[Nephrogenic adenoma of the urinary bladder. A lesion that can be confused with carcinoma. Report of 4 cases].

Nephrogenic Adenoma (NA) was first illustrated in 1949 by Davis, who described a case he interpreted as a "hamartoma". One year later Friedman and Kuhlenbeck described eight further examples in detail and named this lesion nephrogenic adenoma. This process is generally accepted to be metaplastic. At cystoscopy and on microscopic examination nephrogenic adenoma may simulate a neoplasm. The clinical and pathologic findings in four patients are described. The patients were two women and two men 20-60 years of age. All of them had a history of some inciting injury (infection/calculus). The four cases were initially misdiagnosed as a carcinoma. Several features of NA may cause particular diagnostic difficulty. Tiny tubules may simulate signet ring cells, the haphazard distribution of the tubules or single cell growth may also simulate the appearance of an invasive adenocarcinoma. A variety of clinical and pathologic differences should enable the distinction of these lesions. Although this is occasionally difficult. An emphasis here is placed on the diagnostic problems that they may pose for the surgical pathologist. Clinicians and pathologists should be aware about this type of lesions in order to avoid pitfalls in the diagnosis and treatment of them.