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Introduction The traditional investigation pathway for all non-traumatic subarachnoid haemorrhage (SAH) regardless of blood distribution is a CT angiogram (CTA) followed by digital subtraction angiography (DSA) irrespective of CTA findings. However, perimesencephalic SAH (PSAH) in the literature is considered a more ‘benign’ form of SAH, less associated with aneurysm rupture, suggesting that DSA may not be necessary in these circumstances. Judicious resource allocation and young patient cohort are reasons for more circumspect use of DSA as a means of investigating SAH.Aim of study To analyse the additive yield of DSA in patients with SAH stratified by blood distribution and CTA findingsMethod A retrospective analysis of CT head, CTA and fluoroscopic findings in patients investigated for SAH between September 2023 – December 2024 at a tertiary neurovascular centre.Results Ninety-seven patients had a DSA as part of a SAH work-up and PSAH was identified in 18 patients. Of these 7 were DSA-positive for underlying aneurysmal disease (38.9%). Review of CTA demonstrated all 7 were also CTA-positive for aneurysmal disease. Conversely, patients with PSAH who were negative for aneurysm disease on CTA were also DSA-negative.Interestingly, 4 patients, who had normal CT head and CTA but lumbar puncture suggestive of SAH, were all DSA-negative for aneurysmal disease.Abstract A54 Figure 1Conclusion In our experience, PSAH warrants CTA due to the significant prevalence of aneurysm rupture (38.9%). However, as CTA findings in patients with PSAH are congruous with subsequent DSA findings, this suggests that other less-invasive modalities (e.g. vessel wall MRI) could potentially be employed prior to DSA in younger patient cohort.Conflict of Interest No