In combination with the description of the headache and symptoms, a subarachnoid haemorrhage is diagnosed by performing a CT scan and/or lumbar puncture, to confirm the presence of blood on the surface of the brain.
CT scan
This is an x-ray scan that takes pictures of the brain at different levels. It is most commonly performed soon after admission to hospital. The procedure is painless and only takes a few minutes. You will lie on a scanning table and the scanner rotates around your head. The scan may show the presence of blood around the brain and/or any other problems.
attached file is image of CT scan showing normal anatomy