Xanthogranulomatous pyelonephritis: sonographic--pathologic correlation of 16 cases.

Xanthogranulomatous pyelonephritis (XGP) is an uncommon renal inflammatory disease characterized by the destruction and replacement of normal parenchyma by sheets of lipid-laden histiocytes. The process may be diffuse or segmental. Sonograms of 16 cases of XGP (13 diffuse, three segmental) were retrospectively reviewed and correlated with their pathologic findings. The typical case of diffuse XGP demonstrates the following: renal enlargement, replacement of normal architecture by multiple fluid-filled masses, pelvic contraction or only moderate separation of the central echo complex, and a pelvic calculus. Although most cases have a large staghorn calculus, its sonographic demonstration may be difficult, perhaps as a consequence of peripelvic fibrosis. Atypical cases of diffuse XGP mimic pyelonephrosis with massive hydronephrosis and fluid--debris levels. In these atypical cases, a staghorn calculus is often conspicuously absent. Segmental XGP is recognized as an area of parenchymal destruction surrounding one calyx or one pole of duplication. Segmental XGP should be distinguished from focal xanthogranulomatous inflammation of the kidney, which is a distinct pathologic entity (cortical location, no pelvic communication, absent pyelitis). When typical gross pathologic features are present, sonography should make possible accurate identification of diffuse and segmental XGP.