Screening Computed Tomography Angiography to Identify Patients at Low Risk for Delayed Cerebral Ischemia Following Aneurysmal Subarachnoid Hemorrhage

Introduction Delayed cerebral ischemia (DCI) occurs during a risk period of 3-21 days following aneurysmal subarachnoid hemorrhage (aSAH) and is associated with worse outcomes. The identification of patients at low risk for DCI might permit triage to less intense monitoring and management. While large-vessel vasospasm (LVV) is a distinct clinical entity from DCI, the presence of moderate-to-severe LVV is associated with a higher risk of DCI. Our hypothesis was that the absence of moderate-to-severe LVV on screening Computed Tomographic Angiography (CTA) performed within the first few days of the DCI risk period will accurately identify patients at low risk for subsequent DCI. Methods This was a retrospective cohort study. Our institutional SAH outcomes registry was queried for all aSAH patients admitted 2016 – 2019 who underwent screening CTA brain between days 4-8 following ictus. We excluded patients diagnosed with DCI prior to the first CTA performed during this time period. All variables are prospectively entered into the registry, and outcomes including DCI and LVV are prospectively adjudicated. We evaluated the predictive value and accuracy of moderate-to-severe LVV on CTA performed 4-8 days following ictus for the prediction of subsequent DCI. Results A total of 243 aSAH patients were admitted during the study timeframe. Of 54 patients meeting eligibility criteria, 11 (20%) had moderate-to-severe LVV on the screening CTA study performed during the risk period. Seven of 11 (64%) patients with moderate-to-severe LVV on the day 4-8 screening CTA, vs. 6 of 43 (14%) patients without, subsequently developed DCI. On multivariate analysis, the presence of LVV on day 4-8 screening CTA was an independent predictor of DCI (Odds Ratio 10.26, 95%CI 1.69-62.24, p=0.011). NPV for the subsequent development of DCI was 86% (95%CI 77-92%). Sensitivity was 54% (25-81%), Specificity 90% (77-97%), and Positive Predictive Value 64% (38-83%). Conclusions The presence of moderate-to-severe LVV on screening CTA performed between days 4-8 following aSAH was an independent predictor of DCI, but achieved only moderate diagnostic accuracy, with NPV 86% and sensitivity 54%. Complementary risk-stratification strategies are likely necessary.