Malignant struma ovarii with papillary thyroid carcinoma: a case report

Abstract Struma ovarii is a rare monodermal ovarian teratoma predominantly composed of thyroid tissue, accounting for <5% of mature ovarian teratomas. Malignant transformation, most commonly to papillary thyroid carcinoma, occurs in 5%–10% of cases and represents an exceptionally rare entity with no established management consensus. We report a 40-year-old woman presenting with acute pelvic pain and a 13 cm heterogeneous left adnexal mass with elevated CA-125 (125 U/ml). Emergency laparotomy with left salpingo-oophorectomy revealed a 1 cm papillary thyroid carcinoma arising within an 11 cm struma ovarii, without capsular or vascular invasion. Postoperative thyroid workup was normal. Despite multidisciplinary recommendations for completion thyroidectomy and contralateral adnexectomy, the patient declined further surgery, opting for clinical and biochemical surveillance alone. This case underscores the importance of managing malignant struma ovarii according to thyroid carcinoma protocols while respecting patient autonomy.