REPEAT STEREOTAXIC RADIOSURGERY OF ARTERIOVENOUS-MALFORMATIONS - FACTORS ASSOCIATED WITH INCOMPLETE OBLITERATION

SECOND STEREOTACTIC RADIOSURGERY procedures were required in 45 patien ts with arteriovenous malformations (AVMs) who initially had incomplet e obliteration. Repeat radiosurgery was performed at a median of 39 mo nths (range, 24-71 mo) after the first stage. The median AVM volume at the first procedure was 6.0 mi (range, 0.2-18.0 ml). Thirty-seven pat ients (82%) had AVMs of Spetzler-Martin Grades III through VI. A retro spective analysis revealed definite causes for incomplete obliteration after the first procedure in 33 patients (73%). Incomplete angiograph ic definition of the nidus was the most frequent factor (57%) associat ed with failed radiosurgery. Three patients (7%) had recanalization of the AVM nidus after prior embolization; four patients (9%) had incomp lete nidus recognition, because AVM vessels were not visualized in the presence of a hematoma. ''Radiobiological resistance'' was another po tential factor associated with failed radiosurgery in 17 patients (38% ). Our current technique for volume determination and dose planning in cludes stereotactic magnetic resonance angiography, magnetic resonance imaging, and complete cerebral angiography (including superselective and external carotid artery injections, as indicated). Integrated mult iplanar high-resolution imaging will likely increase the rate of AVM o bliteration after stereotactic radiosurgery.