Cystic struma ovarii: a frequently unrecognized tumor. A report of 20 cases

Twenty cases of cystic struma ovarii in women aged 23 to 83 (average, 46) years are described. The patients had the usual signs and symptoms of an adnexal mass. The tumors, all of which were unilateral and confined to the ovary, ranged from 2 to 19 (average, 13.5) cm in greatest dimension. Eighteen were multilocular, two unilocular. They were typically filled with clear to green-brown fluid. Microscopic examination showed cysts of various sizes separated by fibrous septa, which in many areas appeared nonspecific, but in all the cases contained at least small numbers of thyroid follicles. The cysts were typically lined by nonspecific-appearing, flat to cuboidal epithelial cells. The paucity of thyroid follicles in many areas and the nonspecific appearance of the epithelial cells lining the cysts often caused the diagnosis of struma ovarii to be overlooked. Clues to the correct diagnosis, in addition to the thyroid follicles in the septa, included the presence of larger areas of typical struma in a few cases and the association with a dermoid cyst in three cases. Immunohistochemical staining for thyroglobulin confirmed the nature of the tumor in all three cases in which it was performed. The diagnosis of cystic struma should be entertained when examining a multilocular or unilocular cystic ovarian neoplasm whose features are not obviously those of another tumor type, and a careful search for thyroid follicles should be undertaken to establish the diagnosis. In problematic cases, immunohistochemical staining for thyroglobulin may be required to establish the diagnosis.