Systematic evaluation of computed tomography angiography collateral scores for estimation of long-term outcome after mechanical thrombectomy in acute ischaemic stroke

Abstract

Purpose: This study compares computed tomography angiography-based collateral scoring systems in regard to their inter-rater reliability and potential to predict functional outcome after endovascular thrombectomy, and relates them to parenchymal perfusion as measured by computed tomography perfusion.

Methods: Eighty-four patients undergoing endovascular thrombectomy in anterior circulation ischaemic stroke were enrolled. Modified Tan Score, Miteff Score, Maas Score and Opercular Index Score ratio were assessed in pre-interventional computed tomography angiographies independently by two readers. Collateral scores were tested for inter-rater reliability by weighted-kappa, for correlations with three-months modified Rankin Scale, and their potential to differentiate between patients with favourable (modified Rankin Scale ≤2) and poor outcome (modified Rankin Scale ≥3). Correlations with relative cerebral blood volume and relative cerebral blood flow were tested in patients with available computed tomography perfusion.

Results: Very good inter-rater reliability was found for Modified Tan, Miteff and Opercular Index Score ratio, and substantial reliability for Maas. There were no significant correlations between collateral scores and three-months modified Rankin Scale, but significant group differences between patients with favourable and poor outcome for Maas, Miteff and Opercular Index Score ratio. Miteff and Maas were significant predictors of favourable outcome in binary logistic regression analysis. Miteff best differentiated between both outcome groups in receiver-operating characteristics, and Maas reached highest sensitivity for favourable outcome prediction of 96%. All collateral scores significantly correlated with mean relative cerebral blood volume and relative cerebral blood flow.

Conclusions: Computed tomography angiography scores are valuable in estimating functional outcome after mechanical thrombectomy and reliable across readers. The more complex scores, Maas and Miteff, show the best performances in predicting favourable outcome.

Keywords: Collateral scores; computed tomography angiography; computed tomography perfusion; ischaemic stroke; thrombectomy.

Figure 1.

Examples of computed tomography angiography (CT-A) scans and survey of collateral scores. Exemplary CT-A scans of two patients with right middle cerebral artery (MCA) occlusion. A representative axial and two coronal CT-A maximum intensity projections (MIPs) are shown. (a) Patient with insufficient collaterals. Modified Tan (mTan) Score was one, Miteff Score was one, Maas Score was one, Opercular Index Score ratio was >2, modified Rankin Scale (mRS) after three months was six. (b) Patient with good collaterals. mTan Score was two, Miteff Score was three, Maas Score was three, Opercular-Index-Score-ratio was one, mRS after three months was zero.

Figure 2.

Receiver operating characteristic analyses. Receiver operating characteristic curves for (a) Modified Tan (mTan) Score, Miteff Score, Maas Score and Opercular Index Score (OIS) ratio and for (b) relative cerebral blood flow (rCBF) mean and relative cerebral blood volume (rCBV) mean to estimate long term functional outcome by means of three-months modified Rankin Scale (mRS). For illustration purposes, receiver operating characteristic analysis for OIS ratio was referred to poor outcome prediction to facilitate visual comparability.

Figure 3.

Binary logistic regression analyses. Forest plots indicating odds ratios (ORs) and confidence intervals (CIs) for the binary logistic regression models for each collateral score and corresponding National Institutes of Health Stroke Scale (NIHSS) are shown. For illustration purposes, binary logistic regression for Opercular Index Score ratio (OISr) was referred to poor outcome prediction to facilitate visual comparability. mTan: modified Tan.