What angiographic sign is indicative of fibromuscular dysplasia in the renal artery?

The "string of beads sign" is a classic angiographic finding associated with fibromuscular dysplasia (FMD) affecting the renal arteries. This sign is characterized by alternating segments of stenosis and aneurysm, creating a pattern that resembles a string of beads on imaging studies.

Typically, FMD is a vascular condition predominantly affecting younger women and leads to renovascular hypertension. The characteristic "string of beads" appearance arises due to the alternating areas of luminal narrowing (stenosis) and dilation (aneurysm) of the renal artery. This finding is highly suggestive of FMD and can help differentiate it from other causes of renal artery stenosis, such as atherosclerosis, which usually presents differently.

In contrast, other possibilities like long smooth segments of stenosis, single focal stenosis, or aneurysms without stenosis do not capture the distinct pattern seen in FMD. Atherosclerosis more commonly shows single, focal lesions without the concatenation of stenosis and aneurysms seen in the "string of beads." This signature pattern is quite specific and helps clinicians accurately diagnose fibromuscular dysplasia.