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.

The most common cause of SAH is head injury and this is called

traumatic SAH

. In the absence of trauma, SAH is termed

spontaneous SAH

. The rest of this note focuses on spontaneous SAH.

Causes of spontaneous SAH include:

• intracranial aneurysm (saccular 'berry' aneurysms)
  • accounts for around 85% of cases
  • conditions associated with berry aneurysms include hypertension,adult polycystic kidney disease, Ehlers-Danlos syndrome and coarctation of the aorta
• arteriovenous malformation
• pituitary apoplexy
• mycotic (infective) aneurysms

Classical presenting features include:

• headache
  • usually of sudden-onset ('thunderclap' or 'hit with a baseball bat')
  • severe ('worst of my life')
  • occipital
  • typically peaking in intensity within 1 to 5 minutes
  • there may be a history of a less-severe 'sentinel' headache in the weeks prior to presentation
• nausea and vomiting
• meningism (photophobia, neck stiffness)
• coma
• seizures
• ECG changes including ST elevation may be seen
  • this may be secondary to either autonomic neural stimulation from the hypothalamus or elevated levels of circulating catecholamines

Investigation