Brain, disorders of

Defects and disorders of the brain, which may have one of numerous causes including infection, injury, brain tumour, or a lack of blood or oxygen ( hypoxia). Because the brain is encased in the skull, any space-occupying tumour, brain abscess, or haematoma creates raised pressure, which impairs the function of the whole brain. Brain disorders that are localized in a small region may affect a specific function such as speech (see aphasia). More often, damage is more diffuse and the symptoms can be varied and numerous. Some brain disorders are congenital due to genetic or chromosomal disorders, as in Down’s syndrome. Structural defects that arise during the development of the fetus in the womb include hydrocephalus and anencephaly. Reduced oxygen supply may occur at birth, causing cerebral palsy. Later in life, cerebral hypoxia can result from choking or from arrest of breathing and heartbeat. From middle age onwards, cerebrovascular disease is the most important cause of brain disorder. If an artery within the brain becomes blocked or ruptures, leading to haemorrhage, the result is a stroke. The brain may also be damaged by a blow to the head see head injury). Infection within the brain ( encephalitis) may be due to viral infection. Infection of the membranes surrounding the brain ( meningitis) is generally due to bacterial infection. Creutzfeldt–Jakob disease is a rare, fatal brain disease associated with an infective agent called a prion which, in some cases, has been linked with BSE ( bovine spongiform encephalopathy), a disease in cattle. Multiple sclerosis is a progressive disease of the brain and spinal cord. Degenerative brain diseases include Alzheimer’s disease and Parkinson’s disease. Emotional or behavioural disorders are generally described as psychiatric illnesses; but the distinction between neurological and psychiatric disorders is now much less clear.