A shunt is a drainage system that's surgically inserted into the brain. It's a long, thin tube with a valve that helps brain fluid flow properly.
One end of the tube is put in the brain, while the other is put under the skin to another part of the body like the stomach. This other part of the body can absorb any excess fluid.
If you have hydrocephalus, you will usually need a shunt for the rest of your life.