A 26-year-old woman has palpitations, heat intolerance, weight loss despite appetite, and a diffuse goitre with suppressed TSH. Pelvic ultrasound performed during evaluation shows an 8 cm right ovarian cyst with echogenic areas and calcification. Which of the following best explains her thyrotoxicosis?

• A Ectopic secretion of TSH by a germ cell tumour
• B Oestrogen excess from a granulosa cell tumour increasing thyroxine-binding globulin
• C hCG-mediated stimulation of the thyroid by a choriocarcinoma
• D Thyroid tissue within a mature cystic teratoma autonomously producing thyroid hormone ✓

Explanation

Struma ovarii is a monodermal mature teratoma composed predominantly of functional thyroid tissue; it can autonomously produce sufficient hormone to cause true biochemical thyrotoxicosis. Treatment is excision of the adnexal mass, after which the thyrotoxicosis resolves. Option C describes hCG-driven stimulation, which causes only mild biochemical changes, not frank Graves-like disease, and option B raises binding globulin, elevating total but not free T4.

Reference: Williams Gynecology, 3rd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.