Extracerebral haemorrhages are situated between the skull and the cortex of the brain. A subarachnoid haemorrhage - beneath the arachnoid meninx - mostly occurs out of a tear in a blood vessel, nearly always at the base of the brain. Vehement headache and loss of consciousness are important characteristics. Skull traumas and fractures can result in haemorrhages between the two layers of the dural meninx or beneath the dura mater and above the arachnoid. Patients with these respectively epidural and subdural hematomas often show a lucid (clear) interval before losing consciousness. The chronic form of subdural hematoma can mimic the onset of dementia or the effects of drug abuse. The cause is often a not memorised head trauma.