Subarachnoid Haemorrhage – CSF Diagnosis — SCE Neurology MCQ

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ModerateCerebrovascular DiseaseSubarachnoid Haemorrhage – CSF DiagnosisSCE Neurology

A 35-year-old man presents with a thunderclap headache. CT head is normal at 3 hours. LP is performed at 14 hours. CSF shows uniform red cells (1,200 per µL in tube 1 and 1,180 per µL in tube 3) and xanthochromia is detected by spectrophotometry. What is the most likely interpretation?

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Correct answer: B — Subarachnoid haemorrhage

Explanation lettering: C = shown as A · D = shown as C · E = shown as D · A = shown as E

The presence of uniform red cell counts across sequential CSF tubes (not decreasing, unlike traumatic LP) combined with xanthochromia detected by spectrophotometry is diagnostic of subarachnoid haemorrhage. Spectrophotometry is more reliable than visual inspection for detecting xanthochromia. A: Traumatic LP would show a decreasing RBC count between tubes. C/E: Xanthochromia with uniform RBCs is not a normal or artefactual finding. D: Meningitis does not typically cause xanthochromia.

Reference: RCP National Clinical Guideline for Stroke (2023); ABN Guidelines on LP for SAH