A 55-year-old man develops a sudden-onset 'thunderclap' headache described as the worst of his life. CT head is normal. Lumbar puncture performed 12 hours later shows xanthochromia. The most likely diagnosis is:
- A Bacterial meningitis
- B Hypertensive intracerebral haemorrhage
- C Subarachnoid haemorrhage ✓
- D Migraine with aura
Correct answer: C. Subarachnoid haemorrhage
Explanation
A sudden-onset thunderclap headache with xanthochromia on lumbar puncture (caused by bilirubin from haemoglobin degradation, detectable from 2-4 hours to 2 weeks) is diagnostic of subarachnoid haemorrhage (SAH), even when CT is negative. CT detects SAH in approximately 98% of cases within 6 hours but sensitivity falls thereafter, making LP essential when CT is negative. The most common cause is rupture of a berry (saccular) aneurysm at the circle of Willis. Urgent neurosurgical referral for CT angiography and aneurysm treatment is required.
Reference: Bailey & Love's Short Practice of Surgery, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.