Ewing Sarcoma of the Pelvis with an Atypical Radiographic Appearance: A Mimicker of Non-malignant Etiologies

Ewing sarcoma (ES) is a primary malignant bone tumor which most commonly arises in children and young adults. The common clinical presentation with ES includes nighttime pain or pain related to activity, though patients may also present with a combination of localized swelling, a palpable mass, pathologic fracture, and constitutional symptoms. Clinical diagnosis may be delayed when a patient presents with clinical or imaging findings that overlap with non-malignant etiologies, such as fibrous dysplasia (FD) or osteomyelitis. Furthermore, multimodality imaging, including computed tomography (CT), magnetic resonance imaging (MRI), and nuclear medicine may prove inconclusive in particular cases. Suspicion for malignancy should not be overlooked. A biopsy must be considered, unless the diagnosis is evident, such as a clinical response to antibiotics in the setting of osteomyelitis.