A 28-year-old female presents with sudden-onset severe headache ('thunderclap headache', 'worst headache of her life'). CT head is negative. LP is performed and shows xanthochromia. What is the most likely diagnosis and next most appropriate investigation?

• A Migraine; MRI brain with contrast
• B Meningitis; blood cultures and start antibiotics
• C Venous sinus thrombosis; MR venography
• D Subarachnoid hemorrhage; CT cerebral angiography or digital subtraction angiography to identify aneurysm ✓

Explanation

Xanthochromia (yellow CSF due to hemoglobin breakdown products) on lumbar puncture after a negative CT is diagnostic of subarachnoid hemorrhage (SAH), which is caused by a ruptured intracranial aneurysm in approximately 85% of cases. The next step is cerebral vascular imaging (CT angiography as first-line, or digital subtraction angiography as gold standard) to identify the responsible aneurysm. Early identification and securing of the aneurysm (surgical clipping or endovascular coiling) prevents rebleeding.

Reference: Bailey & Love's Short Practice of Surgery, 27th ed.

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Written and medically reviewed by the StethoPrep medical team.