Follicular variant of papillary thyroid carcinoma arising in struma ovarii: A case report

Abstract

Objective: Struma ovarii is a rare form of ovarian mature teratoma and is the most common type of monodermal teratoma (3% of all ovarian teratomas). 5-10% of such tumors are malignant with papillary carcinoma as the most common type (70%) while 26% of them are a follicular variant of papillary thyroid carcinoma (FVOPTC). We report a case of FVOPTC arising in struma ovarii focusing on the clinical, histopathological and immunohistochemical features. Material and Methods: A 29-year old nulliparous female underwent laparoscopic surgery of a 7 cm a large right ovarian cyst, diagnosed by ultrasound. Clinically and biochemically she was euthyroid with normal serum TSH level, and without previous significant medical or gynecological history. Results: Grossly, a laparoscopically obtained material consisted of 8x3 cm fragment of cyst wall measuring 0.2 to 0.6 cm in thickness with a focus of 5 mm large grayish-white tumor. Histology of the cyst wall showed thyroid tissue characteristic of cystic struma ovarii while the tumor showed typical nuclear features of papillary thyroid carcinoma with follicle formation and minimal presence of papillary structures typical for FVOPTC arising in thyroid tissue. Immunohistochemical staining showed positive expression for thyroglobulin, TTF-1, and cytokeratin-19 in the tumor cells. Conclusions: FVOPTC arising in struma ovarii is difficult to assess because it is a rare tumor with about 60 published cases and lacking standard criteria for diagnosis. Thus, the morphological criteria for the diagnosis of this tumor are based on classical criteria for primary thyroid carcinoma. Prognostically, FVOPTCs measuring less than 2 cm arising in struma ovarii are considered as low-risk lesions with a low rate of recurrence and metastasis.