Hashimoto's thyroiditis in a benign cystic teratoma of the ovary: case report and literature review.

Ectopic thyroid tissue in ovarian teratoma or in struma ovarii appears to be histologically identical to the thyroid gland tissue and may virtually exhibit all the pathological patterns found in the thyroid gland. However, the concurrent lymphocytic infiltration of the thyroid gland, as found in Hashimoto's thyroiditis, and of the ectopic thyroid tissue is extremely rare. We describe the case of an 18-years old patient, in which a right ovarian 4 cm cyst has been found during pelvic ultrasound exam. The cyst was resected and microscopic examination of the mass revealed a mature cystic teratoma in which epidermal-like lining with skin adnexa, admixed with respiratory type epithelium, and areas of mature fatty, chondroid and dentigerous tissues were found. In a peripheral area of 0.7 cm  ×  0.5 cm, a prominent lymphocytic infiltrate surrounding thyroid follicles was identifiable. Thyroid function evaluation at different time points after surgery, revealed the development of mild hypothyroidism. Anti-TPO and anti-Tg autoantibodies were elevated, at fine needle aspiration biopsy a lymphocytic infiltrate, compatible with Hashimoto's thyroiditis, was present. We report here a rare case of Hashimoto's thyroiditis occurring both in the thyroid and in the ectopic thyroid tissue in the context of a benign cystic teratoma of the ovary.