Primary mucinous lesions of the urinary system are extremely rare. We describe two cases of primary mucinous lesions of the urothelial tract. One case is of mucinous metaplasia in the bladder of a 40-year-old man presenting with frequent urination, urgency, and gross hematuria. The other case is of mucinous adenocarcinoma in the pelvis of an otherwise healthy 67-year-old man with left nephrolithiasis. The histological images of the two cases demonstrate a spectrum from benign mucinous metaplasia to malignant mucinous adenocarcinoma, and suggest that mucinous metaplasia in urothelial tract may be the precancerous lesion of mucinous adenocarcinoma.
Keywords: Mucinous metaplasia; precancerous lesion; urothelium.