Benign cortical defects are seen in up to 40% of all children at some time in their development. They are most prevalent in children between ages 4-6. The term non-ossifying fibroma is used for lesions >2 cm. They are found emanating from the cortex of long bone metaphyses. The most common location is the distal femur.

Radiographically, these lesions appear as lucent, eccentric, well-defined lesions with a thin, sclerotic border. They are typically round or oval in shape.

These lesions are not painful, do not exhibit periostitis, and they usually spontaneously regress over time.

Benign Cortical Defect in a 7-year-old male. AP view of the right knee shows a radiolucent defect in the distal femoral metaphysis measuring 2cm X 1cm. Note the slight sclerotic margin surrounding the lucency.