A case of rete mirabile with congenital dysplasia of bilateral internal carotid arteries

We report a case of dysplasia of the congenital bilateral internal carotid arteries with the rete mirabile. The rete mirabile is not usually seen in the course of human growth, but it is a common finding in other mammals. Accordingly, some investigators have thought that the rete mirabile is "developmental shift". Our case has dysplasia of the bilateral internal carotid arteries (one is aplasia and the other is hypoplasia), but the patient had suffered from no ischemic symptom because her brain had been sufficiently fed by each of the rete mirabile. Angiographically, the frequency of the rete mirabile formation is about 1/10,000. There were 20 cases reported until 1997 (including our case). There were 5 cases (27.8%) with ischemic symptoms in spite of internal carotid artery dysplasia, 2 cases (11.1%) with intracerebral hemorrhage, 6 cases (33.3%) with subarachnoid hemorrhage (there were only two cases with aneurysm) and 5 cases without symptoms. We have tried to class the rete mirabile by angiographical findings. One is the M type finding resembling moyamoya vessels in stages 3 & 4 of moyamoya disease, and the other is the N type finding resembling a nidus of arteriovenous malformation. M type occurred in younger patients more often than N type, so M type may be the previous stage of N type.