Stromal decidualization of endometriosis in the rhesus macaque (Macaca mulatta): a case report.

During exploratory laparotomy, a 10-year-old female rhesus macaque was found to have a 6.0 x 9.5 x 2.0-cm multichambered, yellow, cystic mass cranial to the uterus, from which large amounts of opaque, white fluid were discharged into the abdominal cavity. The animal was euthanized, and the body was submitted for gross and histologic evaluation. Sections of the mass examined microscopically consisted of sheets of polygonal to round cells, with well defined cell borders and moderate amounts of eosinophilic cytoplasm. Scattered throughout these cells were few, variably sized glandular structures composed of columnar to cuboidal epithelium. Glandular epithelial cells were positive for keratin, and the sheets of polygonal cells were positive for vimentin and negative for keratin and CD 68. Gross and histologic appearance, immunohistochemical findings, and history of medroxyprogesterone acetate injections were compatible with a diagnosis of stromal decidualization of endometriosis. Subsequent biopsies of similar lesions in other rhesus macaques in the colony being treated with medroxyprogesterone acetate for endometriosis revealed comparable histologic findings.