Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. A subarachnoid hemorrhage 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 ruptured cerebral aneurysm, or may result from head injury. Symptoms of SAH include a severe headache with a rapid onset ("thunderclap headache"), vomiting, confusion or a lowered level of consciousness, and sometimes seizures. The diagnosis is generally confirmed with a CT scan of the head, or occasionally by lumbar puncture. Treatment is by prompt neurosurgery or radiologically guided interventions with medications and other treatments to help prevent recurrence of the bleeding and complications. Surgery for aneurysms was introduced in the 1930s, but since the 1990s many aneurysms are treated by a less invasive procedure called "coiling", which is carried out by instrumentation through large blood vessels.