Staging a great escape -Incidentally detected renal urothelial carcinoma with extensive squamous metaplasia presenting as pyonephrosis.

Incidentally, detected upper urinary tract urothelial carcinoma is a rare entity. We report the case of a 70-year-old female patient who presented with flank pain, pyuria, fever, and a unilateral nonfunctioning kidney with nephrolithiasis and pyonephrosis on pyelography. Routine imaging failed to identify a mass lesion. In an Indian setting, the clinical differential of tuberculosis was considered likely. A nephrectomy was performed in view of the poor perfusion and functional status of the right kidney. Histopathological examination of the kidney showed a tumor of urothelial origin arising at the renal pelvis displaying extensive squamous metaplasia. Such a near total metaplastic change is rare and has hitherto been undescribed in the renal pelvis. Activation of pleuripotent urothelial stem cells in the setting of chronic irritation and inflammation may be the pathogenetic process behind such an occurrence.