Sheela, a middle aged diabetic female presented with flank pain and fever. On U/S the kidney was irregular and showed fat density lesion with calculi. The diagnosis is most probably -

Xanthogranulomatous pyelonephritis Xantho means lipid laden 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.