Brain damage

Degeneration or death of nerve cells and tracts within the brain that may be localized to a particular area of the brain or diffuse. Diffuse damage most commonly results from prolonged cerebral hypoxia (which may occur in a baby during a difficult birth), cardiac arrest, respiratory arrest, or causes such as poisoning or status epilepticus (prolonged convulsions). The damage may also occur gradually due to environmental pollutants such as lead or mercury compounds (see Minamata disease) or if nerve-cell poisons build up in the brain, as in untreated phenylketonuria. Other possible causes include brain infections such as encephalitis. Localized brain damage may occur as a result of a head injury, stroke, brain tumour, or brain abscess. At birth, a raised blood level of bilirubin (in haemolytic disease of the newborn) causes local damage to the basal ganglia deep within the brain. This leads to a condition called kernicterus. Brain damage that occurs before, during, or after birth may result in cerebral palsy. Damage to the brain may result in disabilities such as learning difficulties or disturbances of movement or speech. Nerve cells and tracts in the brain and spinal cord cannot repair themselves once they have been damaged, but some return of function may be possible.