This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Kidney & Ureturs, Subject name: Surgery
Sheela, a middle aged diabetic female presented with flank pain and fever. On U/S the kidney was irregular and showed fat density with calculi. The diagnosis is most probably: 
Select and explain. 
A. TB kidney, B. Xanthogranulomatous kidney, C. Chronic pyelonephritis, D. Renal abscess
B: Xanthogranulomatous kidney
Answer: B: Xanthogranulomatous kidney 
Explanation: Ans. (b) Xanthogranulomatous kidneyRef: Smith 17th Edition, Pages 204-206; Campbell 10th Edition, Page 308Xantho Granulomatous pyelonephritis (XGP)* Xantho means lipid foam cells* Xanthogranulomatous pyelonephritis is a variant of chronic pyelonephritis that characteristically presents in middle aged patients with a poorly functioning kidney (as in diabetic)* On histology there are areas of clear cells that are lipid-laiden macrophages* These areas of lipid-laiden macrophage appear as fat density lesion on U/S* This pyelonephritis is often accompanied by a calculus and proteus infection.* Kidney sparing surgery is indicated for XGP.