Expression of a latent ophthalmic artery collateral circulation after extracranial-intracranial bypass.

We present the case of an unexpected response by the cerebral vasculature to bypass surgery. A 66-year-old man sustained a subarachnoid haemorrhage and cerebral angiography showed a large fusiform anterior communicating artery (ACoA) aneurysm and an anomalous anterior circulation. The right A1 segment was hypoplastic and blood supply to the entire right A2 was from the left anterior circulation via the ACoA.