SUN-603 A Case of Papillary Thyroid Cancer and EXTRAOVARIAN Pelvic Teratoma

INTRODUCTION Teratomas comprise a spectrum of tumors that have striking imaging appearances and are commonly considered when evaluating a mass in the female pelvis. A subgroup of these tumors located in an extragonadal abdominopelvic location, in contrast, are extremely rare. Thyroid tissue in teratoma may demonstrate the same spectrum of pathological features as in the normal thyroid including benign and malignant changes. Herein, we describe a case of papillary thyroid cancer of the thyroid gland with incidentally diagnosed extraovarian pelvic teratoma. CASE 52 y.o. woman with locally-invasive, multifocal, papillary thyroid carcinoma (PTC) s/p radical thyroidectomy and left central neck dissection. She was treated with thyrogen stimulated 100 mCi I-131, and her post-therapy whole body scan showed uptake in thyroid bed and in the right lower quadrant, for which SPECT imaging was acquired to assess this region better. SPECT imaging showed a heterogeneous, solid lesion seemed to be arising from the left adnexa, which correlated with the region of tracer uptake. The lesion contained fat and dystrophic calcifications with differential considerations including ovarian teratoma/struma ovarii. Her thyrogen stimulated thyroglobulin level was 66 ng/ml. She underwent laparoscopic exploration of the pelvis. Interestingly, the pelvic mass was noted to be completely separate from the left ovary. Pathology result showed a dermoid cyst with thyroid tissue. DISCUSSION A dermoid cyst is a cystic teratoma, usually benign, that contains an array of developmentally mature, solid tissues. In most cases, thyroid tissues found in teratomas are ovarian, not extra-ovarian. There are some case reports of thyroid carcinoma arising in a struma ovarii (thyroid tissue in ovarian teratoma) and a few case reports of synchronous carcinoma in the thyroid gland and the struma ovary. For cases with incidentally found teratoma with thyroid tissue, the next step is to proceed with further work up to confirm the diagnosis and to explore the possibility of a malignant lesion in the mass- either primary or metastasis. For our case, suspicion for metastasis was low as thyrogen stimulated thyroglobulin level was not very high to suggest a distant metastasis. Another important clinical question is whether the iodine uptake in the thyroid tissue in the teratoma will interfere the radio-iodine uptake of the micrometastasis and the long-term outcome. CONCLUSION Radioiodine uptake in the pelvic mass raises the question of possible thyroid tissue- teratoma vs. metastasis. Although teratoma with thyroid tissue might be an incidental finding, this might change the long-term outcome of patients with thyroid cancer treated with radioiodine.