Metastatic malignant struma ovarii to the pituitary presenting as a sellar mass and responding to total thyroidectomy with adjuvant radioactive iodine therapy.

Malignant struma ovarii (MSO) is a rare ovarian teratoma composed primarily of thyroid tissue. Common sites of metastasis include peritoneum, bone, liver, lung, gastrointestinal tract and omentum. We present a woman in her 50s with a history of remote oophorectomy presenting with hypopituitarism and a 2.7 cm sellar mass. Trans-sphenoidal surgery for presumed pituitary macroadenoma achieved near total resection and resultant pathology surprisingly showed ectopic thyroid tissue. The patient acquired her ovarian pathology report from Southeast Asia which showed struma ovarii of the left ovary. The pituitary mass was thus determined to be a metastatic lesion from MSO. She underwent total thyroidectomy and radioactive iodine ablation therapy with good initial response and no regrowth of the tissue or emergence of distant metastases after 5 years of annual follow-up. To our knowledge, this is the first reported case of MSO to the pituitary.