The early effects of gamma knife on 40 cases of acoustic neurinoma.

Early results of gamma radiosurgery on 44 cases of acoustic neurinoma were studied by follow-up MRIs and changes of neurological signs every 3 months. Mean follow-up period was 12 (3 to 20) months. Enhanced MRI revealed that the central low intensity signal area (LISA) appeared at 3 to 6 months after the treatment, which was re-enhanced at 6 to 9 months, then the tumours begun to decrease in size at 9 to 12 months, which observation was noted in 11 out of 44 cases (25%). The other tumours were unchanged in size. Regarding the side effects, facial palsy appeared in 7 cases (16%) after the treatment, of whom 3 cases have improved. Trigeminal nerve palsy was found in 3 cases (7%). Deterioration of hearing was found in 11 out of 21 cases (52%) who had hearing disturbances before treatment. The pathological study of a treated tumour at 11 months revealed that central LISA was found as complete necrosis and degeneration of tumour cells and vessels with thickening walls found at the margin of the tumour. MRI is not only useful for the dose planning of radiosurgery but valuable for the follow-up study of treated tumours.