A 43 years-old man presented to our stone clinic complaining of back pain for the last 3 months. He had significant past medical history for nephrolithiasis: he had undergone unsuccessful SWL for left renal calculi five years ago and also presented with several episodes of pyelonephritis in the last months, requiring hospitalization for intravenous antibiotics. Initial laboratory work-up revealed normal serum creatinine (0.92 mg/dL) and hemoglobin levels (15.3 g/dL); urine culture was negative. Abdominal computed tomography (CT) revealed a 140 mm2 stone in the left renal pelvis with 1500 Hounsfield Units (Figure-1a); thickening of the urothelium surrounding the stone was suspected after contrast infusion (Figure-1b) and confirmed in the excretory phase (Figure-1c).