STEREOTAXIC RADIOSURGERY FOR POSTGENICULATE VISUAL PATHWAY ARTERIOVENOUS-MALFORMATIONS

Arteriovenous malformations (AVMs) that are located within the postgen iculate optic radiations or striate cortex are difficult to resect wit hout creating postoperative visual defects. To reduce the risk of an A VM hemorrhage and to enhance the possibility of preserving visual func tion, the authors performed stereotactic radiosurgery in 34 patients w ith newly diagnosed or residual AVMs of the visual pathways. The mean AVM volume was 4.7 mi, and the average radiation dose to the AVM margi n was 21 Gy. The median follow up was 47 months (range 16-83 months). Two (6%) of 34 patients had documented new visual field defects (centr al scotoma in one, and partial hemianopsia in one) after single-stage radiosurgery, but no patient developed a new permanent homonymous hemi anopsia. Angiography was performed in all patients at a median of 26 m onths after radiosurgery: 22 (65%) had complete obliteration, 10 (29%) had a significant decrease in AVM volume, one (3%) had only a persist ent early draining vein without residual nidus, and one (3%) had no ch ange in the AVM. Thirteen (81%) of 16 patients with AVMs less of than 4 ml had complete obliteration. Five patients had second-stage stereot actic radiosurgery after angiography revealed a persistent AVM nidus; two patients eligible for follow-up angiography had complete obliterat ion, thereby increasing the overall series obliteration rate to 71%. T he calculated annual risk of AVM bleeding (before radiographic evidenc e of obliteration) was 2.4%. No patient bled after angiographically co nfirmed obliteration. In most patients stereotactic radiosurgery oblit erates visual pathway AVMs and also preserves preoperative visual func tion. Multimodality management (embolization, microsurgery, or staged radiosurgery) enhances AVM obliteration and visual preservation rates.