Fibrous and Fibroosseous tumors of bone
Fibrous dysplasia

Author: Nat Pernick, M.D. (see Authors page)

Revised: 20 November 2018, last major update August 2013

Copyright: (c) 2003-2018,, Inc.

PubMed Search: Fibrous dysplasia[title]

Related topics: Monostotic, Polyostotic, McCune-Albright syndrome, Mazabraud syndrome, Fibrous dysplasia protuberans

Cite this page: Pernick, N. Fibrous dysplasia. website. Accessed December 12th, 2018.
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

Images hosted on Pathout server:

Femur Xray - contributed by Dr. Mark R. Wick

Ulna Xray - contributed by Dr. Mark R. Wick

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

Images hosted on Pathout server:

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

Images hosted on Pathout server:

Fibrous dysplasia - contributed by Dr. Mark R. Wick

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