Figure 162 is the right shoulder radiograph of a 5-year-old boy who fell and now has right shoulder pain. Prior to the fall he had no history of symptoms. What is the best next step?

Figure A is the biopsy specimen of a 30-year-old man with a 4-month history of a painless, slow-growing mass in his medial thigh. Local imaging (orthogonal radiographs and MR images with intravenous gadolinium) reveals a 6- x 5- x 7-cm heterogeneous mass in the adductor magnus muscle.

An 11-year-old presents with 6-month history of groin pain. X-rays and biopsy specimen are shown in Figure A and B. What is the etiology of the lesion?