Small AVMs

Abstract

Small arteriovenous malformations (AVMs) of the brain are typically categorized as smaller than 3 cm. Using this definition, we consider small AVMs to include typical AVMs with nidus size <3 cm, pial single-channel AV fistulas, and so-called “micro”-AVMs. Small AVMs are believed to have a higher risk of hemorrhage than larger AVMs. Because their size (<3 cm) accrues only one point for size in the Spetzler-Martin Grading System, small AVMs are all Spetzler-Martin Grades I–III, depending on the presence of deep venous drainage and/or eloquent location (each given an additional point). Thus, many believe direct surgical extirpation should be the preferred treatment for small AVMs because several series have demonstrated excellent surgical outcomes for Spetzler-Martin Grades I–III AVMs. However, stereotactic radiosurgery offers an alternative therapeutic option. The best radiosurgical clinical outcomes and obliteration rates have been associated with small AVMs with diameters <3 cm or volumes <10 cm 3. At the Massachusetts General Hospital, a multidisciplinary neurovascular unit treats AVMs with surgery, radiosurgery, and embolization. From 1991 to 1999, this multidisciplinary neurovascular unit treated 424 AVMs, of which 216 (51%) were small AVMs: 105 by surgery alone, 29 by surgery with preoperative embolization, 39 by radiosurgery, 6 by radiosurgery with preradiosurgical embolization, 35 by embolization alone, and 2 by surgery after incomplete radiosurgical obliteration. This article discusses aspects of our operative techniques for treating these small AVMs.