21 year old, mild leg pain

MRI Correlation
Findings, DDx?

Answers
Aneurysmal Bone Cyst
*Images showed an expansile, “bubbly” lesion involving the mid-femur
*MRI confirmed multiple cysts within, Some containing fluid-fluid levels (blood breakdown products at different ages)
*Age range ~10 to 30 year old; typically involves spine & long bones
*DDx: Giant cell tumor (can have fluid-fluid levels, but should not be expansile); telangiectatic osteosarcoma, cystic renal cell or thyroid mets; fibrous dysplasia (no evidence of fibrous bone)