HSC Section 3 - Trauma, Critical Care and Sleep Medicine

Surgical Management of Acute Facial Palsy

piece of temporoparietal fascia is harvested for later use before retracting the tempo- ralis muscle anteriorly. An anteriorly based temporalis muscle flap is elevated from the outer cortex of the skull. A 4 4 cm craniotomy centered over the zygomatic root is then performed with cutting and diamond burrs. The bone flap is dissected from the temporal lobe dura with attention paid to the middle meningeal artery, which may be encased within the bone. Under magnification, the dura is elevated from the MCF floor in a posterolateral to anteromedial direction. The limits of exposure are the petrous ridge posteromedially and the foramen spinosum anteriorly; the middle meningeal artery may be sacrificed if necessary for adequate exposure or temporal lobe retraction. The arcuate eminence and greater superficial petrosal nerve (GSPN) are identified. The GG is dehiscent 5% to 15% of the time. 43–46 As elevation proceeds anteromedially along the petrous ridge, a lip of bone is usually encountered that denotes the approximate location of the porus acosticus. A House-Urban retractor is placed to retract the temporal lobe with the retractor blade tip carefully placed at the medial margin of the petrous ridge. The superior semi- circular canal (SSCC), which is always perpendicular to the petrous ridge, is identified by blue lining, taking note of the transition from the membranous bone of the mastoid to the yellow-white, dense bone of the otic capsule. Identification of the SSCC allows localization of the IAC, cochlea, GG, and tympanic cavity. The meatal plane is then drilled to identify the IAC, which is skeletonized frommedial to lateral. A rim of bone at the porus acosticus may be kept intact to prevent slippage of the retractor blade. As the dissection advances laterally, the IAC courses lateral and cephalad. Using the blue-lined SSCC as a guide, the labyrinthine segment is approached, taking care to avoid the SSCC ampulla and vestibule posteriorly and the cochlea anteriorly. Once the meatus of the labyrinthine segment has been identi- fied at the Bill’s bar, the bony canal is removed from the meatal foramen to the GG, which is triangulated by the courses of labyrinthine segment, GSPN, and tympanic segment. The tympanic segment may be visualized by opening the epitympanum with the drill, taking care to avoid injury to the head of the malleus. Bone removal over the labyrinthine segment is approximately 90 of the canal. This limited exposure provides decompression while reducing the risk of inadvertent injury to the basal turn of the cochlea, which is less than 1 mm anterior and inferior to the labyrinthine segment of the nerve, and the SSCC ampulla posteriorly. The bone over the GG is then removed ( Fig. 6 ). The fallopian canal should be opened to the cochleariform pro- cess ( Fig. 7 ). A very thin layer of bone should be left over the course of the nerve until the entire nerve is exposed. This entire bony layer is then removed with a small right- angled hook or Fisch nerve dissector. Following removal of bone from the nerve, a microscalpel (Beaver no. 59-10) is used to open the dura of the IAC from proximal to distal. The tight arachnoid band at the meatal foramen is then incised ( Fig. 8 ). Following nerve decompression, intraoperative EEMG is performed. A facial nerve stimulator, such as a Prass probe or Parsons-McCabe facial stimulator, is used to locate the exact site of conduction block. The scrub nurse should visualize the fore- head, eye, mouth, and chin to serve as a backup to intraoperative EMG. The tympanic segment is stimulated first to ensure that a signal can be obtained distally. If so, the intracanalicular, labyrinthine, and geniculate segments are then stimulated to locate the conduction block. Although rare, stimulation failure of the proximal tympanic segment indicates a conduction block more distally. The postauricular limb of the skin incision may then be extended inferiorly and a concurrent transmastoid approach may be undertaken for decompression of the distal tympanic and descend- ing segments.

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