Andrew Micieli, MMI MD

Lau HL, Gardener H, Coutts SB, Saini V, Field TS, Dowlatshahi D, Smith EE, Hill DM, Romano JG, Demchuk AM, et al. Radiographic Characteristics of Mild Ischemic Stroke Patients With Visible Intracranial Occlusion: The INTERRSeCT Study. Stroke. 2021.

Vascular imaging of the head and neck in the hyperacute stroke setting has important diagnostic and prognostic implications, especially in patients with mild stroke. The presence of an intracranial large vessel occlusion is a strong predictor of early neurological and radiographic deterioration in patients with mild stroke. Recanalization is associated with improved functional outcomes; however, the safety in mild stroke patients is less clear.

The authors sought to analyze thrombus characteristics, collateral blood flow and recanalization rates with or without intravenous alteplase in patients with mild ischemic stroke (NIHSS ≤5) and compare these with patients with moderate/severe symptoms (NIHSS >5) from the previously published INTERRSeCT study.

The INTERRSeCT study included patients with ischemic stroke and a symptomatic visible intracranial occlusion on CTA, within 12 hours from last known well. Repeat CTA was completed at 4±2 hours to assess early recanalization with intravenous alteplase. Extent of intracranial thrombus was assessed using the clot burden score (score from 0-10). Permeability of intracranial thrombus to contrast was assessed using the residual flow grade (grade 0: no contrast permeation of thrombus; grade 1: contrast permeating diffusely through thrombus; grade 2: tiny hairline lumen or streak of well-defined contrast within the thrombus extending either through its entire length or part of thrombus). Collateral blood flow was calculated using the Calgary Collateral Scoring System (maximum score of 10 points). Recanalization of intracranial thrombus was assessed using the revised Arterial Occlusion Scale on repeat CTA head or on first angiographic acquisition of the affected intracranial circulation before endovascular therapy. The primary outcome was successful recanalization (defined as revised arterial occlusion scale score of 2b or 3) on repeat CTA or conventional cerebral angiogram obtained within 6 hours of initial CTA.

A total of 74 (12.9%) participants had a mild ischemic stroke (NIHSS score ≤5). Favorable thrombus permeability (residual flow grades 1 and 2) was similar between mild and moderate/severe groups (21% versus 19%; P=0.75). Mild strokes had higher collateral scores (9.1 [n=58] versus 7.6 [n=460]; P<0.001) excluding patients with distal occlusion.

A total of 82% patients received intravenous alteplase in the study. Mild stroke patients were less likely to receive intravenous alteplase (55% versus 85%; P<0.001). The overall rate of successful recanalization for the mild stroke group was 45% with alteplase and 25% without alteplase. For the moderate/severe stroke groups, successful recanalization occurred in 26% with alteplase and 9% without.

Specifically for mild stroke patients, recanalization occurred at a rate of 32% in the internal carotid artery/M1, 38% in M2 MCA, and 47% in distal occlusions, whereas in moderate/severe strokes, 22% in proximal, 32% in M2 MCA, and 41% in distal occlusions. A higher residual flow grade was associated with successful recanalization in both mild and more severe strokes. Additionally, higher residual flow grade was associated with milder symptoms among those with M2 occlusions but not among those with more proximal or distal occlusion sites.

This article demonstrates successful recanalization in mild stroke patients is independently associated with intravenous alteplase use and higher thrombus permeability. Additionally, collateral blood flow is qualitatively higher in patients with mild symptoms. Importantly, these radiographic markers may assist clinicians for risk stratification of patients during acute stroke decision making. Further studies are needed to assess the efficacy of new thrombolytics (such as Tenecteplase ) and endovascular therapy in this specific patient population.

Limitations of the study include potential selection bias (patients screened vs those enrolled) and an increased average latency from initial CTA to second vessel imaging in mild compared with more severe strokes, which may influence in the rate of recanalization reported.