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Papillary transitional cell carcinoma arising in a calyceal cyst and masquerading as a renal cyst.

We report the case of a 74-year-old man with a papillary transitional cell carcinoma, grade 1-2/3, growing within a bilobated calyceal cyst, measuring up to 8.5 cm in diameter, and masquerading as a simple renal cyst. The cyst was lined by atrophic simple and transitional epithelium and showed intracystic hemorrhage. Leakage of blood into the calyx was probably the cause of the hematuria for which the patient presented. However, with retrograde pyelography and careful gross examination of the excised kidney, no communication of the pyelocalyceal system with the cyst could be identified. By ultrasound examination and computerized tomographic scan the lesion showed several small renal cysts, measuring up to 1.1 cm in diameter, as well as several hepatic parenchymal cysts. To our knowledge, this is the first report of a papillary transitional cell carcinoma arising from a cyst of calyceal origin.