Metastatic malignant struma ovarii with coexistence of Hashimoto’s thyroiditis

Struma ovarii is a rare ovarian teratoma characterized by the presence of thyroid tissue as the major component. Malignant transformation of the thyroidal component (malignant struma ovarii) has been reported in approximately 5% of struma ovarii. The management and follow-up of this unusual disease remain controversial. We report the case of a woman with a history of autoimmune thyroiditis and a previous resection of a benign struma ovarii that underwent hystero-annexiectomy for malignant struma ovarii with multiple papillary thyroid cancer foci and peritoneal involvement. Total thyroidectomy and subsequent radioiodine treatment lead to complete disease remission after 104 months of follow-up. The diagnosis and natural progression of malignant struma ovarii are difficult to discern, and relapses can occur several years after diagnosis. A multidisciplinary approach is mandatory; after surgical excision of malignant struma, thyroidectomy in combination with (131)I therapy should be considered after risk stratification in accordance with a standard approach in differentiated thyroid cancer patients. LEARNING POINTS: Malignant struma ovarii is a rare disease; diagnosis is difficult and management is not well defined. Predominant sites of metastasis are adjacent pelvic structures. Thyroidectomy and (131)I therapy should be considered after risk stratification in accordance with standard approaches in DTC patients.