Ewing Sarcoma of the Pelvis

Figures 1 & 2: Coronal reformatted CT images of the pelvis of a 16-year-old man show a large heterogeneous soft tissue mass (arrows) involving the right iliac bone. The mass is enhanced and contains ring and arc calcifications. Note lytic lesions in the lumbar vertebral body (arrowhead).
Figure 3: Anterior bone scan image of the pelvis shows focal increased uptake in the right iliac bone and L4 vertebral body, corresponding with findings on the CT scan.

Facts

• First described by Ewing in 1921
• Family of small round cell neoplasms including: 'classic' Ewing sarcoma of bone, extraskeletal Ewing sarcoma, small cell tumor of thoracopulmonary region (Askin tumor), and soft tissue-based primitive neuroectodermal tumors (PNET).
• Currently believed to be due to spontaneous genetic transolocation
• Second most common bone cancer in adolescents and young adults (after osteosarcoma)
• 5-20 years old, male slightly more than female
• Whites much more common than Asians or Africans

Imaging Appearance

• Permeative lytic lesion with soft tissue components
• Ring and arc calcifications (chondroid matrix)
• Codman triangle or onion multi-layered periosteal reaction
• Common locations: pelvic bones (26%), femur (20%), tibia/fibula (18%), chest wall (16%)
• In long bone, diaphysis > metaphysis
• Increased uptake on bone scan

Work-up

• Aim to distinguish localized disease from metastatic disease
• MRI +/- CT of the lesion
• Chest CT to look for pulmonary metastasis
• Whole body bone scan or PET
• Bone marrow biopsy or MRI of the spine
• Tumor at nonaxial skeleton primary site, age <>

Our case: Ewing sarcoma with bone metastases

Reference:

Ludwig JA. Ewing sarcoma: historical perspectives, current state-of-the-art, and opportunities for targeted therapy in the future. Curr Opin Oncol 2008; 20:412-418.