CT appearance of subarachnoid haemorrhage

A CT scan is the first line investigation in SAH. The sensitivity depends upon the interval after the event, the quality of the equipment and the radiologist. Under optimum conditions, bleeding can be detected in 95% of cases within a day compared to 50% after a week. The value of CT is:

• helps identify the site of a ruptured aneurysm, especially if there is an associated haematoma. This helps to guide subsequent angiography. Common sites include the Sylvian fissure, the interhemisphere fissure, the basal cisterns, over the tentorium, cerebelli, in the ventricular system or over the hemisphere surface
  
  
• identifies other associated lesions - an intraparenchymal haematoma in the basal ganglia, the cerebral white matter, or the cerebellum, suggests an arteriovenous malformation, ruptured artery, e.g. middle cerebral, or amyloid angiopathy