SUN-361 - Papillary Thyroid Carcinoma Arising in A Thyroglossal Duct Cyst with Synchronous Thyroid and Nodal Involvement

Thyroglossal duct (TGDs) cysts are common congenital neck lesions originated from an abnormal remnant of thyroid development. Malignant transformation occurs in approximately 1% of cases, most frequently as papillary thyroid carcinoma (PTC). TGD carcinoma is typically diagnosed incidentally after surgical excision, and optimal management remains controversial, particularly when synchronous thyroid or lymph node involvement is present.
A 39-year-old man with non-ischemic cardiomyopathy was admitted for acute heart failure exacerbation and evaluated for a progressively enlarging anterior neck mass first noted 18 months prior. He denied thyroid dysfunction symptoms, prior neck radiation, tobacco use, or family history of thyroid disease, but reported intermittent nocturnal dyspnea attributed to airway compression. Neck ultrasound demonstrated bilateral TI-RADS 3 thyroid nodules (right: 1.7 × 1.5 × 1.7 cm, left: 1.7 × 1.8 × 3.8 cm) and a large midline cystic mass anterior to the thyroid isthmus measuring 8.2 x 5.6 x 8.7cm, containing a heterogeneous 3.7-cm TI-RADS 4 solid component concerning for malignancy. Laboratory evaluation showed mildly elevated TSH 5.5 IU/mL with normal free T4 and negative calcitonin. Serum thyroglobulin was markedly elevated 257.5 ng/mL.
Ultrasound-guided fine-needle aspiration of the cystic lesion, its solid component, and the left thyroid nodule revealed PTC. The patient underwent thyroglossal duct cyst excision via the Sistrunk procedure, total thyroidectomy, and resection of a firm peri-isthmic lesion. Final pathology confirmed PTC involving the thyroglossal duct cyst, thyroid gland, and one metastatic lymph node. Postoperatively, he was started on levothyroxine with plans for adjuvant RAI, though he was subsequently lost to follow-up. Molecular profiling showed BRAF and RET mutations.
This case highlights a rare preoperative diagnosis of synchronous intrathyroidal, TGD cyst and regional lymph node PTC. This could represent either a metastasis from a primary carcinoma in the cyst, a primary thyroid carcinoma with metastatic involvement of the TGD, or two independent primary carcinomas (extremely rare). While isolated TGD carcinoma may be adequately treated with the Sistrunk procedure alone, the presence of extra-TGD disease may require more extensive surgical intervention such as thyroidectomy and selective nodal dissection. There is no consensus on the use of thyroid suppression therapy and radioactive iodine, therefore treatment should be individualized.

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