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Fibromuscular Dysplasia
Fibromuscular Hyperplasia, FMH
Submitted by Ab Shrivastava, MD


  • General Considerations

    • Incidence
      • 0.6% via angiography
      • 1.1% via autopsy
    • Female to male ratio 3:1
    • Presenting age 25-50

  • Pathology

    • Developmental lesion of unknown etiology which can affect multiple vessels.
    • Consists of areas of heaped intima, adventitia, and media alternating with areas of medial destruction resulting in small focal aneurysms.
    • 3 histologic types
      • Intimal fibroplasia
      • Medial fibroplasia, and
      • Subadventitial (perimedial) fibroplasia of the arterial wall 
      • 3 subtypes not always apparent on imaging.  Classic “string of beads” appearance on angiography for medial fibroplasias
    • Some authors describe 5 total subtypes.  Medial fibroplasias divided into medial fibroplasia with aneurysm and medial fibromuscular dysplasia.  Perimedial fibroplasias subdivided into subadventitial and adventitial fibroplasias
    • Medial fibroplasias most common

  • Clinical Findings

    • Renovascular hypertension (if bilateral renal arteries involved).
    • Transient ischemic attack
    • Intracranial aneurysm/thromboembolic stroke
    • Often asymptomatic

  • Location

    • Renal arteries 85%
      • Only 40% have bilateral renal artery involvement
    • Most often middle and distal 1/3 of renal arteries involved
    • Less commonly affected: Internal carotid (often bilateral), vertebral, mesenteric, celiac, hepatic, iliac arteries
    • If FMD is found at any location, one must evaluate carotid arteries for lesions

  • Imaging Findings

    • Angiography considered gold standard.  CTA and MRA becoming more sensitive.
    • FMD is characterized by
      • Narrowing of the affected vessel with a “string of beads” or nodular appearance , due to focal annular repetitive intimal and medial proliferative changes

  • Differential Diagnosis

    • Really a classic appearance
    • Only entity on differential is atherosclerosis

  • Treatment

    • If symptomatic (intractable hypertension), improvement to renal blood flow can be me made via surgery or angioplasty
    • Angioplasty is less invasive and cure rate is approximately 50% and improvement in 30% of patients 
    • Angioplasty suitable for noncalcified short segments
    • Surgery reported to have lower re-stenosis rate and greater improvement in GFR


Fibromuscular Dysplasia.  CT of the abdomen with IV contrast demonstrates nodularity (string-of-beads sign) of the right renal artery (arrows) characteristic of fibromuscular dysplasia (hyperplasia)