What is the characteristic imaging finding in fibromuscular dysplasia?

The characteristic imaging finding in fibromuscular dysplasia is indeed the "string of beads" appearance on angiography. This distinctive pattern is due to alternating stenoses and aneurysms that occur in the mid-distal segments of the renal arteries or other affected arteries.

In fibromuscular dysplasia, abnormal growth of cells in the arterial wall leads to segmental changes, including alternating areas of narrowing (stenosis) and dilation (aneurysm), giving rise to the appearance of beads strung along a wire. This imaging finding is particularly notable in younger women and can help differentiate fibromuscular dysplasia from other causes of renal artery stenosis.

Other imaging findings, such as uniform arterial narrowing, stenosis with post-stenotic dilation, or thickening of arterial walls, are more commonly associated with different vascular pathologies like atherosclerosis or chronic occlusive diseases. These findings do not capture the unique and pathognomonic "string of beads" pattern associated specifically with fibromuscular dysplasia.