Given the age of the patient and radiographic appearance, what is the most likely diagnosis?
Fibrous dysplasia is most likely, with simple bone cyst less likely. Other differentials could be entertained, but would be atypical or extremely rare.
The proximal humeral metaphysis and visualized portion of the proximal diaphysis demonstrate a well-defined lesion with minimal trabeculation, cortical thinning and areas of varying density that appear somewhat ground-glass in nature. There is no associated periosteal reaction or soft-tissue mass. There is an obliquely oriented, cominuted fracture through the lesion with moderate offset of the most distally visualized fragment. A long-bone study of the right humerus is nececary to asses the distal extent of the lesion.