CyberKnife Ablation for Intramedullary Spinal Cord Arteriovenous Malformations (AVMs): A New Promising New Therapeutic Approach

Objective: Intramedullary spinal cord arteriovenous malformations (AVMs) are very rare lesions which are characteristically associated with recurrent hemorrhage and progressive ischemia. Although favorable location, size and vascular anatomy make it sometimes possible to manage this condition with embolization and/or microsurgical resection, there are no good treatment options for many, if not most, of these lesions. Given such poor prospects, the senior author began in 1997 investigating CyberKnife radiosurgical ablation as a tool for managing selected patients with intramedullary spinal cord AVMs. Although a previous paper in 2006 reported the preliminary experience from Stanford, our understanding has grown significantly as follow-up was extended and more patients were treated. Herein, we retrospectively analyze our longer term experience with a primary radiosurgical approach to spinal cord AVM. Methods: Thirty patients (17 females: 13 males) with a median age of 33 years and intramedullary spinal cord AVMs (18 cervical, nine thoracic, and three conus medullaris) were treated with CyberKnife SRS between 1997 and 2008. A history of hemorrhage was present in 57% of cases, while in 50% of patients previous treatment included microsurgery (6/29) or embolization (11/29). The mean AVM volume was 2.8 cc (0.2-15cc) and was treated to mean marginal dose of 20Gy in one to four sessions (median 2). Based on our growing experience, the biologically effective dose (BED) of radiation was escalated gradually over the course of this study. Clinical and magnetic resonance imaging follow-up were carried out annually, and spinal angiography was repeated at three years. Results: After a mean follow-up period of 63 months (median 54), the treated AVM was completely obliterated in eight cases (27%) and significantly decreased in size in an additional 11 cases (64%) among the 22 angiographically studied patients with more than three years of follow-up. Pre-radiosurgery neurologic symptoms improved in more than 50% of cases, but worsened in three (10%). There was one instance (3%) of radiation-induced myelopathy occurring within one year of radiosurgery. Notably, after 158 years of collective post-SRS follow-up, no patient suffered a hemorrhage. Conclusions: Although our understanding is still incomplete, CyberKnife radiosurgery results in total obliteration or shrinkage for most intramedullary spinal cord AVM, a phenomenon that may be accompanied by a marked decrease in the risk of bleeding. Symptom improvement is also common in most cases. More experience is required to determine the optimal radiosurgical dosing and consequent related efficacy. Given the significant therapeutic challenges inherent to spinal cord AVM patients, the rate of radiosurgical complications appears acceptable.