Alexander E. Merkler, MD
Intracranial atherosclerotic disease (ICAD) is a common cause of stroke; patients with ICAD face high rates of recurrent stroke despite aggressive medical and lifestyle modification. Currently, the diagnosis of ICAD is based on the degree of vessel stenosis, but perhaps, as Drs. Qiao et al discuss, this is not the best measure of either plaque burden, or more importantly, stroke risk.
Based on coronary plaque research, Drs. Qiao et al studied the impact of vessel remodeling in ICAD. Although plaque may lead to hemodynamic stenosis, remodeling of the vessel may either preserve (positive remodeling) or further impair (negative remodeling) the degree of stenosis. In addition, although positive remodeling may preserve the vessel lumen, it may make plaque more vulnerable to rupture or lead to clinical symptoms.
In this study, the authors used High-resolution black blood MRI (BBMRI) to assess vessel remodeling in ICAD and its association with ischemic events. Forty-five patients with ICAD with >50% stenosis in a large intracranial artery who also had a stroke or TIA in the distribution referable to that stenosis were included. The authors identified 137 plaques, of which 56 exhibited positive remodeling, 53 negative remodeling, and 28 intermediate remodeling. There was higher burden of plaque within the posterior circulation as compared to the anterior circulation and positive remodeling was more frequent in the posterior circulation (58% vs 31%). Furthermore, positive remodeling was associated with a trend towards culprit plaque classification. Finally, the authors found that the lumen begins to narrow (ie when remodeling fails to preserve the lumen) when plaque burden reached 55.3%.
This study challenges the current theory that ICAD is purely based on degree of vessel stenosis. As in the coronary vessels, remodeling occurs when plaque is present and may either augment or decrease the vessel lumen size. Furthermore, intracranial remodeling may lead to an underestimation of plaque burden (based on the current definition of vessel stenosis >50%), and therefore an underdiagnosis of ICAD, particularly in the posterior circulation. Further research to assess remodeling and its impact on stroke risk is warranted.