Transitional cell carcinoma arising in a pyelocaliceal cyst - An unusual cystic renal lesion with cytologic and imaging findings

The differentiation between benign and malignant cystic lesions of the kidn ey is a diagnostic challenge. Medical imaging aids in this task, but many c ystic renal lesions require further work-up, frequently by computed tomogra phy-guided fine needle aspiration. We report on the pathological findings i n a case of moderately differentiated papillary transitional carcinoma, whi ch arose in a pre-existing pyelocaliceal cyst in a 53-year-old man. In the case of this lesion, the distinction between a benign and a malignant renal cyst is blurred. To our knowledge, this is the third such occurrence to be reported and the first to be diagnosed by fine needle aspiration biopsy.