Gamma Knife surgery for schwannomas originating from cranial nerves III, IV, and VI

Schwannomas from the motor cranial nerves controlling eye movement are rare. The authors evaluated the role of Gamma Knife surgery (GKS) in the management of schwannomas originating from cranial nerves III, IV, and VI.

Over a 7-year period, 8 patients with schwannomas originating from the oculomotor (2 patients), trochlear (5 patients), or abducent (1) nerve underwent GKS. The mean patient age was 46.1 years (range 19-59 years). The presenting symptoms included diplopia in 5 patients, ptosis in 1 patient, ophthalmoplegia in 1 patient, and headache in 1 patient. Two patients had a history of neurofibromatosis Type 2. Gamma Knife surgery was performed as primary management in 7 patients and after prior resection in 1 patient. The median and mean tumor volumes were 0.22 and 1.32 cm(3) (range 0.03-7.4 cm(3)). A median margin dose of 12.5 Gy (range 11.0-13.0 Gy) was prescribed to the tumor margin. Clinical and imaging follow-up data were available for all 8 patients.

Magnetic resonance imaging showed tumor regression in all patients. The progression-free period varied from 4 to 42 months, with a mean of 21 months. Over a mean of 23 months, 4 of the 5 patients with a trochlear schwannoma and symptoms of diplopia noted symptomatic improvement. No improvement was noted in the 2 patients with oculomotor nerve palsies. Headache was improved in the 1 patient with an abducent neuroma.

Gamma Knife surgery is an effective and minimally invasive approach capable of inactivating schwannomas originating from the oculomotor, trochlear, and abducent nerves. Accompanying trochlear function may improve. Longer follow-up and larger patient samples are needed to confirm the authors' initial observations.