Extra- to intracranial arterial anastomoses in therapeutic embolization: recognition and role.

Anastomoses from extra- to intracranial vessels have been shown in normal patients and, more commonly, in patients with arteriosclerotic occlusive disease, arteriovenous malformation, and postligation of the carotid artery. These channels may be of clinical importance during therapeutic embolization and probably account for two cases of complication, posterior fossa strokes that occurred after blockage of occipital arteries. By identifying these channels and then monitoring the ever-decreasing vessel acceptance of contrast agent and emboli, patient safety may be enhanced.