An unusual presentation of osteosarcoma in the proximal femur with peculiar diagnostic characteristics: a retrospective series

Background: Diagnosis of osteosarcoma in the proximal femur is challenging because of its atypical features. Hence, further characterization of the tumors of this location is necessary. In this study, we evaluated the characteristic features and outcomes of osteosarcoma in the proximal femur. Methods: Fifteen patients with proximal femoral osteosarcoma proximal to the intertrochanteric region were evaluated. The demographic, clinical, and radiologic characteristics of the patients were investigated. A modified Lodwick-Madewell system was used for the classification of the osteolysis pattern. Results: From a total of the 446 patients who had osteosarcoma, 24(5.4%) were identified in the proximal femur. The main clinical symptom was pain without mass. The osteolysis pattern was ill-defined in 10, “moth-eaten” in three, change of margin in one, and well-defined without sclerotic rim in one patient. Bone matrix mineralization was present in nine patients, which was in osteoid form in seven patients and in calcified form in two patients. Cortical destruction was seen in six patients. Peripheral edema and joint effusion were identified in nine and seven, respectively, out of 12 patients who had an MRI. Soft-tissue component and periosteal reaction were not seen in any patient. At a mean follow-up of 7.3 yr, four patients were deceased. Conclusions: Osteosarcoma of the proximal femur generally presents without classical features. Most notably, the tumor almost never has an extraosseous tumor mass. Therefore, the absence of an extraosseous component does not preclude the diagnosis of osteosarcoma in the femoral neck. Level of Evidence: Level IV.