Original ArticleParametric Digital Subtraction Angiography Imaging for the Objective Grading of Collateral Flow in Acute Middle Cerebral Artery Occlusion
Introduction
Leptomeningeal collateral, also known as pial collateral, is one of the most important collateral filling pathways for patients with acute ischemic stroke. For patients with inadequate antegrade blood flow, pial collaterals are major determinants of tissue fate1 and reported to be correlated with smaller infarction volume compared with the poor ones.2, 3 It also indicates a greater possibility of reperfusion and better clinical outcome in patients with acute middle cerebral artery (MCA) occlusion who received endovascular therapy.4, 5
There has been no direct, quantitative way to assess cerebral collateral. They usually are assessed indirectly by different modalities of images, namely digital subtraction angiography (DSA), computed tomography angiography, dynamic computed tomography angiography, and arterial spin-labeling, to name a few.6 DSA stands out for its high spatial and time resolution and often is taken as the reference in many studies that focus on collateral assessment.7, 8, 9 The most widely used collateral grading system based on DSA is the American Society of Interventional and Therapeutic Neuroradiology collateral grading system (ACG). The ACG evaluates both the extent of perfusion and the speed of retrograde filling and has been recommended by the Cerebral Angiographic Revascularization Grading panels10 for collateral assessment.
In clinical practice, however, the differentiation between partial and complete perfusion of ischemic area (ACG grade 2 or 3) requires extensive experience, especially when MCA territory is overlapped by the branches of the anterior cerebral artery (ACA). Moreover, “partial” or “complete” might not be precise enough to characterize leptomeningeal collaterals because acute MCA occlusion patients with ACG grade 2 often have heterogeneous clinical outcomes.5, 11, 12 In this study, we reported the feasibility of using a parametric color-coded DSA analysis method13, 14 for the quantitative assessment of leptomeningeal collaterals in patients with acute MCA occlusion.
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Patients
The study was approved by our institutional ethical committee. Patients with acute ischemic stroke who received endovascular recanalization treatment in our center during September 1, 2013, to April 20, 2015, were reviewed retrospectively for this study. The inclusion criteria were as follows: 1) unilateral MCA/M1 segment occlusion confirmed by DSA; and 2) image data compatible with the quantitative DSA analysis tool (syngo iFlow, Siemens Medical GmbH, Forchheim, Germany). Exclusion criteria
Clinical Characteristics
The age of included patients varied from 34 to 85 years of age; 6 were women. National Institute of Health Stroke Scale scores ranged from 7 to 26. Four of the 18 patients were evaluated to be ACG grade 1, 6 to be grade 2, and 7 to be grade 3; 1 patient had complete and rapid retrograde blood flow (grade 4). Fourteen cases were successfully reperfused after endovascular intervention, 10 had favorable clinical outcome within 3 months (mRS ≤ 2), and 3 were moderately to severely impaired in
Discussion
An optimal angiographic collateral assessment criterion should have high interrater reproducibility, high correlation with clinical outcome, and simplicity and feasibility in implementation while ensuring characterization of relevant angiographic findings.10
The parameter rDensitymax roughly reflects the extent of collateral perfusion within TDT. Because the MCA region is overlapped by itself in the anteroposterior view, we infer that rDensitymax represented the maximum coverage of collateral as
Conclusions
The relative maximum contrast density of MCA territory on 2D DSA measured by parametric imaging technique appears to be a simple and reliable metric for the assessment of leptomeningeal collaterals in acute MCA occlusion cases. Further studies with larger sample sizes are needed.
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Conflict of interest statement: Supported by Natural Science Foundation of China, grant number 81171092, Shanghai Science and Technology Innovation Plan, grant number 13411950300, and Subjects construction 1255 plan of Changhai hospital, grant number CH125520100, but there is no conflict of interest in association with the work that could have affected the results and there has been no significant financial support for this work that could have influenced its outcome.
Wan-ling Wen and Yi-bin Fang contributed equally to the work.