General Considerations

• Also called a non-ossifying fibroma or fibrous cortical defect
  • Non-ossifying fibroma frequently reserved for lesions > 2cm in size in older children
• Usually arises in metaphysis of distal femur or tibia
• Solitary lesion (75%) or multiple (25%)
• Most commonly seen in children 2-15 years of age
• May be secondary to a prior trauma injury (traction) as they tend to occur at sites of insertion of tendons and ligaments

Clinical Findings

• Usually asymptomatic
• Found serendipitously

Imaging Findings

• Geographic lytic lesion
• Septated
• Metaphyseal
• Eccentric
• Well-marginated
• Sclerotic rim
• Endosteal scalloping
• On healing
  • Marginal sclerosis increases
• Lesions “fill-in” from diaphyseal side of bone
• Bone scan
• May show increased activity on healing of the lesion
• MRI
• Variable signal intensity depending on healing stage
• Central decreased T2-W signal
• From collagen and hemosiderin deposits

Differential Diagnosis

• Image on conventional radiography is usually diagnostic

Treatment

• None required

Complications

• Rarely may undergo pathologic fracture
• Do not undergo malignant transformation

Prognosis

• Migrate away from epiphysis towards diaphysis with age
• Most lesions heal spontaneously by being replaced with normal bone

 

 

 

Benign Cortical Defect. White arrow (left) points to a well-circumscribed, lytic lesion in the metaphysis of this child's distal femur. It has a sclerotic rim. On the lateral view, its cortical nature is again demonstrated (yellow arrow).
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