Focal xanthogranulomatous pyelonephritis with associated bone metaplasia

Focal xanthogranulomatous pyelonephritis of the left lower pole was accidentally discovered in a 34-year-old woman at sonography. The patient had no history of stones and urinary tract infection and both conventional radiology and CT scan revealed radiated calcifications within a well-circumscribed mass. Surgical treatment consisted of enucleoresection of the lesion, and histopathology revealed a nucleus of bone metaplasia. To the best of our knowledge, metaplastic bone formation has never been documented before with xanthogranulomatous pyelonephritis.