Venous-phase Tan-based collateral assessment on CTP-derived CTA for outcome stratification after reperfusion therapy in acute ischemic stroke.

BACKGROUND: Collateral status is closely related to functional outcome after reperfusion therapy in acute ischemic stroke. Conventional single-phase computed tomography angiography (CTA) Tan score may be affected by scan timing and delayed collateral filling, whereas CTA reconstructed from computed tomography perfusion (CTP) source images provides time-resolved vascular information. This study compared conventional CTA Tan score with time-specific Tan-based collateral scores on CTP-derived CTA for predicting 90-day functional outcome. METHODS: This single-center retrospective study included 104 stroke events from 103 patients with acute anterior circulation ischemic stroke who underwent intravenous thrombolysis and/or mechanical thrombectomy. Conventional CTA Tan score and CTP-derived CTA arterial-phase, arteriovenous-phase, and venous-phase time-specific Tan-based scores were assessed. The primary outcome was favorable functional outcome, defined as a modified Rankin Scale score of 0-2 at 90 days. Logistic regression, receiver operating characteristic curve analysis, DeLong tests, treatment-stratified analyses, and exploratory thrombectomy sensitivity analyses were performed. RESULTS: Sixty-two stroke events were associated with a favorable outcome. Forty-three events were treated with mechanical thrombectomy (37 direct thrombectomy and six bridging therapy), and 61 were treated with intravenous thrombolysis without subsequent thrombectomy. The areas under the curve for conventional CTA Tan score and CTP-derived arterial-phase, arteriovenous-phase, and venous-phase scores were 0.811, 0.811, 0.814, and 0.856, respectively. The venous-phase score showed the highest discriminative performance, although the overall difference compared with conventional CTA Tan score did not reach statistical significance (p = 0.079). In multivariable analysis, the venous-phase score remained associated with favorable outcome after adjustment for measured covariates. In the mechanical thrombectomy subgroup, the venous-phase score showed a higher AUC than conventional CTA Tan score (0.833 vs. 0.684; p = 0.004), whereas no significant difference was observed in the intravenous thrombolysis subgroup; however, the treatment-by-score interaction was not statistically significant (p = 0.788). CONCLUSION: The venous-phase Tan-based score on CTP-derived CTA may reflect delayed collateral filling and was associated with 90-day favorable outcome. Its AUC was numerically higher than that of the conventional CTA Tan score, but the difference was not statistically significant; incremental prognostic value remains to be confirmed. The mechanical thrombectomy subgroup finding should be considered exploratory and hypothesis-generating.