Xanthogranulomatous pyelonephritis presenting as a mass-like renal lesion mimicking neoplasia in a dog: first documented case and diagnostic considerations

Xanthogranulomatous pyelonephritis (XGP) in humans is a rare and severe form of chronic renal inflammation, characterized by extensive destruction of renal parenchyma and the formation of granulomatous tissue with lipid-laden macrophages. We present the case of a 6-year-old male Pomeranian dog exhibiting mild lethargy over the past month. Imaging studies, including abdominal ultrasonography and an abdominal computed tomography (CT) scan, revealed a markedly enlarged right kidney with multiple hypoattenuating areas. A radical nephrectomy was performed to remove the affected kidney. Histopathological examination of the nephrectomy specimen confirmed a diagnosis of XGP, demonstrating extensive parenchymal destruction, abscess formation, and infiltration of CD68 + vacuolated macrophages. To the best of our knowledge, this is the first documented case of XGP in a dog. This report highlights the importance of considering XGP in the differential diagnosis of canine patients presenting with imaging findings suggestive of renal masses or abscesses.