Dilation of the ventricles (or hydrocephalus) occurs when the circulation of CSF is blocked or its absorption is impeded, while the CSF formation continues to occur at a constant rate. This results in an increase in ventricular pressure that, in turn, causes ventricular dilation. The ventricular dilation exerts pressure on the adjacent tissue, causing impairment of such structures as the corticobulbar and corticospinal tracts. Therefore, a progressive loss of motor function ensues. Hydrocephalus may occur before birth and is usually noted during the first few months of life.

When movement of CSF out of the ventricular system is impeded (e.g., by blockage at the cerebral aqueduct or foramina of the fourth ventricle), the ensuing hydrocephalus is classified as a noncommunicating hydrocephalus. If the movement of the CSF into the dural venous sinuses is impeded or blocked by an obstruction at the arachnoid villi, hydrocephalus developed in this manner is called a communicating hydrocephalus. In communicating hydrocephalus, a tracer dye injected into the lateral ventricle does not appear in the lumbar CSF, indicating that there is an obstruction to the flow of CSF in the ventricular pathways.

Hydrocephalus is either too much or too little CSF.

The commonest cause of hydrocephalus is either too much or too little CSF.

Blockage of the movement of CSF out of the ventricles through foramina or into the venous circulation via arachnoid villi results in a condition called hydrocephalus.

This condition leads to expanded ventricles, resulting in damage to brain tissue or expansion of the skull in infants.
- Increased water in the head.  Could be caused by blockage of ventricles.  Blockage of ventricles in the brain can be caused by tumours of ependymal cells.