Focal xanthogranulomatous pyelonephritis simulating a renal tumor: CT characteristics.

Xanthogranulomatous pyelonephritis is the replacement of renal parenchyma by large lipid-filled macrophages clinically associated with an enlarged, nonfunctioning kidney containing a calculus in the diffuse form or tissue destruction in one pole of a duplicated kidney associated with a calculus in the focal form. We report a case where a focal mass in a functioning kidney with no evidence of calculus, duplication, or fat density simulated a primary renal tumor.