Operative Technique

After anesthesia induction and patient positioning, the postauricular incision is injected with 1% lido-caine with 1:100,000 epinephrine. The patient is prepped and draped as if for a tympanomastoidec-tomy. A No. 15 Bard-Parker blade is used to incise 0.5 cm posterior to the postauricular crease while palpating the mastoid tip to avoid excessive inferior dissection. The No. 15 blade is used to cut until the temporalis muscle superiorly and mastoid periosteum inferiorly is encountered. Blunt finger dissection is used over the top of the temporalis muscle to increase exposure. A No. 15 blade is used to incise the deep temporalis fascia, or true fascia, until muscle fibers are revealed beneath. Using a Brown-Adson and iris scissors, a 1.5-cm-square area of fascia is harvested. Two sets of fascia are trimmed into two different sizes in advance that are appropriately sized for packing the PSCC. A standard T incision is made in the mastoid periosteum, and it is elevated. Preparation of the fibrinogen glue should commence in anticipation of its use. A simple mastoidectomy is performed exposing the horizontal semicircular canal (HSCC) and PSCC. Thinning of the tegmen and development of the digastric ridge

Donaldson Line
FIGURE 26-1 Donaldson's line along the plane of the horizontal semicircular canal (HSCC). D, Donaldson's line; E, epitympanum; EAC, external auditory canal; PCW, posterior canal wall; PSCC, posterior semicircular canal; SS, sigmoid sinus.

are unnecessary. Donaldson's line, which is a line drawn through the HSCC extending posteriorly, is identified (Fig. 26-1). This line bisects the PSCC in the middle of the area to be exposed.

The posterior half of the PSCC is identified and outlined with a diamond bur. A 1- or 2-mm diamond bur is then used to create a 5-mm bony island in the

Posterior Semicircular Canal Occlusion

CHAPTER 26 POSTERIOR SEMICIRCULAR CANAL OCCLUSION

middle of the exposed PSCC by blue-lining the canal around the bony island. It is critical that the membranous labyrinth be kept intact (Fig. 26-2). Set the suction aside and switch to neurosurgical cottonoids for blotting. Gently remove the bony island with a 90-degree hook while not violating the membranous labyrinth (Fig. 26-3). Often, the membranous labyrinth partially collapses with wick-ing. Select the appropriate-sized temporalis fascia piece and mix with one to two drops of fibrinogen glue. It will begin to get sticky and malleable, and then is ready for packing. Now pack the exposed ends of the PSCC with temporalis fascia atraumatically (Fig. 26-4). The intervening PSCC between the packed ends should be drilled away (Fig. 26-5). The remaining pieces of temporalis fascia are draped over the exposed packed ends of the PSCC. Several drops of fibrinogen glue are placed on the draped temporalis fascia. The soft tissues are closed and dressing applied per surgeon preference.

FIGURE 26-3 (A,B) Removal of bony island while preserving the membranous labyrinth.

FIGURE 26-4 Plugging the posterior semicircular canal (PSCC) with temporalis fascia and fibrinogen glue.

FIGURE 26-5 Removal of the intervening PSCC remnant.

FIGURE 26-3 (A,B) Removal of bony island while preserving the membranous labyrinth.

FIGURE 26-4 Plugging the posterior semicircular canal (PSCC) with temporalis fascia and fibrinogen glue.

FIGURE 26-5 Removal of the intervening PSCC remnant.

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