Papillary follicular variant thyroid cancer in a malignant struma ovarii: a report of a rare case

SUMMARY: A 33-year-old female presented in 2013 with left flank pain. Ultrasound and MRI pelvis showed a complex mass 9 × 7 cm arising from the left ovary suggestive of ovarian torsion. She underwent a laparoscopic cystectomy, but the patient was lost to follow-up. Three years later, she presented with abdominal distension. Ultrasound and CT scan revealed a solid left ovarian mass with ascites and multiple peritoneal metastasis. Investigations showed elevated CA 125, CA 19-9. Ovarian malignancy was suspected. She underwent total abdominal hysterectomy and bilateral salpingo-oophorectomy on November 2016. The histopathology confirmed a well-differentiated thyroid cancer of ovarian origin with features of a papillary follicular variant without evidence of ovarian cancer and the thyroglobulin (Tg) level was elevated, more than 400 consistent with the diagnosis of malignant struma ovarii. The follow-up post-surgery showed normalization of CA 125, CA 19-9 and Tg. The patient underwent total thyroidectomy on January 2017. The histology was benign excluding thyroid cancer metastases to the ovary. She was started on thyroxine suppression, following which she received two ablation doses (131)iodine ((131)I) each 5.3 GBq. The Tg remains slightly elevated at less than 10. (131)I WBS showed no residual neck uptake and no distant avid metastasis. She was planned for molecular analysis which may indicate disease severity. We describe a case of malignant struma ovarii with widespread metastatic dissemination and a good response to surgery and (131)I treatment without recurrence after 5 years of follow-up. The Tg remains slightly elevated indicating minimal stable residual disease. LEARNING POINTS: Malignant struma ovarii is a rare disease; diagnosis is difficult and management is not well defined. Presentation may mimic advanced carcinoma of the ovary. Predominant sites of metastasis are adjacent pelvic structures. Thyroidectomy and (131)iodine therapy should be considered. The management should be similar to that of metastatic thyroid cancer.