Most intracranial schwannomas arise from cranial nerve (CN) VIII. Stereotactic radiosurgery is a mainstay of treatment for vestibular schwannomas. Intracranial schwannomas arising from other CNs are much less common. We evaluate the efficacy of Gamma Knife surgery on nonvestibular schwannomas including trigeminal, hypoglossal, abducent, facial, trochlear, oculomotor, glossopharyngeal, and jugular foramen tumors.
Thirty-six patients with nonvestibular schwannomas were treated at the University of Virginia Gamma Knife center from 1989 to 2008. The median patient age was 48 years (mean 45.6 years, range 10–72 years). Schwannomas arose from the following CNs: CN III (in 1 patient), CN IV (in 1), CN V (in 25), CN VI (in 2), CN VII (in 1), CN IX (in 1), and CN XII (in 3). In 2 patients, tumors arose from the jugular foramen. The median tumor volume was 2.9 cm3 (mean 3.3 cm3, range 0.07–8.8 cm3). The median margin dose was 13.5 Gy (range 9.3–20 Gy); the median maximum dose was 30 Gy (range 21.7–50.0 Gy).
The mean and median follow-up times of 36 patients were 54 and 37 months, respectively (range 2–180 months). At the last radiological follow-up, the tumor size had decreased in 20 patients, remained stable in 9 patients, and increased in 7 patients. The 2-year actuarial progression-free survival was 91%. Higher maximum dose was statistically related to tumor control (p = 0.027).
Thirty-three patients had adequate clinical follow-up. Among them, 21 patients had improvement in their presenting symptoms, 8 patients were stable after treatment with no worsening of their presenting symptoms, 2 patients developed new symptoms, and 1 patient experienced symptom deterioration. Notably, 1 patient with neurofibromatosis Type 2 developed new symptoms that were unrelated to the tumor treated with Gamma Knife surgery.
Gamma Knife surgery is a reasonably effective treatment option for patients with nonvestibular schwannomas. Patients require careful follow-up for tumor progression and signs of neurological deterioration.