B) Chronic pyelonephritis and shrunken scarred kidneys

This patient is presenting with signs and symptoms of pyelonephritis symptoms. This, combined with the past medical history of vesicoureteral reflux and complicated urinary tract infections, suggest a progression to chronic pyelonephritis. The kidney biopsy findings solidify a diagnosis of chronic pyelonephritis. Tubular atrophy and loss of architecture demonstrate the effects of repeated immune responses. On microscopic exam, one might also expect to see “thryoidization of the kidney.” Grossly, the kidney will appear small and scarred.

Answer choice A: Acute pyelonephritis with enlarged kidneys and loss of corticomedullary junction. Acute pyelonephritis would present with cellular infiltration. Chronic pyelonephritis does not present this way.

Answer choice C: Renal cell carcinoma with fatty laden mass in the upper pole, is incorrect. Renal cell carcinoma is uncommon in children. Additionally, the biopsy would reveal cells with clear cytoplasm arranged in nests (clear cell carcinoma).

Answer choice D: Wilms tumor and large mass in the kidney parenchyma, is incorrect. Wilms tumor, or nephroblastoma, is a common pediatric tumor. However, the renal biopsy would reveal triphasic histology (blastema, epithelial, and stromal). Additionally, the patient’s clinical presentation is not typically how a nephroblastoma presents.

Answer choice E: Xanthogranulomatous pyelonephritis with enlarged kidneys and abnormal renal outline, is incorrect. Xanthogranulomatous pyelonephritis is an aggressive form of chronic pyelonephritis. One would expect to see granulomas on histology.

Key Learning Point

A pediatric patient with a known congenital ureteral disorder and recurrent complicated bouts of pyelonephritis can lead to chronic pyelonephritis. This is characterized by gross shrunken and scarred kidneys and microscopic tubular atrophy with blunting of the renal calyces.