Primary epithelial tumor of the renal pelvis is rare, and adenocarcinomas account for less than 1% of malignancies arising from the epithelium of the renal pelvis. We describe in this study a case of a 56-year old male patient who presented with an abdominal mass and dull aching pain for one year. A diagnosis of hydronephrosis of the right kidney was made based on imaging studies. Grossly, the entire kidney was converted into a cystic mass measuring 16 × 12 × 10 cm and filled with gelatinous material along with staghorn calculi in the pelvis measuring 7 × 4 × 3 cm. Histological examination of the tumor showed glands, cysts, and papillae lined by pseudostratified columnar epithelium with hyperchromatic nuclei. Scattered signet ring-type cells were also seen floating in large pools of extracellular mucin. Sections from the ureter showed a component of adenocarcinoma in situ. No invasive tumor was identified in ureteric tissue. Thus, a diagnosis of mucinous adenocarcinoma of the renal pelvis with in situ adenocarcinoma of the ureter was made.

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