Mesothelial papilloma: a case of mistaken identity in a pericardial effusion

Mesothelial cells are notorious for their ability to mimic carcinoma in body cavity effusions. Not only do individual cells demonstrate nuclear atypia that might be confused with cancer, but they also form aggregates including acinar and papillary structures suggesting metastatic or invasive adenocarcinoma. In a man of 33, copious exfoliated mesothelial cells, often in large sheets and papillary fragments, were erroneously diagnosed as adenocarcinoma in a pericardial effusion. The probable source was a minute benign mesothelial 'papilloma' subsequently found at autopsy. The patient had Crohn's disease (3 laparotomies), an ileocutaneous fistula and a fistula between the small bowel and colon.