USMLE – Hydrocephalus
Hydrocephalus (dilatation of the ventricular system) may be due to obstruction of the CSF circulation. Hydrocephalus is said to be ‘communicating’ if the obstruction is outside the ventricular system (usually in the basal cisterns). Obstruction within the ventricles is most common in the narrow channels of the third ventricle and aqueduct. and may be caused by tumor or a congenital anomaly such as aqueduct stenosis.
Diversion of the CSF by means of a shunt procedure between the ventricular system and the peritoneal cavity or right atrium may result in prompt relief of symptoms in obstructive or communicating hydrocephalus.
NORMAL PRESSURE HYDROCEPHALUS
In this condition the dilatation of the ventricular system is caused by intermittent rises in CSF pressure, which occur particularly at night. It occurs predominantly in old age and is suggested by the combination of gait apraxia and dementia, with urinary incontinence as an early feature.
This cause of dilatation of the ventricles needs to be distinguished from that occurring in cerebral atrophy, where the conical sulci are also dilated. The result of shunting procedures for normal pressure hydrocephalus is unpredictable.