Incidence of delayed cerebral ischaemia following subarachnoid haemorrhage of unknown cause.

A retrospective study was made of 50 consecutive patients with spontaneous subarachnoid haemorrhage for which no cause was found, looking for evidence of delayed cerebral ischaemia particularly during the first 2 weeks after the bleed. Twenty-three patients had blood visible on the CT scan but only 4-6% developed delayed ischaemia, all of whom made a good recovery. The low incidence of this complication in this group of patients suggests that subarachnoid blood is not a sufficient cause for delayed ischaemia.