Eosinophilic pleural effusion is an uncommon disorder characterized by a very high number of eosinophils, usually more than 10% of the cells. Some cases occur in the setting of a predisposing cause, but in about one-third of cases the origin remains obscure. Most cases resolve spontaneously. Eosinophilic pericardial and peritoneal effusions are even more rare.
Causes of eosinophilic pleuritis (>10%)
- Autoimmune disorders
- Pneumonia (bacterial or viral)
- Pulmonary infarcts
- Infections (fungal, parasitic)
- Pneumothorax, hemothorax
- Thoracic trauma (pneumothorax, thoracotomy, repeated aspiration)
Cytologic preparations are usually cellular, with a high concentration of eosinophils. On alcohol-fixed Papanicolaou-stained slides, the eosinophilic granules are either orangeophilic or pale-green and inconspicuous, and the cells are identified more on the basis of their bilobed nuclei. The granules are brightly eosinophilic on cell block preparations stained with hematoxylin and eosin as well as on air-dried Romanowsky-stained slides. Charcot-Leyden crystals are present in some cases.