Death or degeneration of tracts and nerve cells within the brain, that may be localised to a certain area of the brain or may be diffuse.
Prolonged cerebral hypoxia (an insufficient supply of oxygen to the brain) is one of the most common causes of difuse brain damage. This may occur in a baby during a difficult birth. Other causes of difuse damage to the brain include respiratory arrest ( cessation of breathing), cardiac arrest (cessation of the heartbeat), certain types of poisoning, drowning and status epilepticus (prolonged seizures).
Diffuse brain damage can also come about gradually as a result of exposure to environmental pollutants, such as mercury compounds or lead, or if nerve cell poisons build up in the brain, as seen in untreated phennylketonuria such as encephalitis.
A brain tumour, brain abscess, head injury or stroke can all cause localised brain damage.
At birth a raised blood level of the bile pigment bilirubin can cause local damage to the basal ganglia (the nerve clusters, deep in the brain). This then leads to the condition called kernicterus. Cerebral palsy results from brain damage either before, during or after birth.
Severe physical disability and learning difficulties can all arise from difuse damage to the brain. Localised brain damage can cause specific deficits in brain function, such as disturbances of speech or movement. Tracts and nerve cells in the brain and spinal cord cannot repair themselves after being damaged, but it is possible that some of the function can return, with intense training, as patients learn to use other parts of the brain.