Presentation
Left flank pain and abdominal distension 4 months. Associated episodes of low-grade pyrexia. No history of trauma.
Patient Data
Enlarged left kidney with multiple radiopaque calculi and staghorn calculus at renal hilum. There is destruction and replacement of the renal parenchyma by hypodense material with the appearance that resembles a bear paw. No extension into perinephric space or retroperitoneum. Globular urinary bladder calculus with moderate vesical mural thickening.
Case Discussion
The image findings are classic for xanthogranulomatous pyelonephritis (stage I). The patient underwent resection with histopathologic confirmation of mixed cellular infiltrates and lipid-laden macrophages. Differential diagnoses on imaging include renal replacement lipomatosis and chronic granulomatous infection from tuberculosis.