Abstract
Xanthogranulomatous pyelonephritis (XGP) is a rare and aggressive form of chronic pyelonephritis, often resulting in a nonfunctional kidney. It typically occurs in the context of chronic urinary obstruction, renal calculi, and persistent infection, with Escherichia coli as the most common pathogen. XGP is frequently referred to as "the great imitator" because its clinical and radiographic features can mimic those of other renal conditions, including tumors. Radiologically, XGP is characterized by the "bear paw" sign, a distinctive finding on imaging that represents dilated renal calyces and pelvis filled with pus, which can aid in differentiating it from other diseases. Early diagnosis and intervention are critical, as untreated XGP can lead to progressive renal destruction, involving surrounding structures and potentially causing life-threatening complications. The role of imaging, particularly CT, in diagnosing and staging the disease cannot be overstated, as it provides crucial information to guide treatment and improve patient outcomes. We report the case of a 56-year-old diabetic male who presented with left-sided lumbar pain and fever. Laboratory findings indicated leukocyturia and bacteriuria with E coli growth. Renal ultrasound showed kidney enlargement and pyelocaliceal dilation. A CT scan revealed the characteristic "bear paw" sign, strongly suggesting the diagnosis of XGP. The patient was treated with antibiotics and a percutaneous drainage of the thick pyelocaliceal content was performed. This case highlights the importance of imaging in diagnosing XGP and guiding management.