Infectious Conditions
Donna M. Coffey, MD
Key Facts
Clinical Issues
Infectious effusions are most commonly parapneumonic effusions associated with bacterial pneumonia
Cytopathology
Inflammatory cells of various types depending on nature and duration of infectious process, histiocytes, and mesothelial cells
Most infectious effusions are bacterial in origin and have nonspecific mixed inflammation with predominance of neutrophils
Top Differential Diagnoses
Effusions with nonspecific inflammatory background can be caused by neoplasms, pulmonary emboli, metabolic or autoimmune diseases, and others
 (A) Pap stain  and (B) PAS special stain  show filamentous clusters of gram-positive organisms identified in a pleural fluid. The organisms might be a contaminant. Actinomyces organisms should be differentiated from Candida and Nocardia. (C) Pap stain shows Cryptococcus neoformans  in pleural fluid of an immunocompromised patient with disseminated disease. C. neoformans is a yeast-like fungus that reproduces by a single attenuated teardrop-shaped bud. (D) Mucicarmine stain highlights the thick mucin-positive capsule  . |
TERMINOLOGY
