Wall Shear Stress Distribution in Intracranial Atherosclerotic Disease and Associations With Vessel and Plaque Morphology.

BACKGROUND AND AIMS: Wall shear stress (WSS) may govern the initiation and progression of atherosclerosis. We aimed to depict WSS distribution in symptomatic, atherosclerotic M1 middle cerebral artery (MCA-M1) stenosis, and its associations with adjacent vessel and plaque geometry. METHODS: Patients with symptomatic, atherosclerotic, 50%-99% MCA-M1 stenosis were analyzed. MCA-M1 vessel curve orientation and tortuosity, luminal stenosis, plaque length and longitudinal asymmetry were assessed on CT angiography (CTA). Relative WSS (rWSS) was calculated by the absolute WSS divided by mean WSS at the proximal, normal vessel segment, in a CTA-based computational fluid dynamics model. rWSS < 1.0, 1.0-3.0, and > 3.0 were respectively defined as low, normal, and high WSS; low- and high-WSS areas were measured. The vessel and plaque geometry was associated with the rWSS measures, across a plaque as a whole, and separately in upstream and downstream plaque segments divided at the stenotic throat. RESULTS: In 176 patients, rWSS increased progressively along the upstream plaque segment but highly varied downstream. rWSS was lower on the inner than on the outer wall of the MCA-M1 vessel curve. Patients with ventrally (than dorsally), inferiorly (than superiorly) oriented MCA-M1 vessel curves and higher tortuosity of the affected vessel segment exhibited lower rWSS and larger low-WSS areas at the downstream plaque segment. More severe luminal stenosis and upstream dominance in the plaque were associated with higher rWSS and larger high-WSS areas in the upstream and downstream plaque segments. CONCLUSIONS: Wall shear stress (WSS) distribution across symptomatic MCA-M1 stenosis was variable and strongly associated with adjacent vessel and plaque geometry, independent of systemic factors.