Evolution of Hypodensity on Non-Contrast CT in Correlation with Collaterals in Anterior Circulation Stroke with Successful Endovascular Reperfusion

Introduction: The aim of the study was to assess the impact of collaterals on the evolution of hypodensity on non-contrast CT (NCCT) in anterior circulation stroke with reperfusion by mechanical thrombectomy (MT).

Methods: Stroke patients with middle cerebral artery occlusion reperfused by MT in early and late time windows were retrospectively included. AI-based software calculated hypodensity volumes at baseline NCCT (V1) and follow-up NCCT 24 hours after MT (V2), along with V2−V1 and the V2/V1 ratio, and classified collateral status on a 4-point scale (0 = no collaterals, 3 = filling of all collaterals). Volumetric values were correlated with collateral scores.

Results: Collateral scores had a significant negative correlation with V1 (p = 0.035), V2, V2−V1, and V2/V1 (p < 0.001). With a score of 3, V2 was significantly smaller or absent than V1; with a score of 2, V2 was slightly larger; and with scores 1 and 0, V2 was significantly larger. These relationships held in both early and late time windows.

Conclusions: Collateral status determined the evolution of baseline hypodensity on NCCT after MT reperfusion. With good collaterals damage is stable or reversible, while with poor collaterals normal-looking tissue frequently becomes necrotic at follow-up. Hence, acute hypodensity represents different states of ischemic brain parenchyma.