Subarachnoi hemorrhage (SAH, pronounced /sʌbərəknuːd heɪmɔrhɛgɛ/), or subarachnoid haemorrhage in British English, is bleeding into the subarachnoid space — the area between the arachnoid membrane and the pia mater surrounding the brain. This may occur spontaneously, usually from a cerebral aneurysm, or may result from trauma. Symptoms include an intense headache with a rapid onset ('thunderclap headache'), vomiting, and an altered level of consciousness.Diagnosis is generally made with computed tomography (CT scanning) or occasionally by lumbar puncture. Treatment is made with close observation and prompt neurosurgical investigations, medications and other treatment methods to help prevent recurrence and complications.