Gamma knife radiosurgery for trigeminal schwannomas

Objective To evaluate the role of gamma knife(GK) in the treatment of trigeminal schwannomas. Methods From June 1994 to June 2000, 38 patients with trigeminal schwannoma treated with GK radiosurgery were reviewed. GK was the primary treatment modality in 30 cases and followed microsurgery in 8 cases. Of the 38 tumors, 12 had small cysts within the tumors, the rest were solid. The mean diameter of the 38 tumors was 32 mm (range:16～48 mm) and the tumors ranged in volume from 2 to 33 cm 3 (with a mean mean volume of 9 cm 3). The maximum dose irradiated to tumor was 20 to 33 Gy (mean: 26 Gy), the tumor margin dose ranged from 11 to 15 Gy (mean: 13 Gy). Results 35 patients had been followed for 26 to 98 months (mean: 65 months). 20 had been followed more than 60 months. Mild numbness or diplopia relieved completely in 12 patients after GK treatment. Improvement of neurological deficits was seen in 11, unchanged dysfunction or slightly worsening of trigeminal nerve deficits in 9. Three patients had mild worsened symptoms at different time because of tumor progression. Tumor growth control: tumor disappeared after GK treatment was observed in 5 cases from 18 to 36 months after, a marked decrease in volume was observed in 24 cases, unchange in 2 cases and increase in 3 cases at 5, 26, and 60 months after respectively. One patient with resolved symptom refused to have MRI examination for more than 6 years. Of the three increased tumors, one recurrent malignant schwannoma elapsed 26 months after GK treatment. The second was a small tumor and started to progress 5 years after, but after second GK treatment, the tumor decreased again. The third was large tumor and was subtotally removed through surgery because of tumor swelling 5 months after. At last follow up, the residual tumor remained stable. The control rate of the 35 tumors was 91%(32/35).Conclusion Small and middle size trigeminal schwannomas are the best candidates for GK radiosurgery. The control dose is 13 to 14 Gy.