Variety of conditions characterized by an excess of fluid within the cranial vault, subarachnoid space, or both

Occurs because of interference with cerebrospinal fluid (CSF) flow caused by increased fluid production, obstruction within the ventricular system, or defective reabsorption of CSF

Types:

Obstruction of CSF flow associated with hydrocephalus produces dilation of the ventricles proximal to the obstruction.

Obstructed CSF under pressure causes atrophy of the cerebral cortex and degeneration of the white matter tracts; selective preservation of gray matter also occurs.

When excess CSF fills a defect caused by atrophy, a degenerative disorder, or a surgical excision, the fluid isn’t under pressure and atrophy and degenerative changes aren’t induced.