• Annabel Vincent, Scott Pearson, John W Pickering, James Weaver, Leanne Toney, Laura Hamill, Michael Hurrell, and Martin Than.
• Christchurch Hospital Emergency Department, Canterbury District Health Board, Christchurch, Canterbury, New Zealand.
• Emerg Med J. 2022 Nov 1; 39 (11): 810-817.

BackgroundCT performed within 6 hours of headache onset is highly sensitive for the detection of subarachnoid haemorrhage (SAH). Beyond this time frame, if the CT is negative for blood, a lumbar puncture is often performed. Technology improvements in image noise reduction, resolution and motion artefact have enhanced the performance of multislice CT (MSCT) and may have further improved sensitivity. We aimed to describe how the sensitivity to SAH of modern MSCT changes with time from headache onset.MethodsThis was a retrospective analysis of electronic data collected as part of routine care among all patients presenting to Christchurch Hospital diagnosed with a SAH between 1 January 2008 and 31 December 2017. Patients were imaged with MSCT. The primary outcome was the proportion of patients with spontaneous aneurysmal SAH (identified via coding and confirmed by clinical and radiological records) that had a positive MSCT. The secondary outcome was the proportion of patients with any type of spontaneous SAH that had a positive MSCT.ResultsThere were 347 patients with an SAH of whom 260 were aneurysmal SAH. MSCT identified 253 (97.3%) of all aneurysmal SAH and 332 (95.7%) of all SAH. The sensitivity of MSCT was 99.6% (95% CI 97.6 to 100) for aneurysmal SAH and 99.0% (95% CI 97.1 to 99.8) for all SAH at 48 hours after headache onset. At 24 hours after headache onset, the sensitivity for aneurysmal SAH was 100% (95% CI 98.3 to 100).ConclusionThese data suggest that it may be possible to extend the timeframe from headache onset within which modern MSCT can be used to rule out aneurysmal SAH.© Author(s) (or their employer(s)) 2022. No commercial re-use. See rights and permissions. Published by BMJ.

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