Pathologically proven Ewing sarcoma.

Ewing sarcoma is an aggressive bone tumor observed in the first two decades of life. Second most common malignant bone tumor in children, presenting a higher prevalence in boys than in girls (3:1 ratio).

The typical clinical presentation includes:

• Pain and swelling at the site of the tumor. Pain often referred to the adjacent joint.
• Patients may present with nonspecific symptoms such as fever, increased erythrocyte sedimentation rate, and leukocytosis, or with weight loss and anemia.

Radiographic findings:

Mainly located near the metaphysis/diaphysis of long bones. Less often in flat bones or vertebral bodies.

Usually osteolytic lesions (motheaten, or permeative) with a soft-tissue component.

Periosteal reactions are common:

• Spiculation (periosteal new bone formation radiating into the soft tissues)
• Onionskin periosteal ossification.
• Codman triangle: elevated ossified periosteum at the margin of the subperiosteal tumor.
• "Sunburst" appearance

On imaging, the main differential diagnosis is osteosarcoma.