Prachi Mehndiratta, MD

Elnan Kvistad CE, Oygarden H, Logallo N, Moen G, Thomassen L, Waje-Andreassen U, and Naess H. A Dark Side of Subcortical Diffusion-Weighted Lesions? Characteristics, Cause, and Outcome in Large Subcortical Infarction: The Bergen Norwegian Stroke Cooperation Study. Stroke. 2014

While we have all read plenty about small vessel disease infarcts or lacunar infarcts, less has been said about large subcortical infarcts (LSI) that can be colloquially referred to as lagoons. In this study the authors aimed to identify the differences in clinical characteristics, etiologic factors and outcome amongst patients with LSI when compared with lacunar infarcts (LI), cortical infarcts (CI) or infarcts elsewhere (no LSI).

All patients admitted to the Stroke unit between Feb 2006 and July 2013 were screened. In total, MRI scanning was performed on 1979 patients and 1886 with positive diffusion weighted lesions were included in the analysis. Infarcts were classified as subcortical >15mm and <15mm in size. LSI were found in 6.8% of the patients with the remainder being LI (16.8%), CI (28.8%) and no LSI (47.6). LSI infarcts were further classified as belonging to the following territories- lenticulostriate, anterior choroidal, thalamic and white matter. Clinically, patients with LSI had more severe strokes than those with LI, CI or no LSI. There was a significantly greater proportion of patients with atrial fibrillation (p=0.003) and fewer number of smokers in the LSI group (p=0.014).

Vascular imaging demonstrated that complete or partial occlusion of the proximal MCA segment was more frequent in the LSI group as compared to those with LI (39.1% vs. 1.6%, p<0.001), CI (15 [7.9%], p<0.001) and no-LSI (39.1% vs. 17.1%, p<0.001). Large artery disease and cardio-embolism was more common in patients with LSI as compared to those with LI. Cryptogenic stroke mechanism was found in 60.9% of LSI patients which was significantly higher than the number of cryptogenic strokes in all other groups. Intuitively, due the larger stroke size and higher likelihood of a proximal vessel occlusion, patients with LSI were more likely to have progressive symptoms and had a worse overall short term outcome (graded on the modified Rankin scale) and these results were statistically significant. Those with anterior choroidal artery infarcts did worse than others.

This study highlights how a large subcortical infarct may initially “look like a duck” but “not quack like one”. Clinically a LSI may appear to mimic a lacunar syndrome; however there is a higher likelihood for progression of symptoms and presence of a large vessel occlusion. These characteristics underscore the importance for early treatment with IV tpa and need for diffusion weighted imaging. Although a large proportion of these patients had unclear mechanism of stroke, I would have liked to know more about the extent of stroke workup that these patients were subjected to. Also, were the raters of clinical symptoms and MRI findings independent?  If not, there definitely could have been introduction of bias.  As one would have expected with a larger stroke size, these patients had worse short term outcome. But, how about long term outcome? I hope to see more literature in the near to help answer some of these questions.