Cystic Lesions With Suspected Soft Tissue Infiltration

In April 2010, a 19-year-old soccer player presented with a 4-week history of pain after a tap against his right knee. Medical and family histories were unremarkable and no abnormalities were found on physical examination. A radiograph of the right knee showed osteolytic lesions in the distal femur and the head of the tibia. On magnetic resonance imaging, the epiphyseal lesions were visualized as cystic and nonsclerotic and extended to the articular surface of the distal femur and proximal tibia (Figure 1). Soft tissue extension was suspected from the tibia. Laboratory test results showed normal blood cell count, renal function, and concentration of C-reactive protein. Aneurysmatic bone cysts were suspected and a biopsy was performed. Histopathological examination detected spindle cell infiltrates with hemorrhages, fragmented trabecular bone, and numerous osteoclastic giant cells proliferating at a rate of 10% suggesting an aggressive giant cell lesion. Since it was still not determined whether the lesions were malignant, flourodeoxyglucose F 18positron emission tomography/computed tomographywasperformedand foundadditional lesions in the left distal femur and the leftmandible. Biopsyof themandible showed the same type of tissue as seen in the right femur and tibia. Quiz at jamasurgery.com A B