Fibromuscular dysplasia (FMD)

Created 14/03/2022, last revision 05/09/2022

  • mostly sporadic, rarely hereditary, non-inflammatory disease of unknown etiology involving medium-sized arteries
  • localization (usually sparing the origin of the vessel):
    • an extracranial portion of ICA / vertebral arteries
    • renal arteries (most common)
    • splanchnic arteries (rare)
    • subclavian, axillary, and illiac arteries (rare)
  • usually occurs in young to middle-aged women
    • a female to male ratio of 3:1
    • typically between 30-50 years of age
  • involved arteries show segmental stenoses and enlargements,  ~ 1/3 of patients have multiple arterial lesions
  • FMD may lead to serious complications including TIA/stroke, spontaneous dissection, and aneurysm formation


  • unknown etiology
  • fibrous or fibromuscular thickening of the arterial wall (intima, media, and adventitia) leading to segmental stenoses and microaneurysms
    • intima is involved in < 5% of cases (⇒ intimal fibroplasia, also called carotid web)
    • media involvement prevails – 90-95% of cases
    • adventitia (rare, < 1%)
  • histology
    • accumulations of dysplastic muscle cells + disruption of the internal elastic membrane
    • no inflammatory cells are present
  • carotid lesions are typically localized in the middle and distal segments of the extracranial internal carotid artery, not rarely extending to the skull base
  • FMD predisposes to the development of aneurysms (extra- and intracranial) and arterial dissections
    • ⇒ in all patients with dissection, it is advisable to examine the renal arteries
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Clinical presentation and diagnostic evaluation

  • carotid artery lesions are often asymptomatic but can lead to TIA/stroke
    • due to distal thromboembolism (e.g., from the aneurysm)
    • due to the dissection
  • renal arteries involvement leads to renovascular hypertension (by activating RAAS) or renal impairment
  • coronary artery involvement can cause angina pectoris, myocardial infarction, or cardiac death
  • FMD is diagnosed by a typical appearance on vessel imaging (CTA, MRA, DSA, ultrasound)
    • involved arteries usually have a rosary-like appearance, caused by concentric luminal narrowing alternating with areas of mural dilatation (a string of beads appearance)   Fibromuscular dysplasia (FMD) - carotid artery in ultrasound imaging Fibromuscular dysplasia (FMD) - renal arteries on CTA
      • this finding is present in up to 90% of patients with FMD
    • less commonly, there is a concentric, long-segment tubular stenosis
  • FMD can present with carotid dissection (best seen on fat-saturated T1 imaging)  ICA dissection with intramural hematoma (fat-saturated T1)
  • less typical features include intracranial aneurysms, which can cause subarachnoid hemorrhage (SAH)
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Differential diagnosis

  • atherosclerosis – usually at origin or proximal portion of ICA
  • vasculitides
    • elevated ESR
    • more diffuse thickening of the wall (Takayasu)
  • segmental arterial mediolysis (Chao, 2009)
  • vasospasms


Stroke prevention

  • asymptomatic carotid lesions – most commonly conservative approach is preferred, antiplatelet therapy is not recommended
  • stroke patients with FMD:
    • strict blood pressure and other vascular risk factors control
    • antiplatelet therapy  (AHA/ASA 2021 I/C-LD)
      • ASA is most commonly used (based on expert opinion, no studies available)
      • statins are not routinely used in FMD unless otherwise indicated
    • in case of stroke due to carotid dissection without thrombosis, antiplatelet therapy is usually used (AHA/ASA 2021 2a/C-EO)
    • in case of treatment failure or significant carotid artery stenosis, consider angioplasty (AHA/ASA 2021 2b/C-LD)   (Tekieli, 2015)
      • angioplasty in FMD has high long-term patency rates; the stent is not always required
      • robust data regarding the clinical benefit of CAS over conservative therapy are lacking

Renovascular hypertension

  • angioplasty with stenting of the renal artery is indicated in case of proven renovascular hypertension
    • RAA system provides sufficient glomerular pressure by vasoconstriction
    • ACE inhibitors would lead to renal hypoperfusion
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