A RARE CASE OF PRIMARY MALIGNANT MESOTHELIOMA ORIGINATING FROM THE RECTOVAGINAL TISSUE

A 35 year-old female patient with pelvic malignant mesothelioma is des cribed. The patient underwent total pelvic excentration due to a pelvi c tumor. Macroscopically, the resected tumor was located in the rectov aginal lesion with invasion into the rectal and vaginal wall, and arou nd the internal urethral ostium. Light microscopically, the tumor pred ominantly consisted of sheets of plump round cells with acidophilic cy toplasm, and focally of tumor cells showing papillary growth pattern. The tumor cells showed remarkable cellular pleomorphism, and were both alcian blue and periodic acid-Schiff stain negative. Electron microsc opically, these tumor cells had numerous long bush-like microvilli on their surface with increased length/width ratios. Positive staining wi th epithelial membrane antigen, cytokeratin, and vimentin, and negativ e staining with the carcinoembryonic antigen and S-100 protein were ob served immunohistochemically. Based on these histological and immunohi stochemical estimations, the tumor was diagnosed as a primary malignan t mesothelioma originating from the rectovaginal tissue. Review of the literature confirmed the rarity of pelvic malignant mesothelioma. The possibilities of the pathogenesis of the tumor include the tumor's ar ising from the peritoneal remnant in the rectovaginal tissues, or from the epithelium of the secondary Mullerian system, which shares the sa me ancestry with the peritoneum.