Low-grade neoplasms of the peritoneum are rare but include 2 entities that are more often encountered in the peritoneum than the pleura, namely, multicystic mesothelioma and well-differentiated papillary mesothelioma. Adenomatoid tumor is most common in the genital tract, but can occur in the peritoneum where it is sometimes found as a component of either multicystic mesothelioma or well-differentiated papillary mesothelioma. Indeed, all 3 tumors can occur in combination. The histological differential diagnosis of these neoplasms can include reactive mesothelial proliferations, malignant mesothelioma, and metastatic carcinoma. Cystic conditions such as lymphangioma can also enter the differential diagnosis. The question of whether cystic mesothelial lesions are neoplastic or reactive is controversial—multicystic lesions of the type that can recur after surgery and involve multiple sites are clinically neoplastic, and the presence of genetic abnormalities consistent with neoplasia has been described. However, the possibility that small, isolated mesothelial cysts are simple inclusions may be difficult to refute.
From the Peritoneal Malignancy Institute, Department of Histopathology, Basingstoke and North Hampshire Hospital, Basingstoke, United Kingdom.
Reprints: Norman John Carr, Peritoneal Malignancy Institute, Department of Histopathology, Basingstoke and North Hampshire Hospital, Aldermaston Rd, Basingstoke, United Kingdom RG24 9NA. E-mail: firstname.lastname@example.org.
The author has no funding or conflicts to declare.