BK polyomavirus-infected nephrogenic adenoma of the urinary bladder in a renal transplant recipient: A case report

This report describes the morphological and immunohistochemical features of the first case of a nephrogenic adenoma (NA) of the urinary bladder infected with polyomavirus. The findings occurred in a female patient, 6 months post cadaveric renal transplant. Voided urine cytology was positive for decoy cells. Renal transplant biopsy showed no evidence of BKV allograft nephropathy. Cystoscopy demonstrated multiple erythematous patchy and nodular areas. These were found in the left and right posterior wall, and the right lateral wall toward the bladder neck, and were suspicious for either chronic inflammation or neoplasia.Hematoxylin-eosin stained sections showed a NA with scattered pleomorphic nuclei demonstrating smudged chromatin and amorphous basophilic ground glass inclusions. Strong expression of polyomavirus large T antigen (SV40) and VP1 was seen in atypical lesional cells, consistent with cytopathic lytic polyomavirus infection. Positive staining with PAX8 supports the renal cell derivation of NA. The findings in the present case suggest that polyomavirus infection, as an irritant of the bladder mucosa, contributed to the cytologic atypia of infected lesional cells but is not a pathogenic factor of NA.