False-colour computed tomography (CT) scan of the brain of a 79 year old woman suffering from a left subdural haematoma, which appears as the solid red region over the centre-right area of the brain. A haematoma is an accumulation of blood within tissue that clots to form a solid swelling. Subdural haematomas occur in elderly people, where a relatively slight head injury may tear veins in the space beneath the dura, the outermost of the three membranes, or meninges, which surround the brain. The condition may be rectified by surgery.