Double kidneys.....

Bilateral fusion of a supernumerary kidney in a cat

Juneo Freitas Silva 1, Jankerle Neves Boeloni, Adriana Monteiro Cima, Rogéria Serakides, Natália M Ocarino

Background
Supernumerary kidneys are extremely rare congenital anomalies of the genitourinary tract, especially in animals, with only two prior reports in non-feline species. This case report describes what is believed to be the first documented occurrence of bilateral supernumerary kidneys in a domestic cat, discovered during necropsy.

Methods
A necropsy was conducted on an 8-year-old female mixed-breed cat with clinical signs of weight loss, anorexia, diarrhea, azotemia, and elevated renal biomarkers. The examination included gross anatomical assessment, histopathology with hematoxylin and eosin staining, and special stains (Masson’s trichrome and von Kossa) to assess fibrosis and mineralization.

Results
Four kidneys were identified—two on each side of the sublumbar region—with partially fused renal pelvises sharing a single ureter on each side. Each kidney had distinct cortical and medullary regions, and all showed signs of hypoplasia, glomerulosclerosis, nephrocalcinosis, and interstitial fibrosis. Histological evaluation confirmed both mature and immature glomerular structures, consistent with developmental anomalies. No abnormalities were observed in the lower urinary tract, and other systemic organs were histologically normal apart from chronic enteritis.

Limitations
As a single case report, generalization is not possible. Additionally, functional evaluation of the kidneys prior to death was limited, and the cause of death—though associated with renal pathology—was also linked to enteric disease, complicating attribution of clinical signs solely to the renal anomaly.

Conclusions
This case represents a novel finding of bilateral fused supernumerary kidneys in a cat, highlighting a rare congenital anomaly. Despite the presence of renal hypoplasia and acquired pathological changes, the anomaly was only detected post-mortem. This underscores the importance of considering developmental abnormalities in differential diagnoses of renal dysfunction, even when clinical imaging is unavailable.

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