Ventricular shunt. Coloured X-ray of the head of a 38-year-old patient with hydrocephalus, showing the position of a ventricular shunt (dark lines) and its external valve (round, centre right). Hydrocephalus, or water on the brain, is a medical condition in which there is an abnormal accumulation of cerebrospinal fluid (CSF) in the ventricles (cavities) of the brain. A ventricular shunt is a neurosurgical implant that allows the drainage of excess CSF from the affected ventricle.