Microscopic Description:

H & E-stained section shows papillary arrangement of tumor cells lined by simple cuboidal cells. The cells show scant cytoplasm, finely granular uniform chromatin, and inconspicuous nucleoli with associated acute and chronic inflammation in the stroma.

Immunohistochemistry was positive for PAX8, CK7, AMACR in tumor cells.

Discussion:

Nephrogenic adenoma (NA) or nephrogenic metaplasia was initially characterized in 1949 as ‘bladder hamartoma’.

It is a rare entity with male predilection.

The most common site is urinary bladder followed by the urethra, ureter, renal pelvis and rarely prostate.

It is a benign reactive lesion linked to genitourinary trauma, calculi, chronic inflammation, previous surgery, repetitive instrumentation, intravesical BCG therapy, and bladder diverticula.

Recently, it is thought to arise from the seeding of exfoliated renal tubular cells in the urinary tract as NA in kidney transplant patient showed same chromosome status as of donor kidney tubular cells rather than urothelial mucosa.

NA characteristically shows presence of multiple architectural patterns like nested, tubular, papillary, cystic, and solid within the same lesion.

The IHC profile of NA shows expression of renal tubule markers (CK7, CD10, AMACR, PAX2, and PAX8), and the absence of urothelial markers (thrombomodulin and p63).

This entity is important because it usually presents after multiple bladder instrumentation/procedures and can pose similarities to malignant growth on cystoscopy.

Although there is no increased risk of bladder carcinoma but due to tendency to recur, follow-up with cystoscopy within 6 to 12 months and again later if symptoms reappears.

References:

Davis TA. Hamartoma of the urinary bladder. Northwest Med. 1949;48:182–185.

Kunju LP. Nephrogenic adenoma: report of a case and review of morphologic mimics. Arch Pathol Lab Med 2010;134(10): 1455–1459

Sakatani T, Adachi Y, Sakaida N, et al. Nephrogenic adenomain elderly patients: three case reports. Mol Clin Oncol 2016;5(02):253–256.

Turcan D, Acikalin MF, Yilmaz E, Canaz F, Arik D. Nephrogenic adenoma of the urinary tract: a 6-year single center experience. Pathol Res Pract 2017;213(07):831–835.

Piña-Oviedo S, Shen SS, Truong LD, Ayala AG, Ro JY. Flat pattern of nephrogenic adenoma: previously unrecognized pattern unveiled using PAX2 and PAX8 immunohistochemistry. Mod Pathol 2013;26(06):792–798.

Yi Y, Wu A, Cameron AP. Nephrogenic adenoma of the bladder: a single institution experience assessing clinical factors. Int Braz J Urol 2018;44(03):506–511.

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