Traumatic Facial Nerve Paralysis

Traumatic facial nerve paralysis is the second most common cause of facial paralysis after idiopathic Bell palsy. Etiology categories: (1) Temporal bone fractures: longitudinal fractures (70-90% of all temporal bone fractures, parallel to long axis of petrous bone, usually from temporoparietal blows, facial nerve injury in 10-25% — typically perigeniculate or labyrinthine segment), transverse fractures (less common 10-30%, perpendicular to long axis, from frontal or occipital blows, facial nerve injury in 30-50% — at internal auditory canal or labyrinthine segment, often more severe), oblique/mixed fractures (most common in modern classification, intermediate severity). (2) Penetrating trauma: gunshot wounds, stab wounds, glass injuries to face or temporal area; injury can occur at any segment but extratemporal segment most accessible. (3) Iatrogenic injury: parotidectomy (most common surgical cause, 0.5-5% transient, less than 1% permanent), mastoidectomy/middle ear surgery (0.6-3.6%), acoustic neuroma resection, parotid bed surgery, mandibular surgery, facelift surgery. (4) Birth trauma: forceps delivery, prolonged labor, prematurity (peripheral facial weakness in newborn — usually transient).

Pathophysiology and Sunderland classification of nerve injury: (1) Neurapraxia (Sunderland I): conduction block without axonal injury, complete recovery within days to weeks. (2) Axonotmesis (Sunderland II-IV): axonal injury with intact endoneurium (II), perineurium (III), or epineurium (IV); Wallerian degeneration distal to injury, recovery via axonal regrowth (1 mm/day) with variable completeness. (3) Neurotmesis (Sunderland V): complete nerve transection, no spontaneous recovery, requires surgical repair. House-Brackmann grading clinically: I (normal), II (mild dysfunction), III (moderate, complete eye closure with effort), IV (moderately severe, incomplete eye closure), V (severe, barely perceptible motion), VI (total paralysis). Onset timing is critical prognostically: immediate complete paralysis suggests nerve transection or severe injury at impact (worse prognosis), while delayed-onset paralysis (within 24-72 hours) suggests progressive edema or hematoma compressing nerve in bony canal (better prognosis with conservative therapy or limited decompression).

Workup: high-resolution non-contrast temporal bone CT (1 mm slices) is the imaging modality of choice for all temporal bone trauma — identifies fracture patterns, otic capsule involvement (otic capsule-violating versus otic capsule-sparing classification, with violating fractures having higher rates of facial paralysis, hearing loss, and CSF leak), facial nerve canal involvement, ossicular discontinuity, and CSF leak. MRI for soft tissue visualization, suspected nerve hematoma, or atypical cases. Electrodiagnostic testing is critical for prognosis and surgical decision-making in immediate-onset complete paralysis: nerve excitability test (NET) and minimal nerve excitability test (MNET) early; electroneuronography (ENoG) is the gold standard between days 3-21 (compares amplitude of compound muscle action potential on injured side versus uninjured side — more than 90% degeneration within 14 days indicates surgical decompression); electromyography (EMG) after day 14-21 detects fibrillation potentials (denervation) versus volitional motor unit potentials (preserved or recovering function). Audiometry to document hearing status. Treatment: immediate-onset complete paralysis with more than 90% degeneration on ENoG within 14 days is the indication for surgical decompression — middle cranial fossa approach for labyrinthine and perigeniculate segments (most common injury location), transmastoid approach for tympanic and mastoid segments. Delayed-onset paralysis is treated with corticosteroids (prednisone 1 mg/kg/day for 7-10 days, then taper) and observation; recovery rate exceeds 90%. Penetrating injuries with transected nerve require immediate primary anastomosis (ideal) or cable nerve grafting with sural or great auricular nerve. Iatrogenic transection during surgery should be repaired immediately. Delayed reconstruction (more than 12 months) options: hypoglossal-facial nerve transfer (XII-VII), masseteric-facial nerve transfer (V-VII), cross-facial nerve grafting; static slings (temporalis transfer, fascia lata, palmaris longus) and dynamic procedures (gracilis free flap with masseteric or cross-facial neurotization) for long-standing complete paralysis. Adjunctive measures: artificial tears, taping eye closed at night, lateral tarsorrhaphy, gold weight implant, lower lid procedures for paralytic ectropion.