The natural history of nephrogenic adenoma of the urinary bladder.

The nephrogenic adenoma is a peculiar lesion of the urinary bladder characterized partly by villous and partly by gland-like structures. The two layered surface epithelium consists of an eosinophilic cell layer, which covers a clear cell layer, the latter resting upon a delicate basal layer. The clear cells disappear when approaching the tip of the villi. There exists a 200 micron wide zone of transition between the urinary bladder epithelium and that of the neprogenic adenoma. At the base of the villi there are scattered nodules of gland-like structures lined either by eosinophilic cells or by clear cells. These epithelial cells are derived from the corresponding surface epithelial cells from which they had separated by active downwards growth.