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Facial Nerve Decompression and Repair
Elizabeth H. Toh and Barry E. Hirsch
The primary goal of facial nerve decompression with or without repair is to optimize functional recovery following facial nerve trauma or inflammation. Decompression is offered only when surgery improves functional outcome relative to observation and medical management alone.
- Electrical testing of the facial nerve Electroneurography (ENoG) and electromyography (EMG) are used to determine surgical candidacy when no clinical function is appreciable with Bell’s palsy and with immediate facial paralysis following temporal bone trauma. Between days 3 and 10 following onset of complete paralysis, if ENoG testing indicate 10% or less muscle function on the affected side relative to the normal side, and voluntary motor unit action potentials are absent on EMG testing, surgical decompression may be offered.
- Temporal bone imaging High-resolution axial and coronal CT imaging of the temporal bone using bone algorithms is indicated primarily for temporal bone trauma. Magnetic resonance imaging (MRI) of the facial nerve is used to diagnose facial nerve tumors, which generally present with progressive facial palsy, with or without hyperkinesis.
- Systemic steroids Usually administered upon initial diagnosis of acute facial palsy (prednisone 1 mg/kg/day for 10 to 14 days).
- Eye care The affected eye should be aggressively lubricated and protected at the time of initial diagnosis and continued until adequate eye closure is achieved.
The choice of approach is determined by location of injury and hearing status in the affected ear.
- Used to explore the facial nerve at and proximal to the geniculate ganglion in a hearing ear (Bell’s palsy, temporal bone trauma, facial neuromas). Patients over 60 years of age are poor surgical candidates for this approach since they tend to have thin dura which tears easily with dissection, and do not tolerate prolonged temporal lobe retraction.
- The operating table is rotated 180 degrees away from anesthesia. The surgeon is seated at the end of the operating table across from the anesthesiologist and the operating microscope and scrub nurse/technician on either side of the patient. The patient should be secured to the operating table, and the endotracheal tube to the patient.
- The patient is positioned supine with the head turned such that the operated ear is facing up.
- Intraoperative facial nerve monitoring (in case distal facial nerve stimulation is performed intraoperatively) and auditory brainstem response monitoring is set up at the beginning of the procedure.
- Perioperative medications administered at induction include broad-spectrum antibiotics with good cerebrospinal fluid (CSF) penetration (ceftriaxone), Lasix 20 mg, mannitol 0.5 mg/kg, and dexamethasone 10 mg.
- A 4 × 5 cm craniotomy is marked on the skin, centered two thirds anterior and one third posterior to the external auditory canal, and based inferiorly on the root of the zygoma (approximate level of middle fossa floor).
- The skin incision is begun in the preauricular crease at the level of the lower border of the zygoma, then extended superiorly above and behind the auricle to form a reverse question mark which extends superiorly to the upper craniotomy border. Anterior and posterior skin flaps lateral to the temporalis fascia are elevated to expose the temporalis muscle.
- An anteroinferiorly based temporalis muscle flap is created by incising the muscle along linea temporalis using Bovie electrocautery.
- A craniotomy measuring 4 × 5 cm is created in the location described above, using a 4 mm cutting burr or craniotome. The bone flap is then carefully elevated from underlying dura using a blunt dural elevator and soaked in bacitracin solution until the end of the procedure. Any bleeding from the dura at this point may be controlled with bipolar electrocautery. The inferior border of the craniotomy is lowered to the level of the middle fossa floor using a drill or rongeur.
- Dura is then carefully elevated off the middle fossa floor in a posterior to anterior direction to expose the anatomy illustrated in Fig. 28–1
