You expect to see blood in the CSF but are confused to see a crescent shaped area of increased attenuation.

“That’s a subdural haemorrhage” announces the voice of a popular local radiologist, creepily floating by your ear. Although your initial on-the-spot diagnosis was wrong you made the right choice in investigation and disproved your own theory.

The patient has a chronic subdural haemorrhage. This is a collection of blood between the brain and the dura mater. Chronic (>3weeks) subdural haematomas are more common in the elderly on anticoagulants (eg warfarin in this case) following a fall. A headache appears 7-14 days after the fall.

A CT head should be performed which would reveal a crescent shaped haematoma.

A convex shaped haematoma indicating an extradural haematoma usually occurs due to rupture of the middle meningeal artery underneath the pterion following trauma.

Blood in the CSF spaces would be suggestive of a subarachnoid haemorrhage which presents with the famous ‘thunderclap’ headache.