Eosinophilic effusions: A clinicocytologic study of 12 cases

Our aim is to study the prevalence of eosinophilic effusions (EEs) in our institution, to highlight their cytologic patterns, potential interpretation pitfalls, diagnostic importance, and to investigate their possible causes and clinical associations.

We conducted a retrospective review study for over 13 years. We retrieved all of the cytology reports of pleural, pericardial, and peritoneal effusions with eosinophils. We reviewed and screened the cytology slides looking for eosinophils that constitute >10% of the cells. We extracted the clinical, radiologic, and laboratory findings and follow-up data for each patient.

We found 12 patients (0.7%) with EEs. They included five pleural, five peritoneal, and two pericardial fluids. The age range was between 16 and 75 with a mean age of 36.5 years. The male to female ratio was 3:1. We have recognized three cytomorphologic patterns; purely eosinophilic, dominantly eosinophilic, and mixed inflammatory infiltrate that correlated with peripheral blood eosinophilia. Two cases demonstrated extracellular and intracellular Charcot-Leyden crystals. Certain cellular and crystal features are potential cytologic pitfalls. EEs were associated with miscellaneous specific and non-specific medical conditions. None was associated with tuberculosis, malignancy, drugs, or parasites.

EEs are uncommon. They mostly occur in young adult males. There are three cytomorphologic patterns that correlate with peripheral eosinophilia. Etiologies are diverse or obscure. EEs with a very high eosinophilia are less likely malignant, tuberculous, parasitic, and seldom associated with drugs. Cytopathologists should be aware of certain potential diagnostic pitfalls. Correct cytologic recognition is clinically important since some causes are treatable.