Bone & joints

Other tumors

Fibrous dysplasia


Editor-in-Chief: Debra L. Zynger, M.D.
Kristina Wakeman, M.D.
Jose G. Mantilla, M.D.

Last author update: 2 January 2020
Last staff update: 12 October 2023

Copyright: 2019-2024, PathologyOutlines.com, Inc.

PubMed Search: Bone fibrous dysplasia

See Also: McCune-Albright syndrome, Mazabraud syndrome

Kristina Wakeman, M.D.
Jose G. Mantilla, M.D.
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Cite this page: Wakeman K, Mantilla J. Fibrous dysplasia. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/bonefibrousdysplasia.html. Accessed May 19th, 2024.
Definition / general
  • Benign fibro-osseous lesion that may involve one (monostotic) or multiple (polyostotic) bones
  • Developmental disorder of bone resulting in the failure to form mature lamellar bone
  • Mass forming developmental defect composed of woven bone and fibroblast-like spindle cells
  • Caused by failure in bone maturation, with arrest as woven bone (see Pathophysiology)
  • Associated clinical or syndromic manifestations (see Clinical features)
Essential features
  • Slow growing expansion of bone, composed of a proliferation of irregular woven bone trabeculae lacking conspicuous osteoblastic rimming, within a background of fibrous tissue with cytologically bland spindle cells
  • Intramedullary lesions without cortical destruction
  • May be congenital or hereditary (but differs from cherubism)
Terminology
  • Historically, osteitis fibrosa or generalized fibrocystic disease of bone (both terms not conventionally used)
  • 2 basic clinical forms: monostotic and polyostotic
ICD coding
  • ICD-10:
    • M85.00 - fibrous dysplasia (monostotic), unspecified site
    • Q78.1 - polyostotic fibrous dysplasia of bone
  • ICD-11:
    • FB80.0 - fibrous dysplasia of bone
Epidemiology
Sites
  • Can affect any bone; however, involvement of the spine is very rare (J Orthop Case Rep 2014;4:73)
  • Monostotic forms are more common in ribs, craniofacial bones (maxilla > mandible) and femur
  • Polyostotic forms frequently affects lower extremities and pelvis
Pathophysiology
  • Arrest in development of cortical bone, leading to lesions composed of irregular woven bone and immature fibroblast-like spindle cells
  • Gain of function mutations in GNAS (guanine nucleotide-binding protein / α-subunit), located in 20q13.2-3, lead to overexpression of Gsα protein and increased downstream adenyl cyclase activity (Appl Immunohistochem Mol Morphol 2016;24:660)
  • Activation of c-jun, c-fos and Wnt/β-catenin are associated with activation of Gsα protein
  • Variable expression of GNAS mutations may explain the variability in clinical manifestations
Clinical features
  • Can be associated with McCune-Albright syndrome (endocrine abnormalities, café au lait spots) or Mazabraud syndrome (soft tissue myxomas)
  • Transformation into sarcoma is extremely rare but has been reported, typically decades after initial diagnosis (J Formos Med Assoc 2004;103:711)
  • Unilateral painless swelling of mandible or maxilla in men / women ages 25 - 35 years
Diagnosis
  • Radiologic imaging (plain Xray films, CT scan) and biopsy
  • Usually diagnosed by age 20 years
Laboratory
  • Alkaline phosphatase can be elevated in certain cases, especially when tumor is growing
  • Endocrine abnormalities (gonads, thyroid) can be seen in patients with McCune-Albright syndrome
Radiology description
  • Ill defined margins; diffusely radiopaque with ground glass image
  • Single or multiple well circumscribed intramedullary lesions with a sclerotic rim
  • May see cortical thinning as lesion expands
  • Centered in metaphysis or diaphysis
  • Radiolucent or ground glass appearance on Xray (Dorfman and Czerniak: Bone Tumors, 2nd Edition, 2015)
Radiology images

Contributed by Jose G. Mantilla, M.D., Mark R. Wick, M.D. and AFIP images
Femur

Femur

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Femur coronal

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Mandible

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Femur

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Ulna

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Expanded rib

Prognostic factors
  • Unknown
Case reports
Treatment
  • No treatment since growth is self limited and responsive to pubertal hormonal changes
  • Usually conservative / symptomatic management
  • Surgery in cases with fracture or bony deformity
    • Surgical recontouring performed if facial deformity, although may regrow in 25%
Clinical images

Images hosted on other servers:
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Craniofacial lesions

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Buccal protrusion

Gross description
Gross images

Contributed by Jose G. Mantilla, M.D. and AFIP images
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Bone lesion

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Expanded rib

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Expanded lesion of calvarium

Microscopic (histologic) description
  • Branching and anastomosing irregular trabeculae of woven bone ("C" and "S" shapes) with no conspicuous osteoblastic rimming
  • No / rare osteoclasts
  • Intervening fibrous stroma containing cytologically bland spindle cells, without prominent cytologic atypia
  • Mitotic figures rare
  • Stromal changes, including myxoid change and fatty metaplasia, may be seen in some cases (BMC Musculoskelet Disord 2003;4:20)
  • Secondary aneurysmal bone cyst-like changes may also be seen (Turk Patoloji Derg 2018;34:234)
  • Fibrocartilaginous dysplasia: uncommon variant containing variable proportions of cartilaginous differentiation and enchondral ossification (Am J Surg Pathol 1993;17:924)
  • Growing collagen (Sharpey's fibers) may form perpendicular to the sites of bone formation but are not essential for diagnosis (Oral Dis 2017;23:697)
Microscopic (histologic) images

Contributed by Jose G. Mantilla, M.D., Kelly Magliocca, D.D.S., M.P.H. and @JMGardnerMD on Twitter

Irregular trabeculae

Stromal cells

Aneurysmal bone cyst

Fibrous dysplasia

Fibrous dysplasia


Fibrous dysplasia Fibrous dysplasia

Fibrous dysplasia

Fibrous dysplasia Fibrous dysplasia

Fibrous dysplasia

Fibrous dysplasia

Fibrous dysplasia

Positive stains
Negative stains
Molecular / cytogenetics description
Sample pathology report
  • Right tibia, biopsy:
    • Benign fibro-osseous proliferation, consistent with fibrous dysplasia
Differential diagnosis
Board review style question #1
    What is the underlying genetic mutation in patients with McCune-Albright syndrome?

  1. GNAS1
  2. p53
  3. PTH1R
  4. SDH
Board review style answer #1
A. Mutations in GNAS1 are seen in patients with McCune-Albright and Mazabraud syndrome

Comment Here

Reference: Fibrous dysplasia
Board review style question #2

    Histologically, fibrous dysplasia frequently shows

  1. Lamellar bone trabeculae
  2. Numerous mitotic figures
  3. Osteoblastic rimming
  4. Woven bone trabeculae
Board review style answer #2
D. Woven bone trabeculae. The trabeculae in fibrous dysplasia are composed of woven bone with various phases of mineralization. Mature lamellar bone can be seen at the periphery but should not be part of the lesion itself.

Comment Here

Reference: Fibrous dysplasia
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