MONDO_0003332 (malignant struma ovarii) is an ovarian mature teratoma characterized by the presence of aberrant thyroid tissue with morphologic changes identical to thyroid carcinoma. Patients may present with abdominal mass and unusual symptoms due to thyrotoxicosis, or with Meigs syndrome (ascites and pleural effusion). Also known as: struma ovarii, malignant, struma ovarii, malignant (morphologic abnormality).