A 29-year-old woman has palpitations, weight loss and heat intolerance. She has no goitre and no eye signs. Ultrasound shows a 7 cm left adnexal mass that on histology consists predominantly of mature thyroid tissue arising within a mature cystic teratoma. What is the most likely diagnosis?

• A Metastatic papillary thyroid carcinoma to the ovary
• B Serous cystadenoma with ectopic thyroid tissue
• C Primary ovarian carcinoid tumour
• D Struma ovarii ✓

Explanation

Struma ovarii is a monodermal mature teratoma composed predominantly of thyroid tissue and is the commonest cause of ectopic thyroid hormone production in the ovary, occasionally producing thyrotoxicosis. Ovarian carcinoid would produce flushing and diarrhoea rather than thyrotoxicosis and shows neuroendocrine histology. Metastatic thyroid carcinoma does not arise within a dermoid and retains its papillary architecture.

Reference: Te Linde's Operative Gynecology, 12th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.