Subarachnoid haemorrhage

Overview

•Thunderclap headache - sudden onset, maximal intensity within 1-5 minutes, often occipital; 'worst headache of my life' / 'like a blow to the back of the head'

•Meningism - neck stiffness, photophobia, phonophobia (blood irritates meninges; may take hours to develop)

•Nausea and vomiting - raised ICP

•Transient loss of consciousness - sudden ICP surge at rupture

•Third nerve palsy - ptosis, dilated pupil, 'down and out' eye; from posterior communicating artery aneurysm

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A thunderclap headache in a migraine sufferer who says 'this is different' is SAH until proven otherwise. ADPKD is the classic genetic risk factor - berry aneurysm in ~1 in 10 patients.

Investigations

Step 1 · All patients
1Non-contrast CT head - first-line; never contrast CT (contrast appears white and masks blood); shows hyperdensity in basal cisterns/subarachnoid space
↓
CT performed ≤6 hours of onset and normal
SAH excluded - seek alternative diagnosis; LP not routinely indicated
CT performed >6 hours of onset and normal
Perform lumbar puncture at 12 hours post-symptom onset - check for xanthochromia by spectrophotometry
CT positive for SAH
Urgent neurosurgical referral + CT angiography to identify aneurysm/AVM
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Step 3 · If SAH confirmed
1CT cerebral angiography - identifies causative aneurysm or AVM and guides treatment; MR angiography if CT angiography inconclusive

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LP must be ≥12 hours after symptom onset: RBCs lyse → haemoglobin → bilirubin (xanthochromia) takes ~12 hours to develop. Earlier LP risks false-negative. Xanthochromia also distinguishes true SAH from a traumatic tap (no bilirubin in traumatic tap as blood is fresh).

Management

•Immediate: ABCDE; IV access; analgesia; antiemetics; strict bed rest; urgent neurosurgical referral once SAH confirmed

•Vasospasm prevention: nimodipine 60 mg orally every 4 hours for 21 days - calcium channel blocker targeting cerebral vasculature; reduces delayed cerebral ischaemia

•Aneurysm treatment within 24 hours to prevent rebleeding

Aneurysm treatment: coiling vs clipping
FeatureEndovascular coilingSurgical clipping
ApproachInterventional neuroradiology - soft metallic coils inserted into aneurysm lumenCraniotomy - clip applied to aneurysm neck
InvasivenessLess invasive - preferredMore invasive
First-line?Yes - first-line for most ruptured aneurysms (ISAT trial)Alternative if coiling not feasible

Feature	Endovascular coiling	Surgical clipping
Approach	Interventional neuroradiology - soft metallic coils inserted into aneurysm lumen	Craniotomy - clip applied to aneurysm neck
Invasiveness	Less invasive - preferred	More invasive
First-line?	Yes - first-line for most ruptured aneurysms (ISAT trial)	Alternative if coiling not feasible

🎯
Coiling by an interventional neuroradiologist is first-line, not surgical clipping - a common exam distinction.

Complications

•Rebleeding - highest risk in first 24 hours; prevented by urgent aneurysm treatment

•Vasospasm/delayed cerebral ischaemia - peaks 7-14 days post-SAH; prevented by nimodipine

•Hydrocephalus - blood obstructs CSF drainage; acute → external ventricular drain (EVD); chronic → ventriculoperitoneal (VP) shunt

•Hyponatraemia - most commonly SIADH; cerebral salt wasting is alternative (treatment differs - distinguish carefully)

•Cardiac complications - catecholamine surge → deep T-wave inversions, QTc prolongation, troponin rise, neurogenic pulmonary oedema; do not misattribute to ACS