Endocrine Abstracts

Introduction: Struma ovarii (SO) is a specialized monodermal teratoma predominantly composed of mature thyroid tissue (>50%). It accounts for ~5% of all ovarian teratomas. Thyrotoxicosis is seen in about 8% of patients with SO. Most struma ovarii are benign with only 5–10% being malignant. Malignant SO causing thyrotoxicosis is very uncommon.

Case presentation: A 64-year-old woman had been diagnosed with thyrotoxicosis 2 years ago. The thyroid gland is palpable with micronodular texture and the patient is euthyroid under carbimazole. She presents abdominal pain and progressive enlargement of the abdomen over a two-month period. An abdominal ultrasonography (U/S) revealed a pelvic mass and a large fluid collection. Subsequently, Computed Tomography (CT) of the abdomen and Magnetic Resonance Imaging (MRI) of the pelvis confirmed the presence of a complex right ovarian mass measuring 13 cm.

The patient underwent total abdominal hysterectomy and bilateral salpingo-oopherectomy, omentectomy and appendectomy. Histological examination of multiple sections from the excised tumor revealed the presence of ‘follicular thyroid-type carcinoma arising in struma ovarii of the right ovary. Metastatic infiltration was seen in the tissue fragments submitted from the pouch of Douglas. The immunohistochemistry analysis showed positivity for TTF1, TH6, HMBE1, focally positive for NSE and negative for panCK and CK19’.

Anti-thyroid treatment was discontinued one month post-surgery, in light of the pathology result. During the 4-year follow-up the patient remains euthyroid.

Conclusion: There has been controversy about the management of malignant SO which is a very rare entity. Even more uncommon is malignant SO causing thyrotoxicosis. As clinical signs are non specific other causes of thyrotoxicosis must be considered for differential diagnosis. Our case is one of the very few cases ever reported.