Benign Cortical Defect
Fibrous Cortical Defect, Non-ossifying fibroma

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 (top) 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).
For more information, click on the link if you see this icon
For this same photo without the annotations, click here and here