Ossifying fibroma (osteofibrous dysplasia)

Tumor biology and incidence

• Benign active or aggressive lesion
• Very rare
• May possibly progress to adamantinoma in later stages

Age

• Most commonly manifests during first and second decade of life
• 50% of patients less than 5 years old

Gender

M:F = 1.5:1 

Presentation

• Often asymptomatic
• Pathologic fracture a rare initial event
• Bowing or swelling in tibia most common presenting complaint

Physical findings

Often demonstrates anterior bowing of tibia

Plain films

Site

• Largely tibial involvement (proximal third of tibia, anterior cortex), occasionally the fibula
• Eccentrically located diaphyseal lesion
• Less commonly found in metaphysis

Size

Variable

Tumor effect on bone

• Osteolytic, intracortical lesion
• Generally geographic

Bone response to tumor

• Lesion may lead to solitary or multiple blister-like areas of cortical lucency or ground glass density surrounded by dense sclerosis
• Margin is sharply demarcated (geographic)
• Periosteal expansion in response to cortical lesions produces bulging cortex

Matrix

Usually radiolucent, no matrix

Cortex

• May be irregular and thinned, but usually remains intact and expanded
• Cortical continuity may be lost with aggressive lesion

Soft tissue mass

None

Differential diagnosis

• Adamantinoma
  • May be identical to ossifying fibroma on radiographic analysis
  • Patient's age will aid in differentiating between lesions – adamantinoma is more likely in older patients
  • Biopsy lesion to obtain an accurate diagnosis
• Fibrous dysplasia
• Nonossifying fibroma
• Osteoblastoma
• Aneurysmal bone cyst 

Natural history

• Lesions have little tendency to progress in patients less than 5 years old
• Lesions may continue to enlarge until skeletal maturity; after skeletal maturity, expansion of lesion not expected
• Some lesions heal spontaneously
• Progression to adamantinoma may be observed

Pathology

• Gross: Fibrous tissue with admixed bone spicules
• Microscopic: Trabeculae of woven bone in a fibrous stroma
• Bone rimmed by osteoblasts and osteoclasts; distinct from stroma, which helps differentiate it from fibrous dysplasia

Diagnosis and treatment

• If asymptomatic: observe 
• Delay excision and bone graft until age 10, if possible; before this age, excision associated with high rate of recurrence