Carotid I's, L's and T's: collaterals shape the outcome of intracranial carotid occlusion in acute ischemic stroke

Abstract

Background: Collaterals may affect revascularization, ischemic severity, and clinical outcomes in acute stroke owing to internal carotid artery (ICA) occlusion.

Objective: To examine the hypothesis that morphology of occlusive thrombus and collateral flow patterns may influence the outcome of ICA occlusions after mechanical thrombectomy.

Methods: Pooled analyses of ICA occlusions in the MERCI and Multi-MERCI trials employed central angiography review readings to categorize lesions as I, L, or T clots and functional lesions based on collateral flow patterns. Demographic variables, procedural details, and clinical outcomes were compared across ICA lesion types.

Results: A total of 72 subjects (mean age 67 years (SD 16), 51% female, median National Institutes of Health Stroke Scale 20 (range 8-35)) were included, with 90-day modified Rankin score ≤2 in 28% and 51% mortality. Clots were categorized as an I lesion in 9/72 (12.5%), L lesion in 12/72 (16.7%), and T lesion in 51/72 (70.8%). Based on collateral flow patterns, cases were categorized as having a functional I lesion in 7/72 (9.7%), functional L in 38/72 (52.8%), and functional T in only 27/72 (37.5%). Multivariate analyses showed that a functional T lesion, with insufficient collateral flow to ipsilateral anterior cerebral arteries via the contralateral ICA, was a strong predictor of both revascularization success and subsequent clinical outcomes.

Conclusions: Collateral flow patterns distinguish the nature and impact of ICA occlusions on expected revascularization and subsequent clinical outcomes in acute ischemic stroke. The nomenclature of terminal ICA occlusions introduced here (carotid I's, L's, and T's) may enhance future endovascular trials targeting such proximal occlusions.

Trial registration number: NCT00318071 (http://clinicaltrials.gov). MERCI was not registered because enrollment began before July 1, 2005.

Keywords: Angiography; Blood Flow; Stroke; Thrombectomy.

Figure 1

Schematic diagram of terminal internal carotid artery occlusions with I (left), L (center), or T (right) morphology, indicating occlusive thrombus (red), collateral flow (yellow) and ischemic territory (blue). Other configurations exist such as an L-shaped clot that may function as a T occlusion owing to absent contralateral flow, or alternatively, a T-shaped clot that may function as an L occlusion owing to robust collateral flow across the circle of Willis.

Figure 2

‘Characterization of terminal internal carotid artery (ICA) occlusions as functional L or functional T lesions based on perfusion of the ipsilateral anterior cerebral arteries territory from the contralateral ICA injection at DSA showed dramatically superior revascularization and clinical outcomes with functional L compared with functional T lesions. DSA reveals a T-shaped clot with a functional L lesion pattern on arterial (A) and venous (B) phase images with robust collateral flow. In another case, an L-shaped clot with patency of the ipsilateral A1 segment demonstrates a functional T lesion pattern with marginal collateral perfusion in the arterial (C) and venous (D) phase images.