Presentation
Pain after trauma.
Patient Data
Pathological fracture through a proximal lytic lesion with smooth margins and narrow transition zone, and with a fragment in the dependent part (fallen fragment sign).
Yellow circle highlights position of the fallen bone fragment in the bone cyst.
Case Discussion
Unicameral bone cysts are benign fluid containing lesions. The etiology is unknown. The cortical bone is not interrupted and the transition zone is narrow. There are usually asymptomatic, and are often an incidental finding, discovered before age 20. Sometimes they are diagnosed after pathological fracture. The typical location is the proximal end (metaphysis) of the humerus. Rare in other places, with the exception of the heel, in this location lipoma should be considered in the differential diagnosis.