Thyroid Tissue Gone Rogue: Malignant Struma Ovarii

Abstract

Background: Malignant struma ovarii is an exceptionally rare ovarian tumor arising from thyroid tissue within a monodermal teratoma. Papillary thyroid carcinoma is the most common malignant transformation, and management remains controversial due to the absence of standardized guidelines.

Case Presentation: A 34-year-old woman with polycystic ovarian syndrome presented with intermittent lower abdominal pain and was found to have bilateral ovarian cysts. She underwent robotic bilateral ovarian cystectomy at an outside facility. Histopathology revealed an immature teratoma of the left ovary (stage IC, post-cystectomy) and a mature teratoma of the right ovary containing a microscopic 3 mm focus of papillary thyroid carcinoma (infiltrative follicular subtype). Imaging showed no evidence of peritoneal disease or lymphadenopathy. Neck ultrasonography did not reveal any thyroid lesion. Serum tumour markers and thyroid function tests were within normal limits.

Management and Outcome: Following slide review and multidisciplinary evaluation, the patient underwent laparoscopic bilateral salpingo-oophorectomy with omental biopsy, along with total thyroidectomy. Histopathology confirmed malignant Struma ovarii with papillary thyroid carcinoma-type malignant transformation and vascular invasion. In view of the microscopic tumour burden and absence of extra-ovarian spread, radioactive iodine therapy was deferred. The patient was initiated on thyroid hormone replacement therapy and planned for long-term surveillance with serial serum thyroglobulin monitoring.

Conclusion: This case highlights the diagnostic and therapeutic challenges of malignant Struma ovarii. Treatment should be individualized based on
disease extent and histopathological risk factors. Long-term follow-up is essential due to the possibility of delayed recurrence.