A 32-year-old woman presents with palpitations, weight loss, tremor, and heat intolerance. Thyroid function tests confirm thyrotoxicosis but the thyroid gland is normal on examination and ultrasound. Pelvic imaging reveals a 9 cm right adnexal cystic mass with echogenic areas. What is the most likely diagnosis?

• A Strumal carcinoid of the ovary secreting serotonin
• B Mature cystic teratoma with predominant thyroid tissue (struma ovarii) ✓
• C Granulosa cell tumor producing excess inhibin B
• D Sertoli-Leydig cell tumor with heterologous elements

Explanation

Struma ovarii is a monodermal teratoma composed predominantly of functional thyroid tissue. It can synthesize thyroid hormone and cause clinically significant thyrotoxicosis despite a sonographically normal neck thyroid, because the ovarian tissue escapes normal feedback suppression less predictably than nodular goiter. Serotonin-secreting strumal carcinoid causes carcinoid syndrome without flushing-driven thyrotoxicosis. Granulosa and Sertoli-Leydig cell tumors produce estrogenic or androgenic effects respectively, not thyroid hormone. Treatment is surgical excision, which is curative.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.