What is your diagnosis?
This photomicrograph shows a high power view of the renal interstitium with histiocytic inflammation and numerous histocytes with PAS-positive material within their cytoplasm. Within the center of the field is a small, target-shaped structure—a Michalis-Gutmann (MG) body. These findings are consistent with Malakoplakia which often forms mass lesions mimicking a neoplasm. Malakoplakia results from dysregulated lysosomal breakdown and processing of bacteria (typically E. coli) with resulting foamy macrophages with PAS-positive intracellular accumulations. Partially digested bacteria can also form a nidus for calcium and iron deposition, thus MG-body formation. Malakoplakia is an unusual finding and is not expected in an otherwise healthy person. It is frequently associated with an altered immune status such as HIV/AIDS, underlying malignancy, or immunosuppressive therapy.
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