Mesothelial inclusion cysts (so-called benign cystic mesothelioma)--a clinicopathological analysis of six cases.

The report presents six cases of mesothelial inclusion cysts (MIC), detected in five females (22-53 years of age) and one male (47 years old). The lesions were unifocal (four cases) and multifocal (two cases), and were located on the surface of the peritoneum in the cul de sac, on the intestines, urinary bladder, uterine adnexa, also involved round ligament within the pelvis and in the inguinal canal (one patient). Additionally, in one female, small cysts, free-floating in the peritoneal cavity were present. In three patients, clinical signs resulted directly from the presence of MIC. One female had been 7 years previously operated on due to endometrioid ovarian cysts. Apart from MIC, three patients presented with concomitant diseases: appendicitis (two cases), peritoneal pseudomyxoma or primary ovarian carcinoma. Gross appearance: the lesions were polycystic, the surgical materials ranging from three fragments measuring 0.5 cm each to seven fragments, with the maximum size of 14x6 cm. The cysts were from microscopic size to 2 cm in diameter, the majority were thin-walled, semitranslucent, filled with clear or yellowish fluid or gelatinous contents. In one case, the cyst walls were thicker and showed intense inflammatory lesions and fibrinous exudate. Microscopically, the majority of cysts were lined with a single layer of flattened or cuboid mesothelial cells (CK+, calretinin+). In two patients, the mesothelium demonstrated diffuse squamous cell metaplasia; in one individual, the cells focally formed small papillae and were vacuolated. No mucus was observed either in the cytoplasm or outside the cells. Immunohistochemical reactions to CEA, ER, PR and MIB-1 were negative. Intramural proliferations and intracystic detached clumps of cells showed both mesothelial cells (without any mitotic activity and signs of atypia) and macrophages (CD68+). To date, the follow-up has been 7 years and 3 years in two individuals, and from 1 to 7 months in the remaining three patients--all of them are free from recurrent disease. One female failed to report for follow-up examinations. The report also presents the review of literature.