Subarachnoid haemorrhage (SAH) is bleeding from a blood vessel on the surface of the brain into the subarachnoid space: the area between the inner layers of the meninges (membranes covering the brain) that is normally filled with cerebrospinal fluid. Blood in this space rapidly spreads around the brain, causing intense headache and potentially life-threatening complications.
The most common cause of spontaneous (non-traumatic) SAH is rupture of an intracranial aneurysm: a bulge in the wall of a cerebral artery, typically at a vessel junction at the base of the brain (the Circle of Willis). The characteristic presentation is a sudden, extremely severe headache, often described as ‘the worst headache of my life’ or a thunderclap headache, which may be accompanied by loss of consciousness, vomiting, neck stiffness, and light sensitivity.
SAH is a recognised cause of cardiac arrest. Blood in the subarachnoid space can trigger a massive sympathetic nervous system response, causing severe ECG changes, Takotsubo cardiomyopathy, and ventricular fibrillation. This cardiac involvement is known as neurogenic stunned myocardium. In some cases, SAH presents as cardiac arrest before the neurological cause is identified on investigation.
Diagnosis is by urgent CT scan of the head, followed by lumbar puncture if CT is inconclusive. Definitive treatment involves securing the ruptured aneurysm by endovascular coiling (a catheter-based procedure) or surgical clipping, to prevent re-bleeding. SAH carries significant mortality and morbidity; many survivors have lasting neurological and neuropsychological consequences.
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