Mimicry and Pitfalls in Effusion Cytology

Abstract

Effusion cytology is one of the most common and yet challenging of nongynecologic cytology specimens. The difficulty in interpretation of the cytomorphology of the cells in effusion samples results from extensive mimicry. Benign conditions may mimic malignancy through introduction of unanticipated interlopers or through mesothelial cell alterations masquerading as malignant cells. Alternatively, malignant tumors may evade detection in effusions by subterfuge and adopting a deceptively benign appearance mimicking mesothelial cells or by stealth, allowing them to blend into their background. Despite their mastery of disguise, both the benign and malignant conditions leave behind morphologic clues to their true identity that may be unearthed through diligent examination and deductive reasoning.