Two cases of Gamma Knife radiosurgery for low-grade optic chiasm glioma.

The effect of radiosurgery on optic gliomas is uncertain. We report two cases of low-grade glioma of the optic nerve and chiasm treated by transcranial subtotal removal and Gamma Knife radiosurgery. The first case was a 2-year-old boy, admitted with visual disturbance and nystagmus. Histopathological examination showed a pilocytic astrocytoma. The tumor volume was 14.4 cm3. Dose planning was performed using axial and coronal T1-weighted enhanced images. The marginal dose was 12 Gy at the 40% isodose line. The dose to the optic apparatus was less than 9 Gy. The second case was a 47-year-old woman, admitted to our hospital with headache and visual disturbance. The histopathological findings showed a fibrillary astrocytoma. The tumor volume was 12.3 cm3. The marginal dose was 14.4 Gy at the 40% isodose curve. The follow-up periods for the two cases were 24 and 43 months, respectively. In both cases the most recent follow-up magnetic resonance scan showed a marked decrease in tumor size, and visual symptoms were improved. No postradiosurgical complications have developed to date. Gamma Knife radiosurgery could be an effective adjuvant therapy for low-grade optic glioma. However, long-term follow-up is required for further evaluation of the efficacy and potential side effects.