The velocity of collateral filling predicts recanalization in acute ischemic stroke after intravenous thrombolysis

Abstract

The aim of this study was to evaluate the impact of pretreatment quality of collaterals, involving velocity and extent of collateral filling, on recanalization after intravenous thrombolysis (IVT). A retrospective analysis was performed of 66 patients with acute middle cerebral artery (MCA) M1 segment occlusion who underwent MR perfusion (MRP) imaging before IVT. The velocity of collateral filling was defined as arrival time delay (ATD) of contrast bolus to Sylvian fissure between the normal and the affected hemisphere. The extent of collateral filling was assessed according to the Alberta Stroke Program Early CT (ASPECT) score on temporally fused maximum intensity projections (tMIP). Arterial occlusive lesion (AOL) score was used to assess the degree of arterial recanalization. ATD (OR = 0.775, 95% CI = 0.626-0.960, p = 0.020), but not tMIP-ASPECT score (OR = 1.073, 95% CI = 0.820-1.405, p = 0.607), was independently associated with recanalization (AOL score of 2 and 3) at 24 hours after IVT. When recanalization was achieved, hemorrhagic transformation (HT) occurred more frequently in patients with slow collaterals (ATD ≥ 2.3 seconds) than those with rapid collaterals (ATD < 2.3 seconds) (88.9% vs 38.1%, p = 0.011). In conclusion, the velocity of collaterals related to recanalization, which may guide the decision-making of revascularization therapy in acute ischemic stroke.

Figure 1. The time attenuation curves (TACs) of the ischemic and contralateral hemisphere.

Hollow dots indicate time points before contrast inflow. Point a and b indicate the first time point when contrast reached the selected artery on the arterial input function (AIF) curve of the contralateral and ischemic hemisphere, respectively. Arrival time delay (ATD) was defined as the time difference between these two points. In this case, the first time point of contrast inflow of both sides were 21.86 seconds and 24.46 seconds, respectively. Thus, the ATD was 3.6 seconds.

Figure 2. Six consecutive slices on PWI tMIP images that cover almost the whole territory of the middle cerebral artery were used to assess the extent of collateral filling.

tMIP-ASPECT score is based on scoring the degree of contrast opacification (0 - no or less, 1 – equal contrast opacification compared with matching region in contralateral hemisphere) in 10 regions, including C caudate, L lentiform nucleus, IC internal capsule, I insular ribbon and M1–6 cortical regions of the middle cerebral artery (M1–3 at the level of basal ganglia, M4–6 at the level rostral to the ganglionic structures). In this patient, the deficit of collateral blood flow involved M2–3, M5–6, and I, and the tMIP-ASPECT score was 5.

Figure 3. Degree of recanalization depending on the velocity of collaterals.

Figure 4. Relationship between categories of hemorrhagic transformation (HT) with the velocity of collaterals (x-axis) and the degree of recanalization (y-axis).