Facial Recess, EpitympanumStep 1 (Fig. 10)TopographyThe facial recess is a collection of air cells lying immediately lateral to tho/'facial nerve at the external genu. It occasionally serves as a route formiddle ear disease to extend into the mastoid area via cells other thanthe antrum. Cholesteatoma that frequently invades these cells will beextremely difficult to remove via standard trans canal approaches. We feelthat opening of the facial recess in any chronically diseased ear is of valuein providing an additional avenue of mastoid aeration. This exposure alsoallows better visualization of the middle ear cavity in chronic ear diseaseand exposure of the horizontal portion of the facial nerve during facialnerve decompression. It is also the route to the round window for Iinsertion of the cochlear implant electrode! The landmarks used toexpose the facial recess are the external genu of the facial nerve mediallyIthe fossa incudis superiorly, the chorda tympani nerve laterally, and thetympanic membrane anteriorly and laterally./

@Chorda tympani (roof) Posterior canal wall Fossa incudis §)

Incus buttress (wall) Zygomatic root

\

Sigmoid sinusFacial nerve (floor)

TegmenHorizontal semicircular canal

Sinodural angle

Landmarks:Horizontal canalFossa incudisPosterior canal wallExternal genu of VII

'l?\ ~\})\i 0

UJ~

~~ee~~

Step 2 [Fig. 11):Opening the Facial Recess

One begins dissection of the facial recess by identifying the external genuor the'descending portion of the facial nerve in the mastoid cavity. AspreViously indicated, a free flow of irrigating fluid is used to allow clearand constant visualization of the underlying bone so that color variationsin it may be easily identified. The microscope is turned to 10 power. Thecolor of the facial nerve is pearly white in the preserved bone and pinkish(from the vascularity of the facial canal and the nerve sheath) in a livingspecimen. Generally, this dissection is accomplished with a cutting burr_until a change in bone character is identified; further dissection isperformed with a diamond burr. A thin layer of bone is preserved over thefacial nerve and, because color changes in the bone will occur before thefacial sheath is uncovered, the soft tissue is not injured.

Identification of a facial recess cell tract is often possible by thinning theposterior canal wall enough to see the shadow of an instrument throughthe bone. One must not perforate the canal wall, disrupt the chordatympani, or transect the annulus.

Posterior canal wallMastoid tip

Zygomatic root

\ Incus

ISigmoid sinus

Landmarks:Posterior canal wallHorizontal canalFossa incudisFacial recess cells (if

present)External genu

Step 3 (Fig. 12):Completing the Recess

With the new landmark of the facial sheath, the nerve is skeletonizeddistally along its descending portion in the mastoid and then medially asit follows the floor of the facial recess into the middle ear space. Smallerburrs will be necessary to accomplish most of the dissection in the facialrecess since the recess itself rarely exceeds two or three millimeters.Inferiorly the chorda tympani nerve is detected as it leaves the facialnerve. Dissection does not sacrifice this structure. The chorda tympaninerve joins with the tympanic membrane anteriorly and laterally at theannular edge; thus, following the chorda tympani generally preventsdisruption of the tympanic membrane.

Landmarks:

Facial nerveIncusFossa incudisChorda tympaniStapesHorizontal canal

Long process of incus

Buttress \) ~~VJ\ ~ VChorda tympani

Descending segment of facial nerve

Digastric mu::'e1Sigmoid sinus

StapesExternal genu

TegmenHorizontal semicircular canal

Step 4 (Fig. 13):The Middle Ear Through the Facial Recess

With the facial recess fully opened, one can easily visualize the horizontalportion of the facial nerve, the lenticular process of the incus, theincudostapedial joint, the capitulum of the stapes, the stapedial tendon,and, with proper angulation, the cochleariform process.

The round window may be easily identified inferior to the stapediallandmarks. Superiorly, a buttress of bone is preserved between the shortprocess of the incus and the facial recess. This is commonly termed "thebuttress." Drilling through the buttress causes disruption of theligaments to the short process of the incus and incudal dislocation is a /possibility ..

Posterior canal wall

!

Promontory External genu

Pyramidal process .

Landmarks:Facial nerveIncusLenticular processIncudostapedial jointStapesRound windowCochleariform processChorda tympaniHorizontal canal

Step 7 (Fig. 16):Exposure of the Anterior Epitympanum

After removal of the head of the malleus and body of the incus, thisdissection allows unimpeded inspection of all epitympanic areas. In a wellpneumatized bone, air cells extending anteriorly into the petrous apexmay also be seen.

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

Cochleariform processChorda tympani

Zygomatic root

I

HypotympanumPeritubular cells

PromontoryEustachian tube

TegmenHorizontal semicircular canal

Facial nerveCanal of tensor tympani

Pyramidal process

Landmarks:StapesFacial nerveCochleariform processLong process of malleusEustachian tubeCog