Spontaneous angiographic obliteration of cerebral arteriovenous malformations

OBJECTIVE: The factors associated with spontaneous angiographic obliteratio n of cerebral arteriovenous malformations (AVMs) are not well understood. W e present a review of the literature and a report of our experience with si x cases (four with no previous treatment intervention and two postoperative residual malformations) that were identified as having occurred during a 2 0-year period and describe the clinical and lesion features associated with this rare phenomenon. We present the first detailed histological study of a spontaneously thrombosed AVM specimen, including immunohistochemical anal ysis of angiogenesis factor expression. METHODS: A combined experience in the management of approximately 700 AVMs during 20 years identified six cases of spontaneous angiographic obliterati on of cerebral AVMs. A literature review revealed another 24 cases with ang iographic documentation of the initial AVMs and follow-up data showing nonf illing of the lesions. Histological analysis of a recently excised lesion i ncluded immunostaining with monoclonal antibodies to the antigens of Factor VIII, Tie, vascular endothelial growth factor, and its receptors, Flt-1 an d Flk. RESULTS: A single draining vein was a feature in each of our 6 cases and in 12 of 14 (86%) cases from the literature. Hemorrhage as the presenting sym ptom was identified in 5 of our 6 (83%) cases and in 17 of 24 (71%) of the literature cases. The size of the AVM was less than 6 cm in each of our 6 c ases and in 22 of 24 (92%) of the literature cases. A histological examinat ion of a thrombosed AVM surgical specimen revealed persistent patent vascul ar channels within the lesion. Immunohistochemical analysis with angiogenes is and endothelia-specific factors showed expression of these factors withi n the lumen of the thrombosed nidus vessels. CONCLUSION: We propose that the occlusion of a single draining vein may lea d to total venous outflow obstruction and lesion thrombosis. Hemorrhagic pr esentation and small nidus may also predispose to this phenomenon. Immunohi stochemical analysis of a thrombosed AVM revealed possible ongoing angiogen ic changes within the AVM vessels 1 month after angiographically documented thrombosis. It is possible that neovascularization within a thrombosed AVM may lead to lesion recanalization; however, this phenomenon seems to be cl inically exceedingly rare.