Cystic adenomatoid tumor of the uterus.

We describe a case of cystic adenomatoid tumor of the uterus in a 38-year-old woman. The tumor was a subserosal cystic mass with a maximum diameter of 8 cm and located at the posterior wall of the right cornual region. Histologically, the tumor was composed of multiple cavities lined by flattened cells, lying among thin septa of connective tissue. The neoplasm showed small solid areas with a more typical histologic pattern of adenomatoid tumor. Immunohistochemical techniques showed the cells to be positive for keratins. They showed desmosomes, abundant intracytoplasmic filaments, and microvilli on ultrastructural study. The histologic, immunohistochemical, and ultrastructural characteristics of the present case closely resemble those of benign cystic mesothelioma and strongly support the mesothelial origin of the adenomatoid tumor of the uterus.