Pelvic Ewing's Sarcoma

A pelvic radiograph of a 5-year-old girl shows a large lytic lesion in the left iliac bone (arrows).

An axial FDG PET/CT image shows high metabolic activity of the mass involving the left iliac bone with soft tissue component and bone destruction. A coronal T2W MR image reveals an extensive soft tissue mass with necrotic areas and involvement of the adjacent musculature. 

Differential Diagnosis

• Metastatic neuroblastoma. Given her age at five years old, this needs to be in differentials
• Ewing's sarcoma
• Telangiectatic osteosarcoma
• Osteomyelitis. Great mimics of aggressive-looking bone tumor. Symptoms may overlap with round-cell tumor, including fever

This case: Ewing's sarcoma by tissue diagnosis (+ve PAS and vimentin).

Facts: Ewing's Sarcoma

• Malignant round-cell tumors of the bone with neural cell origin
• Tumors of children and young adults, most between 10-20 years old. Less than 2% occur in children less than 5 years old
• Most common sites = femur >> pelvis
• Pelvic Ewing's -- bad prognosis because there is no anatomic barrier to tumor spread, close proximity to viscera and neurovascular bundles, prone to recur

Reference:

Bhagat S, Sharma H, Pillai DS, Jane MJ. Pelvic Ewing's sarcoma: a review from Swedish Bone Tumour Registry. J Orthop Surg 2008;16:333-8