Safety and Effectiveness of Gamma Knife Radiosurgery in the Treatment of Abducens Nerve Schwannomas

Introduction: Abducens nerve (AN) schwannomas are very rare and limited literature exists regarding their management. The present study evaluates the role of Gamma Knife radiosurgery (GKRS, [Elekta, Stockholm, Sweden]) in this setting. Material and Methods: A retrospective chart review (1997-2010) at a national university hospital studied patients with isolated AN paresis and a mass with MRI characteristics typical of a schwannoma along the course of the involved nerve. Patients with multiple cranial nerve deficits and type II neurofibromatosis were excluded. GKRS was delivered using a Leksell model B unit, Gamma Plan 5.0 and stereotactic contrast MR images. Results: Seven patients (M:F, 3:4) of mean age 39.7 years (range 17-60 years) received primary GKRS. Five tumors were prepontine while two tumors were intracavernous. The mean tumor volume was 4.25 cm³ (range 2-10.3 cm³). All patients received a 12 Gy (50% isodose) marginal dose using an average of six isocenters. One patient was lost to follow-up. The mean follow-up duration was 24 months (range 8-42 months). Symptoms improved in three patients (50%) and were stable in the rest. MRI at last follow-up, showed tumor volumes that were reduced in three patients (50%) and stable in the rest. The tumor control rate was 100%. One patient (16%) experienced transient worsening of diplopia 2 months after GKRS, which resolved in the next 3 months. Conclusions: GKRS is a safe and effective treatment modality for AN schwannomas. Short-term follow-up indicates a 100% tumor control rate and a 50% chance of relieving diplopia.