Although malignant bone tumors are uncommon in children, they pose a significant diagnostic and therapeutic challenge to clinicians. Radiologic advances have allowed more thorough evaluation of these tumors. MR imaging has improved the ability to assess tumor margins and more accurately stage these lesions.1 Computed tomography and conventional radiography are often used in the initial evaluation of bone tumors, and osseous scintigraphy is the study of choice for the evaluation of suspected metastases, which are a relatively common phenomenon. Along with bone scanning, these 2 modalities are also used in the diagnosis of distant metastasis of these tumors, which is a very common finding.
Ewing's sarcoma was first identified by Dr. Ewing in the 1920s.2 As the second most common pediatric bone tumor, it most frequently develops in the axial skeleton, particularly in the pelvis.1 The diaphyses of the femur, tibia, and humerus are also common sites of primary tumor involvement.1,3 Approximately 70% of cases have disseminated disease with involvement of multiple osseous and visceral sites (lung and bone marrow are most common) in the later course of the disease.1,4 Roughly 10% have multiple lesions at diagnosis, which could be multiple primaries or a primary lesion with metastases.3 Imaging findings often resemble those of osteosarcoma, and definitive diagnosis is made by biopsy and histological evaluation.
The classic radiographic appearance of Ewing's sarcoma is onionskin periostitis and is often used as a preliminary means of differentiating these tumors. The spiculated or "sunburst" type of periosteal reaction can also be seen with Ewing's sarcoma, but is more often seen in osteosarcoma.5 Recent advances in MR imaging have contributed to the staging of these tumors by allowing soft tissue visualization, especially of the nearby neurovascular structures.3 Staging helps to minimize mistakes in biopsy and aids in the treatment of these lesions.3 Staging with MR imaging can often eliminate the need for total limb amputation by giving the clinician the exact location and extent of the disease and can also be used to access the tumor response to therapy.
The recommended treatment of Ewing's sarcoma is surgical resection or radiation ablation of the primary tumor, followed by multidrug chemo therapy for possible distant metastasis.3 Resectable extremity lesions have a more favorable outcome than do axial skeletal lesions.1 However, despite treatment, these tumors are often recurrent and metastatic.
The "onionskin" periostitis is classic for Ewing's sarcoma. The MR appearance is often a large soft-tissue mass. The definitive diagnosis is made by biopsy, and a close look for metastatic lesions at the time of presentation is appropriate.