# Hydrocephalus Pathology > Hydrocephalus in MBBS Pathology: communicating versus non-communicating, CSF dynamics, normal pressure hydrocephalus and TB meningitis in India. - Canonical URL: https://prepelephant.com/topics/mbbs/pathology/hydrocephalus-pathology - Exam / course: MBBS · Subject: Pathology - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-02 - Last updated: 2026-10-02 - How to cite: "Hydrocephalus Pathology", PrepElephant, https://prepelephant.com/topics/mbbs/pathology/hydrocephalus-pathology ## Direct answer Excess cerebrospinal fluid under increased pressure within the ventricles defines hydrocephalus, and the single useful classification is anatomical: non-communicating (obstructive), where a block within the ventricular system — classically aqueductal stenosis — prevents CSF reaching the subarachnoid space, versus communicating, where production outpaces absorption at the arachnoid granulations after haemorrhage or meningitis. The choroid plexus makes about 500 mL daily against a total volume near 150 mL, so complete obstruction raises pressure within hours. Children present with macrocephaly, a bulging fontanelle and the setting-sun sign; adults get papilloedema and headache. Normal pressure hydrocephalus, a communicating form of the elderly, delivers the triad of gait apraxia, urinary incontinence and dementia; hydrocephalus ex vacuo is atrophy, not disease. ## What you must remember - **CSF arithmetic:** roughly 500 mL produced daily (0.3-0.4 mL per minute) by choroid plexus, total volume about 125-150 mL, absorbed at arachnoid granulations into dural venous sinuses — a threefold daily turnover. - **Non-communicating causes:** aqueductal stenosis (commonest congenital), colloid cyst of the third ventricle at the foramen of Monro (positional headache), fourth ventricular outlet obstruction, and posterior fossa tumours — medulloblastoma in a child — compressing the fourth ventricle. - **Communicating causes:** subarachnoid haemorrhage and meningitis clogging the granulations; tuberculous basal meningitis is the leading paediatric cause in India, its basal exudate glueing the cisterns. - **Paediatric signs:** enlarging head circumference crossing centiles, tense bulging anterior fontanelle, scalp vein prominence, setting-sun eyes from tectal pressure, Macewen cracked-pot sign, and lower-limb spasticity from stretching of periventricular corticospinal fibres. - **Normal pressure hydrocephalus:** gait apraxia first and most responsive (magnetic, shuffling), then urinary incontinence and subcortical dementia; ventriculomegaly out of proportion to sulcal widening; CSF tap test predicts shunt response. - **Hydrocephalus ex vacuo:** compensatory ventricular enlargement with cortical atrophy — sulci are prominent, pressure normal, and shunting is harmful. - **Treatment logic:** ventriculoperitoneal shunt for most; endoscopic third ventriculostomy for obstructive lesions of the aqueduct and fourth ventricle; the underlying cause (tumour, tuberculosis) treated in parallel. ## Big ventricles: three interpretations An imaging report of dilated ventricles means one of three things, and the sulci decide. Ventriculomegaly with effaced sulci and periventricular transudate means pressure — true hydrocephalus — and the next question is where the block sits. All four ventricles dilated equally with a patent fourth outlet means communicating disease: recent haemorrhage, previous meningitis, or in an Indian child a tuberculous basal exudate thick enough to seal the cisterns, where anti-tubercular therapy accompanies the shunt. Ventricles dilated but only down to the aqueduct, with a normal fourth, means the aqueduct itself — stenosis or a tectal glioma — and opens the endoscopic third ventriculostomy conversation. The third interpretation is the commonest trap: dilated ventricles with proportionately widened sulci in a demented elder is ex vacuo atrophy, and inserting a shunt there produces subdural haematomas, not improvement. Between these poles sits normal pressure hydrocephalus, where the ventricles are large, the sulci are not, the pressure tracks normal on spot measurement, and the gait — wide-based, magnetic, arm-swing preserved — separates it from Parkinson's disease and from Alzheimer's before any tap test. ## Where the localisation slips The viva trick is asymmetry. A single dilated lateral ventricle localises to the ipsilateral foramen of Monro (colloid cyst); both lateral ventricles plus the third dilated, fourth spared, localises to the aqueduct; all four dilated points below the fourth ventricle or to the absorptive surface. Students who memorise causes without this anatomical ladder cannot answer the one-image question examiners actually ask. ## Frequently asked questions ### How is communicating hydrocephalus distinguished from non-communicating? By whether CSF can reach the lumbar subarachnoid space: non-communicating disease obstructs within the ventricular system (classically aqueductal stenosis), communicating disease blocks absorption or flow at the basal cisterns and granulations. ### What is the CSF production rate and site? About 500 mL per day from the choroid plexus, absorbed at arachnoid granulations — against a total volume near 150 mL. ### What is the classical triad of normal pressure hydrocephalus? Gait apraxia (earliest and most shunt-responsive), urinary incontinence and dementia — remembered as wet, wobbly and weird, in any order the examiner chooses. ### Which infection most often causes childhood communicating hydrocephalus in India? Tuberculous meningitis, whose gelatinous basal exudate blocks the cisterns and requires shunting alongside anti-tubercular therapy. ### What is hydrocephalus ex vacuo? Ventricular enlargement compensating for cortical atrophy, with normal pressure, prominent sulci and no indication for shunting.