Mesothelial Cysts

Abstract Objectives Peritoneal mesothelial cysts have been reported under various terms, including benign cystic mesothelioma, usually in the form of case reports/series, whereas extraperitoneal cases are rarely reported. Our objective was to report the detailed characteristics of cystic lesions of the serosal cavities. Methods We retrospectively examined the clinicopathologic findings of a series of mesothelial cystic lesions (n = 79). Results Most cases (n = 68, 86%) concerned the peritoneum, whereas 11 (14%) concerned the pericardium. No pleural cases were found. A total of 51 (64.5%) lesions were solitary, whereas 28 (35.5%) were multiple. Peritoneal lesions harbored a plump eosinophilic mesothelium and a loose connective stroma, whereas pericardial lesions showed a cuboidal/flattened mesothelium, collagenous stroma, intense inflammation, and other tissue types, like adipose and muscle tissue. Solitary peritoneal lesions are usually extrapelvic and found in older patients incidentally during other surgeries, whereas multiple lesions are found in younger patients and usually in the pelvis. The lesions show a benign clinical course with rare recurrences but no malignant transformation. Conclusions Most mesothelial cysts are peritoneal and rarely pericardial. Peritoneal cysts differ from pericardial cysts. Peritoneal solitary lesions differ from multiple lesions, also suggesting their pathogenetic differences.