Analysis of the causes of treatment failure in gamma knife radiosurgery for intracranial arteriovenous malformations

Object. The authors sought to analyze causes for treatment failure followin g gamma knife radiosurgery (GKS) for intracranial arteriovenous malformatio ns (AVMs), in cases in which the nidus could still be observed on angiograp hy 3 years postsurgery. Methods. Four hundred fifteen patients with AVMs were treated with GKS betw een April 1990 and March 2000. The mean margin dose was 23.6 Cy (range 10-2 5 Gy), and the mean nidus volume was 5.3 cm(3) (range 0.4-41.7 cm3). The KU LA treatment planning system and conventional subtraction angiography were used in treatment planning. One hundred twenty-three of these 415 patients underwent follow-up angiogra phy after GKS. After 3 years the nidus was totally obliterated in 98 patien ts (80%) and partial obliteration was noted in the remaining 25. There were several reasons why complete obliteration was not achieved in al l cases: inadequate nidus definition in four patients, changes in the size and location of the nidus in five patients due to recanalization after embo lization or reexpansion after hematoma reabsorption, a large AVM volume in five patients, a suboptimal radiation dose to the thalamic and basal gangli a in eight patients, and radioresistance in three patients with an intranid al fistula. Conclusions. The causes of failed GKS for treatment of AVMs seen on 3-year follow-up angiograms include inadequate nidus definition, large nidus volum e, suboptimal radiation dose, recanalization/reexpansion, and radioresistan ce associated with an intranidal fistula.