Diagnosis and investigations
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.
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.
CT scan showing normal anatomy
CT scan showing subarachnoid haemorrhage
The cerebro-spinal fluid (CSF) that is within the subarachnoid space also surrounds the spinal cord. On some occasions it may not be possible to perform a CT scan, or it may be inconclusive, in which case a lumbar puncture may be used to detect the presence of blood. To obtain a sample of CSF, a needle is passed between two of the vertebrae, or spinal bones, at the lower end of the spine, and a small amount of fluid is drawn off. The CSF is sent to the laboratory so any signs of blood may be detected. The procedure may be slightly uncomfortable, but local anaesthetic will be injected to numb the area first.
Diagram of spine and position of lumber puncture insertion
Once a subarachnoid haemorrhage has been diagnosed, cerebral angiography will be performed to find out what caused it.