Abstract

A detailed clinical and radiological study of 51 patients presenting with a subarachnoid haemorrhage, for which no cause could be found, has been described. Although selection for full investigation has favoured the inclusion of younger and fitter patients, analysis of the information obtained suggests that haemorrhage could be due to: (a) aneurysms undergoing thrombosis at the time of haemorrhage, in which subsequent recanalisation will produce a low incidence of further bleeding; (b) minute (2 mm) aneurysms, destroyed at the time of haemorrhage and posing no subsequent threat.