CT of xanthogranulomatous pyelonephritis: radiologic-pathologic correlation.

A clinical-radiologic-pathologic correlation study was performed in 18 (17 female) patients with xanthogranulomatous pyelonephritis (XGP) with CT scans available for analysis. Presenting signs and symptoms included pain (66%), urinary frequency (66%), dysuria (66%), nocturia (66%), palpable mass (56%), leukocytosis (50%), and fever (50%). The duration of symptoms was usually relatively short (less than 6 months), considering the extent of the pathologic process. In 14 patients, the disease was diffuse; the kidney was enlarged with preservation of the reniform outline in 13. The renal pelvis, lined with sheets of lipid-laden macrophages and surrounded by a marked fibrotic reaction, was contracted in 11 and contained pelvic calculi in 12. The parenchyma was replaced by multiple, rounded, low-density areas on CT that corresponded to dilated calices and/or inflammatory tissue. These areas had enhancing rims (10 cases) that corresponded to preserved, compressed normal parenchyma and/or inflammatory tissue. There was CT identification of unsuspected extension through the renal capsule with involvement of the perirenal space in 11 patients, the pararenal spaces in 13, and the psoas muscle in six. The pararenal space and the psoas muscle were often extensively involved with minimal perirenal disease in six patients, a reflection of chronic indolent infection. There were four cases of focal XGP that appeared on CT as low-density mass lesions with wall enhancement surrounding dilated, stone-filled calices or as focal masses occupying one pole of a duplication. Extensive pararenal disease was present in two of the four cases of focal XGP. The preoperative diagnosis of XGP was suspected in only 44% of cases. It is concluded that CT should play a role in diagnosis and preoperative planning to demonstrate the extent of extrarenal disease that is poorly depicted by other means.