History: 18-year-old female complaining of left thigh pain.

Radiological Findings:

Plain film: An aggressive lesion of the left femoral dimetaphysis is seen with both intramedullary and cortical involvement. The lesion has a permeative appearance with starburst periosteal reaction.

MRI: Sagittal and coronal T1, coronal FSE-IR, axial FSE T2 and axial fat saturated T1 post contrast sequences demonstrate a large diametaphyseal soft tissue mass measuring 17.0 cm in length x 15.0 cm in transverse and AP dimension, with extensive bone marrow involvement. The distal aspect of this lesion crosses the expected location of the physeal scar. The proximal aspect of the bone marrow involvement extends 5.0 cm proximal to the upper margin of the soft tissue mass. The lesion enhances with contrast and demonstrates extensive high signal on T2 FSE-IR sequences. There is no evidence of skip lesions. The popliteal and femoral vessels are posteriorly displaced without evidence of encasement. The profunda femoris artery becomes completely encased and non-visualized upon entry into the upper margin of the soft tissue mass.

99mTc MDP bone scan: Intense radiopharmaceutical uptake is present in the mid and distal left femur as well as in the surrounding soft tissues. No scintigraphic evidence of metastasis is seen. Incidentally, stress changes of the left tibia and ankle are present.

CT of the Chest: A noncontrast CT examination of the chest demonstrates two subpleural pulmonary nodules in the apical posterior segment of the left lung consistent with metastatic disease.

Diagnosis: Osteosarcoma (with pathology conformation) of the left femur with possible metastasis to the left lung.

Differential Diagnosis: Osteosarcoma, osteomyelitis.

Discussion:

Osteosarcoma is the most common primary malignant bone tumor in children. Peak incidence is between the ages of 10-20 and is most commonly seen in the distal femoral metaphysis (40%), proximal tibia (20%) and proximal humerus (15%). Flat bones can also be involved, particularly the ileum and mandible (1). Pain and local swelling are the most common clinical symptoms.

Radiologic findings include an aggressive bone forming lesion which may present with a mixed presentation of bone destruction and sclerosis with an associated soft tissue mass. Irregular, spiculated periosteal reaction that is aligned perpendicular to the cortex is commonly seen. Codman triangles (periosteal elevation) are also frequently observed. The primary modality for further evaluation and treatment planning is MRI, where the extent of the lesion is better determined.
   Bone scan is useful for detecting skip lesions and distant metastasis. Additionally, scintigraphy with 201-Tl has been shown to be a good indicator of chemotheraputic response, where a reduction of radiopharmaceutical uptake in the 201-Tl-avid tumor suggests an excellent response (2-5)
   CT examinations are helpful for evaluation of pulmonary metastasis.

Treatment: Surgery with adjuvant chemotherapy is the treatment of choice for osteosarcoma of the appendicular skeleton. Limb sparing procedures are performed in approximately 80% of patients with osteosarcoma (6). The incorporation of adjuvant chemotherapy with surgery has improved the prognosis significantly with 5 and 10-year survival after diagnosis to 77% and 72% respectively (7). Death usually results from pulmonary metastasis, however, aggressive surgical management, to include resection of all pulmonary metastasis, has improved the prognosis in this situation as long as the nodules do not abut the pleura (8).