Normal adult CSF pressure measured by lumbar puncture in the lateral decubitus position is 7–18 cmH2O. A patient has a pressure of 28 cmH2O with normal CSF composition. Which condition most commonly causes raised CSF pressure with normal composition?

• A Bacterial meningitis
• B Normal pressure hydrocephalus
• C Subarachnoid haemorrhage
• D Idiopathic intracranial hypertension (pseudotumour cerebri) ✓

Explanation

Idiopathic intracranial hypertension (IIH) is characterized by elevated opening CSF pressure (>25 cmH2O in adults, measured in lateral decubitus) with completely normal CSF composition (cells, glucose, protein), no space-occupying lesion, and no identifiable cause. It presents with headache, visual obscurations, and papilloedema. In bacterial meningitis the CSF shows pleocytosis, raised protein, and low glucose. Subarachnoid haemorrhage shows xanthochromia/blood. Normal pressure hydrocephalus has normal or near-normal pressure despite dilated ventricles.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

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