Diagnosis

To diagnose a subarachnoid hemorrhage, your doctor is likely to recommend:

• CT scan. This imaging test can detect bleeding in your brain.Your doctor may inject a contrast dye to view your blood vessels in greater detail (CT angiogram).
• MRI. This imaging test also can detect bleeding in your brain. Your doctor might inject a dye into a blood vessel to view the arteries and veins in greater detail (MR angiogram) and to highlight blood flow.
• Cerebral angiography. You doctor inserts a long, thin tube (catheter) into an artery in your leg and threads it to your brain. Dye is injected into the blood vessels of your brain to make them visible under X-ray imaging. Your doctor might recommend cerebral angiography to obtain more-detailed images or if a subarachnoid hemorrhage is suspected but the cause isn't clear or doesn't appear on other imaging.

Up to 22% of aneurysmal subarachnoid hemorrhages don't appear on initial imaging tests. If your initial tests don't show bleeding, your doctor might recommend:

• Lumbar puncture. Your doctor inserts a needle into your lower back to withdraw a small amount of fluid that surrounds your brain and spinal cord (cerebrospinal fluid). The fluid is examined for the presence of blood, which can indicate a subarachnoid hemorrhage.
• Repeated imaging. The tests might be repeated several days after the initial testing.