Hyperthyroidism in thyroid carcinoma originating in struma ovarii.

Summary: Thyroid carcinoma originating in Struma Ovarii (SO) is a rare thyroid ectopic cancer that accounts for 0.01% of all ovarian malignancies and is associated with hyperthyroidism in less than 15% of cases. In a 44-year-old patient with pelvic pain, the CT scan revealed a solid-cystic formation in the ovarium. A left oophorectomy was performed and showed a borderline serous tumor and papillary thyroid carcinoma ('thyroid carcinoma originating in Struma Ovarii') measuring 10 cm. Thyroid function was assessed, and hyperthyroidism was diagnosed. Surgical complementation and a pelvic re-approach were performed. The histological findings showed a papillary thyroid carcinoma in the uterine serosa and the right adnexa. Thyroid function was re-evaluated, and despite normal thyroid function, the TRAb test remained positive. The patient underwent total thyroidectomy and radioiodine therapy (RIT), after which the TRAb test became negative. During 3 years of follow-up, no evidence of tumor was observed. In our case of thyroid carcinoma originating in SO, hyperthyroidism was treated with ovarian surgery, total thyroidectomy, and RIT. It is worth noting that thyroid function was normalized after ovarian surgery, but the TRAb test only became negative after total thyroidectomy. We hope to draw attention to the importance of evaluating thyroid function in patients with SO and treating high-risk SO patients with RIT after total thyroidectomy to achieve disease remission. Learning points: Struma ovarii can cause hyperthyroidism. Thyroid carcinoma can originate in Struma Ovarii. Differentiated thyroid carcinoma and hyperthyroidism originating in Struma Ovarii are rare conditions.