A shunt is a tube that drains the cerebrospinal fluid (CSF) from the ventricles in the brain to another space in the body, which reabsorbs the fluid. Most often the abdominal cavity (the space around the stomach and intestines) is used. The shunt's small, soft tubing is placed, or tunneled, under the skin, and the end of the tubing is placed in the abdominal space. This is done in the operating room.

A valve is attached to the shunt tubing. It controls the direction the cerebrospinal fluid flows and keeps a normal amount of cerebrospinal fluid in the ventricles. The valve adjusts the amount of cerebrospinal fluid that flows from the ventricles and prevents the ventricles from over-draining, which is called over-shunting.