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Obstructive Hydrocephalus – Posterior Fossa Mass — SCE Neurology MCQ

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ModerateNeuro-oncologyObstructive Hydrocephalus – Posterior Fossa MassSCE Neurology

A 55-year-old man presents with a progressively enlarging head circumference over 6 months. He has headaches, bilateral papilloedema, and bilateral 6th nerve palsies. CT head shows marked ventriculomegaly with enlarged temporal horns. CSF pressure is elevated at 35 cmH₂O. MRI brain shows an enhancing mass in the posterior fossa causing obstruction of the fourth ventricle. What type of hydrocephalus does he have?

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Correct answer: E — Obstructive (non-communicating) hydrocephalus

A posterior fossa mass obstructing the fourth ventricle causes obstructive (non-communicating) hydrocephalus — CSF cannot flow from the ventricular system to the subarachnoid space. Ventriculomegaly with enlarged temporal horns and raised CSF pressure confirm active hydrocephalus. The bilateral 6th nerve palsies are false localising signs from raised ICP. Treatment requires addressing the obstruction (surgical tumour removal, VP shunt, or endoscopic third ventriculostomy). A: NPH has normal CSF pressure. B: Communicating hydrocephalus has patent CSF pathways. D: Ex vacuo is from brain atrophy (ventricles enlarge passively). E: IIH has no ventriculomegaly.

Reference: NICE NG99; Clinical Neuroanatomy