- AKA Fibroxanthoma. AKA Fibrous cortical defect.
- Benign fibroblastic mass.
- Typically arises in the metaphyses of long bones, particularly the distal femur and tibia.
- Common, possibly affecting more than 40% of boys and 30% of girls.
- Thought to originate at the insertion site of a ligament or tendon and it has been suggested that it may reflect a previous traction injury.
- Lesions are usually asymptomatic, although they are occasionally associated with pathological fractures.
 Imaging Findings
 Plain film
- Eccentric lucent lesion with thinned cortex, which may have a multilocular appearance and often a sclerotic margin.
- The lesions spontaneously regress with time and radiographs will show increasing marginal sclerosis followed by progressive ossification of the lesion extending from its diaphyseal aspect.
- The appearance on plain films is characteristic and no further imaging is indicated.