Written by Millie Cossé
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There is a very low likelihood of missing aneurysmal SAH if CT brain imaging is obtained within 24 hours of symptoms onset, but these results are not enough to change practice.
Can you get away with just a scan?
Current international guidelines suggest that a non-contrasted CT head can rule out SAH if performed within 6 hours of symptom onset. This prospective observational cohort study evaluated the safety of using CT imaging of the brain to rule out subarachnoid hemorrhage (SAH) beyond 6 hours of headache onset.
CT brain within 24 hours of symptom onset was performed in 2,008 patients across multiple sites. It had a sensitivity of 94.6% (95%CI 91.0% to 97.0%) for detecting SAH. The authors found that the posttest probability of SAH after a negative CT head within 24 hours was less than 1%, and the majority of missed SAH cases were non-aneurysmal (posttest probability for aneurysmal SAH was 0.1% in this group).
How will this change my practice?
When I have serious concern for SAH, I tend to start with CT angiography rather than a non-contrasted CT head. If no bleed and no aneurysmal source are identified, I have a conversation with the patient about the limitations of our studies and the possibility of a SAH that would likely be conservatively managed anyway. Still haven’t had anyone take me up on the offer of a lumbar puncture.
Source
Subarachnoid haemorrhage in the emergency department (SHED): a prospective, observational, multicentre cohort study. Emerg Med J. 2024 Nov 21;41(12):719-727. doi: 10.1136/emermed-2024-214068. PMID: 39266054.
