Multisession cyberknife radiosurgery for intramedullary spinal cord arteriovenous malformations

OBJECTIVE: Intramedullary spinal cord arteriovenous malformations (AVMs) have an unfavorable natural history that characteristically involves myelopathy secondary to progressive ischemia and/or recurrent hemorrhage. Although some lesions can be managed successfully with embolization and surgery, AVM size, location, and angioarchitecture precludes treatment in many circumstances. Given the poor outlook for such patients, and building on the successful experience with radiosurgical ablation of cerebral AVMs, our group at Stanford University has used CyberKnife (Accuray, Inc., Sunnyvale, CA) stereotactic radiosurgery (SRS) to treat selected spinal cord AVMs since 1997. In this article, we retrospectively analyze our preliminary experience with this technique. METHODS: Fifteen patients with intramedullary spinal cord AVMs (nine cervical, three thoracic, and three conus medullaris) were treated by image-guided SRS between 1997 and 2005. SRS was delivered in two to five sessions with an average marginal dose of 20.5 Gy. The biologically effective dose used in individual patients 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 3 years. RESULTS: After a mean follow-up period of 27.9 months (range, 3-59 mo), six of the seven patients who were more than 3 years from SRS had significant reductions in AVM volumes on interim magnetic resonance imaging examinations. In four of the five patients who underwent postoperative spinal angiography, persistent AVM was confirmed, albeit reduced in size. One patient demonstrated complete angiographic obliteration of a conus medullaris AVM 26 months after radiosurgery. There was no evidence of further hemorrhage after CyberKnife treatment or neurological deterioration attributable to SRS. CONCLUSION: This description of CyberKnife radiosurgical ablation demonstrates its feasibility and apparent safety for selected intramedullary spinal cord AVMs. Additional experience is necessary to ascertain the optimal radiosurgical dose and ultimate efficacy of this technique.