Overall, 59% of the examples were associated with cerebral aneurysms. Different terminology such as carotid-anterior cerebral artery anastomosis and infraoptic anterior cerebral artery has been used. Having analyzed the reports of infraoptic A1, we found the vascular configurations of the A1 could be better described by classifying them into four types. Such a classification can facilitate analysis of the embryogenesis explanation for this anomaly and the pathogenesis of the associated aneurysms. Besides, such a classification also has some practical implications.

Pathophysiological mechanisms of the associated ipsilateral cerebral and brainstem hemiatrophy are discussed. The authors postulate that the gradual obliteration of the perforating arteries to the diencephalon especially the lenticulostriate arteries of the prebifurcation middle cerebral artery may be the major mechanism of the associated hemiatrophy.

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In a specific group of patients with CRN of the temporal lobe in whom the CRN lesions were causing a mass-occupying effect beyond the temporal lobe, excision of the contrast-enhancing region was safe and could achieve prompt resolution of brain edema and a low incidence of recurrence of CRN.