Subarachnoid haemorrhage (SAH)
Definition and importance
Subarachnoid haemorrhage is bleeding into the subarachnoid space, most commonly due to rupture of a cerebral saccular (berry) aneurysm. It is a neurological emergency with high early morbidity and mortality; prompt recognition, urgent neuroimaging and immediate specialist discussion are essential to reduce rebleeding and secondary brain injury (NICE NG228).
Epidemiology and risk factors
- Non‑traumatic SAH is aneurysmal in about 75-80% of cases; perimesencephalic and other non‑aneurysmal causes account for most of the remainder.
- Unruptured intracranial saccular aneurysms are present in roughly 2-3% of the population.
- Important risk factors include cigarette smoking, hypertension, excess alcohol use, autosomal dominant polycystic kidney disease, a family history of SAH in first‑degree relatives and connective tissue disorders (e.g. vascular Ehlers-Danlos, Marfan).
- Other causes include arteriovenous malformations, dissections and intracranial tumours, which are less common.
Clinical presentation and red flags
- Typical presentation is a sudden severe headache - a “thunderclap” or the “worst headache of life” with maximal intensity at onset.
- Associated features include vomiting, meningism (neck stiffness, photophobia), transient loss of consciousness, seizures and acute confusion.
- High‑risk features that increase likelihood of aneurysmal SAH or poorer prognosis are reduced level of consciousness (fall in GCS), focal neurological deficit, seizure at onset and haemodynamic instability.
- Maintain a high index of suspicion for any unexplained acute severe headache (NICE NG228).