Vertebral artery dissection not detected by initial angiography--case report.

A 57-year-old male presented with subarachnoid hemorrhage caused by vertebral artery dissection. The first cerebral angiogram on the day of ictus found minimal caliber change with lower contrast density at the V4 segment, but repeat angiography showed typical segmental narrowing of the artery on the 14th day. Repeat angiography with magnetic resonance imaging in the subacute stage would be useful to identify the cause of "angiogram-negative" subarachnoid hemorrhage.