Rajbeer Singh Sangha, MD
A higher degree of extracranial carotid stenosis is associated with increased stroke risk and has become a key determinant in treatment decision-making. The dominant mechanism via which strokes occur is thought to be thrombo-embolic, however it has been postulated that hemodynamically-consequential narrowing of the vessel lumen can also result in cerebral hypoperfusion and may even potentiate the effects of distal embolization. Shakur et al. looked to characterize impact of degree of stenosis, stenosis length, and residual lumen on intracranial blood flow in patients with extracranial carotid stenosis.
The study was a retrospective analysis of 105 patients that were identified having ≥ 50% carotid stenosis who underwent revascularization. Patients in this study had undergone quantitative flow measurements of the extracranial and intracranial arteries using quantitative magnetic resonance angiography (QMRA). On multivariate analysis, MCA flow ratio was not significantly associated with percentage stenosis, stenosis length, or residual lumen. However, mean MCA flow ratio was significantly lower in symptomatic compared to asymptomatic patients (0.92 vs. 1.22, P=0.001). In contrast, mean ICA flow ratio was similar among these two groups (0.55 vs. 0.55, P=0.99).
The study findings suggest that in symptomatic extracranial carotid disease, the reduction in MCA flow may play an important role, thus implicating intracranial hemodynamics in the pathophysiology of this disease. It would be interesting to be able to classify the level of collaterals in these patients as this may be a determinant in whether patients remain asymptomatic. Furthermore, more studies should be conducted to better quantify the characteristics present in patients who suffer from symptomatic extracranial carotid disease vs asymptomatic extracranial carotid disease. Elucidating the pathophysiological mechanisms will better allow us to stratify ischemic stroke risk in the asymptomatic population.