Supplementary Material for: Dimensions of Subcortical Infarcts Associated with First- to Third-Order Branches of the Basal Ganglia Arteries

Background: It has been described that lacunar infarct is characterized by its smallish size (15-20 mm) in the axial plane. However, the size of the basal ganglia artery responsible for this type of infarct is uncertain. Detection of small arterial occlusion is not possible with current angiography, hindering correlation of arterial occlusion with subcortical infarct size. Recently, investigators have published microangiographic templates of arteries supplying the basal ganglia. These templates display first-order (proximal) to third-order (distal) branching of these arteries and can help with estimating the likely site of arterial disease in subcortical infarcts. We correlated the dimensions of subcortical infarcts with the order of arterial branching described in a microangiographic template. Such data may provide further clues about the type of arteries associated with subcortical infarcts and assist in refining the concept of lacunar infarction. Method: Patients with subcortical infarcts on MR imaging (MRI) admitted to our institution between 2009 and 2011 were included in the study. Infarcts were manually segmented and registered to a standard brain template. These segmented infarcts were scaled and overlapped with published microangiographic templates, and used by 6 raters who independently estimated the branching order of arterial disease that might result in these infarcts. We used regression analysis to relate these ratings to infarct dimensions. Results: Among 777 patients, there were 33 (58% male) patients with subcortical infarcts. The mean age was 63.1 ± 15.1 years. Infarct dimensions for the groups were as follows: group 1 (first-order branch): height 37.6 ± 7.4 mm, horizontal width 21.2 ± 11.6 mm, anterior-posterior length 36.8 ± 20.1 mm; group 2 (second-order branch): height 25.2 ± 7.9 mm, horizontal width 16.6 ± 22.8 mm, anterior-posterior length 16.1 ± 8.0 mm; group 3 (third-order branch): height 11.6 ± 5.7 mm, axial width 5.3 ± 3.1 mm, anterior-posterior length 5.5 ± 3.8 mm. Increasing vessel branching order (from large to small vessels) was linearly and negatively associated with infarct height (β = -16.7 mm per change in branching order disease, 95% CI -20.3, -13.1 mm, p < 0.01) and anterior-posterior length (β = -16.8 mm per change in branching order disease, 95% CI -23.2, -10.5 mm, p < 0.01). Discussion: Based on MRI infarct dimensions and a microangiographic template, it may be possible to estimate the branching order of the artery involved in subcortical infarcts. Further, our small data set suggests that reliance on an axial dimension of 15-20 mm may not be the best approach to classifying lacunar infarct. This finding needs to be confirmed in a larger data set.