Michelle Christina Johansen, MD

Selwaness M, van den Bouwhuijsen Q, van Onkelen RS, Hofman A, Franco OH, van der Lugt A, et al. Atherosclerotic Plaque in the Left Carotid Artery Is More Vulnerable Than in the Right. Stroke. 2014

Left hemispheric strokes can be devastating, impacting the patient’s language center and leading to hemiparesis and hemiplegia. Large vessel atherosclerosis is an established stroke subtype and plaque located at the carotid bifurcation has been implicated in as high as 18% of all strokes. Selwaness et al open their paper by noting that a significantly higher proportion of ischemic events are diagnosed in the left hemisphere compared to the right.  The team hypothesize that the higher incidence of events occurring in the lefthemisphere is related to either a higher prevalence, severity or vulnerability of atherosclerotic disease in the left carotid artery. 

Carotid MRI’s were performed on 1414 stroke free participants to assess not only the location but also degree of stenosis and components of the carotid plaque. The authors invited participants from The Rotterdam Study, a prospective population based cohort study who were routinely undergoing carotid ultrasound to also undergo MRI imaging of the bilateral carotids. The mean age of the final cohort was 72 and 53% were male.  Image quality was considered sufficient in 95% of scans. Luminal stenosis was calculated using the NASCET criteria.  The investigators classified the composition of plaques as either lipid-rich, containing intraplaque hemorrhage or calcification based on imaging characteristics. 

Overall, 1196 subjects or 85% had plaque in both carotid arteries meaning only 218 subjects had unilateral plaques. Within these patients, the investigators found that left sided plaques were twice as prevalent as right sided with no sex predominance but those with unilateral left sided plaques tended to be younger (68 vs 71). The degree of luminal stenosis did not differ between right and left and clinically relevant stenosis defined by NASCET also did not differ. When the components were analyzed individually, lipid-rich plaques was slightly more prevalent on the left (27.6% vs 23.4% p 0.006) and intraplaque hemorrhage (IPH) was also more frequent in left carotid artery plaques (23.1% vs 19.7% p 0.01).  Calcification was equal on both sides. When a single or predominant component was assigned, IPH and lipid were most prevalent in left-sided plaques but this time right sided plaques were predominantly composed of calcification.

The conclusion of the investigators is that carotid atherosclerotic plaque size and composition are not symmetrically distributed and that plaques on the left are more vulnerable than on the right due to the presence of IPH versus calcification. 

This inference should give the practicing vascular neurologist pause. In treatment of asymptomatic carotid stenosis, the mantra has been best medical management. Many are familiar with the CREST data which showed that among asymptomatic patients, the primary outcome (periprocedural stroke, death and myocardial infarction rates) did not differ significantly between stenting and surgery (4.9% vs. 5.6%) but the study was not powered to obtain significance (p=0.07). There are ongoing trails (CREST-2) to evaluate if optimal medical management is in fact sufficient in these patients. If in fact left sided plaques are more vulnerable to rupture, while we wait for the outcome of clinical trials should a practicing Neurologist change practice? For example, would one lower the blood pressure of a patient with left sided stenosis more aggressively than their right sided counterpart? Is dual antiplatelet therapy warranted even in the absence of intracranial stenosis? The authors appropriately discuss many limitations in evaluation of their data to include the fact that significance was only obtained when the plaques were assigned a predominant component, a small n and potential observer bias. This limits the broad application of their study results but the questions raised demand further research and consideration. 

“Let not the right side of your brain know what the left side doeth.”
~ George Bernard Shaw