Woman with lower abdomen and flank pain

A 58-year-old female presented to the emergency department (ED) with lower abdominal pain for 1 month. Two days prior to presentation, she developed left flank discomfort, fevers, and chills. Physical examination was performed that showed a temperature of 101.3°F, heart rate of 118 beats/min, and lower abdomen and left flank tenderness. The patient's urine was turbid with large leukocyte esterase, large blood, elevated White Blood Cells (WBC), and many bacteria. Ultrasonography of the left kidney showed a "bear paw" sign (Figures 1 and 2), and computed tomography (CT) showed a diffusely enlarged upper pole with multiple fluid locules and a large stone in the infundibulum (Figures 3 and 4). Xanthogranulomatous pyelonephritis (XGP) is a rare and aggressive variant of chronic pyelonephritis, most commonly due to chronic nephrolithiasis and infection.1 Characteristic ultrasound findings include an enlarged kidney with grossly distorted architecture including dilated and multiloculated calyces indicating pyelitis, staghorn calculi seen as large amorphous echogenicities with posterior acoustic shadowing, and a "bear paw" sign similar to the CT finding created by multiple adjacent anechoic/hypoechoic masses that are xanthomatous conglomerates.2 Imaging characteristics can mimic malignancy creating a diagnostic dilemma. Urinary cytology and presence of staghorn calculi with perirenal inflammatory changes help differentiate from urothelial cell carcinoma.3 Diffusion weighted imaging helps differentiate from renal cell carcinoma (RCC) showing marked restricted diffusion in the cystic infiltrate of XGP compared to RCC.3 Acute infections are treated with antibiotics; however, definitive management is nephrectomy.1 The patient was admitted and treated with IV ceftriaxone for acute sepsis. Urine cultures grew Proteus mirabilis. She was discharged on oral cefpodoxime and underwent a left total nephrectomy 6 weeks later. The authors declare no conflicts of interest.