Gamma Knife Radiosurgery-Induced Acute Facial Palsy in Vestibular Schwannoma: A Case Report.

Stereotactic radiosurgery (SRS) is an established treatment for vestibular schwannoma, offering high tumor control rates and a favorable safety profile. SRS-induced facial palsy is typically a late-onset complication, with acute-onset cases being exceedingly rare. We report the case of a 42-year-old man with a left-sided Koos grade I vestibular schwannoma who underwent single-fraction Gamma Knife radiosurgery with a prescription dose of 11 Gy to the 50% isodose line. Baseline facial nerve function was intact. Seventy-two hours post-treatment, the patient developed House-Brackmann (HB) grade V peripheral facial palsy, accompanied by severe vestibular symptoms. Magnetic resonance imaging obtained on post-treatment day 6 demonstrated reduced contrast enhancement, partial capsular breakdown, and central hypointensity within the tumor, suggestive of acute necrotic change. Vestibular symptoms improved rapidly following corticosteroid therapy; however, facial palsy recovery was gradual, improving to HB grade II at 12 months, with persistence at final follow-up (20 months). The tumor remained radiologically stable. Acute-onset facial palsy following SRS for vestibular schwannoma is extremely rare, with only four previous cases reported in the literature. This is the first reported case to occur following a relatively low margin dose-11 Gy-in contrast to the 13-14 Gy doses prescribed in earlier reports.