A subarachnoid haemorrhage (SAH) is a type of stroke caused by bleeding into the subarachnoid space. The subarachnoid space is the area between the brain and the arachnoid membrane, a delicate membrane that covers the brain and spinal cord.

SAHs are typically caused by a ruptured aneurysm, which is a ballooning or weakening of a blood vessel. Other causes of SAHs include head trauma, arteriovenous malformations (abnormal connections between arteries and veins in the brain), and bleeding disorders.

SAHs can range in severity from minor to life-threatening. Symptoms of a SAH may include a sudden, severe headache; nausea; vomiting; stiff neck; sensitivity to light; seizures; and vision problems.

Treatment for a SAH will vary depending on the size and location of the bleeding, as well as the patient's condition. Treatment may include surgery to clip or coil the aneurysm; medication to reduce the pressure in the brain; and rehabilitation to help patients regain strength and function.