Hydrocephalus

DEFINITION

Hydrocephalus is an increase in cerebrospinal fluid (CSF) volume, usually resulting from impaired absorption, rarely from excessive secretion.

This definition excludes ventricular expansion secondary to brain shrinkage from a diffuse atrophic process (hydrocephalus ex vacuo).

CSF FORMATION AND ABSORPTION

CSF forms at a rate of 500 ml/day

Arachnoid granulations

Lateral ventricle

Foramen of Munro lllrd ventricle --

(0.35 ml/'min), secreted predominantly by the choroid plexus of the lateral, third and fourth ventricles. CSF flows in a caudal direction through the ventricular system and exits through the foramina of Luschka and Magendie into the subarachnoid space. After passing through the tentorial hiatus and over the hemispheric convexity, absorption occurs through the arachnoid granulations into the venous system. CLASSIFICATION

'Obstructive' hydrocephalus - obstruction of CSF flow within the ventricular system. 'Communicating' hydrocephalus - obstruction to CSF flow outwith the ventricular system i.e.

ventricular CSF 'communicates' with the subarachnoid space.

Arachnoid granulations

Lateral ventricle

Foramen of Munro lllrd ventricle --

IVth ventricle

Foramina of Luschka --and Magendie

IVth ventricle

Foramina of Luschka --and Magendie

CAUSES OF HYDROCEPHALUS Obstructive

Acquired - Acquired aqueduct stenosis (adhesions following infection or haemorrhage)

- Supratentorial masses causing tentorial herniation

- Intraventricular haematoma

colloid cyst

- pineal region

- posterior fossa

- Abscesses/granuioma

- Arachnoid cysts

Congenital - Aqueduct stenosis or forking

- Dandy-Walker syndrome (atresia of foramina of Magendie and Luschka)

- Chiari malformation

- Vein of Galen aneurysm

Communicating

Thickening of the leptomeninges and/or involvement of the arachnoid granulations

- infection (pyogenic, TB, fungal)

- subarachnoid haemorrhage

- spontaneous

- trauma

- postoperative

- carcinomatous meningitis Increased CSF viscosity, e.g. high protein content Excessive CSF production -choroid plexus papilloma (rare)

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