Temporal Bone Surgical Dissection Manual

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TemporalBoneSurgicalDissection'Manual by

RalphA. Nelson,M.D. HouseEanInstituteandotologicMedicalGroup,Inc.,Los Angeles

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Publishedby HouseEar lnstitute, Los Angeles

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House Ear Institute,256 South Lake Street, Los Angeles, California 9OO57O f 982 by House Ear Institute. All rights, including that of translation into othelanguages, reserved.No part of this manual maybe repr rced,str system, or transmitted, in any form or by any mp. photocopying, recording, oi' otherwise, without, publisher.

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Preface This voiume is intended as a basic introduction to surgical dissection of the temporal bone. The idea for this project originated with my initial attempts in my residency to dissect a temporal bone. I found no single source that would guide me in setting up a dissection bench and then drilling a bone in such a way that I could learn the anatomy from a surgical approach. I later found that not only was a surgical approach important, but also that an organized approach that would enable me to utilize each and every bone to its fullest extent was just as vital.

Drawings were selected over photographs in order to concentrate on specific details and to obtain the depth of field felt necessary to adequatelv depict the dissections. In certain areas, actual surgical procedures are used to better illustrate the anatomic detail and its applicability to the dissection. This manual is organized to introduce a student of the temporal bone to basic techniques and basic anatomy in a stepwise fashion, with each dissection building upon a previous one. All of the procedures in this manual can be accomplished in ten drilling sessions with a maximum of two temporal bones. Each chapter occupies a full two- or three-hour dissection period for the introductory student. Midway through the exercises, time may be taken for review. The volume has been designed for ready reference during drilling in the dissection laboratory. Again let me emphasize that this manual is an introduction to temporal bone dissection and in no way should be construed as a definitive treatise on the subject. I feel that it will aid those who have previously studied the temporal bone to review already acquired skills. The repeated use of these dissections will allow the temporal bone surgeon to become skilled and knowledgeable enough to complete actual surgeries with confidence. Rar.pg A. NELSoN, M.D.

Table of Gontents Intnoduction: Equipment, General Considerations . . 1 1. Basic Mastoidectomy 2 . Facial Recess,Epitympanum. 3. Postauricular Facial Nerve Decompression

......19 . . .26

4. Endolymphatic Sac and Extended F ac ialR e c e s s D i s s e c t i o n s.

......3 6

5. Tympanic Ring Remonal

......47

6. Postaurieularlabyrinthectomy 7. Int ernalA u d i t o r y C a n a l . 8 . M iddle Fo s s aA p p r o a c h . . . 9 . Middle Ear Dissection 10. Wall Dow n T e c h n i q u e s . Index

....49 ......5 7 ....6 7 . . .73 ......8 5 ... 9 1

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BenchlFig. 1l The bench is important to a temporal bone dissection laboratory. Although the dissection could be performed on any available table in any availabTeroom, a pleasant environment increases the likelihood of repeating the exercises. This is also increased by (1) the ability quickly to aid break down the equipment, (2) adequate gquipm€nt' and (3) ""?.tp use oi the same equipment and techniques that will be used in the operating room. Ideally, the temporal bone dissection bench should: (1) always be available and not be in use for Some other purpose, (2) be large and deep enough to allow prolonged sitting without undue discomfort, (3) have a readily accessible powei source for either an electrically driven drill o^ran air-driven driil, ( i have an easily cleaned and serviceably large trap for a suction apparatus so that prolonged dissections can be performed _ without interruptions for emptying the trap; (5) allow for the installation of an arm capable of supporting a microscope similar to the one used in the operating suite (unfortunately, the large floor stands used in the operaiing suJte are not flexible enough to be easily used around the a'oerageSench), and (6) contain enough storage so that the instruments to be-used are readily available for anyone to perform a dissection.

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Ghair The chair should be comfortable, similar to the chair in the operating suite, and adjustable for individual preferences for height-. Choose a chair with castors ior mobility so that the dissector can move closer or farther away from the bone for proper extension and support of the arms.

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Drill The drill ideally should resemble the equipm_ent in the operating suit-e' Any drilt with i variety of burr sizes will suffice, but reliability should be a cbnsideration. Burr shank support is necessary to prevent whippin$; the electrically driven Wullstein-Wpe (geared) drill with that support has been widety ana successfully used. Whatever system is used should allow enough too- for movement of the drill e-ngi-neon the bench so that both left- ind right-handed persons can use the bench. Both diamond and cutting bulrs should b-eavailable and cutting burrs should be sharp'

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The microscope should closely resemble the unit used in the operating room. Again, ihis i" to familiarize the dissection student with instrum-ents to be used in Surgery. We have found the Zeiss operating microscope to be durable and satisfactory.

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Equipment Suction-lrrigationlFig. 2l

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We advise the use of suction-irrigation in both the operating room and the bone dissection laboratory. Adherence to techniques that mimic operatin$ room procedure is important to instill confidence and familiarity in the dissector and thereby decreaseanxiety about actual operating room procedures. In the laboratory, the use of the suctionirrigator is not only to mimic operating room procedure, but also to insure that no bone dust or other debris obscures the fleld being dissected. A constant flow of cool moisture cools the drill and also keeps the burr free of bone dust, thereby allowing for better cutting edges.Any easily available water source can supply irrigation. It should flow simply by force of gravity, as it does in the operating room. We prefer suction tips of a simple configuration to avoid problems with handling. A straight House suction-irrigator has the least error in transfer from a suctionirrigator to a straight suction. The suction unit should be reliable and attached to a large, easily accessible,and easily cleaned trap.

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Although almost any device that stabilizes the bone for drilling purpos€s can be used, we have found the House-Urban s+ainleqs steel bone holder very satisfactory. It is easily cleaned, stable, and allows three-point flxation of the bone, which enables movement of the bone to an5r desired position for dissection. The bone cup should always be placed in a faqger pan that will contain spilled irrigation fluids and accumulated bone dust-

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Temporal bones cut from specimens should include all the mastoid air cells, a small portion of the squamosal part of the bone, the tympanic ring, and the petrous tip. Bones can usually be obtained during postmortem examinations without damage that would interfere with preparation of the body for viewing. Complaints from morticians can be avoided by fixing the facial bones to the cranial vault by wire sutures, as in repair of a facial fracture, and by filling in any defects in the base of the skull with plaster of paris to prevent leakage of embalming fluids. This manner of taking bones leaves no external deformity of the skull.

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Examinationand Orientation of Bones Before dissection, the temporal bone should be examined thoroughly in al effort to learn the external anatomy. Knowledge of this anatomy will ultimately be useful in identiffing external features during surgical exposure and also in gaining three-dimensional orientation. Once the external topography has been reviewed, soft tissue overlying the mastoid area should be removed. A11excess tissue that is not to be used in the dissection should be remor-ed from the bone before it ls secured in the stainless steel bone cup. The bone is then flxed in the stainless steel bone cup. It is oriented under the microscope for the standard surgical approach: u-ith the postauricular axis of the mastoid tip and the middle fossa floor in the horizontal plane and the temporomandibular joint away from the surgeon.

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GeneralGonsiderations

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The dissector should be comfortably positioned to prevent strain on extension of the arms or backache due to slouching. The chair should be adjusted to maintain a comfortable position at all-.times.A waterproof apron is recommended to protect clothing since dissection with copious a'mounts of irrigating fiuici will result in widesprbad moist bone dust. The microscope sho"utd bE adjusted to maintain constant focus regardless of the powei of magnification used. This is done by setting the proper distance between the eyes before starting and by focusing ",?"! "y.^ indiviaually at the highest power of the microscope-' You will then find that upon iurning to"lower powers you remain parfocal. Suction and irrigation shouldbe checked and regulated so that when suction is not useE, there is a constant stream of water, and when the thumb is placed upon the suction valve, the stream is directly shunted into the suction aiparatus. The drill should be tested to verify that the burr turns in the piop.t direction and that its cutting edges are not reversed. With all fqr-tip-.nt in proper working orderl the surgeon may now proceed with the dissection.

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Large-scale bone removal, such as on the cortex, is done u'ith the largest porEibt" cutting burr. The burr should be angled so that the flukes that 'are largest o.t ih. sides of the burr are directll- against the surface' Cuttin! with the smaller flukes at the tip of tl e burr results in more heat and sldwer cuttin$. Burring with the tip also obscures the area that is being dissected.

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A fundamental principle of temporal bone dissection is no blind dissection. Drilling should nevel proceed on the sense of touch alone. For better visualizatioil of underlying bone while it is being cut, bone dust and accumulated blood shouid be removed by adjusting the suctionirrigation. This is done by shifting the suction tip to various positions aroind the burr so that travel of the burr pushes irri$ation fluid and, bone dust into the suction tip. This keeps the drill burr cool, the field clear, and the flukes of the burr free of bone dust, which would otherwise interfere with good cutting.

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The handpiBce of the drill should always be grasped firmly' Torque from the drill, especially if it is air-driven, will commonly cause unwanted movement in the Leginning. Once the burr is at its full speed, larger cutting burrs tend t6 "r,-tn"because the burr chews ag-ainst the bone' This w-ill be accentuated by pressure or placement of the burr agailsta bone on which the buir flukes can catch. To prevent this difflculty' flp "f the burr so that the flukes cut perpendicular to the ridge' In "ttift particularly ti$ht areas, a diamond burr should be substituted and' 'preferably,-thJdri1 reversed so that it tends to run in the opposite direction.

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Temporal bone surgery is based upon laldmanks. Landmarks should cutting and should always be preserved until uf*"jo be identifi"d'b.fo.. at deeper levels. The most complete exp-osure 5 located othei landmarks are available landmarks' A general rule of i]' of assures the best utilization is This area' '*, u for a burr possible largest the $iven dissection is to use plunge could burr a where areas l* approaching especially true when cavity. a into plate or through dural .*Fj.,S*.r**

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\ Surface topography on exposure of the lateral surface of the mastoid bone before dissection is the external acoustic meatus (ear canal) anteriorl]-. the suprameatal spine (of Henle) at the superior posterior portion of the canal, and the suprameatal triangle (of Macewen) immediately behind the spine of Henle, where subperiosteal abscesses might form secondary to mastoid infection. The temporal line, forming a ridge continuous from the superior border of the zygomatic arch posteriorly onto the mastoid cortex, is the inferior limit of the temporalis muscle insertion. The lateral wall of the mastoid process (tip) is the point of insertion of the sternocleidomastoid muscle.

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External auditory canal Spine of Henle Macewen's triangle Temporal line Mastoid process

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The largest available burr and the largest available suction-irrigator should be used during initial cortical exposure. An absence of important structures in the cortex allows safe and rapid removal of this bone, conserving the surgeon's time and energr for more tedious and delicate dissection elsewhere. A high rate of irrigation is necessary to prevent overheating of the burrs and clogged burr flukes, which decrease cutting ability.

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The surface of the bone is wet with irrigation fluid from the suctionirrigator and the drill is applied to the mastoid cortex immediately posterior to the spine of Henle. A straight cut drawn along the temporal line posteriorly into the sinodural angle delineates the upper portion of rhe dissection. A second cut is made perpendicular to the first and rov-ard the mastoid tip. This cut is immediately posterior to the posterior cana-lrvall. The mastoid cortex is then removed in a s\-stematic fashion of saucerizatron. $-ith the deepest portion of penetration at the junction benreen the tu-o perpendicr:lar lines. This area behind the spine of Henle rrhich acruallr or-erlIes thr mlastoid antrum is ca-lled the suprameatal iangle of llacerl-en.

Landmarks: External auditory canal Spine of Henle Macewen's triangle Mastoid tip Temporal line

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\ To avoid a constricted dissection that prevents adequate angular visualization of deeper-lying structures, wide cortical removal should be completed before deeper penetration into the antrum. The mastoid cortex should be unroofed from the posterior canal wall back to and slightly beyond the sigmoid sinus and at an adequate distance into the mastoid tip. The posterior canal wall should be thinned so that the shadow of an instrument can be seen through the bone when the canal skin is elevated. This wide saucerization cannot be emphasized enough. Insufficiently wide saucerization is the single most common reason for- inadequate recognition of landmarks and awkward exposure during deeper dissection.

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External auditory canal Posterior canal wall Tegmen tympani Mastoid tip

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When adequate cortical removal has been accomplished, a kidney beanshaped cavity will result.'The inferior portion of the shape is formed by the mastoid tip below the sigmoid sinus and ear canal. The upper portion is above the sigmoid sinus, extending posteflorly into the sinodural angle and anteriorly into the zygomatic root. Anteriorly, the posterior bony canal wall will constrict the center of the cavity. This type of cortical removal is basic to all posterior approach procedures on the mastoid cavity. Again, be reminded that failure to perform this [pe of exposure while deepening the dissection toward the antrum can lead to a bothersome constriction of the cavity at more medial levels.

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Step 4 lFig. 6r: ldentificationof the MiddleFossaDural Plate Dtrlmg mastoidectomy, it is important to expose the middle fossa dural plate {tegmen tympani) for best possible access into the antrum and epin-rnpanic areas. This exposure is critical to a well dissected sinodural angle. u'hich provides visual access into the internal auditory canal area after labl-rinthectomy. Failure to locate the middle fossa plate usually leads to insufficient femoval of cells along the superior border and causes compromised exposure and decreased access to the epitympanum and hard angle.

Landmarks: Posterior canal wall Tegmen tympani (middle fossa dural plate)

\Ve have found that the best way to expose the middle fossa plate is to burr the cortex into the area of the linea temporalis until bone color changes indicate that the middle fossa dura has been reached. The dissection should round off the edge of the superior lip roughly paralleling the curve of the dura. This plate exposure can be followed into the antrum without lacerating the dura. At this stage of the dissection, do not use #24 burrs for extensive thinning of the plate, since larger cortical burrs tend to fracture the thin plate and create large dural dehiscences that mav become lacerated. Once the heavier bone is removed., thiniring cin be performed with a diamond, which results in less bleeding.

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ldentificationof the Lateral Sinus

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When the middle fossa plate is well established, the surgeon locates the sigmoid sinus by drilling out the posterior portion of the mastoid cavity a sufficient distance from the bony canal wall. Well aerated mastoid bone is frequently found in neurotologic dissections, and it is possible to conlinue drilling in the posterior direction until the occiput is exposed. If a sufficient amount of bone has been removed posteriorly, the dissection may proceed deeper into the mastoid cavity in an attempt to find the sigmoid sinus. The sigmoid sinus generally appears in the posterior portion of the dissection as a blue discoloration of smooth dural bony plate. Dural plate of both the middle fossa and the posterior fossa tends to be somewhat uniform and is not cellular; therefore, one should inspect any area 6f smooth plate carefully for color changes that indicate an underlying soft structure, such as the sigmoid sinus. Because this plate can be quite thin, one proceeds with caution. Thinned dural plate usually can be identified by changes in the sound of the burr vibrating on it. Once the sigmoid sinus has been located under its plate, the area between the sigmoid and the middle fossa plate, the sinodural angle, can be fully evacuated of air cells. In dissection of the sinodural angle, penetration of the plate results in exposure of the superior petrosal sinus. This sinus lies immediately deep to the sinodural angle in its entire extent', and represents the posterior superior lip of the temporal bone where the middle fossa and posterior fossa meet. The si$moid sinus usually lies a few millimeters deep to the cortex in the mastoid ca\-iq-. This structure is the posterior limit of the standard mastoid dissection. It is not more widely exposed unless the posterior fossa is to be entered. Inferior to the sigmoid sinus lies the largely air-containing mastoid tip' Laterally, there is no danger of entering any vital structures, so the tip may be cleaned of air cells to gain better exposure in the jugular bulb area.

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Posterior canal wall Tegmen tympani Sinodural angle Mastoid tip

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The areas dissected and the structures identified thus become landmarks for deeper penetration into the temporal bone. The cortical landmarks of the external canal, spine of Henle, linea temporalis, and mastoid tip now become the mid-level landmarks of the middle fossa plate, sinodural angle plate, sigmoid sinus plate, mastoid tip air cells, and the thinned posterior external canal bony wall. Knowledgeable and safe penetration deeper in the temporal bone depends upon complete identification of these structures. The principle of temporal bone surgery is to move from one known landmark to the next, guided by the relationships between each. Only in this way can the temporal bone surgeon avoid the danger of being lost within a nebulous network of vital structures.

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The most important landmark at the next level of this dissection is the mastoid antrum. Although the size of this air-containing pocket varies considerably between pneumatized and nonpneumatized bones, one rarely encounters a totally absent antrum. The antrum lies immediately below the deepest point of penetration into the temporal bone posterior to the spine of Henle and the zygomatic root. Koerner's septum (Fig. 5) often lies deep to the mastoid cortex within the air cells of the well pneumatized temporal bone. It is a segment of the petrosquamous suture line representing the fusion of the squamous and petrous bones. It is usually a solid wall of nonpneumatized bone extending across the entire mastoid cavity separating the more superficial mastoid cortex (squamous) cells from the deeper (petrous) cells and antrum. It extends from the posterior canal wall at the tympanomastoid suture line and blends with the air cells in immediate approximation to the middle fossa plate, sinodural angle, and sigmoid sinus plate. This structure is often initially mistaken for the hard bone of the labyrinth and horizontal semicircular canal. These structures, of course, lie deep to Koerner's septum. After the septum is penetrated in the anterior superior quadrant of dissection, the true antrum will be seen as a very large air-containing cavity. By keeping the canal wall bone thin and avoiding the nearby middle fossa dura. frogressively deeper penetration will reveal the antrum. Normallv. the antrum can be identified as a larger air-containing space at whose bottom lies the basic landmark of the smoothly contoured. hard" labyrinthine bone of the horizontal lateral semicircular canal. Location of the horizontal semicircular canal (lateral canal) allows exposure of the fossa incudis, the epitympanum anteriorly and superiorly, and the external genu of the facial nerve medially and inferiorly. The hard labyrinthine bone extends posteriorly from the horizontal canal to the posterior canal, which lies anterior and medial to the sigmoid sinus. By removing cells between the horizontal canal and the sinodural angle, one encounters the hardest bone of the body, the socalled "hard angle," which is part of the otic capsule. Posterior to the labyrinth there may be some air cells in continuity with the petrous apex. Inferior to the posterior canal, the posterior fossa dural plate overlies the endolymphatic sac. More inferior to this area the bone of the mastoid tip may be thinned to expose periosteum of the digastric muscle. The digastric ridge runs in a posterior-to-anterior and lateral-to-medial direction, starting inferior to the sigmoid and ending at the stylomastoid foramen where the mastoid segment of the facial nerve exits the temporal bone. The periosteum generally is arranged in a semi-lunar shape and seems to turn superiorly to blend with the facial nerve sheath at the foremen. Finding the digastric is one method of locating the facial nerve in the mastoid cavity. Cells medially lead through the retrofacial area above the jugular bulb. After the mastoid portion of the facial nerve (discussed later) has been deflnitively identified, the continuity between the jugular bulb and sigmoid sinus can be followed along the smooth dural-type plate.

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Tegmen tympani Posterior canal wall Sinodural angle Sigmoid sinus Lateral semicircular canal

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The fossa incudis is most easily identified by removing bone in the zygomatic root overlying the antrum. The incus can normally be seen before actual exposure because of the light-bending refraction of the irrigating fluid (Fig. 9A). As the fluid is removed, the incus appears to disappear. As fluid fills the antrum, the incus once again appears. The facial nerve is normally located inferior and slightly medial to the horizontal semicircular canal by thinning the posterior canal wall bone and carefully removing bone in the facial recess area. The facial recess is delineated by the fossa incudis, the chorda tympani, and the facial nerve (Fig. 9E}). Generally, under increased magnification, a cutting burr is used during irrigation with copious amounts of fluid to remove bone dust and to provide optimal visualization of underlying bone. In this way, the blood vessels and sheath of the facial nerve will impart discoloration to the bone, normally pink in the living specimen and stark white in the cadaver. upon location of this discoloration, the sheath of the nerye can be followed inferiorly toward the mastoid tip and superiorly and anteriorly into the facial recess.

Landmarks:

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Posterior canal wall Tegmen tympani Lateral semicircular canal Fossa incudis and incus Sinodural angle Digastric ridge Posterior semicircular canal

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We have now delineated a new set of landmarks that are used for further dissection of the temporal bone. The dissection thus far has created n-hat is commonly called a simple mastoidectomv.

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Topography The facial recess is a collection of air cells lr'ing immediatelr- lateral :c :ht facial nerve at the external genu. It occasionallv sen'es as a roule ior middle ear disease to extend into the mastoid area via cells other than the antrum. Cholesteatoma that frequently invades these cells u-ill be extremely difficult to remove via standard transcanal approaches. We feel that opening of the facial recess in any chronically diseased ear is of value additional avenue of mastoid aeration. This exposure also in providin{an allows better visualization of the middle ear cavity in chronic ear disease and exposure of the horizontal portion of the facial nerve during facial It is also the route to the round window for nerve deco-p.ession. insertion of ftre cochlear implant electrode. The landmarks used to expose the facial recess are the external genu of the facial nerve medially, th^e fossa incudis superiorly, the chorda tympani nerve laterally, and the tympanic membrane anteriorly and laterally.

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Figure 1O Tegmen

Sigmoid sinus Facial newe (floor)

20

Horizontal

Sinodural angle

semicircular

canal

d I

7

-a

4

a

Step 2 [Fig,111: Openingthe FacialRecess

/a

4 -t -J t,

a,

ul

-:-: negrns dissection of the facial recess by identifying the external genu :: :he descending portion of the facial nerve in the mastoid cavity. As l:e',-:ouslv indicated, a free flow of irrigating fluid is used to allow clear ,:r: '::rstant Yisualization of the underlying bone so that color variations --- --,:nal-be easilv identified. The microscope is turned to 1O power. The :,-:: o: the facial nen'e is pearlr-u-hite in the presen'edbone and pinkish :r:rn the r-ascularin'of rhe -acri':;l-al a::i -he :re:*.'esheaihr in a ll\-ing s:ecrmen, Ge:elll-',- :hrs :-s>e,:,.-:- :s a:: -::.p,-s:r:-i ,,',--:h' c'-.::i::Eburr '- -- : -' --:- --:::---_-- -: -:-_---.: :

.-

-

----:

-:

--. . --=

-

j-

-

Landmarks: Posterior canal wall Horizontal canal Fossa incudis Facial recess cells fif p re s e n t ) External qenu

-

{ { { J

J

{ { { Facial recess

Cell tract

v

Zygoma tic root

Posterior canal i,

ncus

llasroid tip

t,

\'"'

{

J*

v

-4

Figure 11

Incus buttress

-Emo id s inus Horizontal

semicircular

canal

Step 3 lFig. 121=

t{

Gompletingthe Recess

\

j

\

\

With the new landmark of the facial sheath, the nerve is skeletonized distally along its descending portion in the mastoid and then medially as it foUows thJfloor of the faciat recess into the mtddle ear space. Smaller burrs will be necessary to accomplish most of the dissection in the facial recess since the recesi itself rarely exceeds two or three millimeters' Inferiorly the chorda tympani nerve is detected as it leaves the facial nerve. Dissection doei not sacrifice this structure. The chorda t1'rnpani nerve joins with the tympanic membrane anteriorly and laterally at the annulir edge; thus, following the chorda tympani generally prevents disruplion of the tympanic membrane.

Posterior canal wall Chorda tymPan Descending segment of facial nerve

Landmarks: Facial nerve Incus Fossa incudis Chorda tympani Stapes Horizontal canal

\

= 5r

= = =

Long process of incus Buttress

a

Fossa incudis

I

t

\ fr I t

t ; i

t

Figure 12 Digastric muscle Sigmoid sinus

Tegmen Stapes Horizontal semicircular canal External genu Posterior semicircular canal

t lF

i

t t I

!

{

C -

t a a a a 4

-o -o T

a a c a fr

suep4 tFig.131: The Middle Ear Throughthe FacialRecess T[ ith the facial recess fully opened, one can easily visualize the horizontal por-tion of the facial nerve, the lenticular process of the incus, the lncudostapedial joint, the capitulum of the stapes, the stapedial tendon, al-ld. n-ith proper angulation, the cochleariform process. The round u'indou' ma]'be easilr- identified inferior to the stapedial nandrrrarks. Superiorlr-. a burtreis of bone is presen-ed betg-een the short process of the incus a,nd rhe -aana-:ecess. This ls cornn-lon-lvterrned -the htl:t:ress - Dnllrng ihr:u{h :he b,ut--r-eii r-A1n
Landmarks: Facial nerve Incus Lenticular process Incudostapedial joint Stapes Round window Cochlearifo-rm process Chorda q'mpani Horizontal canal

I

fr Lenticular process

4 Fm;rcrior

canal well

Incudostapedial

II

-

joint

Incus

t

g

t tt

a b

J

.A -a -ra

{

b rA 3

'it € !A

-

+ * *-

2 4 4

Figure 13 tympani Round window Promontorv Pyramidal

pes Stapedius tendon genu

Tegmen Buttress Horizontal

canal

step 5 tFig. 141= Unroofingthe Epitympanum In chronic otitis media, the epitl'mpanum is a common reposl:oF-lc: cholesteatoma. It often has destror-edossicles: more frequendv it ha: involved the body of the incus and the head of the malleus u-ithout complete destruction. Complete exposure of the epin'mpanum u-ithout destruction of the scutum can be obtained by removal of additional air cells in the root of the zygorna. This is done with use of the middle fossa dura and the thinned posterior canal wall as landmarks.

Landmarks: T^ IiIL -.. L-l: la^1'^-. \t/l ri

\-

Todmen

Horizonra: canal Facial nen'e

Often a small diamond burr is necessary if the middle fossa dura and its underlying bony plate, the tegmen tympani, lie low. A small burr also prevents shattering of the thin plate. If necessary, this dissection may be carried anteriorly through the zygomatic root to the glenoid fossa. The floor of the dissection is the horizontal canal, the superior semicircular canal, and the facial nerve.

Posterior canal wall

;/

In c u d o ma l l e a r i o i nt E pi n mpanum

Buttress

Head of malleus

Zvgomari c roct

Figure 14 Tegmen

Lenticular process

Superior ligament Horizontal segment of VII

24

Ligament of short Process

J

D >,

Step 6 tFig. 151:

h b

Remouingthe Buttress

a a

-:- :::-nic disorders in which cholesteatoma involves the incus, the facial :..trs lnav be connected to the attic and the epitympanic exposure by :.::r!I,ing the buttress after the incus has been disarticulated from the ::tr:es This continuity between atticus and facial recess gives an r-ierv of the middle ear from behind. In cases in which :,-,--::rsi'"-e -:::-esteatoma invoh-es the stapes. this technique can be used to provide :'::h an anterior and a pos:erior tx'"r,tsureo::he slapes. This allou's more r:nplete and sa:e::.il -','a, ,: -,::: -h,-:st:.:-:lla -::m:hese difficult :...1-:---lr -- :h: :a-'.' :€:€ss :s so compiere a::;s -,i,--.:-,:-.s ::::-:-:-

4 3 ?

e 4

:..-

. . -.t

.

, <:

9r

.:'- - - .- :- ' ,' -- :- :

:- :S

1:

- :- :
- ::: :

::' -

j:

: - ::.1;- tr - :

;:Il ]!- i - i -

Landmarks: Facial nerye Horizontal canal Chorda tympani Stapes Posterior canal wall

Of

\

3 4 e, Cochleariforur

3

+ +

Superior ligament

process

Chorda q'mpani

Malleus head

Zygornatic root Tegmen

Promontory Jacobson's nerve

2t

;

; 2

3 A A .a -v

"0 .-l t

t

F"igu:re 15

-z,

a e ) a

) ?j

Round window

Pyramidal Process

Horizontal

sern :jiciruular

ca-u.a-l

-{r'cicu-lar process Stapedius tendon

Anterior

stapedial. cru.s

rY

step 7 lFig. 161:

$

Exposureof the Anterior Epitympanum

ti

After removal of the head of the malleus and body of the incus. this dissection allows unimpeded inspection of all epi[rnpanic areas. In a rrell pneumatized bone, air cells extending anteriorly into the petrous apex may also be seen.

!r

GI (lr

The flgure shows the expansive exposure obtained with this technique. Note the cog, a bony ledge extending into the epitympanum from the tegmen anterior to the amputated head of the malleus. This spicule may separate the epitympanum into posterior and anterior compartments. Removal of cholesteatoma that is harbored anteriorly, which is common, requires careful burring away of the cog.

Stapes Facial ner'{ie Cochlearifonn process Long process of manleus Eustachien tube

cog

t\

CJ tt t! J s

This step completes dissection of the facial recess and epitympanum.

v tt !r

C Cochleariform process Chorda tympani

Manubrium Umbo

Zygornattc root cog

!}

I

\' t

6 !Y

tb

v U

q

1 c 6 €

Figure 16 Peritubular cells

Promontory Eustachian tube

Tegmen Horizontal semicircular canal Facial nerve Canal of tensor tympani Pyramidal process

t r ; : 3 . - '': : . . - ;

t (F

J

.) t

U'

PostauricularFacialNerue Decompression Step 1= SimpleMastoidectomy(See Ghapter1l

the FacialRecesstsee Ghapter2l Step 2= Opening

\ F F

s \

s. g*'

Orientatton: Fig. 17 shows the general orientation of the facial nerve. Notice the position of the nerve in relation to the posterior canal wall, the fossa incudis, and the horizontal semicircular canal. The facial recess is a key to facial nerve decompression.

ts ab

!

Posterior canal wall Tympanic membrane tr,

Ossicles

Descending segment

3 L 1r

at I L 3

t t, t

€ 7

Figure 17 Stylomastoid foramen Chorda tymPani

External genu

U IU

Tympanic segment of VII l

t, !t,

tlt

U q

I

, !

2a

I

/

)

Step 3 tFig.181:

/, /'

I rt

the DescendingPortion of Vll Skeletonizing

4

lrLinnE complete simple mastoidectomy, most of the facial nerve has been 'rell delineated. For decompression, the nerve is followed from the erposed external genu and the mastoid segment to the stylomastoid :':rarnen, As the stylomastoid foramen is approached, the periosteum of --:,: digastric muscle will blend with the sheath of the facial nerve. This, ,r essence. is the stylomastoid foramen. The digastric itself is occasionallv used as a landmark to flnd the descendine. portion of the iacial at the str-lomastoid forarnen. In :his method. after the nen-e is located a: ilie :rra:r:e:" :he n.s:':io seEnenr ls ioLiou-edsuperiorlr- back a:1|-:a,':a*l-efess.Fl $'er-er.this methOd :: ::-: :::a :::;1..:':-::::i -t;-'-: a--lhe lerei of fhe qenu or :--t:'-.'. :--. :s ::^-a:-e .. . -: "-"'-a:i:l;:he :riel-!-e porfion is ihinned :t:f t:rclnJ l---: :::-: :,-l-.--:- -':::i--t --:.:-- -:.:-r ;---:- >t :: = :-r::-::-- :*=:ld pr::JSe lrrngation to pre\-ent frictiona-l :-tr.-:-:ii :: --::=:-.:*,-e -1,:leig::le-l cor-erlng oibone is presen-ed over the :".::.:--: ::::-::a- - :he descending portion of the nen'e. This is ::.:.si::--- :: aB.on-npressthe nen-e satisfactorill' and to prevent its :r{::-*s:::r :nrough a narrow opening in the bone. This part of the nerve -s l:.: routr"neh' uncovered anteriorly because of the external auditory cana-i. lateral.ll- because of the chorda tympani, or medially because it is not necessan'.

/7

/, -t 1 tt

4 1 -,, t

,t

.;

Descending segment of VII Mastoid tip Digastric muscle

Landmarks: External genu Vasa vasorum of facial nerve Chorda tympani Stylomastoid foramen Digastric muscle

Long process of incus Chorda tvmpani F a c i a l recess

Posterior

canal wall

Body of incus

\

t

t t

t

t

t

tt

Figure 18 Stapes External genu 4

orizontal semicircular canal Posterior semicircular canal

e

Step 4 tFigure.191:

G

e( e

The HorizontalPortion of Vll

\ The nerve is further exposed medial to its external genu into the facial recess, as in the approach to the facial recess for chronic otitis media. This exposure allows visualization of the horizontal portion of the nen€ anteriorly toward the cochleariform process and then superiorly to the tegmen, where the geniculate ganglion is located. Dissection of the epitympanic space through the normal antrum-attic approach frequenfly allows some exposure of the more medial portions of the horizontal segment. The bone over the nerve is thinned enough so that the bone can be easily lifted off the nerve with an elevator. The facial recess area will normally admit the smallest diamond burrs (O0 and OO0) under the incus without dislocation of the ossicular chain. Rarely must the incus be disarticulated from the stapes. A very small suction-irrigator removes bone dust and debris from the tiny facial recess opening. Again, irrigation must be adequate to prevent frictional heating of the nerye. Suction may be inserted through the epitympanic space to provide circulation of irrigating fluid while the burr is used in the facial recess. The surgeon may choose to change the burr to the opposite hand for proper angulation into the recess.

Lanrirnarks:

\

Facial nerre Chorda t-\rnpa-oi Incus buttress Fossa incudis Incus (long processJ Stapes Horizontal cand

L ! L

l-

e tb

!

Bone should be thinned f 80 degrees across the lateral aspecr of the external genu, and over the entire inferior one-hal,f of ttre horizonml (tympanic) part of the facial. a. b

Cochleariform process Lenticular process of incus Chorda tympani

L

Buttress

tt,

Posterior canal wall Incus

rt rl' !9

I

€ €

2 !t

II

U

I I I

I

v

i I

,,,,rc

N I

I I

v

e

Figure 19 Tegmen

Descending segment of VII 30

'i

U

Stapes

Tympanic segment of VII

€,

7

/, /t,

n 4 4 -t tt

-u -, -t -, tt t t

-t

step 5 tFig.2ol: "Balter Poling"the FacialNerve Eo'ne fuinning for bone removal is performed in a "barber pole" fashion. ]|tlis effect is produced when: (1) the descending portion of the mastoid rgrnent between the stylomastoid foramen and the external genu is unroofed on the posterior aspect; (2) the external genu and facial recess pcrTlon of the nerve is unroofed on its lateral aspect; and (3) the horizontal segment of the nerve is unroofed along its inferior border to ftre ler-el of the cochleariform process. This rotation of the unroofing process from posterior to lateral to anterior allows safe removal of bone uithout injury- to the surrounding structures. In the descending portion, decornpression on the lateral side will result in sacrifice of the chorda ;'-n:pani" -{t the ler-el of the external genu, removal of bone on the p'rs:emor side rdll lead to fenestration of the horizontal canal. Burring p,oe:er-r,orX1or superiorlv in the horizontal segment will lead to injury of *jre horizonmi canal. This thinning process should be completed over the enLtinenmastoid and middle ear segments of the facial nerve. Then the burr rs set aside.

Landmarks: Facial nerye Horizontal canal Stapes Chorda tympani Incus Cochleariform process

t I t

Chorda tympani

t

Posterioi v

canal wall

Fossa incudis Buttress

Di.Eastric muscle

I v t

I

, , t,

) t

t q

I t

t

Figure 20

t t

Stylomastoid

foramen

Horizontal Posterior

)t t t

1 I

4

sern icircular

sern i circular

canal

canal

?! ^{ tlt

Step 6 lFigs. 21,221=

-t

tJ ti

Uncoveringthe Sheath

I

\

The eggshell-thin bone is gently pried off the sheath of the facial. An1' thin, sharp pick may be used; a small dental excavator. with its tulst like that of the "whirlybird" of middle ear surgery, works extremely well. Right- and left-hand excavators must each be available for optimum angulation. One should not use another portion of the facial as a fulcrum; rather, brace the elevator against nearby bone. Complete control of the tip of the pick can be maintained at all times by proper use of a fulcrum. The accompanying figures show the more familiar Rosen needle being used to elevate the bone.

Landmark:

\

Facial nerre

a tr tl

! -

J a It-t

Stapes Posterior

canal wall

Buttress l

)$ a

a. ir, a t rb rb !]

1 a

c tt

2

a

Figure 2l External genu

Horizontal semicircular canal Posterior semicircular canal

tl t I ? ra !a

e t a

Uncoueringthe Sheath

i't!tu eaa,:,| .::,:4,:l

Digastric muscle Chorda tympani Stylomastoid foramen

Figure 22

F rl

il

,J

Step 7 lFigs. 23,241=

q

Openingthe Sheath

!

!(

'

l

!

The sheath is opened with a #59 BeaverRknife. It is shaped like a sickle knife with slightly less curve. Because it is disposable, it is never dull. A dull blade miltrt tause tugging on the nelve during slicing of the sheath because the sheath is quite tough and relatively thick. It has the white color of connective tissue and the nerve fibers it contains are gray.

Landmark:

\

Facial nerve

i

.

t! c-. j -

Be certain to examine the nerve for circular fibrous bands that will constrict the nerve fibers. These bands must be lysed.

j

i

The mastoid and middle ear portions of the facial nerve are now decompressed. Further decompression of the labyrinthine segment must be carried out through the middle fossa. Although some of the labyrinthine portion may be decompressedvia the mastoid, it is a tedious and difflcult dissection. In addition, the medial porus of the fallopian canal cannot be opened from this approach, and this is the narrowest part of the canal and the area most susceptible to constriction.

J a-

a" rb J ra

f 15

T-T':Epanic s€gmcnt of tr-In L

Buttress L

Descending segment of MI

tl a |l

t

,:

!

i

rt j !

t f t I

a , t a

a !

,ra

Figure 23 External genu Horizontal semicircular canal

F

a

-

a!

Openingthe Sheath Stylomastoidforamen Mastoid

Chordatympani rior canal wall

tip

II

, "*3fitr11 /

/ / Signoid sinus

Figure 24 Sinodural angle

1 1

-<

t?1

EndolymphaticSac Dissection Step 1tFig. 251:

e

Topography'

i

il i

I

{

{ The endolymphatic sac is located in a thickened portion of posterior fossa Landmarks: dura medial to the sigmoid sinus and inferior to the posterior canal. The Horizontal canal sac is readily found by performing a simple mastoidectomy with Posterior canaX particular attention to skeletonizing the sigmoid sinus and thinning the Donaldson's line posterior fossa dural plate immediately medial to the sinus. Although Sinodural angle blue-lining the posterior semicircular canal was once routine, it is only Sigmoid sinus rarely required and is usually avoided because it carries greater incidence Bony fallopian canal of hearing loss. The area of the sac extends from the medial aspect of the Mastoid tip cells sigmoid sinus anteriorly into the retrofacial area inferior to the posterior Dural plate canal and superior to the jugular bulb. The exact location of the sac, which varies, is usually identified by the presence of thickened white dura next to the normally darker, single-layered dura, or by the presence of hypervascularity on the surface of the sac. The sac also has been known to occupy the medial wall of the jugular bulb. The most likely cause of inability to locate the endolymphatic sac is that the dissection is not carried far enough into the retrofacial recess. Of course, to delineate the sac safely in this area, the descending portion of the facial nerve must be located and carefullv presen'ed. Donaldson's line is an imaginan' line in the plane of the horizonta-l caral back to the sign'roid sinus. It often marks the top of the endo[:rnphatic sac.

ri I

:

!

) f, I I g

t d

ll

ry a j

lr

t

Posterior canal wall Area of facial nerve Retrofacial

cells

Posterior

canal sernisircular Horizontal sernicircular

Mastoid tip

t

cenef

t

Fpitympanum

rl I t I a tt I

t

E i:

..it

tl

:rt'iii

tP tl

I

I tt !l

t

t

Figure 25

?I J

Sigmoid sinus Area of endolymphatic sac

Donaldson's line

Tegmen Sinodural angle

t

,

D rt I 4 4 4 sg

a a tt

a

The dural plate over the sac is thinned with a diamond burr' Wide eposure is performed so that sutures may be placed in the dura to seiure a mu^scle plug at the end of the procedure. Retrofacial and mastoid lip cells may be opened for wide exposure and dural plate bone is thinned r,i-\: :o rhe posterior canal. Again, do not blue-line this canal. The emdoh-mphatic duct mav be seen as the apex of a fan-shaped extension of dle sac under the posteior canal. This apex is often tented from the labSrinthine bone ivhene r,he duct e\ists deep to *le canal rt-hen the sac is depressed \\ith arr ener,ato:. The egeshell-thin dural plate is then picked am-ar irom the dura

Landmarks: Sigmoid sinus Labyrinthine bone Dura

a a -

7

Facial nerye Posterior Retrofacial

"

3

Horizontal semicircular

canal

canal wall

Fossa incudis

cells

a a t

t !t lt

t 1'

It

.t t !

rt !

tl

-ra rt

tl

!

*

1e

il

I

!

Figure 26 Tegmen

Endolymphatic sac Sigmoid sinus

Sinodural angle Posterior semicircular

canal

t 1 4

,-t

rc I

39

\{

Step 3 tFig. 271=

l

-t I

lncisingthe Sac

-l

\l

The lateral wall of the sac is incised and the interior exposed. There is a smooth, glistening lining which, in the living specimen, is moist. The incision on the lateral surface of the sac can be made with any relatively sharp instrument that will not penetrate deeply into the sac and beyond into the subarachnoid space. The incision into the medial wall of the sac under higher power magnification may be accomplished with a small hook so as to avoid injury to underlying vessels.This medial incision is generally at right angles to the lateral wall incision and further under the flap to facilitate closure. The medial incision is only a separation of dural fibers allowing the arachnoid to bulge into the sac. This, of course, does not occur with a cadaver specimen.

Landmarks: Endolymphatic sac Sac lumen Subarachnoid space

\r

s,r t-.i

=

=

The shunt tube is inserted through the medial incision into the subarachnoid space, allowing the flange to remain in the sac lumen. The flap is then used to cover the flange. A silk suture holds a muscle plug against the lateral incision of the sac wall.

\\" 9 tf.-

Posterior canal rdl Facial nerye Retrofacial

Postenior

semicircular IlorizOgtal

sq nal

S6'micireular

ea n al

\.

FoSsa incrrrli-s

cells

t L

\, t tt w v

3 3 ra, i.l

a, a

!

l-'1

Figure 27 Sigmoid sinu Lumen of endolymphatic sac

Sinodural Shunt tube

I

\tl

I

,

rl rS

a

ExtendedFacial Recess Dissection Step 1ffiig. 281: Topography

f1,

a 4 4 -a

a 4 4 4 'a

a

Inferlo{:. t}re facial recess dissection may be extended with sacrifice of ufie chorda tympani. Such an exposure provides visualization of the hl'poqmpanic area and access to the so-called "crotch" where the jugular hulb rneets the carotid artery. The primary landmarks for this dissection are the descending portion of the facial nerve as the medial limit of riissection, the annular ligament of the tympanic membrane laterally, and the jugular bulb inferiorlv. This approach is the commonest for smaller glomus tumors. Further dissection in the inferior portion of the mastoid ca\iq' mav be carried out in the retrofacial area, which is inferior to the posterior canal and medial to the facial nerve. This approach enables complete e^xposure of the hypotympanum if it has been invaded by hlpoq,-mpanic and retrofacial cholesteatoma. This also is a route for eryCIsure of larger glomus tumors. Limits of this dissection are the nxrter-tor canal and cochlea superiorly, posterior fossa plate posteriorly, and the jugular bulb inferiorly and anteriorly. This approach can be connbined with transcochlear and translabyrinthine approaches to rerouLte the facial nerve in cases of large congenital cholesteatoma or large gilomus jugulare tumors.

Landmarks: Fossa incudis Incus buttress Facial recess Facial nerye Chorda tympani Stapes

-

fr a -J J

|,

Zygomatic root

Incus Posterior canal wall Chorda tympani

Buttress of incus Fossa incudis

J

-t ., t

/

-.1)t

4 4 rJ

D -

J

-e -t r-

,

-,[t- r' :, It

t 1 4 4 4

Figure 28 eacial nerve

Horizontal semicircular canal

aI

(s

Srep2 tFigs.29,3Ol:

E

j

d

Extendingthe FacialRecess

t

The facial recess is extended at the lateral aspect of the facial nerve by sacrificing the chorda tympani. This allows the recess to be opened inferiorly between the facial nerve and the annulus flbrosis. As the annulus turns anteriorly, it moves away from the facial nerve, which permits the surgeon to remove more bone. The annulus then becomes the prime landmark. As the dissection continues forward through hypotympanic bone, a new structure is encountered: the jugular bulb as it rises into the hypotympanum. This provides the exposure necessary to remove a small glomus tumor or extensive hypotSrmpaniccholesteatoma.

Landmarks:

\

Facial nerve chorda tymPasi Annulus $mpanic membrane

tr

tr t| _l

r

ir

!:

t tj U !ry

Stapes Pyramidal process Chorda tympani

f

Incus buttress

/] )*

Fossa incudis

t& tul 3 j

3 3 f

3 t

rt !

It

tl

!

Figure 29 Facial nerve

Horizontal semicircular canal

a !l

tt

? -

,,,

?

tr

F Extcrndingthe Facial Recess V, V,

Incus buttress

,4D

lfiedial side of tympanic membrane

-a ra

.dnnulus fibrosis

?

a 4 4 ?

a a fr

a a 7 !t

a .t

-a It tt

Figure 30 Hypotyunp'a.nrun

F'aeihll Ererre Horiizomml

a ? { D

-c I

--t-

t l-

i?

i-3

fr I € 4 I

D

scmisireular

cnnalf

G \

Step 3 tFigs. 31 , 321:

!l \

Jugular Bulb/GarotidArtery

\

If the surgeon extends the dissection, the bone of the inferior portion of the tympanic ring and mastoid tip may be removed lateral to the facial nerve. This gives wide exposure of the hypotympanum to the level of the eustachian tube. Removal of retrofacial cells that extend from the mastoid into the middle ear allows one to follow the sigmoid sinus in its continuity with the jugular bulb. Carrying the dissection even more anteriorly, one encounters the carotid artery and sees the confluence of the two large vesselsleaving the carotid sheath and entering the base of the skull. The bone occupying the part of the skull base where the carotid turns anteriorly and the jugular turns posteriorly is called the "crotch" (jugulocarotid spine). Follow these vessels.The jugular bulb can be opened and IX, X, XI found in proximity to the multiple openings of the inferior petrosal sinus.

Lanrlmarks:

\

Facial nerve Annulus fibrosis Sigmoid sinus Jugular bulb Carotid arterv

k F.

tJ

I

!! IL

f-

7 f

D

u le

L

t5

v

Stapediaf

tendon

Buttres-s

Posterior

llr

F'esa insudis

Annulus fibrosis

te

Inqrs

canal wal'

6 a, l}

l' t L !

g

v /

G

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Figure 31 Hypotympanum Extended facial recess Retrofacial cells

Stapes Horizontal semicircular canal Facial nerve

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Removingthe TympanicBone

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Removal of the tympanic ring is often indicated tt'hen there is a carcinoma of the conchal area of the ear or the external ear canal A procedure for cancer must be performed in €rn en bloc fashion u'ith the skin of the ear canal, the tympanic membrane, and the bony canal walls removed together. This can be done by a combination of some procedures described previously and a dissection through the area of the 4rgomatic root and the temporomandibular joint. A standard postauricular simple mastoidectomy is performed, followed by an extended facial recess dissection under the posterior canal wall but lateral to the facial nerve. More anteriorly, the lateral portion of the jugular bulb is the most medial part of the dissection. The lateral wall of the jugular bulb will eventually intersect with the posterior wall of the internal carotid artery in the anterior hypotympanum medial to the eustachian tube. Superiorly, the dissection started in the antrum continues through the epitympanum and zygomatic root below the middle fossa dura until the area of the temporomandibular joint is entered. The auricle or the concha is then removed en bloc with a sleeve of tissue representing the bony and cartilaginous external auditory canal, including the tympanic membrane and malleus. The incus will normally be attached to the malleus and it must be disarticulated from the stapes.

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Zygomatic root Jugular bulb Temporomandibular joint

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Frgure 33

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Topography

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The postauricular labyrinthectomy is designed to eradicate labrrinthine Landmarks: vertigo by complete removal of the semicircular canals and all soft tissue Posterior canal wall of the vestibule. It is also the commonest surgical route to the internal Incus auditory canal. A complete simple mastoidectomy is performed with the Horizontal semicircular posterior canal wall left intact. The sinodural angle must be completely canal drilled out to provide adequate exposure of the area of the vestibule later. Posterior semicircular The middle fossa plate must be thinned completely to provide access to canal the superior semicircular canal. A large cutting burr is used to open the Tegmen tympani sinodural angle posterior to the labyrinth. In this way, the flukes on the side of the cutting burr may be used to better advantage in removal of the Facial nerye Sigmoid sinus extremely hard labyrinthine bone anterior to it. Sinodural angle

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srep 2 tFig.351: Openingthe SemicircularGanals Qr" crrrring into the labyrinth, one should be able to fenestrate the hrorizontal semicircular canal and, by enlarging this dissection, unroof dhe posterior canal and the anterior portion of the superior canal as well. The fenestrated canals are followed in their extent to provide continuing -a:1i,r:rarxis" The surgeon should eventuallv have a dissection that showJ :he ou'-eentarionof eaLchcanal to its neighbors. Anterior to the horizontal canal. tht esrernal genu and honizonral portions of the facial nene can be skeletonized. Preserradon ot the anterior n-ell of the horizontal canal *r.t-es as a protection for these pordons ot the facial nen-e until further :}::mrng or-er rhe facial is n'ecessary- ro epos€ more of the r-estibule.

Landmarks: Semicircular canals Facial nerve Incus Tegmen Sigmoid sinus

kcu':se r:l{aaon is necssa-r1: to remove t?st quantities of bone dust and ailso to prmqn[ trictirnat burning of nearbv bone. The largest burr that is emfortabrle sburld be used to enable qrrick bone removal, decrease fuictional heat- and prerent burr clogging.

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Facial nerve

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Followingthe SemicincularGanals

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The semicircular canals must be followed as they are highways into the Landmarks: vestibule. Transection without following will leave -5nake eyes- and create Facial nerne confusion about which direction to continue the dissection. Try to Tegmen develop a three-dimensional concept of the canal planes. Semicircular canals Sigmoid sinus Superiorly, the superior semicircular canal arches in a posterior-medial direction underneath the middle fossa plate. This canal is traced posteriorly and medially until it becomes the common crus in its junction with the posterior semicircular canal. The subarcuate artery usually penetrates the hard labyrinthine bone in the center of the circle inscribed by the superior canal. The posterior canal is then followed inferiorly and anteriorly under the descending portion of the facial nerve. Look for the endolymphatic duct as it courses from its opening in the medial wall of the vestibule next to the common crus. It travels posteriorly in the medial wall of the common crus and then curyes inferiorly and laterally as it passes under the posterior canal to enter the endolymphatic sac in the posterior fossa dura. There is frequently a bony operculum or small bony cap overlying this portion of the sac as the duct enters it. The sac often causes confusion by appearing to represent torn dura until the true nature of the soft tissue is recognized. The endoh-rrphadc duct appea,rs as a pearly white, thread-like discoloration ire the ha-rd labryrinthlne bone-

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Followingthe SemicircularGanals Facial nelve

Horizontal semicircular canal

Posterior semicircular canal

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Openingand Gleaningthe Vestibule

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The surgeon follows the common crus forward into the vestibule and opens it widely. The bone over the facial nerve is then thinned well to provide good visual access to the vestibule. All the semicircular canals are completely connected, and any soft tissue is removed from the vestibule and semicircular canals to eliminate any remaining vestibular function. Before removing the soft tissue, note the maculae or ttre utricle and saccule. Note the spherical recess of the saccule in the anterior portion of the vestibule and the elliptical recess for the utricle posteriorly. Frobe the -common opening of the endolymphatic duct at the anterior end of the crus. Palpate the stapes footplate from its medial side and notice its proximity to the saccule and utricle. The postauricular labyrinthectomy is now complete.

Landrnarksi

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Facial nerve Tegmen Semicircular canals Elliptical recess Spherical recess Footplate of stapes Endolymphatic duct

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Topography

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The simple mastoidectomy and postauricular labyrinthectomy are the first two stages of the approach to the internal auditory canal. This new and much deeper dissection requires that all the previous steps be accomplished properly to provide wide apcess for adequate visualization and working room deep within the petrous bone. During labyrinthectomy in this procedure, the ampulla of the superior semicircular canal is preserved as a landmark to find the end of the superior vestibular nerye, Bill's bar, and the facial canal. In approaching the internal auditory canal, one must remember that the medial wall of the vestibule represents the lateral wall of the internal auditory canal fundus, where the nerves enter the inner ear structures. Therefore, minimal bone removal on the medial wall of the vestibule will expose the internal auditory canal. Posteriorly, at the posterior fossa dura, the route to the porus acusticus is much deeper because the internal auditory canal is slanting away from the dissector. The plane of the canal, in an anteriorposterior direction, is roughly from the external genu to the sinodural angle. The superior border of the internal auditory canal extends from the facial canal to sinodural angle. The inferior border of tJ e internal auditory canal is at a point approxi-mating the junction of the e-.rternal genu and descending portion of the facial nen'e and parallels the super-ftor border posteriorll' to its junction with the pcterior f6sa-

Landmarks:

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Facial newe Vestibule Tegmen Posterior fossa plate Superior canal ampulla

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A sharp pick is often used to perfor.ate ttre very thin bone of the internal auditory canal fi.rndus in the area of the elliptical recess. Frequent\'a blue-line discoloration appears.

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-ds seen from above, the bone to be removed for exposure of the internal auditory canal forms a wedge or triangle. One side is the roof of the internal auditory canal and the medial portion of the dissection; the second side is the floor of the labyrinthectomy dissection; and the third side is the posterior fossa dura as it extends between the other two sides. The thicker posterior portion of the bone is usually more difficult to remove because it is composed of hard labyrinthine bone. The internal auditory canal can be recognized by color changes in the bone. In the cadaver specimen or the living surgical specimen without a tumor, the color of the canal will be dark blue as in blue-lining of any hollow structure. In the specimen with a tumor, the color is usually ruddy from the vasculariq' of the tumor and overlying stmctures.

Landmarks: Tegmen Sinodural angle Vestibule Ampulla of superior canal Posterior fossa plate Sigmoid sinus Internal auditory canal

Posteriorh- in the sinodural anglg, the blueline of the superior petrosal sinus will show as it runs along the posterior superior border of the temporal bone from the apex to its entrance into the transverse sinus.

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Figure 40 ;osterior fossa dural plate "nal auditonr canal

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Subarcuate artery

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Blue-liningthe Internal Auditory Ganal

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Skeletonization of the internal auditory canal for dissection purposes is accomplished through removal of bone for 180 degrees around the posterior portion of the canal extending from the area of the fundus to the porus acusticus. Such extensive surgical exposure is to prevent the bony overhang that would make work within the canal difficult. Blind dissection under bony ledges carries the possibility of injury to a nerve or blood vessel within the canal. For such extensive exposure, the surgeon must remove all bone superior to the canal extending from the area of the facial canal and petrous apex to the superior midpoint of the porus acusticus. This dissection is usually performed with small diamond burrs and a small suction-irrigator, which prevents the accumulation of bone dust from obscuring the underlying dissection area. The middle fossa dura is located and followed in an ever-deepeningtrench, with preservation of a thin layer of bone over the superior portion of the internal auditory canal. At the deepest portion of this dissection, which is at the superior lip of the porus acusticus, exposure is extremelv limited. With patience and persistence, however, the posterior superior portion of the internal auditory canal can be well exposed. With the posterior portion of the poms acusticus well defined at the juncfion of the pcterftrr fmsa dura and internal auditory canal" the inferior border of the intcrnal auditor-r canal can be better defined. A trench with the jqgular hrlb inferirt-v and the internal auditory canal superior\r is c.onstnrcted between the posterior fossa dura and hard labyrinthine bone anteriorly. This dissection is aarried anteriorly until a small white discoloration in the bone appears. This represents the cochlear aqueduct which, when entered, will often release cerebrospinal fluid. Extension of the dissection anterior to the cochlear aqueduct will involve the jugular bulb and the ninth, tenth, and eleventh cranial nerves. If proper removal of bony covering has occurred throughout the exposure of the internal auditory canal, there should now be an eggshell-thin coverin$ of bone from the fundus of the canal to the area of the jugular bulb inferiorly, to the superior petrosal sinus and middle fossa dura superiorly, and to the sigmoid sinus posteriorly. This bone may be removed for a wide exposure of the internal auditory canal and the posterior fossa dura. For procedures involving section of the vestibular nerye, such edensive exposure is not necessary. However, we encourage wide extrrosureto eliminate blind dissection through a small keyhole into the internal auditory canal fundus. Limited exposure also precludes the abililv to deal with the potential problem of a bleeder from the sectioned nerve.

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e LAndrnarks:

Superior petnosaf sinuLs Superior cpnal arnpulla Vestibule Facial nerye Cochlear aqueduct Tegmen Jugular bulb Sigmoid sinus and posterior fossa plate

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Blue-liningthe Internal Auditory Ganal Internal auditorv canal "blue-lined" Superior semicircular canal ampulla

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The bone removed, the exposed dura of the internal auditory canal is slit along the long axis of the canal at its inferior border. This precludes injury to the facial nerve superiorly in the occasional cases of variation (sometimes a tumor pushes the nerve posteriorly). Within the internal auditory canal, the vestibular nerves are both posterior, whereas the facial nerve is anterior superior and the auditory nerve anterior inferior. To locate these structures from a lateral dissection approach to the internal auditory canal, we use the facial nerve as the principal landmark. The facial nerye is located anterior to the superior vestibular nerve. Therefore, we ordinarily preserve the ampulla to the superior semicircular canal, which makes for easier identification of the superior vestibular nerve. A diamond burr is used to penetrate the medial wall of the superior ampulla. The thinned bone then exposes the superior vestibular nerve as it enters the labyrinth at that point. If the bone has been removed from the superior border of the internal auditory canal far enough anteriorly, the facial canal may be seen descending through its labyrinthine portion from the genicr-rlate into the internal auditory canal.

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Facid nerve

Tegmen

Jugular bulb

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Figure 42 {

SingElar

Porrrs acustlsus

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ldentificationof the Nerves When the superior ampulla is preserved, its medial wall represents the last remaining bone over the superior vestibular nerve at its termination in the ampulla. Wtren this bone is removed, a brush-like ending of the nerve is encountered. After the superior vestibular nerve is identified, a one-millimeter hook may be inseited deep to the vestibular nerve directly anterior and medial to the superior vestibular nerve to palpate the shelf of bone that separates the superior nerve from the facial canal. The superior vestibular nerve occupies a recess medially. The recess may be safely probed and the posterior edge of it palpated. Bill's bar, as this shelf of bone is called, represents the posterior wall of the fallopian canal. With identification of the bar and the fallopian canal, the superior vestibular nerve may then be avulsed from its attachments in the ampulla area. When gently lifting the superior vestibular nerve, one should carefully look for the facial nerye as it exits the fallopian canal into the internal auditory canal. Vestibulofacial anastomoses that occur here should be carefullv sectioned. Directly inferior to the superior vestibular and facial nen'es. a bonlprominence protrudes into the fundus of the internal auditory canalThis shelf of bone. called the transverse crest, falciform crest- or cristadivides the canal into superior and inferior portions. It is €sident during exposure of the fundus and allows easy identification of the inferior vestibular nerve laterally and the auditory nerve medially. The singular nerve to the posterior semicircular canal is an offshoot from the inferior vestibular nerve within the internal auditory canal. This method of vestibular internal auditory canal exposure is used for translabyrinthine approach for acoustic neuroma nerve sections and the translabyrinthine removal. .If bone is removed from the fallopian canal starting at Bill's bar, the facial nerve may be decompressed to the geniculate ganglion and internal genu a few millimeters anteriorlY.

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Landmarks: Falciform crest {tranverse } Superior vestibular nsrvre Bill's bar (vertical crest) Facial newe

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Middle FossaTopography In the middle fossa disseetion of the temporal bone, placement of the bone within the bone cup usually presents some difficulty. The dissector should visualize the bone as if looking through a craniotomy window that has been inscribed in the squamosal portion of the temporal bone (Fig. 45A). This is from the vertex of the head (the surgeon sits at ttre headof the table, not at the side as in the standard postauricular approach). The bone is positioned so that the surgeon looks direcily down upon the middle fossa floor. Then dura should be stripped back from the roof of the temporal bone, as in the surgical procedure for this approach. The topography should be studied (Fig. 458). As dura is reflected away from the squamosal portion of the bone, the floor of the middle fossa ii revealed. Laterally, this is the tegmen overlying the aerated mastoid portion of the bone and epitympanum. Anteriorly beyond the epitympanum, thin bone covers the eustachian tube. More anteriorly, the middle meningeal artery is the flrst major landmark to be encountered in elevating the dura. The foramen spinosum is located where the flat lateral portion of the squamosa intersects with the floor of the middle fossa. Posteriorly the floor of the middle fossa drops abruptlv into the posterior fossa where the tentorium intersects \Aith the temporal bone. The _ superior petrosal sinus is located in the re{lecred dr.ma-}{edral to dre aerated epitympanic bone, the arcuate eminence of the srrtrtritr cqnal is the second major landmark- Anterior to the arcuatc anirsroe rrxl approximately one centimeter medial to the mitrh rrnri4g'ral iltcry is the greater superficial petrosal nerve running anterior to pctcrir into the facial hiatus, where it urill join ttre facial nerve and gpnicrrlate ganglion. This key landmark allows the surgeon to locate the geniculate ganglion for unrooflng the facial nerve. It eventually will become the prime landmark in the middle fossa dissection.

Lanrlrn"arks:

Squanosa Arcuate erninence Middle meningeal artery Superior petrosal sinus

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Petrous apex Greater superflcial petrosal nerve hl ea {ghost) Facia_lnen'e lghostJ Cochlea.r nerre Lghostl

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SuperficialDissection

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The first portion of the dissection involves unrooflng the geniculate ganglion and tracing the facial nerve from the internal genu into the middle ear space. The greater superficial petrosal nerve should be followed to the geniculate ganglion (Fig. 46A). The geniculate ganglion will be superflcial; therefore, a minimum of bone should be removed. The largest diamond burr is used for this procedure with copious amounts of irrigating fluid to remove the bone dust. At the geniculate ganglion the nerve turns laterally, posteriorly, and inferiorly into the epitympanum. Although the nerve can be followed for quite a distance through this approach, the cochleariform process is the normal limit of dissection. Lateral to the facial nerye, the ossicular chain will be noted with the head of the malleus particularly prominent. Because the ampullated end of the superior canal is close to the medial portion of this dissection, one must be careful not to fenestrate the canal through the hard labyrinthine bone. The canal is usually bluelined for definitive identification. From the geniculate ganglion, the labyrinthine portion of the nerve may be followed posteriorly, medially, and inferiorly. past the ampullated end of the superior canal as it turns deep into the anterior superior ponion of the internal auditory canal (Fig. 468). With adequate thi.rrn,me of bone o -er the medial end of the facial nen-e. one can identiLS-the shelf of borae ttrat separates the superior vestibular nen:e as it enters the superior ampulla next to the facial nen€. This [s Bill's bar tFig. 46C]-

Lanrlrnerks:

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Greater superfi cial p€trosal nerve Geniculate ganglion Superior semicircular canal Epitympanum

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Internal auditory canal

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Figure 468 Cochleariform process \\ !'acralnerue Faciat nerue

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Eustachian tube

Figure 46C Greater superflcial petrosal neffe

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Deep Dissection

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Du_ring blue-lining of the internal auditory canal, the exposure ma1-be widened as the posterior fossa is approached. This is possible teciuse the cochlea lies anteriorly and laterally under the geni-date ganglion, and the superior canal turns more posteriorly away from the area of ttre internal auditory canal as the posterior fossa is reached. Because the internal auditory canal can be widely exposed and well delineated, there is no reason to work under a bony shelf when enterin$ the canal, and the same principle for wide exposure in the posterior approach to the canal is used here. Medial to the internal auditory canal is the petrous apex, which is frequently filled with open air cells. Anterior to these apex cells and anterior to the cochlea is the carotid artery. The middle fossa approach can be used for ligation or packing of the medial portion of the carotid artery in uncontrolled bleeding. Laterally the eustachian tube extends from the middle ear cavity forward medial to the middle meningeal artery and lateral to the carotid artery as the tube descends into the nasophar5mx.

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Topography or a Middle ear procedures can be practiced throu$h a canal approach patient'^ ttre in as bone as easily fostauricul,a, approach on the temporal wifh actual operating t*T surgeon the familiarize will ih"". techniqu^es *o:tpio".a,tt. ..t& in"r."se dexterity in procedures--that.are among qt in bone temporal ilmanAing of the otologist's armamentarium. With the placed a speculum the surgicil position, tfre dissector o-peratesthrough the within the external auditory canal. The skin in the canal and and does leather like tympa.ri" membrane of prelerved bones tends to be are bones not simutate the feel of st
r,l Landmarks: Zygomatic root Sbi"; of Hente I\{astoid tip 'i'*p."i""i"g

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An injection of the vascular strip should be attempted to define this area of thickened posterior canal wall soft tissue. The injection will expand the soft tissue between the tympanosquamous and qTnpanomastoicl suture lines. They are prime landmarks for making incisions in an overlay graft technique. Tympanomastoid and t5rmpanosquamoussuture line incisions should then be made with a #1 knife. The incisions should be connected medially along the annulus with a #2 knife and laterally along the bony cartilaginous junction with a scalpel. The sleeveof canal skin which is then removed is the same as in the standard overlay technique. It is removed with a round knife that is constantly kept against bone to avoid perforations of the very thin canal skin. The epithelial layer of the tympanic membrane is removed en bloc with the canal skin preserving the underlying fibrous layer. Then enlargement of the external auditory canal for excision of exostoses,for the lateral graft technique, or for canaloplasty can be practiced. The dissector should also practice suctioning against the instruments, not the soft tissue, to prevent trauma to flaps and other soft tissue structures.

Lanrlrnarks:

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Bony-cartilaginons junction Vascular strip \rmpanosquernous suture suture [mpanomastoid Annulus flbrosis Malleus

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RemovingAnterior GanalBulge In the lateral graft technique, the anterior canal wall bulge overtying the glenoid fossa is usually removed.-superiorly, just anterior to the to achieve a [tmpanosquamous suL.re line, the excess bone is r,emoved to the level calal auditory external coi.to.lt from the cartilaginous that "-obtn prevent blunting helps of the annulus. This bony removal occasionally occurs with this technique. The removal also allows one to determine how deep the temporomandibular joint actually lies without entering the joint iapsute" B-oneis-then removed inferiorly anterior to the tympan"omasioid suture, again to form a smooth contour from the cartitaginous external audi-tory canal to the level of the annulus' This eliminltes any overhang that might prevent adequate visualization of the sulcus inferiorly. These-two areas of bone removal are then connected across the anterior canal wall bulge. usually the chance of entering the temporomandibular joint is minimal since the depth of the joint tras been established. Ultimat6ly, enough bone should be removed so that in a transcanal view throtrgh the microscope, the entire annulus can be observed. There shouli be no need to readjust the microscope to see the anterior sulcus and the posterior anmrlar area'

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After the anterior canal wall bone is removed. the annulus mav be elevated posteriorly in a standard nrnpanoplasq- approach. The n'rnpanic membrane is then folded forward to expose the middle ear structures. Now it is worthwhile to do a standard stapedectomy to become familiar with middle ear structures. During palpation of the malleus, one should be able to see movement of the stapes footplate along with the ossicular chain and. if fluid remains in the inner ear, a round window reflex can be obtained. Observe the.topography of the promontory and note that Jacobson's nerve usually crosses the promontory in a bony groove or canal. Several branches of the tympanic plexus, which includes this nerve, can be seen. The scutum should be curretted for exposure. One can now incise the incudostapedial joint, cut the stapedial tendon, and attempt to fracture the superstructure of the stapes onto the promontory. Unfortunately, in a cadaver bone, these steps will normally result in complete avulsion of the stapedial footplate with its superstructure. One may then practice placing various prostheses upon the incus as in standard stapedectomy. This tympanotomy approach is also used for insertion of an incus replacementprosthesis around the malleus in cases in which the incus is missing follorving a pre-'-io*ss:a:eie,::::lr'"

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The incus is removed by insertion of a three-millimeter hook in tlle incudomalleal joint and rotation of the hook so that tlee ossicle is brought out through the ear canal. A myringoplasty knife is used to incise the mucosa and fibrous attachments to the malleus from the underside. A tunnel is made under the mucoperichondrium of the malleus handle so that the incus replacement prosthesis (I.R.P.) hook can be placed over the malleus without perforation of the tympanic membrane. The loop end of the I.R.P. is then rotated into the oval window. With use of smooth alligator forceps to stabilize the wire, a hook is used to pull the wire into a crimped position around the malleus.

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Another procedure that can be performed is transcanal labyrinthectomy in the oval and round windows. The stapes is removed and the round and oval windows are connected with use of a small burr. This larger opening allows insertion of a three-millimeter hook into the vestibule to remove the ampullae of the semicircular canals.

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We begin the canal wall down (open cavilv) procedures in the same manner as the intact canal wall operations: with the postauricular approach. The essential difference between the two procedures is removal of the posterior bony canal wall. Thus, you may use a bone wittr a completed intact canal wall for this dissection.

The usual problems with open cavity mastoidectomy are incomplete removal of the posterior.canal wall and poor meatoplasty. An incompletely removed buttress or a poorly lowered facial ridge frequently leads to cicatrix formation, which further reduces cavity access. Incomplete cleaning of the cavity is the usual consequence, and new cholesteatoma may form.

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Step 2 tFigs,59, 6O, 611: Removingthe Posterior GanalWall If you are using a fresh temporal bone, proceed through a standard posterior approach to identiff a thinned posterior bony canal wall, ttre skeletonized sigmoid sinus posteriorly, a thinned middle fossa dural plate, and the prominence of the horizontal (lateral) semicircular canal. The fossa incudis and horizontal semicircular canal are then used to begin dissection of the facial recess. The floor of the recess, which is the lateral watl of the fallopian canal at the external genu, will be the most medial part of the dissection. The anterior buttress is that bone where the posterior bony canal wall meets the tegmen. Remove it totally to achieve a smooth continuum between the middle fossa tegmen and the middle ear epit5rmpanic tegmen. The posterior buttress is where the posterior canal wall meets the floor of the external auditory canal lateral to the facial nerve. This area is especially prone to cicatricial blunting and, if not opened well. will result in a deep "blind" pocket at the mastoid tip. The best rva]'to eliminate the area of the posterior buttress is to lower the facial r,idge br skeieroruzring the facial nerye latera[v. Then t]re floor of the external auditory" carral slopes off into ttre mastoid tipAll bone lateral to ttre facial nerve betrcen tlre tqmen and the floor of the external auditory canal is removed to eliminate ttre posterior bony-cenal wall. The remainder of ttre mastoid bowl should be well saucerized, which in actual surgery allows soft tissue to better obliterate and shrink the remaining open @vity.

Landrnarks: Posterior canal wall Incus Facial nerve Horizontal semicircular canal Buttresses (anterior and posterior)

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The flnal step to insure access to the open cavity is adequate soft tissue meatoplasty. This manual does not describe this technique but emphasizes its importance and encourages you to review relevant references and videotaPes.

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ampulla of horizontal semicircular canal. Fig. 3a of posterior semicircular canal, Fig. 38 of superior semicircular canal, 586O, 62, 64, 7O: Fig. 3&42 annular ligament, 4l annulus, 21, 42, 76, 74, aO annulus fibrosis, 42,44: Fig. 30-31,50-51,59 anterior buttress, 60, 86, 88; Fig. 58, 6O anterior canal bulge, 78-79; Fig. 5l anterior canal wall, 8O anterior crus, fig. 52 anterior stapedial crus, Fig. l5 ant rum, 9 , ll, 1 4, 16 ,20 , 4a arachnoid, 4O arcuate eminence, 68; Fig. 45A articular process, Fig. fb articular surface, Fig. 60 attic, 25 auditory canal (external), see external auditory canal auditory nerve, 62, 64 auricle, 48

digastric muscle, \4, 29: Fig. f 2, 18,20,22,24 digasrric ridSle, 14; Fig. 8, I Donaldson's line, 38; W 2:5 dural pl,ate ,l8. S.52,6{), middle fossa,

B barber pole, 3l Beaver knife I#591, 34 Bill's bar, 58, 64, 70,72; Fig; 4H4,4eC body of the incus, 26; Figl. la bone wedge, 59; Fig. 4O bony-cartiliganous junction, 76; Fig. 50 bony fallopian canal, 38 bony operculum, 52 buttress, 23-24, a6: Fig. 13-14, 19-21,23,31 anterior, 60, 86, 88; Fig. 58,60 posterior, 88; Fig. 59 of incus, 4l; Fig. 28-3O posterior, 88; Fig.59

c canal of tensor tympani, Fig. 16, 33 canal skin, 74, 76 canal wall (posterior), sie posterior canal wall canaloplasty, 76 capitulum of the stapes, 23: Fig. 52 carotid artery, 41, 44,72: Fig. 31-32 carotid siphon, 72i Fig. 47 cerebrospinal fluid, 6O cholesteatoma,20, 24-26, 4l-42 chorda tympani, 16, 20-22, 29, 3L, 4l-42: Fi$. 10, 12-13, 15, 16-20, 22, 24, 28-29, 52-53 chronic otitis media, 25, 3O cochlea, 41, 72; Fig. 454, 46C, 47 cochlear aqueduct, 6O; Fi€;. 41 cochlear nerve, Fig. 44,454 cochleaiiform process, 23, 29-3 I, 7O; Fig. 15, 16, 19 , 3 3, 4 6C,6 r cog,26t Fig' 16 common crus, 52, 54; Fig. 36, 38 cranial nerves, 60 craniotomy window, 68 crimper, Fig. 53 crista. see transverse crest crot ch.4 l. 4 4

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eleventh cranial nerve, 60 elliptical recess ofutricle, 54; Fig. 37 endolymphatic duct, 39, 52,54; Fig. 36, 38 endolymphatic sac, 14, 38-40, 52: Frg. 25-27,36 epitympanic tegmen, middle ear, 88 epitympanum, I I, 14, 24, 26,68, 7O;Fig. 14, 16, 25,33 Eustachian tube, 44, 48, 68, 72; Fig. 16, 33, 46C, 6r exostoses, 76 extended facial recess, 48; Fig. 31,33 external acoustic meatus, 8 external auditory canal, 8-9, 12, 29. 48.74. 76. 88: Fig. 3.45A enernal genu -facialnere. li., 2rie2l, 29-31. 51 58" 88: Fig rr-13- 17-15"21.*i" 3S)

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fr.:i2l c-nd, 2f- 54"" 6lL 40, 6{ hcid hiatrrs;68 facial ncf,c- 16" lll 14-:11^4{4..18" 5,[. 6r, 64. 68; 8& lt" rlo. 16,2E €t. S37, t|{}.14. a[i'L€JnC.5a -barber pdlngi. 3f ZL n. 31. 3a, 41, 52, aescenCing f.etE'fl 58: @ rL l7-UL23 external gtmr. f.L 2l>21- 2[L3f , 51, 58, 88; Fig. u-r& r7-lA,21 2Il,39 xt. 23. 30'3r' 51; Fful. horiznntal gls|Ff 14,19 internal$nufl. m labyrinthine- 34- fr) mastoid s€Ecnt. 14. Uf. 3f , 34 3l- 34 middle ear s4mL sheath, 16,2l-t2" 2!1.3i135: FIE 2L,24 tympanic scgmcd- f!+ f5. L7, L9,23 facial recess, f6, 2[>25' 283f . 4f -43, 8u; Fig. 10-16, r8,za.gt (extended), se ffi frcial reccss facial ridge, 86, 88 crEst falciform crest, s€e lrarwrcrs Fallopian canal, 38,81,88: Q' 14: medial porous, 34 foramen spinosum, 68; Fig; 4!iltr{!B footplate, stapes, Fig. 55 fossa incudis, 14, 16, 20, 2a,3(), 41. 84: Fi11 8-10, 12, 20, 26-29, 3r, 57

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G geniculate ganglion, 30, 62,64, 68, 70, 72; F-ig. 464-46C.47 glenoid fossa,24,78 glomus tumors, 41-42 graft technique (lateral), 76, 78 greater superficial petrosal nerve see petrosal nerve

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tl h ardangle, 1 1 , 14 head of malleus, 25-26, 7O; Fig. 15 Henle (spine of), see spine of Henle horizontal semicircular canal see semicircular eanal hypotympanum, 4l-42, 44, 48 Fig. f 6, 30-31

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incudomallear joint, 82; Fig. 14 incudostapedialjoint, 23, 80; Fig. 13,52 incus, 16, 23-25, 30,48, 80, 82; Fig. 11, 13-14, L9-21, 23,28-31, 34-36, 464, 46C, 54, 58-59 body of, 26; Fig. 18 buttress, 3O, 41; Fig. 10-12,29-30 lenticular process, 23; Fig. 14, 19 long process,3O; Fig. L2,18,52 replacement prosthesis, Fig. 56 short process. 23 internal auditory canal, ll, 50, 58-64, 70,72; Fig. 39-44,468 "blue-lined", 60, 70, 72t Fig. 4l inferior border, 6O, 62; Fig. 39-40 posterior superior, 6O superiorborder, 62; Fig. 39-40 dura, Fig. 42 internal carotid artery, see carotid artery internal genu offacial nerve, 64 J

manubrium, Fig. 16, 52-53, 55 mastoid. 8, 70, 88 antrum, see antrum cavTty,12,21, 4l cortex 9-1O, 14; Fig. 5,34 process, 8; Fig. 3 t ip , 9 - 1 2 , 1 4 , . 1 6 , 3 9 , 4 4 , 8 8 ; F i g . 4 - 7 , L O - L I , 18, 24-25, 34, 454, 44, 57 meatoplasty, 86, 88 middle ear cavity,20,72 dissection. 74-83: 48-56 middle fossa. 12, 34 approach, 68-72: Fig. 45-47 dural plate (tegmen tympani), ll-12, 14,25, 48, 50, 52, 60, 88; Fig. 6 middle meningeal artery, 68, 7O, 72; Fig. 464 my'ringoplasty knife, Fig. 55

1{ nasopharynx, 72 ninth cranial nerve, 6O

o occiput. l2 operculum (bony), 52 ossicles. 25, 82: Fig. l7 ossicular chain, 3O, 70, 80 otic capsule, 14 oval window, 82; Fig. 56 overlay graft technique, 76 P

Jacobson's nerve, 80; Fig. 15, 33 j ugularbulb, 12 , 14 ,38 , 4l- 42, 44, 48, 60; 3r-33,4L-42 jugulocarotid septum, see crotch jugulocarotid spine, see crotch

Fig.

K Koerner's septum, lO, 14; Fig. 5 L labyrinth, 5O-51, 62; Fig. 34,37 labyrinthectomy, 50-55, 68,74,86; Fig. 34-38 transcanal, 82 labyrtinthine bone, 14, 39, 50, 52,59-60,70 lateral graft technique, see overlay graft technique lateral sinus, see sigmoid sinus le:iticular process of incus, see incus ligament of short process, Fig. f 4 linea temporalis, I 1-12 long process of incus, see incus long process of malleus, see malleus

T Macewen's triangle, 8, 9; Fig. 3-4 maculae of utricle and saccule, 54 nalleus, 48, 70,78, 80, 82; Fig. 46A, 46C, 51, 54, 58-59 handle (mucoperichondrium), see malleus, 'nanubiium her.l 24: Fig. f4-15 i-'-r:,Er ccess, 26 short Process, Ffu' 49

peritubular cells, Fig. 16 petrosal nerve (superficial, greater), 68, 70; Fig. 45A-458, 464' 46C, 47 petrosal sinus inferior, 44 superior, 12,59-60,68 groove, Fig. 45A petrosquamous suture line, 14 petrous apex, 14, 26, 60, 72; Fig. 45A, 47 petrous bone, 58 porus acusticus, 58, 6O, 64; Fig. 4L-43,47 posterior approach, 88 posterior canal wall, 9-12, 14, 21, 25,28, 38-39, 4t, 48,50, 88; Fig. 5-r3, 14, L7-2L, 24-28, 3r,34-35, 38, 57-6r posterior crus, Fig. 52 posterior fossa, 12, 68, 72 dural plate, 12, 14,38, 41, 52, 58-6O;Fig. 40.42 promontory, 23, 8O; Fig. 13, 15-16,33,53 pyramidal process, 23; Fig. 13, 15-16, 29, 32,6L

R retrofacial area, 38. 41 retrofacial cells, 39, 44 Fig. 25-27, 3l-32 retrofacial recess,38, 4l Rosen needle, 32: Flig.2L-22 round window, 20,23,82; Fig. 13, 15, 32

s saccule, spherical recess, 54; Fig. 37 scutum, 24, 8O; Fig. 53-54, 58

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H semicircular canal ampulla, 59-60, 64, 70: Fig. 4O-42 horizontal, 14, f6, 25,2a' 3f' 38' 51' 88; Fig. 8-13, 15-16, 18, 2oi2L,23,2,5-3L, 35-36, 57-5a,6r posterior, f6, 38, 51-52, &1; Fig.9,12,18' 20-2t, 2*27. 32, 3+35, 38 superior 24,50.-52,68,72; Fig. 35-36, 38, 454.47 shunt tube. 40; Fig.27 sigmoid sinus, lO, 12, 14,38-39, 44, 59-60, 88; Fig. 7, I, lO-12, 18, 24-27,32, 34, 39, 4r, 57-58 plate, 12, 14 singular nerve, 64; ?ig. 42,44 sinodural angle, 9-12, 14, 50, 58-6O; Fig' 6-8, 10, 24-27, 34,39, 4r,57 skull base, 44 snake eyes, 52 spherical recess of saccule, 54; Fig. 37 spine of Henle, 8-9, 12, 14; Fig. 3-4,48 spine (suprameatal), see spine of Henle squamosa, 68 stapedial tendon, 23, 80; Fig. 13, 15,31 stapes, 23-24, 30, 41, 48,82; Figl. l2-L3, L4' 18-19,21, 28-29, 3r,46A, 54, 60 capitulum, 23i Fig.52 footplate, 54, 8O superstructure, 80 wire, Fig. 53 sternocleidomastoid muscle, 8 styloid process, Fig. 454 stylomastoid foramen, 14, 29,3f ; Fi41 l7-aA,m' 2 2.2 4 subarcuate artery, 52; Fig' 36,3&4O subarachnoid space, 40 subperiosteal abcess, 8 sulcus (anterior), 78 superior ligament, Fig. 14-f5 suprameatal spine (of Henle), see spine of Henle

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Y v'asculirr strip. 76: Fig 49,5f vertical s€st- s€e Bill's bar v.estibular nerrte; 6O, 62. 8[ inferior, ltg. +%aa superior, 6.2, 64,72: Flg. 4244,4dC' vestibule, 50-54, 58, 82; Fig. 39-41"t6A

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T tegmen tympani, LO-LI,24,30, 48' 6O, 88; Fig. 5-6, 8-10, 12-16, 19, 23, 25-27, 30' 32-36. 39, 4L-42, 45A, 57-58' 60 temporal line, 8-9; Fig. 3-'1 temporalis muscle, 8 temporomandibular joint, 48' 78; Fig. 33 temporoparietal suture, Fig. 45A tensor ty'rnpani, canal, Fig. 16, 33 tenth cranial nerve, 6O tentorium, 68 transcochlear approach, 41 translaby'rinthine approach, 4l' 64 transverse crest, 64: Fig' 42-44 transverse sinus, 59 tympanic membrane, 20,22' 4l-42' 4a.74' 76' 80, 82; Fig' 17,30 tympanic plexus, 80 tympanic fir:g, 44,48; Fig' 33' 48 tympanic Sleeve,Fig. 33 ty"rnpanomastoid suture, L4' 76' 78; Fig;. 5O tympanomeatal flaP, Fig. 52-54 qrmpanosquamous suture, 76, 78: Fig. 50

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