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.