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
