The majority of spontaneous subarachnoid haemorrhags are caused by berry aneurysms. Although mainly congenital, aneurysms may develop as a result of degenerative and hypertensive changes. Subarachnoid haemorrhage can occur at any age, but it is a particularly important cause of death and disability in the 20- 40 year age group. The typical history of subarachnoid haemorrhage is severe headache of abrupt onset accompanied by neck pain and stiffness, and vomiting.
Drowsiness is common, and there is often confusion and impairment of consciousness.
Some patients will be deeply unconscious at presentation. In such patients, neck stiffness may be absent. Focal hemisphere signs may be present, due to either intracerebral bleeding or vasospasm. Investigation If done within 8 hours of the haemorrhage, the CSF may not contain blood, though the pressure is usually raised. The CSF in subarachnoid haemorrhage is often obviously uniformly bloodstained.