Malignant Struma Ovarii with Papillary Thyroid Carcinoma Presenting with Concurrent Multinodular Goitre and Thyrotoxicosis: A Case Report

Background: Malignant struma ovarii (MSO) is a rare monodermal ovarian teratoma in which thyroid tissue undergoes malignant transformation, most commonly to papillary thyroid carcinoma (PTC). Its rarity and nonspecific presentation make preoperative diagnosis difficult, and management is not standardised.
Case Presentation: A 38-year-old premenopausal woman presented with a two-month history of pelvic pain and thyrotoxic symptoms, a longstanding multinodular goitre, and a complex 9.5 × 7.2 × 6.8 cm left adnexal mass. She underwent laparoscopic left salpingo-oophorectomy; histopathology revealed a 1.5 cm focus of classical PTC within a struma ovarii, with negative margins and peritoneal cytology. Given persistent thyrotoxicosis, multinodular goitre, and a wish to enable thyroglobulin-based surveillance, total thyroidectomy (revealing benign hyperplastic goitre) and adjuvant radioactive iodine (I-131, 120 mCi) were subsequently performed. Serial thyroglobulin was undetectable at 6 and 12 months, and the patient remained recurrence-free at 18 months of follow-up.
Conclusion: MSO warrants a high index of suspicion when pelvic and thyroid pathology coexist. Salpingo-oophorectomy remains the surgical cornerstone; total thyroidectomy and adjuvant radioactive iodine are best reserved for patients with high-risk features or a specific surveillance rationale, since adjuvant thyroid-directed therapy has not been shown to improve survival in unselected patients. Long-term thyroglobulin-based surveillance is warranted given the potential for late recurrence.