This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Kidney and ureter, Subject name: Surgery
Sheela, a middle aged diabetic female presented with flank pain and fever. On USG, the kidney was irregular and showed fat density lesion with calculi. The diagnosis is most probably: 
Select and explain. 
A. TB kidney, B. Xanthogranulomatous pyelonephritis, C. Chronic pyelonephritis, D. Emphysematous pyelonephritis
B: Xanthogranulomatous pyelonephritis
Answer: B: Xanthogranulomatous pyelonephritis 
Explanation: Hints in the question-- Diabetic- Middle aged Female- Flank pain- Fever- Fat density lesion- Associated with calculi. Xanthogranulomatous (due to presence of fat) pyelonephritis (infection with kidney etiology)- It is more common in females as they are more prone to Struvite stone formation- Causative Organism - Proteus Emphysematous pyelonephritis- Most common causative organism- E. coli - Presence of ring of air around kidney or within kidney.