The Results of Gamma Knife Radiosurgery for Vascular Lesions of the Brainstem

ABSTRACT

The optimal management of lesions located in the brainstem(BS) is problematic. As an alternative to microsurgical resection, stereotactic radiosurgery employing the Gamma unit has been used to manage BS lesions, and this can provide relatively safe and effective management. This study describes our experience with 17 patients who underwent Gamma Knife radiosurgery(GKR) for vascular lesions of the brainstem between June 1989 and May 1996. Six of these had BS arteriovenous malformations(AVMs). The minimal radiation dose to the margin of AVMs ranged from 15 to 25Gy(mean, 18.9Gy). Four of six cases were partially obliterated, and on follow-up angiography, one small AVM was seen to be completely obliterated. Twelve months after GKR, one patient experienced a temporary neurologic deficit due to the effects of radiation and another patient, who had a large AVM, showed a permanent deficit as a direct result of treatment. There have been no instances of hemorrhage after GKR and all the patients are still alive. GKR was used to manage 11 patients with angiographically occult vascular malformations (AOVMs) of the BS. The periphery of the lesions received a radiosurgical dose of between 12 and 20Gy(mean, 15.5Gy). In four patients, the lesions became smaller, but in one, an increase was seen. In the remaining six, size change was not documented. One patient's neurological deficit worsened, though that might be related not to GKR but to non-fatal post-GKR rebleeding. At seven months, one patient developed a temporary neurologic deficit in association with perilesional edema that resolved over time. Three patients experienced post-GKR rebleeding, and none died during the follow-up period. We believe that GKR is an excellent option for patients with BS AVMs when the risks of microsurgery are deemed too high, it is a course of action which seems reasonable. GKR does not, though, appear to obliterate AOVMs as effectively as it does AVMs. To assess the long-term effectiveness of the technique on these lesions, longer follow-up intervals will, however, be required.