The wide spectrum of biologic agents to which the lung may be exposed induces different responses in the lining epithelium and surrounding tissues. The resulting cytologic alterations can be specific in some cases, while in other circumstances the reaction may be nonspecific. A granulomatous response, as an example, can be induced by bacteria, fungi, spirochetes, or parasites. However, it can also be in response to drugs, chemicals, hypersensitivity or to the presence of a neoplasm. Granulomas can present as coin lesions with clinical and imaging features that overlap with tumors. The use of BAL has reduced the need for open biopsy to investigate infectious disease in many cases. Special stains, immunostains and microbiologic cultures can be very helpful in correctly identifying the underlying pathogenetic mechanism. The discussion that follows considers viral, bacterial, mycotic and parasitic infections that have fairly characteristic cytomorphologic features.
KeywordsRespiratory Syncytial Virus Invasive Aspergillosis Intranuclear Inclusion Calcium Oxalate Crystal Granulomatous Reaction
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