Atypical Nephrogenic Metaplasia of the Urinary Bladder: a Case Report and Review of the Literature

Nephrogenic metaplasia or nephrogenic adenoma of the urinary tract is an infrequent benign lesion that occurs in patients with a history of genitourinary surgery, stone disease, trauma, chronic urinary tract infection, or renal transplantation. The term “nephrogenic adenoma” was introduced by Friedman and Kuhlenbeck because the structure resembled that of renal collecting tubules. Nephrogenic metaplasia most frequently situated in the bladder; it demonstrates a variety of morphologic patterns including tubulocystic, papillary, and much less frequently solid, that often coexist. Nephrogenic metaplasia with cytologic atypia (atypical nephrogenic metaplasia) is occasionally encountered and displays substantial cytologic abnormalities of no apparent clinical significance. ANM may be confused with malignant neoplasms, especially clear cell carcinoma, some variants of urothelial and prostatic carcinoma. Although to date there is no specific immunohistochemical profile to distinguish this lesion from its malignant mimickers, clinicopathologic correlation with careful attention to morphology remains the milestones in establishing the correct diagnosis. We describe a case of 54-year-old male that underwent a transurethral resection of the urinary bladder lesion due to hematuria. The diagnosis of atypical nephrogenic metaplasia was based on the histological patterns, the absence of p53 immunopositivity and low Ki-67 proliferative index (3.7 %). The clinical long-term follow-up demonstrated the proof for the diagnosis. We present this case because of its rarity and also to emphasize that analysis of immunohistochemical proliferative activity is helpful and leading to accurate identification of the lesion. Awareness of the spectrum of cytologic changes within this entity is critical to prevent overdiagnosis of cancer and avoid unnecessary treatment.