Table 2.

2014 American Heart Association Classification of FMD

	Multifocal FMD	Focal FMD
Angiographic appearance	Alternating dilatation and constriction of the vessel (string of beads) Areas of dilatation are larger than the normal caliber of the artery Occurs in the mid and distal portion of the renal, internal carotid, and vertebral arteries May occur in any other artery in the body*	Focal concentric or tubular stenosis*
Typical histology	Medial fibroplasia (most common) Perimedial fibroplasia (rare)*	Intimal fibroplasia (most common) Adventitial (periarterial) fibroplasia (rare) Medial hyperplasia (rare)
Associated features	Aneurysm, dissection, and vessel tortuosity of medium‐sized arteries may be present; multifocal and focal lesions may coexist in the same patient

Reprinted with permission from Olin et al.¹ FMD indicates fibromuscular dysplasia.

^*Lesions are not necessarily confined to the mid or distal portion of the artery (ie, can occur in any arterial segment).

^*There are no cases of aortic FMD that are well documented pathologically.

^*This rare form of FMD typically occurs in young girls (eg, those 5 to 15 years of age). Although there is a beaded appearance to the renal arteries, the beads are smaller than the normal renal artery and less numerous. Histologically, collagen deposition is localized to the outer portion of the medial layer.