FIBROUS DYSPLASIA

FIBROUS DYSPLASIA

• Fibrous dysplasia is condition where there is fibrous proliferation with spicules of disorganized bone in medullary cavity due to defect in ossification. Stromal cells which are thought to be fibroblasts are now recognized as preosteogenic cells.

• Neoplastic nature of this lesion is also suggested due to the presence of

  • Clonal karyotypic abnormalities like extra co[pies of chromosome 2

  • Rearrangement of of 12p13

  • Monoclonality for the human androgen receptor gene (HUMARA)

  • Mutations of GNAS1 gene

• SIte –

  • It may be mono ostotic (single site) or polyostotic (multiple sites). 30% cases are polyostotic.

  • Common sites – Femur, tibia, skull, facial bones or ribs. but can involve any bone.

• Clinical features – depends  on the bone involved

  • Long bones involved may present as an incidental finding or may present with pathological fracture

  • Jaw bones – facial deformity

  • skull lesions – asymptomatic or present as swelling

  • Polyostotic involvement occurs in 25% of cases. In women mostly it is associated with patchy skin pigmentation (Cafe’ au lait) and various endocrinopathies usually precocious puberty (Albright-Mc Cune syndrome) resulting from germ line mutation in GNAS1 gene

• Age – usually in the first two decades of life

• Sex- Slight female predominance

• Radiographic findings

  • Well defined zone of rarefaction with area of lucency surrounded by thick bone rind

  • Hazy mineralization with in the lesion produces “ground glass” appearance

• Gross finding

  • Bone appear expanded with thinning of the cortex and is replaced with dense, white fibrous tissue that feels gritty on sensation due to the presence of bony spicules

  • Yellow areas present suggest collection of foam cells

• MIcroscopic features

  • Irregular foci of woven (non-lamellar) bone trabeculae in a cellular fibrous strtoma

  • bony spicules are distributed more or less evenly through out the matrix and are often described to resemble letter C or Y or chinese characterisics

  • Osteoclastic resorption is associated with this configuration

  • Osteoblastic rimming is absent or minimal

  • In jaw bones, spicules may be spherical and psammomatous or dense blue nodules or cementicles like structure in fibrous stroma

  • Fibrous stroma may have storiform pattern also

  • Cartilage may also be present

  • In addition other secondary reactive changes caused by pathologic fracture can be present. Multinucleated giant cells, histiocytes and fracture callus and areas of secondary aneurysmal bone cyst may be present.

  • Sarcomatous changes can occur following irradiation

• Treatment and prognosis

  • Solitary lesions may not require treatment and have an excellent prognosis

  • Polyostotic lesions lead to fractures

  • Sarcomatous change can occur

References

• K.Krishnan Unni, Carrie Y. Inwards, Julie A.Bridge, Lars-Gunnar Kind blom, Lester E. Conditions that simulate primary neoplasms of bone. In: Tumors of bone and joints. AFIP Atlas of tumor pathology 2005. Series 4:Chapter 14:pp321-382

• Lauren Vedder Ackerman, David C.Dahlin. Fibrous tumors and tumor like conditions. In:Orhopaedic Pathology by Peter G. Bullough 2004. 5th edition Chapter 18:429-448

 

 

Fibrous dysplasia: Irregular woven trabecular bone embedded in fibrous stroma. Osteoblastic rimming is minimal (H&E,X100)