Renal parenchymal malacoplakia: a different stage of xanthogranulomatous pyelonephritis?

Malacoplakia is a rare inflammatory condition characterized by demonstrative Michaelis-Gutmann bodies, which are foamy histiocytes with distinctive basophilic inclusions. Malacoplakia is caused by the inadequate elimination of bacteria by macrophages or monocytes as a result of defective phagocytic activity. Xanthogranulomatous pyelonephritis is characterized by the destruction of renal parenchyma and its replacement by solid sheets of foamy lipid-laden macrophages. Prolonged infection of the kidney, which is frequently caused by an obstruction of the urinary tract, is the pathologic mechanism of that condition. We present a 6-year-old patient with a poorly functioning kidney who had a prolonged recurrent urinary tract infection. The results of histologic analysis revealed an inflammatory infiltration consisting predominantly of foamy and epithelioid histiocytes that contained round intracytoplasmic concretions characteristic of Michaelis-Gutmann bodies. We suggest that malacoplakia might be a stage of xanthogranulomatous pyelonephritis.