Most intracranial schwannomas arise from the cranial nerve (CN) VIII for whom radiosurgery has proven its safety and efficacy for tumor control and function preservation in small to medium-size tumors. Less common, CN III, IV and VI schwannomas are very disabling due to the associated palsies. We prospectively evaluated the safety and efficacy of Gamma Knife surgery (GKS) in these rare cases.

Five patients with CN IV (3) and VI (2) schwannomas were treated in Lausanne University Hospital between 2010 and 2015. Four were treated with upfront GKS and one by a combined approach (CN VI, subtotal surgery followed by GKS) due to a large tumor volume (7.9 cc). All cases had neuro-ophthalmological evaluation at baseline and at 6 and 12 months and on annual basis after. In one patient, a type II neurofibromatosis was diagnosed.

The mean follow-up period was 29 months (range 6–54). The mean target volume was 1.51 cc (range 0.086–5.8). Initial clinical presentation was diplopia (four cases) and cavernous sinus syndrome (one case). The mean marginal dose was 12Gy (range 12–12). The mean prescription isodose volume was 1.71 cc (range 0.131–6.7). The mean maximal dose to the optic pathways was 1,5Gy (range 0,1–6,6). Following GKS, all patients presented clinical alleviation, with disappearance of baseline symptoms. However, one of them had an additional surgical intervention (left superior oblique tendon folding). Tumor control was achieved in all (100%, 100% decreased).

Our data suggests that first intention GKS is a safe and effective treatment option for CN IV and VI schwannomas, with high rates of both clinical alleviation and tumor control. In cases where the initial tumor volume is too large for first intention GKS, combined approaches can be performed, with favorable results.