= Vascular stenosis
<Vascular stenosis> is narrowing of the lumen of a <blood vessel>. The location, length, shape and cause of the narrowing matter, as does the reference used to express its severity. Narrowing can leave an open lumen; it is not synonymous with complete occlusion. A <vascular stent> supports an existing route, while a <bypass graft> creates an alternative route around a diseased region.
<Diameter versus area stenosis> illustrates an important measurement distinction. If $d_{\min}$ is the narrowest measured diameter and $d_{\mathrm{ref}}$ is the stated reference diameter, define the illustrative diameter reduction
$$
S_d=100\left(1-\frac{d_{\min}}{d_{\mathrm{ref}}}\right).
$$
For circular lumens the associated area reduction is
$$
S_A=100\left[1-\left(\frac{d_{\min}}{d_{\mathrm{ref}}}\right)^2\right].
$$
A narrowing from $4$ to $2\,\mathrm{mm}$ is therefore $50\%$ by diameter and $75\%$ by area. These are geometric calculations using a specified reference, not interchangeable clinical grading conventions. Different reference segments or reconstruction methods can give different reported percentages.
An original ideal-flow example connects geometry to an observation. For incompressible flow with the same instantaneous volume flow through both sections, <conservation of mass> gives $Q=Av$. Reducing circular diameter by half reduces area to one quarter and raises mean velocity fourfold at that maintained $Q$. The real circulation can change $Q$, so this ratio is conditional, not a universal diagnostic cutoff or prediction of tissue perfusion.
<Ultrasound> can examine both vessel appearance and moving blood. The Society for Vascular Surgery’s carotid-duplex description identifies a hand-held sound-wave probe and coupling gel, used to look for narrowing and examine flow. Such an apparatus makes anatomy and flow-related observations available together; a velocity estimate is not itself a direct measurement of every lumen dimension.<Carotid Duplex by the Society for Vascular Surgery>[Test description and ultrasound-probe procedure]{ref}
Characterizing <vascular stenosis> therefore combines the geometric convention, imaging method and physiological question. A percentage alone does not establish the pressure loss, the cause of symptoms or the best intervention. Persistent patency and clinical consequences require separate follow-up observations.
Back to article page
