A CCA stenosis is considered hemodynamically significant when the stenosis exceeds what percent?

• A. >50%
• B. >30%
• C. >70%
• D. >90%

Answer: (A)

The key idea is that when the vessel narrows by about half, the downstream blood flow begins to be meaningfully limited. In the common carotid artery, a stenosis that reduces the lumen by more than 50% increases resistance enough that cerebral perfusion can be compromised, especially if blood pressure drops or if collateral circulation is not sufficient. This level of narrowing is typically what clinicians call hemodynamically significant, because it is at this point that flow dynamics change enough to affect tissue perfusion and raise stroke risk in the right clinical context. While more severe narrowing (70–99%) poses even greater risk and is more clearly flow-limiting, the threshold where flow becomes notably impacted is >50% diameter reduction.