Bone
Fibrous and Fibroosseous tumors of bone
Fibrous dysplasia


Topic Completed: 1 August 2013

Revised: 25 October 2019

Copyright: 2003-2019, PathologyOutlines.com, Inc.

PubMed Search: Fibrous dysplasia[title]

Related topics: McCune-Albright syndrome, Mazabraud syndrome

Nat Pernick, M.D.
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Cite this page: Pernick N. Fibrous dysplasia. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/bonefibrousdysplasia.html. Accessed November 18th, 2019.
Definition / general
  • Developmental, nonneoplastic disorder of bone-forming mesenchyme, causing bone maturation arrest at the woven bone stage
  • Usually associated with activating point mutation in some somatic cells (possibly alpha submit of signal transducing G protein) that leads to elevated intracellular cyclic adenosine monophosphates (cAMP)
  • Usually begins prior to puberty and grows slowly, although mean age at diagnosis is 32 years; 60% males
  • Medulla of diaphysis or metaphysis of craniofacial bones, femur, ribs are most common
  • May be accompanied by intramuscular myxoma in same extremity
  • May be related to cemeto-ossifying fibroma (Am J Surg Pathol 1995;19:775, Arch Pathol Lab Med 1993;117:284)
  • Types: monostotic, polyostotic, McCune-Albright syndrome, Mazabraud syndrome
  • Malignant transformation: rare, monostotic or polyostotic; may represent dedifferentiation of low-grade osteosarcoma; may occur after radiation therapy
Radiology images

Contributed by Dr. Mark R. Wick

Femur Xray

Ulna Xray



AFIP images

Radiograph, expanded rib

Case reports
Gross description
  • Well circumscribed, intramedullary
  • Tan-white-yellow, gritty
  • Large lesions distort bone
  • Cortical bone often thin and expanded
Gross images

AFIP images

Expanded rib

Expanded lesion of calvarium

Microscopic (histologic) description
  • Curvilinear trabeculae (Chinese letters) of metaplastic woven bone (never matures) in hypocellular, fibroblastic stroma
  • No osteoblastic rimming (due to maturation arrest), 20% of cases have cartilaginous nodules (particularly in femoral neck region)
  • Also myxoid areas, rapidly growing secondary aneurysmal bone cysts, hemorrhage, foamy macrophages, calcified spherules (similar to cementifying fibromas), cellular areas, focal hyaline cartilage or cystic areas
  • Usually abrupt transition of normal to abnormal bone
  • No/rare mitotic figures, no atypia (rarely is degenerative)
  • Overall resembles endochondral ossification in skull
Microscopic (histologic) images

Contributed by Dr. Mark R. Wick

Fibrous dysplasia



AFIP images

Irregular shaped trabeculae

Trabeculae of varying configurations

Metaplastic osteoid and bone formation

Broad island of cartilage



Images hosted on other servers:
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Quiz case

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Various images

Negative stains
Electron microscopy description
  • Immature woven bone trabeculae lined by abnormal osteoblasts resembling fibroblasts
Differential diagnosis
Additional references
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