Nephrogenic adenoma of the bladder: a case report and review of the literature.
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BACKGROUND: Nephrogenic adenoma (NA) of the bladder, also known as nephrogenic metaplasia, is a rare benign lesion whose pathogenesis remains incompletely understood. First described in 1949, NA has an etiology that remains controversial, with its proposed origins including embryonic renal tubular remnants or metaplastic changes after epithelial injury. NA predominantly affects adults (male-to-female ratio ~2:1) but can also occur in children. Its nonspecific clinical and imaging features often lead to diagnostic difficulty, especially in distinguishing it from malignancies such as urothelial carcinoma. CASE DESCRIPTION: We report a case of a 76-year-old man with a history of colon cancer and benign prostatic hyperplasia who presented with recurrent urinary frequency, urgency, dysuria, and gross hematuria. His symptoms worsened despite conservative treatment. Imaging revealed bladder wall thickening, and cystoscopy showed erythematous, plaque-like lesions. Transurethral resection of the bladder lesion was performed. Histopathology confirmed NA with chronic granulomatous inflammation, and immunohistochemistry was positive for PAX8, CK7, and GATA3, supporting the diagnosis. Notably, the patient's computed tomography urogram (CTU) also suggested thickening of the left renal pelvis and ureter, raising the possibility of concomitant upper tract NA; however, these findings were radiologically suspected only, because the recommended further evaluation and resection of the upper tract lesions were declined, so upper tract urothelial carcinoma and inflammatory lesions remained possible alternatives. After 3 years of follow-up, his urinary frequency and urgency had not improved, and visible blood in the urine continued to be reported, although a causal relationship between the untreated upper tract lesions and these persistent lower urinary tract symptoms could not be established. CONCLUSIONS: This case underscores the diagnostic challenges of NA, particularly its mimicry of urothelial carcinoma, and highlights the pivotal role of thorough histopathological and immunohistochemical evaluation. The persistence of symptoms after resection of only the bladder lesion, along with radiological evidence of possible upper tract involvement, suggests that when NA is suspected, complete evaluation of the entire urinary tract is necessary, and that suspected upper urinary tract lesions should be carefully evaluated and, whenever feasible, confirmed histologically; however, the present case does not establish that these lesions caused the symptoms or that their resection would have relieved them. Clinicians should maintain a high index of suspicion for NA to ensure accurate diagnosis, appropriate treatment, and avoidance of unnecessary interventions. Long-term follow up is warranted given the potential for recurrence.