Gamma Knife radiosurgery for intravestibular and intracochlear schwannomas

Schwannomas of the VIIIth cranial nerve are benign tumours, with vast majority occurring in vestibular division. Rarely, they can also arise from distal branches of cochlear, superior or inferior vestibular. We review our experience with Gamma Knife radiosurgery (GKR), as first intention treatment for intracochlear (ICS) and intravestibular (IVS) schwannomas.

A total number of five patients were analysed, treated over 8 years, between June 2010 and September 2018, with Leksell Gamma Knife Perfexion or Icon (Elekta Instruments, AB, Sweden). The marginal dose prescribed was 12 Gy at a mean prescription isodose line of 61.4% (range 50–70). Clinical evaluation included auditory and facial function.

The mean age was 49.9 (range 34–63). The mean follow-up period was 52.8 months (range 12–84). The mean target volume (TV) was 0.087 ml (range 0.014–0.281). The mean maximal dose received by the cochlea was 11.2 Gy (range 2.6–20.3). The mean marginal dose received by the vestibule (e.g. utricula) was 14.2 Gy (range 3.8–17.5). No patient experienced an acute or subacute clinical adverse radiation effect after GKR. Four cases had overall symptom stability. In one patient (1/5), the vertigo, which was the main clinical complain, disappeared 1 year after GKR. However, it reappeared 3 years later, with same pretherapeutic characteristics and is currently fluctuating. One patient experienced hearing decrease after GKR, during the first 12 months. This case received 11.2 Gy to the cochlea. Follow-up MRI course showed a decrease in size in four patients, and stability in one.

Gamma Knife radiosurgery is a valuable first intention treatment for ICS or IVS, in selected cases. Special attention should be paid for the dose delivered to the cochlea and the vestibular apparatus. Acute and subacute clinical effects are exceptional, while tumour control was achieved in all cases in our small series.