Gamma Knife Radiosurgery in Vestibular Schwannomas: Clinical and Radiological Impact on the Tumor Course

Abstract

Up to the last decade, therapeutic options for patients with vestibular schwannomas (VS) were limited to total or subtotal excision or expectant serial observation. Stereotactic irradiation, and particularly gamma knife radiosurgery (GKR), have offered an important additional option to the overall management strategy. Clinical results, in terms both of tumor growth control (TGC) and of preserved regional cranial nerve function, have increasingly validated this approach in properly selected indications for either primary or recurrent tumors. Indeed, using current neuroradiological techniques (MRI-CT fusion algorithms) as well as newer radiodosimetry programs and reduced dosages, the reported achievable TGC rate actually exceeds 90% in mid-term follow-up (5 years), whereas the relevance of radio- induced cranial neuropathy has been minimized: facial impairment incidence lower than 3%, with hearing function (Gardner-Robertson [G-R] 1-2) pre- served in over 60% of the patients. Our experience, in a series of 170 treated VS (9.4% NeuroFibromatosis type 2, or NF2) further confirms these data: the group of évaluable cases (112 patients with over 4 years of mean follow-up) shows an overall TGC rate of 93%, with an extremely low incidence of facial impairment (2.7%) and hearing preservation in 66% (G-R 1-2). However, long-term fullow-up results in large series of patients treated by contempo- rary GKR techniques are not yet available: with lowering treatment dosages, surviving tumor cells might sustain a delayed regrowth, eventually decreas- ing TGC rates. To date, GKR may be advocated for small-to-medium-sized VS, with negative cranial nerve staging, absent or minimal hearing deficit, and in several cases with major surgical contraindications or in patients refusing microsurgery. Furthermore, it is worth stressing that particularly for elderly patients with larger schwannomas and for NF2 patients, an integrated program including both GKR and microsurgery should always be considered.