Sudden appearance of occipital-vertebral arterial anastomoses during therapeutic embolization.

A 66-year-old woman with a dural arteriovenous malformation in the posterior fossa, who developed a vertebrobasilar stroke during therapeutic embolization of the occipital artery, is reported. Postembolization arteriograms demonstrated previously invisible anastomoses of the occipital-vertebral artery. The literature is reviewed with respect to the complications and risks of therapeutic embolization of the external carotid artery, and the possible mechanism underlying the opening of these anastomoses is discussed.