Fibromuscular Dysplasia

Fibromuscular Dysplasia
A. Brad Farris, III, MD
Key Facts
Terminology
  • Nonatherosclerotic, noninflammatory fibrous, and fibromuscular proliferation of artery, typically leading to stenosis
Clinical Issues
  • Mostly young and female
  • 60-90% involve renal artery, 50% bilateral
    • Commonly present with hypertension
    • May be asymptomatic
  • Percutaneous transluminal renal angioplasty is treatment of choice
Image Findings
  • “String of beads” pattern on angiography
Microscopic Pathology
  • Intimal
    • Intimal hyperplasia resembles atherosclerosis but without lipid deposition
  • Medial
    • Medial fibroplasia with abnormally oriented smooth muscle and aneurysms is most common
    • Perimedial fibroplasia with fibrous band in outer media
    • Medial hyperplasia with hyperplastic but otherwise normal media
  • Periarterial (adventitial) fibroplasia
    • Circumferential adventitial fibrosis, normal media and intima
Top Differential Diagnoses
  • Atherosclerosis
  • Vasculitis
  • Dissecting aneurysm
Fibromuscular dysplasia occurs in 3 main varieties: A) intimal fibroplasia, B) medial fibromuscular dysplasia, and C) periarterial (adventitial) fibroplasia.
The medial fibroplasia form shows disoriented medial smooth muscle image that protrudes into the lumen of the renal artery (trichrome stain).
TERMINOLOGY
Abbreviations
  • Fibromuscular dysplasia (FMD)
Synonyms
  • Arterial fibrodysplasia
  • Fibromuscular hyperplasia
  • Intimal or periarterial (adventitial) fibroplasia
Definitions
  • Idiopathic, segmental, noninflammatory, nonatherosclerotic small and medium-sized artery diseases causing stenosis and aneurysms
  • 3 major categories
    • Medial
    • Intimal
    • Periarterial (adventitial)
ETIOLOGY/PATHOGENESIS
Genetic
  • Sibling affected in 11% of patients
  • Medial fibroplasia form may be congenital since it appears to be malformation
  • Occasionally, associated Ehlers-Danlos syndrome type IV or Marfan syndrome
  • 1 report of increased prevalence of angiotensin converting enzyme (ACE) I allele
Environment
  • Smoking
Female Gender
  • No link to estrogens or oral contraceptives proved
CLINICAL ISSUES
Epidemiology
  • Incidence
    • Estimated 4/1,000 for symptomatic renal FMD
      • Medial: 60-85%
      • Intimal: 1-5%
      • Periarterial: < 1%
    • 10-20% of patients with renal artery stenosis
  • Age
    • Younger (15-50 years) for fibromuscular dysplasia
    • Older (> 50 years) for fibrotic forms
  • Gender
    • Female predominance (medial form)
      • 85% affect women under 50 years old
    • Male predominance (intimal form)
Site
  • 60-90% involve renal arteries
    • 50% bilateral
    • Distal 2/3 of renal artery
    • Extends into arcuates and interlobular arteries
      • May account for continued hypertension after correction of extrarenal stenosis
    • May have associated aneurysm
  • May involve multiple vascular beds
    • Carotid arteries (26%)
    • Mesenteric/intestinal arteries (9%)
    • Iliac arteries (5%)
    • Popliteal, hepatic, coronary, and subclavian arteries (9%)
    • Less commonly, aorta and brachial, superficial femoral, tibial, and peroneal arteries
Presentation
  • Hypertension
  • Asymptomatic
  • Associated with hypertrophic cardiomyopathy
Laboratory Tests
  • Renin levels elevated
Treatment
  • Surgical approaches
    • Surgical correction curative in ˜ 70%
    • Percutaneous transluminal renal angioplasty (PTRA) is treatment of choice
    • Complex reconstruction, such as aortorenal bypass, is required in difficult cases
  • Drugs
    • Hypertension may respond to ACE inhibitors but not most other antihypertensive agents
Prognosis
  • Good, if corrected
  • If untreated, progressive narrowing may occur over 10 years, as judged by angiography
    • Obstruction, dissecting aneurysms, and emboli may result
    • Sudden death, particularly in FMD of cardiac arteries (e.g., artery supplying the sinus node) may occur
  • Renal failure rare
IMAGE FINDINGS
General Features
  • CT and catheter angiography useful in identifying areas of stenosis or classical “string of beads” appearance
MACROSCOPIC FEATURES
General Features
  • Beaded pattern of aneurysms and stenosis in renal artery branches
Size
  • Kidney may show decreased cortical thickness
MICROSCOPIC PATHOLOGY
Histologic Features
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Jul 7, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Fibromuscular Dysplasia

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