Atypical epidermoid cyst in renal pelvis and histogenetic implications

Since the renal epidermoid cyst is too rare, the mechanisms of squamous morphogenesis have not well characterized. A 73-year-old female was referred with an incidentally detected renal pelvis mass. Abdominopelvic computed tomography scan revealed a noncalcified soft tissue mass in the renal pelvis. Total nephroureterectomy was performed under the impression of a renal pelvis malignancy. The patient was discharged without postoperative complication. The outer surface of mass lesion was lined with urothelia and squamous epithelia, containing keratinous materials. The urothelia were positively stained against uroplakin II and cytokeratin 7, whereas almost of the squamous epithelia were negative with uroplakin II. The two different epithelia were generally sharply demarcated. Interestingly, some part of squamous epithelia contained uroplakin-positive and many more cytokeratin 7-positive cells. The atypical clinical features in our case can reconsider the diagnostic clues of renal epidermoid cysts that have been reported before, and the unique immunohistochemical results may understand the histogenetic implications of the lesion.