Question category: Nephrology
A 72 year old gentleman with type 2 diabetes mellitus has presented with pyrexia, flank pain and haematuria. Bloods reveal an acute deterioration of his renal function. Urine dipstick reveals blood, protein and low urine specific gravity. An ultrasound suggests hydronephrosis. A CT scan is performed and reveals evidence of renal pelvic filling defects, ring shadows and irregular papillae. What is the most likely diagnosis?