Definition

Hydrocephalus (HC) is a hydrodynamic disorder of CSF due to a disturbance of formation, flowor absorption of CSF that leads to an increase in volume occupied by this fluid within CNS. (Note: increased CSF volume also observed in cerebral atrophy but this is not due to a hydrodynamic disorder, but a passive filling of the increased vacant space; hence the old term ‘hydrocephalus ex vacuo’.)

Classification

Functional:

1. Obstructive or non-communicating: block is proximal to arachnoid granulations with an obstruction of CSF flow in the ventricular system or its outlets to the subarachnoid space.

2. Communicating: full communication exists between the ventricles and subarachnoid space with CSF circulation blocked at level of arachnoid granulations. Causes: decreased CSF absorption, venous drainage insufficiency, or CSF overproduction (rare).

Alternative classifications:

1. Acute (over days)/subacute (weeks)/chronic (months or years).

2. Congenital or acquired.

3. Arrested HC: stabilization of known ventricular enlargement after compensation. These patients are prone to decompensation, e.g. with aminor head injury.

4. Normal pressure hydrocephalus (NPH): a triad of dementia, abnormal gait, and urinary incontinence, in the absence of papilloedema and in the presence of normal CSF pressures on lumbar puncture.

Incidence: 3/1000 live births with congenital HC. Incidence of acquired HC unknown, but about 100 000 V-P (ventriculo-peritoneal) shunts performed in developed countries per annum.

Gender: M:F=1:1. In NPH M > F. X-linked HC in Bickers-Adams syndrome.

Age: bi-modal age curve with peaks in infancy and adulthood (40%).