Follicular carcinoma arising from struma ovarii. A case report.

Struma ovarii is a monodermal variant of ovarian teratoma. Thyroid-type carcinoma arising in struma ovarii is rare. The most common type is papillary carcinoma, followed by typical follicular carcinoma. A 75-year-old hypertensive patient consulted for the sensation of a painless pelvic mass that has been progressing for six months. The abdominopelvic ultrasound showed a right lateralized abdominopelvic mass measuring 14x13x8 cm with a solid and cystic double component. The patient underwent a unilateral right adnexectomy. Grossly, the tumor was encapsulated and lobulated. On cut sections, it was solid brown whitish in color and gelatinous. On histological examination, it was formed of follicular structures of variable size filled with a dense colloid. From this goiter a malignant tumor proliferation arose, arranged in sheets, trabeculae and follicular structures, and the tumor cells were cubic or polyhedral moderately atypical with few mitotic figures. There were no papillary-like nuclear features. There was focal capsular and vascular invasion. Immunohistochemical study showed positive immunostaining of tumor cells with TTF1. Postoperative course was uneventful. The exact prognosis of thyroid-type carcinoma arising in struma ovarii is still unclear because of its rarity, inadequate follow-up, and the absence of consensus in diagnosis and treatment.
(Copyright © 2020 Società Italiana di Anatomia Patologica e Citopatologia Diagnostica, Divisione Italiana della International Academy of Pathology.)