Radiological and pathological diagnosis of an incidental Askin tumor.

A 53-year-old male with no significant past medical history presented with an acute traumatic fracture of his thumb. Preoperative chest radiograph before K-wire fixation demonstrated an incidental 9 cm opacity of the left lung. Chest computed tomography revealed a 6.3 cm aggressive appearing pleural-based mass with erosion and destruction of the underlying rib. The patient underwent percutaneous biopsy with interventional radiology, and pathology revealed a small round blue cell tumor with positive CD99 staining and a FUS-ERG chromosomal translocation. The patient was diagnosed with Askin tumor, a peripheral primitive neuroectodermal tumor of the thoracopulmonary region belonging to the Ewing sarcoma tumor family. Computed tomography and magnetic resonance imaging of Askin tumors may show features such as a heterogeneous soft tissue mass, pleural effusion, rib destruction, hemorrhage, necrosis, and cystic degeneration. Askin tumors typically exhibit the EWS-FLI1 fusion mutation, although FUS-ERG chromosomal translocation has been described. Both rarity and variability of Askin tumors present a diagnostic challenge for clinicians. Collaborative effort amongst radiologists and pathologists is essential for diagnosis.