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Struma ovarii in a euthyroid patient: a histopathological diagnosis

Struma ovarii is a rare monodermal variant of ovarian teratoma composed predominantly of thyroid tissue, accounting for approximately 0.3–1% of all ovarian neoplasms. It is rarely associated with thyroid dysfunction. Due to the absence of distinctive clinical and radiological features, establishing a preoperative diagnosis is often challenging, particularly in euthyroid patients. We report a case of benign struma ovarii in a euthyroid patient, diagnosed exclusively by histopathological examination. A 40-year-old woman presented with lower abdominal pain. Clinical examination revealed bilateral adnexal masses. Imaging studies, including ultrasonography (USG) and contrast-enhanced computed tomography (CECT) of the abdomen and pelvis, were suggestive of bilateral ovarian teratomas. Thyroid function tests were within normal limits, confirming her euthyroid status. The patient subsequently underwent total hysterectomy with bilateral salpingo-oophorectomy. Gross examination revealed cystic masses in both ovaries. Histopathological evaluation demonstrated struma ovari in the right ovary, characterized by the presence of predominant thyroid tissue. The left ovary showed features consistent with a mature cystic teratoma. The postoperative period was uneventful, and the patient remained clinically and biochemically euthyroid on follow-up. Struma ovarii is an uncommon ovarian neoplasm that lacks specific clinical and radiological characteristics, rendering preoperative diagnosis difficult, especially in euthyroid individuals. Histopathological examination remains the gold standard for definitive diagnosis.