Where is the greatest turbulence observed relative to a vascular stenosis?

• A. Directly at the stenosis outlet
• B. One to two vessel diameters downstream from the outlet
• C. Two to four diameters upstream
• D. In the distal segment beyond the first branch

Answer: (B)

Turbulence from a stenosis arises when the high-velocity jet exiting the narrowed segment expands into the downstream lumen, causing flow separation and eddies. The greatest turbulence occurs shortly downstream, about one to two vessel diameters from the stenosis outlet, where the jet meets the slower post-stenotic flow and the sudden expansion promotes vortices and chaotic movement. Upstream flow is generally accelerated and relatively smooth, and while turbulence can occur inside the narrow segment, the peak chaotic flow is best seen just beyond the outlet as the jet dissipates energy and eddies form. Farther downstream, the turbulence tends to decay due to viscous dissipation, so the most pronounced turbulent activity is confined to that nearby downstream region.