Nephrogenic adenoma arising in urethral diverticula. A report of five cases.

Five cases of nephrogenic adenoma that arose within urethral diverticula are described. Four of the five women were under 40 years of age and one was 56 years old. Three presented to their gynecologists because of a "vaginal mass." Microscopic examination showed the typical tubular, cystic, and papillary patterns of nephrogenic adenoma. "Hobnail" cells were present in four cases and clear cells in two. The absence of four features, deep invasion, a prominent diffuse growth of glycogen-rich clear cells, significant nuclear atypia, and mitotic activity, argued against the diagnosis of clear-cell adenocarcinoma, which has a predilection to occur within urethral diverticula. Alertness to the possible presence of nephrogenic adenoma within a urethral diverticulum in a patient with predominantly gynecologic symptoms and knowledge of its morphologic variations is essential to prevent its misdiagnosis as clear-cell adenocarcinoma.