Thyroid papillary cancer elements arising from struma ovarii with benign peritoneal strumosis: Utility of iodine-123 imaging in diagnostics and treatment planning.

Struma ovarii is a rare form of mature teratoma defined by a predominance of thyroid tissue. Approximately 5% of all ovarian strumae exhibit malignant transformation. Due to their extreme rarity, there has been a lack of consensus concerning uniform diagnostic criteria. Appropriate, risk-stratified treatment strategies also remain widely unelaborated, based only on a small number of cases reported in the literature. We describe the case of a 35-year-old female, who presented after undergoing unilateral oophorectomy for a right-sided ovarian mass. Histological workup revealed a struma ovarii containing papillary thyroid cancer (PTC). Postoperative I-123 scintigraphy with single photon emission computed tomography (SPECT) detected multifocal extra-ovarian spread to the peritoneum, containing likely benign strumosis upon pathological examination. The subsequent treatment strategy involved an ablative concept including total thyroidectomy and subsequent I-131 radioiodine therapy. Throughout a 3-year follow-up, the patient has remained without recurrence with thyroglobulin levels ranging below detection limits. Surgical resection with adjuvant radioiodine therapy is a curative therapeutic strategy in cases of struma ovarii with thyroid-type carcinoma and peritoneal strumosis. Its benefits lay in avoiding more extensive surgery, potentially maintaining fertility, facilitating follow-up, and minimizing the risk of recurrence. Reliable criteria for risk stratification are needed to identify patients who are most likely to benefit from this treatment approach.