Hydrocephalus. Coloured computed tomography (CT) scan of an axial (horizontal) section through the brain of a child with hydrocephalus (water on the brain). The fluid-filled ventricles (red/green) have been enlarged by the excessive production, or blockage in the circulation, of the cerebrospinal fluid (CSF) that fills the spaces in and around the brain and spinal cord. If the condition devel- ops after birth, the head swells up as its bones have not yet fused. In older patients, however, the inflexible skull means pressure on the brain builds up, causing headaches, loss of coordination and deterioration of mental function. Treatment is by draining excess fluid from the brain.