MON-438 Papillary Thyroid Carcinoma Arising in a Thyroglossal Duct Cyst: A Case Report

Introduction: Thyroglossal duct cysts (TGDCs) are uncommon benign congenital entities. Rarely, thyroid carcinoma can arise from a TGDC; the most common being papillary thyroid carcinoma (PTC). Similar to TGDC, carcinomas originating within them can present as an asymptomatic midline neck mass. Signs of malignancy include dysphagia, dysphonia, weight loss, and rapid growth. Given the rarity of TGDC carcinomas, clinical management remains controversial, particularly regarding the requirement for total thyroidectomy. Case: A 52-year-old female with history of an anterior central neck mass initially noted in 2017. A 0.3-cm left lobe mid-segment cyst and a complex thyroglossal avascular simple cyst measuring 2.4 × 1.1 × 1.8 cm was observed during ultrasound (US). She presented to the endocrinology clinic in April 2019 due to progressive enlargement of the mass. Repeat thyroid US revealed that the cystic structure had become complex with a peripheral solid component and measured 3.3 × 2.1 × 2.2 cm. FNA was performed and found to be suspicious for PTC (Bethesda category V) and positive for the BRAF V600E mutation. Patient was referred for surgical evaluation. Physical examination revealed a midline anterior 10-cm, painless, and fixed mass above the thyroid that moved with deglutition and tongue protrusion. Contrast computed tomography scan showed a large multiloculated cystic structure measuring 4.1 × 4.4 × 5.9 cm. A lobulated soft tissue mass measuring 2.2 × 2.4 × 3.0 cm was noted internally along the inferior margin of the cyst. She underwent en-block resection of the TGDC in addition to a total thyroidectomy. Histopathological examination identified a 7.5 × 5.5 × 5.0 cm cystic mass with fluctuation and a firm, solid area in the lower portion measuring 2.6 × 2.4 cm. Thyroid gland examination was otherwise unremarkable. No areas of extension of the mass into the thyroid tissue were clearly identified and no other gross lesions were observed. The solid area within TGDC contained a tumor with findings characteristic of PTC. Postoperatively, she was placed on thyroid hormone replacement therapy. Conclusion: The main difficulty encountered with cancer developing from TGDC is that the diagnosis is usually made during surgery and from definitive pathological samples. The most common surgical procedure used is the Sistrunk procedure. Some studies have suggested that this procedure alone is an adequate therapy, but others advocate the need for total thyroidectomy. The Sistrunk procedure is considered to be appropriate for low-risk patients, but high-risk patients must undergo total thyroidectomy. The decision to perform a total thyroidectomy in this patient was based on her high-risk classification due to: age, sex, cyst size, and a positive FNA for malignancy. Follow-up includes an annual physical examination, thyroglobulin levels, and an US every 6 months during the first year and annually thereafter.