The most important sign of significance of renal artery stenosis on an angiogram is –
The presence of arterial collaterals indicates that renal artery stenosis is hemodynamically significant. The diameter of stenotic segment may also give an indication of hemodynamic significance, but is only reliable if the stenosis is either very severe or minimal .
A percentage diameter stenosis > 70%
Presence of collaterals
A systolic pressure gradient > 20 mm Hg across the lesion
Post–stenotic dilatation of the renal artery