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Subarachnoid Haemorrhage (SAH)

Summary

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  • Acute bleeding into the subarachnoid space
  • Typically presents with sudden, severe headache ("thunderclap headache")
  • CT is the initial imaging modality of choice, with CSF analysis if CT is negative1

Pathophysiology

  • Rupture of intracranial aneurysm (80-85% of cases)
  • Non-aneurysmal causes:
    • Arteriovenous malformations
    • Perimesencephalic haemorrhage
    • Vasculitis
    • Cerebral venous thrombosis
  • Complications:
    • Rebleeding
    • Vasospasm
    • Hydrocephalus
    • Seizures

Demographics

  • Incidence: 6-10 per 100,000 person-years
  • Mean age of onset: 50-60 years
  • Female predominance (1.6:1)
  • Risk factors:
    • Hypertension
    • Smoking
    • Excessive alcohol consumption
    • Family history of aneurysms

Diagnosis

  • Clinical presentation:
    • Sudden, severe headache
    • Nausea and vomiting
    • Neck stiffness
    • Photophobia
    • Altered consciousness
  • Investigations:
    • Non-contrast CT brain (sensitivity 98% within 12 hours)
    • Lumbar puncture if CT negative (xanthochromia)
    • CT angiography or digital subtraction angiography to identify source

Imaging

  • Non-contrast CT brain:
    • Hyperdense blood in subarachnoid spaces
    • Intraventricular or intraparenchymal extension may be present
    • Fisher grading scale for SAH severity
  • CT angiography:
    • Identification of aneurysms or vascular malformations
    • Sensitivity 98% for aneurysms >3mm
  • MRI:
    • FLAIR sequence sensitive for subacute SAH
    • SWI useful for detecting microbleeds
  • Digital subtraction angiography:
    • Gold standard for aneurysm detection
    • Allows for treatment planning

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  • 60-year-old patient presented obtunded.
  • CT showed a large left supraclinoid ICA aneurysm with extensive basal cistern subarachnoid haemorrhage and acute hydrocephalus.

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  • A 60-year-old patient presented with headache and reduced GCS.
  • CT showed diffuse symmetrical subarachnoid haemorrhage centred on the suprasellar space.
  • CTA and 3D rotation DSA showed a 4 mm anterior communicating aneurysm.

Treatment

  • Secure the aneurysm early by coiling or clipping; nimodipine and monitoring for vasospasm, hydrocephalus and rebleeding
  • A negative CTA with a benign perimesencephalic pattern of blood suggests non-aneurysmal SAH with a good prognosis

Differential diagnosis

Differential Diagnosis Differentiating Feature
Pseudo-subarachnoid haemorrhage Diffuse sulcal hyperdensity on CT due to severe cerebral oedema or hypoxic-ischaemic injury; no aneurysm on CTA; resolves with treatment of underlying cause
Convexity SAH from RCVS Peripheral cortical sulcal blood rather than basilar cistern predominance; multifocal arterial beading on MRA; typically bilateral and small
Convexity SAH from cerebral venous thrombosis Venous sinus or cortical vein filling defect on CT/MR venography; associated venous infarction crossing arterial territories
Pituitary apoplexy Haemorrhage confined to pituitary fossa on MRI; T1 hyperintensity within enlarged pituitary; no basal cistern blood
Intracerebral haemorrhage Blood in brain parenchyma rather than subarachnoid space on CT; intraparenchymal T1 and T2 signal changes
Leptomeningeal carcinomatosis Sulcal FLAIR hyperintensity without CT-hyperdense blood; nodular leptomeningeal enhancement on contrast MRI

  1. Claassen et al. Spontaneous subarachnoid haemorrhage. 2022. Lancet (London, England) - Open in new tab. ↩