Clinical Outcomes of Fractionated Radiation Therapy for Spinal Intramedullary Arteriovenous Malformations: A Single Institutional Retrospective Review.

PURPOSE: Intramedullary spinal arteriovenous malformations (im-sAVMs) have a bleeding risk of up to 4% to 10% annually. Given the rarity of im-sAVMs and the lack of established evidence regarding the efficacy of radiation therapy, we retrospectively reviewed the treatment outcomes of fractionated radiation therapy (fRT) administered for im-sAVMs at our institution. METHODS AND MATERIALS: We examined patients of im-sAVMs treated with fRT at Hokkaido University Hospital between January 2003 and December 2023. The incidences of post-fRT bleeding from the AVMs, nidus occlusion/reduction, and late radiation-induced complications were assessed. RESULTS: Of the 25 patients, we analyzed 21 patients, excluding 4 patients with a follow-up period of less than 180 days. Prior to radiation therapy, 10 patients underwent surgical occlusion of feeding vessels because of coexisting arteriovenous fistulas, 2 and 3 patients underwent surgical occlusion and endovascular embolization for arteriovenous malformation, respectively. The radiation dose was 20 Gy in 4 fractions for 19 patients and 24 Gy in 4 fractions for 2 patients. The follow-up period ranged from 12 to 236 months (median, 56.4 months). Complete nidus occlusion was observed in 2 patients (9.5%), whereas 8 patients (38.1%) showed partial reduction with residual nidus, and 10 patients (47.6%) showed no reduction. One patient showed slight nidus enlargement 12 months after fRT, and another patient developed an aneurysm formation in the feeding artery at the margin of the irradiation field 57 months after fRT. No bleeding and late radiation-induced complications were observed during the follow-up. CONCLUSIONS: Fractionated radiation therapy at doses of 20 to 24 Gy in 4 fractions for im-sAVMs was shown to be safely administered and may be effective in reducing the risk of bleeding.