Mastoidectomy Epitympanum


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Mastoidectomy Epitympanum

  1. 1. Facial Recess, Epitympanum Step 1 (Fig. 10) Topography Landmarks: The 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 for Horizontal canal middle ear disease to extend into the mastoid area via cells other than Fossa incudis the antrum. Cholesteatoma that frequently invades these cells will be Posterior canal wall extremely difficult to remove via standard trans canal approaches. We feel External genu of VII that opening of the facial recess in any chronically diseased ear is of value in providing an additional avenue of mastoid aeration. This exposure also allows better visualization of the middle ear cavity in chronic ear disease and exposure of the horizontal portion of the facial nerve during facial nerve decompression. It is also the route to the round window for I insertion of the cochlear implant electrode! The landmarks used to expose the facial recess are the external genu of the facial nerve mediallyI the fossa incudis superiorly, the chorda tympani nerve laterally, and the tympanic membrane anteriorly and laterally./ @ §) Posterior canal wall Fossa incudis Chorda tympani (roof) Incus buttress (wall) Zygomatic root 'l? ~})i 0 UJ~ ~~ee~~ Tegmen Sigmoid sinus Horizontal semicircular canal Facial nerve (floor) Sinodural angle
  2. 2. Step 2 [Fig. 11): Opening the Facial Recess One begins dissection of the facial recess by identifying the external genu Landmarks: or the'descending portion of the facial nerve in the mastoid cavity. As Posterior canal wall preViously indicated, a free flow of irrigating fluid is used to allow clear Horizontal canal and constant visualization of the underlying bone so that color variations Fossa incudis in it may be easily identified. The microscope is turned to 10 power. The Facial recess cells (if color of the facial nerve is pearly white in the preserved bone and pinkish present) (from the vascularity of the facial canal and the nerve sheath) in a living External genu specimen. Generally, this dissection is accomplished with a cutting burr_ until a change in bone character is identified; further dissection is performed with a diamond burr. A thin layer of bone is preserved over the facial nerve and, because color changes in the bone will occur before the facial sheath is uncovered, the soft tissue is not injured. Identification of a facial recess cell tract is often possible by thinning the posterior canal wall enough to see the shadow of an instrument through the bone. One must not perforate the canal wall, disrupt the chorda tympani, or transect the annulus. Zygomatic root Posterior canal wall Mastoid tip Incus I Sigmoid sinus
  3. 3. Step 3 (Fig. 12): Completing the Recess With the new landmark of the facial sheath, the nerve is skeletonized Landmarks: distally along its descending portion in the mastoid and then medially as Facial nerve it follows the floor of the facial recess into the middle ear space. Smaller Incus burrs will be necessary to accomplish most of the dissection in the facial Fossa incudis recess since the recess itself rarely exceeds two or three millimeters. Chorda tympani Inferiorly the chorda tympani nerve is detected as it leaves the facial Stapes nerve. Dissection does not sacrifice this structure. The chorda tympani Horizontal canal nerve joins with the tympanic membrane anteriorly and laterally at the annular edge; thus, following the chorda tympani generally prevents disruption of the tympanic membrane. Long process of incus V Buttress ) Chorda tympani ~~VJ ~ Descending segment of facial nerve 1 Stapes Tegmen Digastric mu::'e Horizontal semicircular canal External genu Sigmoid sinus
  4. 4. Step 4 (Fig. 13): The Middle Ear Through the Facial Recess With the facial recess fully opened, one can easily visualize the horizontal Landmarks: portion of the facial nerve, the lenticular process of the incus, the Facial nerve incudostapedial joint, the capitulum of the stapes, the stapedial tendon, Incus and, with proper angulation, the cochleariform process. Lenticular process Incudostapedial joint The round window may be easily identified inferior to the stapedial Stapes landmarks. Superiorly, a buttress of bone is preserved between the short Round window process of the incus and the facial recess. This is commonly termed quot;the Cochleariform process buttress.quot; Drilling through the buttress causes disruption of the Chorda tympani ligaments to the short process of the incus and incudal dislocation is a / Horizontal canal possibility .. Posterior canal wall ! Promontory External genu Pyramidal process .
  5. 5. Step 7 (Fig. 16): Exposure of the Anterior Epitympanum Landmarks: After removal of the head of the malleus and body of the incus, this dissection allows unimpeded inspection of all epitympanic areas. In a well Stapes pneumatized bone, air cells extending anteriorly into the petrous apex Facial nerve may also be seen. Cochleariform process Long process of malleus The figure shows the expansive exposure obtained with this technique. Eustachian tube Note the cog. a bony ledge extending into the epitympanum from the Cog 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. Cochleariform process Zygomatic root Chorda tympani I Hypotympanum Tegmen Horizontal semicircular canal Peritubular cells Facial nerve Promontory Eustachian tube Canal of tensor tympani Pyramidal process