A well-demarcated expansile eccentric lytic lesion with scalloped sclerotic margins parallel to the long axis of the metaphyses of long bones is virtually diagnostic of non-ossified fibroma.

Non-ossifying fibroma is also known as fibroxanthoma. Fibrous cortical defect (FCD) is a fibroxantoma smaller than 2 cm. NOF is a "DO NOT TOUCH" lesion. No further work-up is required.

The DDx of NOF is:

• simple bone cyst (SBC): central lytic lesion with fallen fragment sign in case of pathological fractures.
• aneurysmal bone cyst (ABC): eccentrically located lesion with marked bone expansion and periosteal reaction. Fluid/ fluid level is diagnostic.
• fibrous dysplasia: expansile medullary lesion with ground glass attenuation. Fibrous dysplasia is a long disease in a long bone!