A 55-year-old man presents with a sudden-onset severe headache 'like a thunderclap', and CT head performed within 6 hours of symptom onset is negative. What is the next appropriate investigation?

• A MRI brain with gadolinium
• B Repeat CT head after 12 hours
• C Lumbar puncture for xanthochromia and red cell count ✓
• D CT angiography of cerebral vessels immediately

Explanation

A negative CT head within 6 hours does not exclude subarachnoid haemorrhage (SAH); sensitivity of CT for SAH decreases from >98% within 6 hours to ~85% at 24 hours. A lumbar puncture performed 12 hours after symptom onset (to allow lysis of red cells) is performed to detect xanthochromia (yellow CSF from oxyhaemoglobin/bilirubin) — the gold standard confirmation. A positive LP mandates CT angiography to identify a berry aneurysm for coiling or clipping. MRI alone has insufficient sensitivity for acute SAH.

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.