Gamma knife radiosurgery as a single treatment modality for large cerebralarteriovenous malformations

Object. A consecutive series of 240 patients with arteriovenous malformatio ns (AVMs) treated by gamma knife radiosurgery (GKS) between March 1993 and March 1999 was evaluated to assess the efficacy and safety of radiosurgery for cerebral AVMs larger than 10 cm(3) in volume. Methods. Seventy-six patients (32%) had AVM nidus volumes of more than 10 c m(3). During radiosurgery, targeting and delineation of AVM nidi were based on integrated stereotactic magnetic resonance (MR) imaging and x-ray angio graphy. The radiation treatment was performed using multiple small isocente rs to improve conformity of the treatment volume. The mean dose inside the nidus was kept between 20 Gy and 24 Gy. The margin dose ranged between 15 t o 18 Gy placed at the 55 to 60% isodose centers. Follow up ranged from 12 t o 73 months. There was complete obliteration in 24 patients with an AVM volume of more t han 10 cm(3) and in 91 patients with an AVM volume of less than 10 cm3. The latency for complete obliteration in larger volume AVMs was significantly longer. In Kaplan-Meier analysis, the complete obliteration rate in 40 mont hs was 77% in AVMs with volumes between 10 to 15 cm3, as compared with 25% for AVMs with a volume of more than 15 cm(3). In the latter, the obliterati on rate had increased to 58% at 50 months. The follow-up MR images revealed that large-volume AVMs had higher incidences of postradiosurgical edema, p etechiae, and hemorrhage. The bleeding rate before cure was 9.2% (seven of 76) for AVMs with a volume exceeding 10 cm3, and 1.8% (three of 164) for AV Ms with a volume less than 10 cm3. Although focal edema was more frequently found in large AVMs, most of the cases were reversible. permanent neurolog ical complications were found in 3.9% (three of 76) of the patients with an AVM volume of more than 10 cm(3), 3.8% (three of 80) of those with AVM vol ume of 3 to 10 cm(3), and 2.4% (two of 84) of those with an AVM volume less than 3 cm3. These differences in complications rate were not significant. Conclusions. Recent improvement of radiosurgery in conjunction with stereot actic MR targeting and multiplanar dose planning has permitted the treatmen t of larger AVMs. It is suggested that gamma knife radiosurgery is effectiv e for treating AVMs as large as 30 cm(3) in volume with an acceptable risk.