Prachi Mehndiratta, MD

Shoamanesh A, Masoud H, Furey K, Duerfeldt K, Lau H, Romero JR, et al. Larger A1/M1 Diameter Ratio Predicts Embolic Anterior Cerebral Artery Territorial Stroke. Stroke. 2014

This study attempts to answer this question by retrospectively studying the anatomic characteristics of the parent vessel in patients with anterior cerebal artery (ACA) and middle cerebral artery (MCA) ischemic stroke. Twenty seven cases of ACA stroke admitted between 2008 and 2012 were contrasted with twenty eight controls that comprised of MCA territory infarcts. Measurements were rated on a CT angiogram or time of flight MR angiogram if a CT angiogram was not available. Diameters of the proximal ACA and MCA arteries (A1 and M1 respectively) and an A1/M1 diameter ratio was captured by two raters independently. A third rater assessed the branching angle between the Internal carotid artery (ICA) and the ACA and MCA.

The authors found that those with ACA stroke had a greater prevalence of Diabetes Mellitus and were less likely to suffer from atrial fibrillation. Proximal ACA or A1 diameter was larger than proximal MCA diameter (mean: 2.5 vs. 2.1 mm, p=0.003) in patients with ACA stroke and intuitively the A1 to M1 diameter ratio was also higher. ICA-MCA and ICA-ACA bifurcation angles did not differ between cases and controls. When multivariate analysis was performed A1/M1 diameter ratio (C-statistic: 0.81, 95% CI 0.70 – 0.93, p<0.001) was found to be a stronger predictor of embolic ACA stroke than A1 diameter alone (C-statistic: 0.71, 95% CI 0.57 – 0.84, p=0.009). Forty one percent of patients with ACA stroke were found to have contralateral A1 segment hypo/aplasia.

These are interesting findings however as the authors acknowledge, the generalization of the results should be viewed with caution. The number of cases is small; the raters are presumably blinded although not clearly identified as such and majority of the rating is performed on time of flight MR angiograms which are susceptible to a great degree of artifact.  It is unclear what the etiology of stroke is in the 27 ACA stroke cases and if there were any  atherosclerotic changes in the parent vessels that might have contributed to change in flow dynamics and consequently a change in the diameter of the vessel. The results are intriguing and  hypothesis generating but I would wait for a more rigorous study with both anatomic and physiologic data to put my trust in vessel diameter measurements.