In suspected subarachnoid hemorrhage, what is the first-line diagnostic imaging study?

• A. MRI
• B. Ultrasound
• C. X-ray of skull
• D. CT scan

Answer: (D)

Non-contrast head CT is used first because it quickly reveals acute blood in the subarachnoid spaces, guiding urgent management. In the hours after bleed onset, freshly extravasated blood appears as hyperdense material in the cisterns and sulci, making CT highly sensitive for an acute subarachnoid hemorrhage. If the CT is negative but suspicion remains, further testing like a lumbar puncture with CSF analysis for xanthochromia or CT angiography to identify an aneurysm may be pursued. MRI can detect SAH as well, but it’s slower and less practical as an initial ED test. Ultrasound and skull X-ray do not reliably detect SAH and aren’t appropriate first-line choices.