About 20 hours before presentation, a 45-year-old healthy woman experienced abrupt onset of the worst headache of her life. Aside from mild neck stiffness and photophobia, she had no other complaints. Her physical examination was entirely normal. A computed tomography (CT) of her head also showed no abnormality. Lumbar puncture, however, yielded uniformly bloody cerebrospinal fluid throughout 4 successive tubes (Figure 1). A right common carotid arteriogram demonstrated a bilobed aneurysm at the posterior communicating artery (Figure 2). At craniotomy, the aneurysm was clipped, and she went home on the sixth hospital day.

Points to remember: Subarachnoid hemorrhage should always be considered when a patient suffers abrupt onset of the worst headache ever. And, as seen in this patient, the diagnosis requires a lumbar puncture because cranial CT may be normal.

Diagnosis: Subarachnoid hemorrhage from leaking cerebral aneurysm.