Endocrine Abstracts

Introduction: Thyroglossal duct cysts (TDC) are a very frequent congenital neck mass and are mostly benign. Papillary thyroid carcinoma (PTC) originating from a TDC represents an infrequent finding. Usually, the diagnosis is only made postoperatively after cyst’s excision.

Case report: A 38-years old female patient was referred to the Endocrinology department due to Graves’ disease. She had been treated with antithyroid drugs for 18 months without remission. Thyroid ultrasonography (US) showed an enlarged gland, without nodules. Thyroid scintigraphy showed high homogenous uptake of pertechnetate, without extra-thyroidal uptake. TSH receptor antibody levels at that time were 19.10 UI/l (N < 0.55). It was administered 15.5 mCi of radioactive iodine (RAI), with hypothyroidism 3 months later (TSH 77.6 uUI/mL, N 0.55-4.78, and FT4 0.54 ng/dL, N 0.89-1.76). She was started on levothyroxine and remained euthyroid with 150 mg daily (TSH 1.1 uUI/mL, FT4 1.58 ng/dL). 14 months after RAI treatment, she noticed an enlarged and painless nodule on the anterior neck. Thyroid and cervical US showed a small, heterogeneous and hypoechoic thyroid gland with no defined nodules and, at the submandibular region, a 25 mm hypoechoic nodule with hyperechogenic foci, suggestive of a complex TDC. No pathologic lymphadenopathies were described. Cervical magnetic resonance imaging confirmed the presence of a complex TDC. A fine needle aspiration cytology was performed with inconclusive results. She was submitted to Sistrunk procedure to remove the cyst. Histology revealed a 5 mm PTC, without lymphovascular and neural invasion and a tumour-free surgical margin (pT1aNxR0). Postoperatively, cervical US was negative for suspicions lesions, with thyroglobulin (Tg) level of 2.20 ng/mL, anti-Tg of < 1.30 UI/mL and TSH of 0.138 uUI/mL. Since the likelihood of a synchronous multifocal thyroid carcinoma was low, total thyroidectomy (TT) was not proposed, remaining the patient in clinical, analytical and imagiological follow-up.

Conclusion: We report a case of a patient with Graves’ disease successfully treated with RAI, with a submandibular mass noticed 14 months later that turned out to be a TDC harbouring a microPTC. TDC are extremely common and, in the majority of the cases, an expectant attitude is taken. Malignity is rare and cytological analysis is only performed when suspicious characteristics in the US are present or when the patient complains of compressive symptoms. Given its rarity, the decision to perform TT and RAI in this setting depends on initial risk stratification, as with intraglandular tumors.