Xanthogranulomatous pyelonephritis complicated by psoas abscess.

Xanthogranulomatous pyelonephritis is an unusual variant of chronic pyelonephritis. Xanthogranulomatous pyelonephritis is associated with urinary calculi, urinary tract obstruction, and invasion of the renal parenchyma. Pathologically, xanthogranulomatous pyelonephritis consists of a yellow (xantho) colored infiltrate in renal tissue with granulomatous formation. Xanthogranulomatous pyelonephritis may be distinguished from chronic pyelonephritis by renal size. Typically, the kidneys are enlarged in xanthogranulomatous pyelonephritis and are small/shrunken with chronic pyelonephritis. The diagnosis of xanthogranulomatous pyelonephritis is made by abdominal computed tomography scanning showing the characteristic "bear paw" sign, or findings typical for xanthogranulomatous pyelonephritis, eg, multiple hypo dense areas with ring-enhancing lesions. The definitive treatment for xanthogranulomatous pyelonephritis is antimicrobial therapy and nephrectomy. We present a case of xanthogranulomatous pyelonephritis complicated by psoas abscess.