Struma ovarii simulating ovarian tumors of other types. A report of 30 cases.

Thirty cases of struma ovarii with unusual microscopic features are described. They occurred in women 23 to 71 (average 49) years of age. Most of the patients had the usual symptoms and signs of an adnexal mass. Three patients had ascites and two had Meigs' syndrome. The tumors, all unilateral and confined to the ovary, ranged from 4 to 25 (average 12) cm in greatest dimension. They were typically predominantly solid and red-brown but cysts were present within foci of struma in several cases; an associated dermoid cyst was noted grossly in nine cases. Microscopic examination showed a prominent diffuse pattern in 21 cases, prominent microfollicles imparting in many cases a pseudotubular appearance in 20 cases, abundant eosinophilic cytoplasm in nine cases, and abundant clear cytoplasm in four cases. A contiguous dermoid cyst which had not been recognized on gross examination was documented in five cases. The typical paucity of thyroid follicles in cellular areas of these tumors often caused either a failure to consider a diagnosis of struma ovarii or led to serious consideration of other diagnoses. Clues to the correct diagnosis were the presence of rare typical thyroid follicles in foci that were predominantly diffuse or pseudotubular, the presence of larger areas of typical struma in 22 cases, and the association with a dermoid cyst in 14 cases. Immunohistochemical staining for thyroglobulin confirmed the nature of the tumor in all five cases in which it was performed. The diagnosis of struma should be entertained when one is examining an ovarian neoplasm with solid or pseudotubular patterns or a content of oxyphilic or clear cells. A careful search for thyroid follicles should be undertaken to establish the diagnosis and immunohistochemical staining for thyroglobulin performed to confirm it in problematic cases.