Heart & vascular pathology

Ischemic disease

Fibromuscular dysplasia

Last author update: 1 February 2015
Last staff update: 19 September 2023

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PubMed Search: Fibromuscular dysplasia [title] heart

R. Amita, M.D.
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Cite this page: Amita R. Fibromuscular dysplasia. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/heartfibromusculardysplasia.html. Accessed September 25th, 2023.
Definition / general
  • Fibromuscular dysplasia (FMD) is a vascular disease affecting small to medium sized vessels
  • It is a noninflammatory, nonatherosclerotic condition occurring more frequently in younger individuals and women
  • Renal artery involvement is most common (60 - 75%), followed by cervicocranial arteries (25 - 30%), visceral arteries (9%) and arteries in extremities (5%)
Clinical features
  • Symptoms occur when lesions are tightly stenotic producing hypoperfusion, if an associated aneurysm ruptures, if lesions embolize, thrombose or dissect
  • Presenting symptoms include hypertension, headache, altered mentation, tinnitus, vertigo, neck pain
  • Also transient ischemic attack, cerebral infarction, subarachnoid hemorrhage, syncope, Horner syndrome, cranial nerve palsies
  • Deterioration of renal function is rare in fibromuscular dysplasia but common in atherosclerosis
  • Overall, medial fibroplasia is the most common type of fibromuscular dysplasia, but in children, intimal fibroplasia is most common
Radiology description
  • Angiographically a smooth focal stenosis (concentric band) or a long smooth (tubular) stenosis may be present
  • "String of beads" describes its angiographic appearance, where the "bead" diameter is larger than the proximal vessel in medial fibroplasias
  • Perimedial fibroplasia may also appear as arterial beading on an angiogram
    • However, unlike medial fibroplasia, the caliber of the beads does not exceed that of the proximal artery and the beads are usually less numerous
    • This dysplastic lesion results in severe stenosis and may be associated with collateral circulation
  • Medial hyperplasia appears as a concentric, smooth stenosis on an angiogram, making it difficult to differentiate from intimal fibroplasia; sites of vessel involvement are similar to medial fibroplasia but do not affect branches of renal artery as often
Case reports
  • Medical management to treat hypertension
  • Antiplatelet agents
  • Smoking cessation or other risk factor modification
  • Endovascular therapy or surgery indicated if:
    • Hypertension is poorly controlled despite maximum doses of three antihypertensive medications
    • Patient is unable to tolerate medications or is noncompliant
    • As an alternative to lifelong medication in this relatively young population
Clinical images

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Medial fibroplasia

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Intimal fibroplasia

Gross description
  • Medial fibroplasia:
    • Involves distal 2/3 of main renal artery, occasionally extending into its branches
    • Also commonly encountered in internal carotid artery at C1 and C2 vertebrae, compared to atherosclerosis which typically occurs at carotid bifurcation
Microscopic (histologic) description
  • In 1971, a classification system to describe FMD of renal artery was proposed by Harrison and McCormack (Mayo Clin Proc 1971;46:161) based on dominant arterial wall layer involved:
    • Intimal fibroplasia
    • Medial dysplasia
    • Adventitial (periarterial) fibroplasias
  • Intimal fibroplasia:
    • < 10% of all fibrous lesions
    • Circumferential or eccentric deposition of collagen in intima but no lipid or inflammatory component
    • Internal elastic lamina is identifiable but may be fragmented or duplicated
    • This appearance may be mimicked by endarteritis due to inflammation or trauma
    • Can occur as a generalized disorder involving renal, carotid, upper and lower extremity and mesenteric vasculature simultaneously mimicking a multisystem disease such as necrotizing vasculitis
  • Medial dysplasia:
      Divided into medial fibroplasia, perimedial fibroplasia, medial hyperplasia
    • Medial fibroplasia:
      • A subtype of medial FMD, histologic finding in 75 - 80% of all cases of FMD
      • Alternating areas of thinned media and thickened fibromuscular ridges containing collagen
      • Some areas of internal elastic membrane are lost
    • Perimedial fibroplasia:
      • 10 - 15% of all lesions, found in young girls
      • Extensive collagen deposition located in outer half of media and can replace it entirely, but does not extend beyond external elastic lamina
    • Medial hyperplasia:
      • True smooth muscle hyperplasia without fibrosis
      • Found in 1 - 2% of all lesions
  • Adventitial fibroplasias:
    • Rarely seen (< 1%)
    • Dense collagen replaces fibrous tissue of adventitia and may extend into surrounding tissue
    • The other arterial layers and elastic laminae remain intact
Microscopic (histologic) images

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Medial fibroplasia

Differential diagnosis
  • Intimal fibroplasia: necrotizing vasculitis
  • Medial fibroplasia: atherosclerosis
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