Cut section of this specimen shows irregular yellowish areas of renal parenchyma that are related to the calyces. The calyces are are dilated and are lined by irregular necrotic tissue. There is a renal calculus lodged in the renal pelvis at the botton of the photograph. The disease process is essentially infectious. Proteus is a frequent associated causative organism.
Chronic obstruction plays a part in the development of the disorder.
Pathogenesis Most cases are due to ascending infections from urine flow abnormalities. Urinary outflow obstruction results in urine stasis providing an environment for bacterial proliferation. Obstruction also predisposes to vesicoureteral reflux which can enable bacteria to reach the kidney. Xanthogranulomatous pyelonephritis is usually unilateral and may involve all or portion of a kidney. The affected renal parenchymal is brightly yellow and may take on a nodular quality mimicking renal cell carcinoma.