Struma ovarii is a rare ovarian tumour with malignancy occurring in <5% of cases. Metastases are uncommon and are usually visceral. Patients can present with hyperthyroidism together with ascites, pain and other classic effects of a pelvic mass. It is not well known how to best treat and follow patients with extensive disease. Case reports of radioiodine ablative (RAI) therapy following thyroidectomy can reduce recurrence.
We present the case of a 33 year old woman who presented with bone pain and was found to have lytic lesions on MRI. Numerous skeletal metastases were confirmed on biopsy which demonstrated metastatic follicular thyroid carcinoma (FTC). Subsequent thyroidectomy showed no remarkable pathology or evidence of malignancy. At 28, she had an ovarian cyst excised which was diagnosed as a mature cystic teratoma. Pathology confirmed a dermoid cyst at the time. In light of this metastatic FTC diagnosis, the cyst pathology was re-reviewed and the teratoma was determined to comprise thyroid tissue.
She underwent three cycles of RAI over 18 months. Following the RAI, her thyroglobulin dropped three orders of magnitude and is now undetectable. FDG-PET scan demonstrated no avidity and her last RAI uptake scan showed no iodine avid lesions. She remains on replacement thyroxine with a suppressed TSH.
This case demonstrates an unusual presentation of a rare disease and highlights how well malignant struma ovarii can respond to standard treatments for metastatic FTC.