The study is compatible with an elevation in serum alkaline phosphatase. This is a CT scan of the patient. The lesion has extended into the soft tissues to involve the anterior, lateral, and posterior compartments of the leg at this level. The pattern of mineralization is indicative of calcification. The nodule indicated by the arrow is likely a skip metastasis.
Parosteal osteosarcoma is a strong possibility.
The lesion is a Stage II-B osteosarcoma. The extent is significantly greater than anticipated. The lesion would feel soft and fleshy rather than firm and gritty. The histologic features are compatible with the nidus of an osteoid osteoma. The diagnosis is osteosarcoma, and the tissue is pre-chemotherapy.