IS case 548: Xanthogranulomatous pyelonephritis
Imaging Sciences URMC 2010
Publication Date: 2010-09-18
Xanthogranulomatous pyelonephritis (XGP) is a rare granulomatous reaction to chronic infection, often secondary to chronic obstruction caused by a calculus (most common), stricture, or tumor. XGP has a female to male predominance of approximately 4:1; female patients usually having a history of recurrent or chronic urinary tract infections. XGP almost always occurs unilaterally. The kidney is involved either globally (83-90%) or focally (10-17%). There are three stages of XGP described: stage 1 confined to kidney; stage 2 extension to the perirenal space; and stage 3 spread to the pararenal space. Nephrectomy is usually required; radical in complete XGP and possible partial nephrectomy in focal disease. The histological appearance is characteristic, displaying accumulation of lipid laden macrophages and granulomatous infiltrate.
Songoraphic findings of XGP include an enlarged kidney, with multiple anechoic or hypoechoic masses replacing the normal corticomedullary junction. Internal echoes can be seen in a dilated collecting system, with a contracted renal pelvis. An obstructing staghorn calculus is commonly visualized.
CT demonstrates multiple focal low attenuation masses scattered throughout the kidney, with dilated debris filled calyces. The kidney is commonly nonfunctioning, with poor or absent excretion of contrast into the collecting system. Bright enhancement of the rims of the xanthoma may be seen due to inflammatory hypervascularity, however, no enhancement of the collections are visualized. 14% demonstrate perinephric extension with perirenal fibrofatty proliferation. Gas is rarely seen.
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