A rare cause of thunderclap headache

A 44 year old woman presented to the emergency room with a severe headache that had suddenly developed (within seconds) on wakening two days earlier. The headache was diffusely located and radiated to the neck. She was nauseous and had vomited. Several weeks ago she had undergone a colonoscopy because of frequent and bloody diarrhoea and had been diagnosed with ulcerative colitis. She had been receiving mesalazine and prednisolone (40 mg daily) for the past four weeks. She also used a third generation oral contraceptive. Her remaining medical history was unremarkable.

On examination the patient was fully awake. Her blood pressure was 120/90 mm Hg, pulse rate 95 beats/min, and temperature 37^°C. She was photophobic and had slight nuchal rigidity. The remaining neurological examination, including fundoscopy, showed no abnormalities. Initial blood tests showed a C reactive protein concentration of 20 mg/l, a white cell count of 11.4×10⁹/l, and a platelet count of 286×10⁹/l. An urgent computed tomography scan of the brain (non-enhanced) showed a hyperdense aspect of the straight sinus, but was otherwise unremarkable. Subarachnoid haemorrhage was excluded as a possible cause.