Improved outcome prediction using CT angiography in addition to standard ischemic stroke assessment: results from the STOPStroke study

Abstract

Purpose: To improve ischemic stroke outcome prediction using imaging information from a prospective cohort who received admission CT angiography (CTA).

Methods: In a prospectively designed study, 649 stroke patients diagnosed with acute ischemic stroke had admission NIH stroke scale scores, noncontrast CT (NCCT), CTA, and 6-month outcome assessed using the modified Rankin scale (mRS) scores. Poor outcome was defined as mRS>2. Strokes were classified as "major" by the (1) Alberta Stroke Program Early CT Score (ASPECTS+) if NCCT ASPECTS was ≤7; (2) Boston Acute Stroke Imaging Scale (BASIS+) if they were ASPECTS+ or CTA showed occlusion of the distal internal carotid, proximal middle cerebral, or basilar arteries; and (3) NIHSS for scores >10.

Results: Of 649 patients, 253 (39.0%) had poor outcomes. NIHSS, BASIS, and age, but not ASPECTS, were independent predictors of outcome. BASIS and NIHSS had similar sensitivities, both superior to ASPECTS (p<0.0001). Combining NIHSS with BASIS was highly predictive: 77.6% (114/147) classified as NIHSS>10/BASIS+ had poor outcomes, versus 21.5% (77/358) with NIHSS≤10/BASIS- (p<0.0001), regardless of treatment. The odds ratios for poor outcome is 12.6 (95% CI: 7.9 to 20.0) in patients who are NIHSS>10/BASIS+ compared to patients who are NIHSS≤10/BASIS-; the odds ratio is 5.4 (95% CI: 3.5 to 8.5) when compared to patients who are only NIHSS>10 or BASIS+.

Conclusions: BASIS and NIHSS are independent outcome predictors. Their combination is stronger than either instrument alone in predicting outcomes. The findings suggest that CTA is a significant clinical tool in routine acute stroke assessment.

Figure 1. BASIS and ASPECTS classification.

Patients are classified as BASIS+ if there are proximal cerebral artery occlusions observed on CTA or a significant hypodensities on NCCT. The relevant arterial segment occlusions are depicted in drawing on the left and are defined as including the following arteries: distal (intracranial) internal carotid artery (ICA), proximal (M1 or M2) middle cerebral artery (MCA) and/or basilar artery (BA). If none of these arteries are observed to be occluded on the CTA, then the NCCT is scored using the scheme shown on the right for anterior circulation strokes, which is also used for ASPECTS scoring. If a hypodensity deemed to be consistent with acute ischemic infarction is identified in one of the cerebral regions shown, a point is deducted from the maximum score of 10. Patients with scores of 7 or less are both BASIS+ and ASPECTS+. BASIS+ classification for posterior circulation strokes in the absence of basilar artery occlusion requires bilateral pons or bilateral thalamus hypodensities.

Figure 2. Patient outcomes by NIHSS/BASIS classification.

Patient outcomes, regardless of treatment, are grouped into possible combinations of BASIS and NIHSS. There are significant differences in outcomes amongst the categories (3×2 contingency table p<0.0001). Both the NIHSS≤10/BASIS− and the NIHSS>10/BASIS+ groups are significantly different from each other and from the other categories (****, p<0.0001).