the vestibular aqueduct can be observed. After performing a mastoidectomy, identify the lateral and the posterior semicircular canals. Outline the sigmoid sinus preserving a thin bony cover. If the position of the lateral and posterior semicircular canal is uncertain, the labyrinthine bone can be removed until the blue lines of the canals are visualized. The perilymphatic space should not be opened. The position of the posterior semicircular canal should always

18

2  Basic Surgery of the Temporal Bone

be identified by exposing the blue line. In a normally pneumatized mastoid, the facial nerve is close to the inferior part of the posterior canal. Identify the facial nerve without removing the covering bone completely. Remove the bony coverage toward the posterior fossa until the dura (gray) and the sac (white) can be identified. A line from the lateral canal to the posterior fossa (Donaldson’s line) crosses the arch of the posterior canal in its centre. Remove the bone from the dura. The endolymphatic sac is found within the dura slightly underneath this line where it meets the dura of the posterior fossa. Pushing the dura toward the posterior fossa, the duct can be seen entering its canal from the endolymphatic sac (Fig. 2.17). If the posterior canal is not too close to the posterior fossa, the beginning of the endolymphatic duct can be seen in the bone behind the posterior canal after removing the cells between the posterior canal and the posterior fossa. The endolymphatic sac may be either decompressed or opened with a sickle knife, followed by the insertion of a silastic triangle or catheter. This last step is not possible in a temporal specimen where the dura of the posterior fossa has been removed (Fig. 2.18). Fig. 2.17 

Fig. 2.18 

2.9  Epitympanotomy

19

2.8.1 Clinical Application Endolymphatic sac surgery is performed to decompress endolymphatic pressure in patients with Menière’s disease.

Landmarks

Sigmoid or lateral sinus Dura of the posterior fossa Lateral semicircular canal Blue line of the posterior semicircular canal Facial nerve Endolymphatic duct

2.9 Epitympanotomy After removing the bone from the upper wall of the external auditory canal covering the incus and the head of the malleus, the position of the ossicles and the ligaments can be identified. Since cholesteatomas often extend into this region, the anatomy should be studied in detail (Fig. 2.19).

Fig. 2.19 

20

2  Basic Surgery of the Temporal Bone

2.9.1 Clinical Application In cases of attic cholesteatoma, this is a safe way to remove disease, following the cholesteatoma sac. The epitympanotomy is the first step and may be sufficient in small cholesteatomas.

Landmarks

Oval window with stapes Facial nerve Round window Cochleariform process Mastoidal tubal orifice

2.10 Open Mastoid Cavity The radical mastoid cavity (canal wall down) was a classic operation before tympanoplasty was established. It was an open cavity including an open middle ear, generally with removal of the malleus and incus for the treatment of cholesteatoma. Secretion from the open middle ear was often a problem. Today, removal of the disease is combined with closure of the middle ear by a tympanoplasty with or without reconstruction of the ossicular chain. Remove the posterior external meatal wall. This is with minimal risk to the facial nerve, if the nerve is safely identified during the preceding steps. If not, remove the bone over the nerve with a diamond burr until it can be seen through a thin layer of bone. The floor of the external auditory canal must merge into the lower mastoid without irregularities. The roof of the external auditory canal must merge smoothly into the epitympanic roof. This facilitates cleaning of the cavity. A persisting partial posterior meatal wall (facial ridge) is the result of incomplete drilling and complicates postoperative care and wound healing. In cases of extensive pneumatization of the mastoid and the mastoid tip, you should remove the tip of the mastoid to reduce the size of the cavity. The so-called facial ridge does not contain the facial nerve (Fig. 2.20).

2.10.1 Clinical Application A mastoid cavity and closure of the middle ear space with or without reconstruction of the ossicular chain is performed for the treatment of extended cholesteatomas. Alternatively preservation of the posterior meatal wall (canal wall-up technique and

2.11  Facial Nerve Decompression

21

Fig. 2.20 

posterior tympanotomy) or wall reconstruction after removal of disease may be considered. Landmarks

Facial nerve Lateral semicircular canal Bone covering the medial cranial fossa Sigmoid or lateral sinus Bone covering the posterior cranial fossa Middle ear structures

2.11 Facial Nerve Decompression Perform a complete exposure of the tympanic and mastoid part of the facial nerve, from the geniculate ganglion to the stylomastoid foramen, leaving a thin bony covering on the nerve tissue. This bone is removed at the end of the procedure. The facial nerve is found in front of the lateral semicircular canal slightly medial and arching down towards the stylomastoid foramen. Use a large diamond burr to remove bone until the nerve can be identified as a white structure under the bone. Drilling should proceed along the expected course of the nerve (arrows). For decompression, the thin bony layer can finally be elevated (Fig. 2.21). Further decompression toward the geniculate ganglion in the second portion of the nerve can only be performed after removing the incus and the malleus (preserve the ossicles for later reconstruction exercises). Remove the posterior meatal wall. Now the nerve can be followed ventrally (anteriorly) to the lateral semicircular canal, above the oval window and the cochleariform process to the geniculate ­ganglion. Finally, remove the thin bony cover with a Plester knife exposing the

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2  Basic Surgery of the Temporal Bone

Fig. 2.21 

Fig. 2.22 

perineurium. Complete the procedure by incising the perineurium with a sickle knife. Identify the stapedius muscle. It is generally found underneath, and medial to the nerve in its mastoid portion (Fig. 2.22).

2.11.1 Clinical Application Facial nerve decompression was mainly performed for the treatment of Bell’s palsy. Currently, it is performed to ensure the continuity of the nerve after trauma, for the removal of bone fragments or decompressing a perineural hematoma in the nerve canal. Rerouting of the facial nerve is sometimes necessary to access structures medial to it e.g., in glomus tumour surgery. The nerve is exposed from the geniculate

2.12  Labyrinthectomy

23

g­ anglion to the parotid, and then carefully taken out of its canal and displaced forward in to the anterior middle ear. Prior to lifting the nerve out of its position, thin the bone 270° around the nerve and remove the bony covering (Fig. 2.22).

Landmarks

Tympanic portion of the facial nerve Chochleariform process Tubal orifice Oval window Lateral semicircular canal

2.12 Labyrinthectomy The initial steps have been described under the section on “Posterior Tympanotomy”. Remove the cells behind and around the lateral semicircular canal. The bone of the canal is always solid and yellow. Behind the lateral canal and under the superior canal, identify the subarcuate fossa with the subarcuate artery in its centre. Continue the bony work until the posterior semicircular canal is sufficiently exposed. It is located more medial than the lateral canal, and is often separated from the posterior cranial fossa by a narrow tract of air cells. The inferior end might be close to the facial nerve. If the position of any semicircular canal is uncertain, the “blue lines” of the canals can be exposed but without opening the lumen. Next, identify the superior semicircular canal (Fig. 2.23).

Fig. 2.23 

(

A. subarcuata)

24

2  Basic Surgery of the Temporal Bone

Fig. 2.24 

(

A. subarcuata)

The ampullae of the lateral and superior canal are situated close together under the body of the incus. They should not be opened at this point (Fig. 2.24). The superior semicircular canal arches deep medially toward the posterior ­cranial fossa where it meets the posterior canal in the common crus. The beginner generally has difficulties following the superior semicircular canal backwards because a large amount of cellular bone has to be removed above the posterior part. At the end of this step, the semicircular canals should be sculptured clearly and the subarcuate fossa partly excavated. Now open the perilymphatic space of the canals using the cutting burr. Their structures must be recognizable for as long as possible, to provide topographical orientation. First, the lateral semicircular canal is followed from the ampulla as far down as possible. The bone of the canal is always solid and yellowish. The facial nerve is situated in front of the canal. Some bone should be left for nerve protection. Behind the lateral canal and under the superior canal, the subarcuate fossa with the subarcuate artery in its centre can be identified when the posterior canal is opened. The inferior end might be close to the facial nerve. Follow it downwards where it meets the common crus, and upwards to its ampulla. Now completely open the posterior semicircular canal, from its ampulla to the common crus. Finally, open the superior canal from its ampulla to the common crus. At this stage, the canals are open but not completely removed in order to study the three-dimensional anatomy of the temporal bone. You may now perform stepwise removal of the semicircular canals Completely remove the lateral semicircular canal, leaving a bony protection for the facial nerve. Open the vestibule. Drilling the posterior canal, the endolymphatic duct can be identified, leading to the vestibule. The exposure of the common crus is ensured. The end branches of the vestibular nerve can be identified entering the lateral and superior ampulla cranially, and the inferior ampulla caudally. The ampulla of the superior canal protects the facial nerve underneath. The ampullae of the ­superior and posterior canals outline the fundus of the internal auditory canal.

2.13  The Translabyrinthine Approach to the Internal Auditory Canal

25

2.12.1 Clinical Application Labyrinthectomy is performed for labyrinthitis, vertigo, translabyrinthine neurectomy of the vestibular nerves and in the translabyrinthine approach for acoustic neuroma surgery. Landmarks

Facial nerve Semicircular canals Subarcuate fossa After opening the canals: Facial nerve The opened semicircular canals Ampullae of the superior and inferior canals Endolymphatic duct Vestibule

2.13 The Translabyrinthine Approach to the Internal Auditory Canal The first steps are mastoidectomy, identification of the semicircular canals, and stepwise labyrinthectomy as described above. The mastoid must be opened widely to give a good overview. Remove bone up to the middle cranial fossa and posteriorly toward the posterior fossa. A protruding sigmoid sinus can be pushed downward and a high jugular bulb can be lowered. Exposure of the internal auditory canal requires extensive drilling resulting in a circumference around the internal auditory canal of about 300°. While the ­fundus is immediately under the vestibule, more than 1 cm of hard bone must be removed to expose the orifice to the posterior cranial fossa. Beginners usually do not expose the canal sufficiently (Fig. 2.25).

Fig. 2.25 

26

2  Basic Surgery of the Temporal Bone

Fig. 2.26 

Vertical crest

Opening procedure: Before removing the last thin layer of bone over the dura of the internal auditory canal, the surrounding bone must be removed downward toward the jugular bulb. The cochlear aqueduct can often be identified as a landmark to protect the lower cranial nerve group. Cranially, the bone above the canal should be removed up to the middle fossa. Above and below the solid labyrinthine bone, you find softer bone with mastoid cells. The jugular bulb varies in its position. It is located medial to the facial nerve, and might even be found in the hypotympanum. The facial nerve is found under the ampulla of the superior semicircular canal. It can be localized by thinning the bone underneath and towards the fundus. Identify the vertical crest (Bill’s bar) with the nerve entering its canal and open the dura after the internal canal has been exposed in its total length (Fig. 2.26, arrow). The vertical crest is part of the opening for the entrance of the facial nerve into the temporal bone at the fundus of the inner auditory canal. The horizontal crest separates the superior and the inferior vestibular nerves. If the nerves are not torn out during the removal of the specimen, the vestibular nerves can be removed after identifying the facial nerve (Fig. 2.27a, b).

2.13.1 Clinical Application Vestibular vertigo and non-serviceable hearing Approach for translabyrinthine surgery of acoustic neuromas

Landmarks

Facial nerve Vertical crest – entrance of facial nerve into the temporal bone Horizontal crest

2.14  Transtemporal Approach to the Internal Auditory Canal (IAC)

a

27

b

Transverse crest Vestibular nerves Facial nerve Vertical crest

Facial nerve Cochlear nerve

Fig. 2.27 

2.14 Transtemporal Approach to the Internal Auditory Canal (IAC) The transtemporal approach to the IAC is performed from the temporal plane. Identify the subarcuate eminence and the greater petrosal nerve leading to the geniculate ganglion. Expose the “blue line” of the superior semicircular canal that usually does not coincide with the eminence. Expect it to be up to about 10 mm distant. The superior semicircular canal and the internal auditory canal form an angle of approximately 60° opening toward the posterior fossa, varying between 34° and 75° (Fig. 2.28). When drilling the superior semicircular canal, damage to the facial nerve and the cochlea must be avoided. Identify the superior petrosal sinus. The groove of the greater petrosal nerve leading to the geniculate ganglion and the arcuate eminence can be identified. Air cells might be found above the superior semicircular canal before the yellow labyrinthine bone is seen. The “blue line” is identified in a longer stretch without fenestration of the canal. Finding the superior semicircular canal is difficult in a well-pneumatized temporal bone since air cells can be found above the semicircular canal. The cells have to be drilled away before the yellow labyrinthine bone is seen. Air cells can be identified by the exposure and course of “blue circles,” the superior canal by the appearance of the “blue line.”

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2  Basic Surgery of the Temporal Bone

Fig. 2.28 

Facial nerve Geniculate ganglion

lsc

46°

c

ss c ps

Vestibular nerve

Cochlea Greater superficial petrosal nerve

Remove bone in a triangular area outlined by the superior petrosal sinus, the superior semicircular canal, and the 60° line from the anterior crus of the superior canal toward the posterior fossa. Take care not to fenestrate the superior canal and the cochlea. A considerable amount of bone has to be removed to reach the internal auditory canal. Its orifice is situated about 1.2 cm below the superior petrosal sinus. A wide exposure is possible. The internal auditory canal appears as a grey change in colour beneath the bone. The facial nerve is closer to the surface ascending from the internal auditory canal toward the geniculate ganglion. The canal must be identified in its total length and must be exposed at least in 180° of its circumference before removeing the last layer of the remaining thin bone. In actual surgery, this technique avoids cerebrospinal fluid (CSF) displacing the nerves into the field of drilling.

2.14  Transtemporal Approach to the Internal Auditory Canal (IAC)

a

29

b Superior vestibular nerve Vertical crest

Facial nerve

Fig. 2.29 

Identify the nerves control the position of the facial nerve, and section the ­vestibular nerves (Fig. 2.29a, b).

2.14.1 Clinical Application • Vestibular vertigo with serviceable hearing • Small acoustic neuromas

Landmarks

Greater petrosal nerve Arcuate eminence Blue line of the superior semicircular canal

3

Surgical Exercises in the Middle Ear

The posterior external auditory wall should be intact. Some of the above-mentioned exercises should be performed after the middle ear and reconstruction exercises. Incise the skin of the external auditory canal with a No. 15 blade at the ­bottom and at the roof (6 and 12 o’ clock) from inside to outside. Duplicate these incisions with a Plester knife (straight round knife) and lift the skin flap by separating skin from bone using an angled blade knife. Often, the flap is too long and obstructs the view when it is rolled medially toward the tympanic membrane. It can be shortened by cutting off the lateral part. Identify the fibrous annulus and open the middle ear space by lifting the annulus from its sulcus (Fig. 3.1a, b).

a

b

Fig. 3.1  H. Hildmann et al., Manual of Temporal Bone Exercises, DOI:10.1007/978-3-642-19498-6_3, © Springer-Verlag Berlin Heidelberg 2011

31

32

3  Surgical Exercises in the Middle Ear

The skin of the external auditory canal may be very stiff, especially if the s­ pecimen has been treated with formaldehyde. It should be removed close to the annulus. Now remove the posterior attic wall from inside to outside using a curette or a small diamond burr to expose the chorda tympani entering the middle ear space. Continue to remove the attic wall until the stapedius tendon and pyramidal ­process can be seen. Identify the malleus, incus, stapes, facial nerve, promontory with Jacobson’s nerve, round and oval niche, cochleariform process with the tensor tympani tendon, opening of the Eustachian tube, and the pyramidal eminence with the tendon of stapes. Between the oval and the round window, the ponticulus, subiculum promontorii, and sinus tympani can be found. Identify Jacobson’s nerve and its course into the canaliculus tympanicus to the hypotympanum. Check the ossicular chain for mobility by gently elevating the handle of the malleus with a sickle knife.

3.1 Perforation of the Tympanic Membrane Practice underlay grafting a perforation with fascia and closure of a total perforation with cartilage palisades from the auricle. The thickness of the cartilage can be reduced with a No. 10 blade. Create a large perforation of the tympanic membrane, close it with fascia or connective tissue from the specimen using an underlay technique, and reconstruct the chain as shown below (Fig. 3.2a, b).

a

Fig. 3.2 

b

3.2  Ossicular Chain Reconstruction

33

Remove the tympanic membrane totally and reconstruct it with cartilage ­palisades, placing cartilage stripes one beside another, beginning at the tubal orifice.

3.2 Ossicular Chain Reconstruction Ossicular chain reconstruction may be necessary after destruction by chronic inflammation, trauma or fixation, and in cases of otosclerosis, tympanosclerosis, or malformation. Several further exercises may be performed: 1. Incus interposition and PORP (partial ossicular replacement prosthesis). Positioned between the head of the stapes and the tympanic membrane or malleus handle. 2. Interposition between footplate and malleus or tympanic membrane (total ossicular replacement prosthesis, TORP). If the footplate is missing, replace it with a small piece of tissue. 3. Interposition between stapes or footplate and a reconstructed tympanic membrane, using cartilage or fascia for reconstruction. Remove the incus with the hook by pulling it laterally into the external auditory canal, dislocating the malleoincudal joint. Take care not to subluxate the stapes from the oval niche, thus opening the vestibulum. Identify the incudostapedial joint immediately below the lenticular process of the incus. Open the joint using a micro hook (0.6 mm) that is gently moved in the direction of the Eustachian tube. The stapedius tendon will stabilize the stapes.

3.2.1 PORP Position the incus between the head of the stapes and the handle of the malleus. There are several options to shape the incus for further interposition. We prefer to drill the long process of the incus down to its body. We reduce the short process and drill a little cavity to place it on the stapes. The area of the former joint is positioned toward the handle of the malleus to build a stable reconstruction. Check the mobility of the reconstructed chain (Fig. 3.3a, b).

3.2.2 TORP For a total reconstruction of the chain (TORP), preserve the long process of the incus and position the area of the lenticular process on the footplate. Practice chain reconstruction techniques with ossicles, bone, cartilage, and ­alloplastic prostheses (Fig. 3.4a, b).

34

a

3  Surgical Exercises in the Middle Ear

b

Fig. 3.3 

a

Fig. 3.4 

b

3.3  Stapes Surgery

35

3.3 Stapes Surgery Clean the ear canal. Create a tympanomeatal flap, incising the skin at 11 and 7 o’clock, from the annulus outward, with a No. 15 blade. The flap must be short and pushed forward over the tympanic membrane after opening the middle ear, allowing sufficient space for the middle ear procedure. The Chorda tympani should be preserved. Remove bone with a House curette or with a drill until the oval window, the stapes, and the pyramidal eminence are exposed (Fig. 3.5a–d). The pyramidal eminence, the stapedius tendon, and the facial nerve are now exposed. To practice the technique for stapes surgery, divide the incudostapedial joint with an angled hook, carefully fracture the posterior and anterior crus of the stapes with a 0.6 mm hook and remove the suprastructure from the footplate. In cases of otosclerosis the footplate is fixed and fracturing is easier, but the procedure is very difficult in non-diseased specimens with a mobile footplate. The footplate may be stabilized with an instrument in this case. If you are successful, you may attempt to perforate the footplate. Using the microperforator, drill a small perforation into the

Fig. 3.5 

36

3  Surgical Exercises in the Middle Ear

Fig. 3.6 

posterior third of the footplate by rotating the perforator between thumb and forefinger. Remove the fragments with a hook. In non-diseased specimens, with a mobile footplate, the footplate is often removed as a whole (Fig. 3.6a–d). If you have preserved the incus, you can insert the prosthesis and fix it on the long process of the incus. Since the prosthesis is expensive, you may also use stainless steel wire and produce one yourself.

3.4 Malleovestibulopexy Remove the incus and connect the handle of the malleus with the vestibule performing a malleovestibulopexy. Prior to fixation of the prosthesis on the handle, create a tunnel above the handle without perforating the tympanic membrane (Fig. 3.1a–d). If the oval window is obliterated, you can create a promontorial window (Plester) and reconstruct sound conduction from the Scala vestibuli to the handle of the ­malleus using a prosthesis or a wire (Fig. 3.2a–d).

Recommended Reading

Anson BJ, Donaldson JA (1992) Surgical anatomy of the temporal bone. Raven, New York Brackman D, Schelton C, Arriaga MA (2001) Otologic surgery, 2nd edn. Saunders, Philadelphia Hildmann H, Sudhoff H (2006) Middle ear surgery. Springer, Heidelberg/Berlin Lang J (1992) Klinische Anatomie des Ohres. Springer, Heidelberg Plester D, Hildmann H, Steinbach E (1989) Atlas der Ohrchirugie. Kohlhammer, Stuttgart Proctor B (1989) Surgical anatomy of the temporal bone. Thieme, Stuttgart Sanna M, Saleh E, Russo A, Taibah A (1995) Atlas of temporal bone and lateral skull base surgery. Thieme, Stuttgart Sanna M, Sunose H, Mancini F, Russo A, Taibah A (2003) Middle ear and mastoid surgery. Thieme, Stuttgart Tos M (1993, 1995, 1997) Manual of middle ear surgery, 3 volumes. Thieme, Stuttgart Vijayendra H (2008) Color atlas of temporal bone dissection. Self publisher, Bangalore

H. Hildmann et al., Manual of Temporal Bone Exercises, DOI:10.1007/978-3-642-19498-6, © Springer-Verlag Berlin Heidelberg 2011

37

Index

A Acoustic neuroma surgery labyrinthectomy, 21 semicircular canal identification, 12 Antrostomy antrum opening, 5 bone dust removal, 5 clinical application, 8 consequence wide opening, antrum, 7 drilling method, 7 incus, 7, 8 marking the opening, 5 mastoid air cells, 7 mastoid opening, 5 saucerization, 5, 6 sigmoid sinus protrude, 7 B Bell’s palsy, facial nerve decompression, 22 C Cholesteatomas epitympanotomy, attic, 20 open mastoid cavity, 20–21 posterior tympanotomy, chorda tympani, 13 Chorda tympani posterior tympanotomy, 13 stapes surgery, 35 Coalescent mastoiditis, 10 Cochleostomy bone dust, 16 buttress, 15 clinical application, 17 electrode fixing, 15 stapes, 15

E Endolymphatic sac surgery, 17–19 Epitympanotomy, 19–20 External auditory canal attic wall removal, 32 skin removal, 31 F Facial nerve decompression clinical application, 22–23 perineurium exposure, 22 tympanic and mastoid removal, 21 Facial nerve identification, 15 I Inferior surface, 4 Instruments, in surgery drills, 1 microscope, 2 preparation and planning for beginner, 3 connective tissue removal, 2 sitting positions, 2 structure identification, 4 Internal auditory canal (IAC) translabyrinthine approach clinical application, 26 exposure, 25 procedure, open, 26 vestibular nerve removal, 26, 27 transtemporal approach blue circles, 27 clinical application, 29 drilling, 27 facial nerve, 28 nerves, 29

H. Hildmann et al., Manual of Temporal Bone Exercises, DOI:10.1007/978-3-642-19498-6, © Springer-Verlag Berlin Heidelberg 2011

39

40 L Labyrinthectomy canal, blue lines, 23 clinical application, 25 perilymphatic space, 24 semicircular canal removal, 24 semicircular canal identification, 12 Labyrinthitis, 25 Lateral surface, 4 M Malleovestibulopexy, 31, 36 Malleus exposure, 10 Mastoidectomy clinical application, 10 malleus exposure, 10 in young children inner ear structure, 9 size, mastoid, 16 Mastoiditis antrostomy, 8 mastoidectomy, 10 semicircular canal identification, 12 Medial surface, 4 Menière’s disease, endolymphatic pressure, 19 Middle ear, surgical exercises external auditory canal attic wall removal, 32 skin removal, 31 malleovestibulopexy, 31, 36 ossicular chain reconstruction PORP, 33, 34 TORP, 33, 34 stapes surgery bone removal, 35 chorda tympani, 35 footplate, 35 fragments removal, 36 tympanomeatal flap, 35 tympanic membrane perforation, 32–33 O Ossicular chain reconstruction PORP, 33, 34 TORP, 33, 34 P Partial ossicular replacement prosthesis (PORP), 33, 34 Posterior tympanotomy

Index chorda tympani, 13 clinical application, 13 distance, lateral semicircular canal and facial nerve, 13, 14 middle ear cavity exposure, 12 S Semicircular canal identification beginner difficulties, 12 clinical application, 12 subarcuate artery, 11 removal, 24 Stapes surgery bone removal, 35 chorda tympani, 35 footplate, 35 fragments removal, 36 tympanomeatal flap, 35 Superior surface, 4 T Temporal bone surgery antrostomy (see Antrostomy) cochleostomy bone dust, 16 buttress, 15 clinical application, 17 electrode fixing, 15 stapes, 15 endolymphatic sac surgery, 17–19 epitympanotomy, 19–20 facial nerve decompression clinical application, 22–23 perineurium exposure, 22 tympanic and mastoid removal, 21 facial nerve identification, 15 internal auditory canal (see Internal auditory canal (IAC)) labyrinthectomy ampullae, 24 canal, blue lines, 23 clinical application, 25 perilymphatic space, 24 semicircular canal removal, 24 mastoidectomy (see Mastoidectomy) open mastoid cavity, 20 posterior tympanotomy chorda tympani, 13 clinical application, 13

Index distance, lateral semicircular canal and facial nerve, 13, 14 middle ear cavity exposure, 12 semicircular canal identification (see Semicircular canal) Total ossicular replacement prosthesis (TORP), 33, 34 Translabyrinthine approach internal auditory canal clinical application, 26 exposure, 25 procedure, open, 26 vestibular nerve removal, 26, 27

41 vestibular nerve section neurectomy, labyrinthectomy, 25 semicircular canal identification, 12 Transtemporal approach, internal auditory canal. See Internal auditory canal (IAC) Tympanic membrane perforation, 32–33 V Vertigo labyrinthectomy, 25 translabyrinthine, internal auditory canal, 26 transtemporal approach, internal auditory canal, 29