Abstract DP343: Computed Tomography Angiography Misses One-Third of Vasospasm Cases Compared to Digital Subtraction Angiography Following Subarachnoid Hemorrhage

Vasospasm following subarachnoid hemorrhage (SAH) is a major cause of delayed cerebral ischemia, a leading contributor to morbidity and mortality. Early screening and detection of vasospasm are critical for risk stratification and guiding management decisions. Digital subtraction angiography (DSA) is considered the diagnostic gold standard, while computed tomography angiography (CTA) provides a less invasive and more widely available alternative often used for initial screening. We compared the performance of CTA versus DSA in detecting post-SAH vasospasm across 40 baseline-matched patients with paired imaging studies. Patients were stratified into groups based on whether DSA detected more vasospasm (n=24) or not (n=16). Baseline demographics and severity scores (GCS, Hunt&Hess, Modified Fisher) were similar between groups, minimizing confounders. Overall, 32.5% of vasospasm detected by DSA went undetected by CTA (p<0.001). Compared with DSA, CTA performed significantly worse in detecting vasospasm of the ICA, M1, ACA, and Basilar vessels. In the ICA, CTA missed 12 cases detected by DSA while it overcalled only 1, yielding a sensitivity of 42% and specificity of 95% versus DSA (p=0.003). Similar under-detection was observed in the M1 (10 missed, 1 overcalled, sensitivity 67%, specificity 92%, p=0.012), ACA (18 missed, 0 overcalled, sensitivity 47%, specificity 100%, p<0.001), and Basilar (6 missed, 0 overcalled, sensitivity 33%, specificity 100%, p=0.031). In contrast, CTA and DSA did not differ significantly in the detection of vasospasm in the M2, vertebral, and PCA vessels (p=0.453, 0.125, 0.289). CTA also underestimated bilaterality: DSA classified 9 patients as bilateral, whereas CTA identified them as unilateral (p=0.003), yielding excellent ensitivity for bilateral detection of 100.00% (95% CI 78.47-100.00), but poor specificity of 25.00% (95% CI 8.89-53.23). In conclusion, CTA missed nearly one-third of vasospasm cases detected by DSA, particularly in the ICA, M1, ACA, and basilar territories, and frequently underestimated bilaterality. These findings reinforce DSA as the diagnostic gold standard for post-SAH vasospasm, while highlighting important limitations of CTA when used in isolation. Although CTA remains valuable as a rapid, noninvasive screening tool, reliance on it alone risks underestimating vasospasm burden and mischaracterizing disease extent.