A 50-year-old male presents with acute-onset severe headache. He describes it as instantaneous - like being hit on the back of the head. He has mild n...

Question

A 50-year-old male presents with acute-onset severe headache. He describes it as instantaneous - like being hit on the back of the head. He has mild neck stiffness but no focal neurological deficit. His GCS is 15. A CT head performed 2 hours after onset is reported as normal. Does this exclude subarachnoid haemorrhage?

Accepted Answer

No - CT sensitivity for SAH decreases with time from onset; a normal CT within 6 hours has >98% sensitivity, but after 6 hours sensitivity falls; a lumbar puncture at 12 hours is needed to fully exclude SAH

Answer

CT is only 50% sensitive for SAH so it should not be used

Answer

A normal CT means the headache is a migraine

Answer

Yes - a normal CT completely excludes SAH at any time point

Answer

MRI should be performed instead of CT

uk-dipimc MCQ (SBA): SAH - CT Sensitivity and Timing