Discussion

Malakoplakia is a rare mass forming histiocyte-rich disorder that occurs most commonly in the lower urinary tract. However, it has been described in other organs such as kidney, prostate, cervix/vagina, thyroid, lung, adrenal glands, bone, skin, soft tissue and brain. The pathogenesis of malakoplakia is not fully understood. However, it is thought to involve impaired macrophage digestion of phagocytosed infectious organisms. The phagocytosed microorganisms are believed to persist intracellularly within phagolysosomes which subsequently calcify, forming the pathognomonic Michaelis-Gutmann bodies. The most commonly implicated bacteria include E. coli, Proteus spp., and S. aureus. Malakoplakia is often associated with a compromised immunologic system. On cytology samples we may see chronic granulomatous inflammation or a population of large histiocytes with variably sized, intracytoplasmic, round, and acellular inclusions (Michaelis-Gutmann bodies). While the classic Michaelis-Gutmann body is targetoid or lamellated in appearance, some may appear only as round acellular basophilic inclusions without lamellation. PAS and Von Kossa stains highlight intracytoplasmic inclusions and targetoid basophilic concretions of Michaelis-Gutmann bodies, respectively.