Bone & joints
Other tumors
Fibrous dysplasia


Topic Completed: 2 January 2020

Minor changes: 2 January 2020

Copyright: 2019, PathologyOutlines.com, Inc.

PubMed Search: Bone[TI] fibrous dysplasia[TI] free full text[sb]

Related topics: McCune-Albright syndrome, Mazabraud syndrome

Kristina Wakeman, M.D.
Jose G. Mantilla, M.D.
Page views in 2019: 19,192
Page views in 2020 to date: 13,275
Cite this page: Wakeman K, Mantilla J. Fibrous dysplasia. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/bonefibrousdysplasia.html. Accessed September 21st, 2020.
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
Terminology
  • Historically, osteitis fibrosa or generalized fibrocystic disease of bone (both terms not conventionally used)
  • Two basic clinical forms: monostotic and polyostotic
ICD coding
    ICD10:
  • M85.00 - fibrous dysplasia (monostotic), unspecified site
  • CM: 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)
Diagnosis
  • Radiologic imaging (plain Xray films, CT scan) and biopsy
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
  • 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.
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Femur

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Femur coronal

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Mandible


Contributed by Mark R. Wick, M.D.
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Femur

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Ulna


AFIP images
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Expanded rib

Prognostic factors
  • Unknown
Case reports
Treatment
  • Usually conservative / symptomatic management
  • Surgery in cases with fracture or bony deformity
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.
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Bone lesion


AFIP images
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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
  • 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)
Microscopic (histologic) images

Contributed by Jose G. Mantilla, M.D.

Irregular trabeculae

Stromal cells

Aneurysmal bone cyst

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 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 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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