Primary ovarian mixed strumal and mucinous carcinoid arising in an ovarian mature cystic teratoma

Abstract A 39‐year‐old woman presented with low back pain lasting for several weeks. Abdominopelvic computed tomography showed an ovarian cystic mass with an enhancing solid portion, fat and internal calcification. A right salpingo‐oophorectomy was performed. A 9.7 cm round multiseptated cystic mass showed pathology of mature cystic teratoma and contained a solid portion, measuring 4.2 cm, composed mainly of carcinoid cells arranged in a trabecular‐insular configuration admixed with surrounding thyroid follicles containing colloid. Juxtaposed were several nests of columnar cells interspersed with goblet cells and extracellular mucin pools. In the cyst wall of the teratoma, the lining of pseudostratified columnar cells was occasionally mixed with goblet cells transforming to the carcinoid portion. Immunohistochemically, both mucinous and strumal carcinoids were positive for polyclonal carcinoembryonic antigen, caudal type homeobox 2, cytokeratin (CK)7, CK20, synaptophysin, CD56 and focally positive for chromogranin. Thyroid follicles were positive for thyroid transcription factor‐1 and thyroglobulin. After gastrointestinal and respiratory tract evaluation, no evidence of primary tumor, including omentum, was observed. The mass was diagnosed as a mixed strumal and mucinous type carcinoid associated with a mature cystic teratoma.