Reviewers: Elliot Weisenberg, M.D. (see Reviewers page)
Revised: 20 October 2014, last major update September 2011
Copyright: (c) 2003-2014, PathologyOutlines.com, Inc.
● Usually in urinary tract; very rare in lung, usually in immunocompromised patients
● Caused by macrophage dysfunction involving intracellular lysosomal mediated killing of bacteria
● In AIDS patients, usually due to Rhodococcus equi, an animal pathogen causing opportunistic infections (Chest 1999;115:889)
● Two cases in immunocompetent patients (Indian J Pathol Microbiol 2011;54:133)
● Nodular masses or infiltrates with cavitation
Gray-white ill-defined lesion with central cavitation
● Intraalveolar histiocytes with pink or foamy cytoplasm (von Hansemann’s histiocytes) that fill and destroy alveoli, not interstitium
● Histiocytes contain PAS+ bacteria, also Michaelis-Gutmann bodies (round/oval structures, usually intracellular, 5-20 microns, with laminated or targetoid appearance that stain deeply with H&E, iron and calcium stains)
● Also lymphocytes, plasma cells and neutrophils
● Atypical mycobacteria: blue histiocytes, positive acid fast stain
● Also Whipple’s disease, Gaucher’s disease, endogenous lipid pneumonia, amiodorone toxicity
End of Lung-nontumor > Infections > Malakoplakia
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