Mortality of ~50% in 1st month
Rebleeds occur at the rate of 1-5% per day and 15-20% in 1st 2/52
CT scan
may be -ve in 10-15% of patients
false -ve CT scan can result from severe anaemia or small-volume subarachnoid haemorrhage.
location of blood within the subarachnoid space correlates directly with the location of the aneurysm in 70% of cases.
In general, blood localized to the basal cisterns, the sylvian fissure, or the intra-hemispheric fissure indicates rupture of a saccular aneurysm.
Blood lying over the convexities or within the superficial parenchyma of the brain often is indicative of arteriovenous malformation (AVM) or mycotic aneurysm rupture.
Intra-parenchymal haemorrhage may occur with middle communicating artery and posterior communicating artery aneurysms.
Inter-hemispheric and intraventricular haemorrhages may occur with anterior communicating artery aneurysms
The Fisher grading system is used to classify SAH:
Grade 1 - No subarachnoid blood seen on CT scan
Grade 2 - Diffuse or vertical layers of SAH less than 1 mm thick
Grade 3 - Diffuse clot and/or vertical layer greater than 1 mm thick
Grade 4 - Intracerebral or intraventricular clot with diffuse or no subarachnoid blood
Lumbar puncture
may be -ve in 10-15%
may be -ve if performed <2/24, most sensitive 12/24 after onset of symptoms.
examines for RBC's and xanthochromia - traumatic tap will have greater RBC's in 1st tube vs SAH has greater no's in 3rd tube