Spontaneous Regression of Cerebral Arteriovenous Malformation Following Onyx Embolization

Little is known about the natural history of arteriovenous malformations (AVM) and less is known about their potential for spontaneous regression. The advent of endovascular treatment for embolization or pre-surgical embolization of cerebral arteriovenous malformations (cAVM) has seen several reports of spontaneous regression of partial embolization of cAVMs surface in the literature. A 66-year-old patient had an initial diagnostic cerebral angiogram revealing a left frontoparietal region Spetzler-Martin (SM) grading 4 cAVM. The patient underwent three stages of embolization over eight months leading to a 90% reduction in nidal volume, before being lost to follow up for six years. A six-vessel diagnostic cerebral angiogram was performed at that time to assess for any interval changes and surprisingly, the previously visualized left frontoparietal AVM had regressed. There was evidence of prior onyx embolization with no residual filling or recurrence. Spontaneous regression after partial embolization may be under-reported or the natural history is simply unable to temporally unfold because the typical treatment course results in surgery following partial embolization. Given the potential to forgo the risks of an open procedure, we believe this topic deserves further attention.