Endometriosis
in a kidney with focal xanthogranulomatous pyelonephritis and a perinephric abscess. Contrast computerized tomography images. It shows the replacement of the right renal tissue by several rounded, low density areas. A perinephric abscess is noted invading the right psoas muscle (arrows). Renal stones, the frequent etiology of xanthogranulomatous pyelonephritis, are also seen. a Transverse section. b Coronal section