Xanthogranulomatous Pyelonephritis (XGP) is a rare entity that usually occurs in immunocompromised middle-aged females with ureteral obstruction or chronic urinary tract infection induced by the formation of renal stones. Imaging plays a significant role in assessing disease extension and associated complications. CT findings in XGP include multiloculated low-density rounded areas throughout the enlarged kidney (bear`s paw sign). XGP MRI features include hyperintense (or isointense) appearance of the solid component and hypointense cavity fluid on T1-weighted images. The administration of contrast material can reveal strong rim enhancement of the borders. Without treatment, XGP can become a life-threatening disease. Thus, the usual management is nephrectomy.

From the manuscript

Bear Paw Sign: Xanthogranulomatous Pyelonephritis

Abstract
Xanthogranulomatous pyelonephritis is a rare form of chronic pyelonephritis in which the involved areas of the kidneys are destroyed and replaced by foam cells. It usually occurs in immunocompromised middle-aged females with ureteral obstruction or chronic urinary tract infection induced by the formation of renal stones. We herein report the case of a 44-year-old woman, with a history of left kidney staghorn calculi and recurrent urinary tract infections. Abdominal computed tomography showed the `bear paw` sign, typical appearance of XGP and patient underwent a nephrectomy with uneventful post-operative course.