Nephrogenic adenoma of the urinary tract: A 6-year single center experience.

Background: Nephrogenic adenoma is an uncommon benign lesion that occurs at several sites in urinary tract, from the renal pelvis to urethra, with the highest frequency in urinary bladder. Nephrogenic adenoma displays a broad spectrum of architectural and cytological features. Hence, recognition of its characteristic histopathological features is needed to distinguish this lesion from its mimickers.

Materials And Methods: A retrospective series of 21 cases of nephrogenic adenoma in 18 patients, which were diagnosed in our department between 2010 and 2016, were analyzed. All histological slides were reviewed by two pathologists and the diagnosis of each case was confirmed. Immunohistochemistry was performed for PAX-8 in all cases. CK7, PAX-2, PSA, p53, p63, GATA-3 and α-methylacyl-CoA racemase (AMACR) were applied in problematic cases.

Results: The most common location of the lesion was urinary bladder (14 patients) followed by renal pelvis (2 patients), ureter (1 patient) and urethra (1 patient). A history of urothelial carcinoma and repeated TUR procedures were observed in 12 patients. There were 2 pediatric patients aged 3 years. Both of them had undergone previous urosurgery because of megaureter in one and bladder exstrophy in the other. Other clinical antecedents included bladder diverticulum (1 patient), cystitis (1 patient) and nephrolithiasis (1 patient). Recurrence of lesion was seen in two patients (once in one case and twice in the other one). The median time to disease recurrence in these patients was 11 months (range, 2-20 months). Histologically, the lesions exhibited various morphological findings, with mixed (15 cases, 71.4%), pure tubular (3 cases, 14.3%), pure papillary (2 cases, 9.5%) and pure flat (1 case, 4.8%) growth patterns. Of the 15 cases with mixed patterns, 8 cases were tubulocystic and flat, 3 cases were tubular and flat, 2 cases were tubular, papillary and flat, 1 case was tubulocystic, papillary and flat, and 1 case was tubular and papillary. Flat pattern was observed in 15 cases (71.4%). It was seen in association with other patterns in 14 cases (mixed morphology) and purely in 1 case. Our findings suggested that the flat pattern is a frequent finding in nephrogenic adenomas. Notably one case in this series showed superficial extension into bladder muscularis propria.

Conclusions: Histologically nephrogenic adenoma may simulate a variety of malignancies. Awareness of characteristic morphologic features of nephrogenic adenoma is needed to diagnose this lesion correctly.