Neurology

Subarachnoid haemorrhage

Arterial blood bursts into the cerebrospinal fluid around the brain, usually from a ruptured intracranial aneurysm, raising intracranial pressure and irritating the meninges within seconds. Abbreviated SAH.

Definition

Subarachnoid haemorrhage is bleeding into the subarachnoid space, diagnosed when non-contrast CT shows blood there, or when lumbar puncture shows elevated bilirubin (xanthochromia) on spectrophotometry. It is aneurysmal when CT angiography, digital subtraction angiography or magnetic resonance angiography shows an intracranial arterial aneurysm and the pattern of blood fits aneurysm rupture.

First principles

Rate of onset is the clue, not severity

A ruptured artery fills the subarachnoid space in seconds, so the headache peaks within 1 to 5 minutes rather than building. Severity alone is not specific: most thunderclap headaches are not SAH, and cough, exertion, coitus and migraine all produce one. Rate of onset is the question you ask, and a headache that has since settled does not exclude the diagnosis.

You’ve reached the end of the preview

The rest of this extended textbook page is part of full access. Create a free account to read the sample topics in full and try sample questions, then upgrade to unlock every high-yield and extended page, plus the complete question bank.

This page is exam revision material, not medical advice, and must not be used for patient care. Always check drug doses against the BNF and current guidance. Full disclaimer.