The ventricular system can be obstructed anywhere along its path. (See Hydrocephalus: Obstructive Type .)The picture to the left shows a tumor pushing on the IVth ventricle. It is located in the brain structure called the cerebellum at the back and base of the skull. This is a common location where brain tumors cause hydrocephalus, either by invading the IV ventricle and blocking CSF (cerebral spinal fluid) flow, or due to swelling from the tumor causing the ventricle to swell shut. Sometimes strokes or hemorrhages may cause this sequence of events as well. Look at the obstruction of CSF flow below. The CAT Scan below also shows a cross section of the problem in a patient with a cerebellar tumor and swelling.

Cerebellar Brain Tumor pushing on the IV Ventricle

The CSF can flow down its usual pathway, but it is beginning to become obstructed by the tumor. Unless treated, as the tumor grows the ventricle will close off and obstructive hydrocephalus will develop.

Cerebellar Brain Tumor pushing on the IV Ventricle

This patient has a tumor pushing on the IV ventricle. See how the symmetry of the IV ventricle is lost. The black in the IV Ventricle is Cerebral Spinal Fluid. The lighter grey tissue is the cerebellum. The darker grey tissue is tumor plus swollen cerebellum.