Risk of injury to cranial nerves after gamma knife radiosurgery for skull base meningiomas: experience in 88 patients

Object. In this study the authors sought to determine the neurological risk s and potential clinical benefits of gamma knife radiosurgery for skull bas e meningiomas. Methods. A consecutive series of 88 patients harboring skull base meningiom as were treated between 1990 and 1996 by using the Leksell gamma knife in a prospective clinical study that included a strict dose-volume protocol. Fo rty-nine patients had previously undergone surgery, and six had received ex ternal-beam radiotherapy. The median treatment volume was 10 cm(3), and the median dose to the tumor margin was 16 Gy. The radiosurgical dosage to the optic nerve, the cavernous sinus, and Meckel's cave was calculated and cor related with clinical outcome. The median patient follow-up time was 35 mon ths (range 12-83 months). Two tumors (2.3%) progressed after radiosurgery; the progression-free 5-yea r survival rate was 95%. At last follow-up review, 60 (68%) tumors were sma ller and 26 (29.5%) remained unchanged. Clinical improvement (in vision, tr igeminal pain, or other cranial nerve symptoms) occurred in 15 patients. Fu nctioning optic nerves received a median dose of 10 Gy (range 1-16 Gy), and no treatment-induced visual loss occurred. Among nine patients with new tr igeminal neuropathy, six received doses of more than 19 Gy to Meckel's cave . Conclusions. Gamma knife radiosurgery appeared to be an effective method to control the growth of most skull base meningiomas in this intermediate-ter m study. The risk of trigeminal neuropathy seemed to be associated with dos es of more than 19 Gy, and the optic apparatus appeared to tolerate doses g reater than 10 Gy. Considering the risks to cranial nerves associated with open surgery for comparable tumors, the authors believe that gamma knife ra diosurgery is a useful method for the management of properly selected recur rent, residual, or newly diagnosed skull base meningiomas.