Brain disorders can be classified by cause, a useful division because it also indicates something about their amenability to treatment and the treatment required. Circulatory problems of the brain (stroke) include cerebral infarction, and cerebral haemorrhage, in which blood is discharged into brain tissue. Haemorrhages outside the brain but inside the skull (between the meninges) are subarachnoid, subdural and epidural haemorrhage. The last two in particular can occur after an injury involving brain damage. Various tumours, benign and malignant, can occur in and around the brain. The brain can also be affected by infection – encephalitis or meningitis according to the site. Disorders involving decay of brain tissue (degenerative diseases) include Parkinson’s disease, Huntington’s chorea, Friedreich’s ataxia and multiple sclerosis. Chronic alcohol poisoning combined with a shortage of vitamin B can also cause brain cell loss (including Korsakoff’s syndrome and Wernicke’s disease). Extensive brain tissue decay causes dementia. Injuries can cause fractures of the cranium or the base of the skull, with possible concussion. Epilepsy and migraine are functional disturbances of the brain not associated with anatomical abnormality.