A 26-year-old woman presents with palpitations, weight loss, heat intolerance, and a fine tremor. TSH is suppressed with elevated free T4. Thyroid antibodies are negative and a neck ultrasound shows no abnormality. Pelvic examination and ultrasound reveal an 8 cm solid-cystic right adnexal mass. What is the most likely diagnosis?

• A Sertoli-Leydig cell tumour
• B Mucinous cystadenoma
• C Granulosa cell tumour
• D Struma ovarii ✓

Explanation

Struma ovarii is a monodermal mature teratoma composed predominantly of thyroid tissue, accounting for about 2 percent of mature teratomas. It can secrete thyroxine and cause biochemical and clinical thyrotoxicosis with a normal neck examination, because the functional tissue lies in the ovary. Granulosa and Sertoli-Leydig tumours produce oestrogen and androgen respectively, not thyroid hormone, so they cannot explain suppressed TSH.

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

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Written and medically reviewed by the StethoPrep medical team.