Xanthogranulomatous pyelonephritis: Case series - Clinical, radiologic, therapeutic, and histological aspects

Purpose: Xanthogranulomatous pyelonephritis (XGP) is a chronic and severe infection of the kidney. We aimed to review the main clinical, imaging, and histological findings and to assess predictors of surgical complications or hospitalization >10 days (no deaths reported). Materials and Methods: We retrospectively searched all patients with XGP treated at our institution from 2005 to 2019, with 57 patients enrolled. Clinical data were retrieved by a single reader, computed tomographic (CT) examinations by two radiologists, and histopathological specimens by an experienced pathologist. Results: The patients' mean age was 44.3 ± 16.2 years and 41 (71.9%) were female. The most common symptoms were flank/lumbar pain (89.5%), fever (43.9%), and recurrent urinary tract infection (43.9%). The mean time until the presumptive diagnosis was 365.1 days and the median hospitalization period was 11 days. Blood tests showed anemia (78.9%), leukocytosis (43.6%) with left shift (21.6%). Urinalysis showed hematuria (75.6%), bacteriuria (40.9%), and leukocytes (93.2%). Urine cultures showed Escherichia coli in 14.8%, Proteus mirabilis in 7.4%, while 59.3% were negative. Of 40 patients with CT examinations, 38 (95%) presented with hydronephrosis and perinephric inflammatory changes (PIC) and 22 (55%) with Bear Paw sign. PIC was the only independent predictor at multivariate analysis for surgical complications. For prolonged hospitalization, fever and PIC were independent predictors at univariate, but only fever at multivariate analysis. Conclusions: XGP is a worrisome condition, with unclear pathophysiological mechanisms. Fever and PIC at CT examinations were predictors of poor outcomes.