Subarachnoid Haemorrhage

Key points

• Subarachnoid haemorrhage A subarachnoid haemorrhage (SAH) is an intracranial haemorrhage that is defined as the presence of blood within the subarachnoid space, i.e. deep to the subarachnoid layer of the meninges.
• lntracranial aneurysm* (saccular 'berry' aneurysms): this accounts for around 85% of cases. Conditions associated with berry aneurysms include adult polycystic kidney disease, Ehlers-Danlos syndrome and coarctation of the aorta
• Arteriovenous malformation
• Pituitary apoplexy
• Arterial dissection
• DIAGNOSTIC PATHWAY (NICE NG228, 2022): immediate non-contrast CT head · CT is at its most sensitive WITHIN 6 HOURS of symptom onset, and a negative CT in that window makes SAH very unlikely.
• If the CT is negative and it was performed MORE THAN 6 HOURS after onset, do a LUMBAR PUNCTURE — but delay it until at least 12 HOURS from symptom onset, so that red cells have broken down. Diagnose SAH if the sample shows raised BILIRUBIN (xanthochromia) on SPECTROPHOTOMETRY; think about alternative diagnoses if it does not.
• Once SAH is confirmed, CT ANGIOGRAPHY identifies the underlying aneurysm or vascular lesion · discuss urgently with a specialist neurosurgical centre, and do not use a severity score in isolation to decide on transfer.
• The risk of REBLEEDING is highest within the first 24 hours — which is why definitive treatment of the aneurysm is not delayed.
• NIMODIPINE is given to reduce DELAYED CEREBRAL ISCHAEMIA (the other major cause of late deterioration, typically around days 4–10) · BNF dosing for prevention of ischaemic neurological deficit is 60 mg every 4 hours for up to 21 days · note it is used to prevent delayed ischaemia, NOT to treat the bleed itself.