Primary Renal Ewing Sarcoma Presenting With Divergent Radiological Phenotypes: A Radiology-Focused Case Series...

Primary renal Ewing sarcoma/primitive neuroectodermal tumor (PNET) is an exceptionally rare and highly aggressive malignancy belonging to the Ewing sarcoma family of tumors (ESFT). Owing to its nonspecific clinical and imaging appearance, it frequently mimics more common renal malignancies, particularly renal cell carcinoma (RCC), resulting in diagnostic difficulty and delayed therapeutic decision-making. We present a radiology-oriented case report of two female patients with histopathologically confirmed primary renal Ewing sarcoma demonstrating markedly different imaging phenotypes. The first patient presented with a large infiltrative renal mass showing extensive venous tumor thrombus closely simulating aggressive RCC. The second patient, presenting in the elderly age group, demonstrated diffuse pelvicalyceal and ureteric involvement with preservation of renal contour and contiguous urothelial extension, closely resembling upper tract urothelial carcinoma/transitional cell carcinoma (TCC). Both tumors demonstrated large size, heterogeneous enhancement, internal necrosis, an infiltrative growth pattern, and aggressive locoregional disease. Positron emission tomography-computed tomography (PET-CT) demonstrated intense fluorodeoxyglucose (FDG) avidity and metastatic disease in both cases. Histopathological and immunohistochemical (IHC) analysis confirmed Ewing sarcoma/PNET in both patients. This case series highlights the broad radiologic spectrum of primary renal Ewing sarcoma and emphasizes imaging features that should raise suspicion for this rare diagnosis, including large rapidly enlarging infiltrative renal masses, disproportionate necrosis, marked vascular involvement, diffusion restriction on MRI, early metastatic disease, and atypical imaging behavior not entirely conforming to conventional RCC or urothelial malignancy. Awareness of these features may facilitate earlier diagnosis and appropriate multidisciplinary management.