Endocrine Abstracts

Introduction: The thyroglossal duct is an embryonic structure, lined predominantly by respiratory and squamous epithelium and typically involutes by the 10th week of gestation. If the thyroglossal duct does not involute, it can form cysts due to recurrent inflammation or infection, as it is lined by epithelium that is secretory in nature, with or without the presence of ectopic thyroid tissue. Thyroid tissue is present in the wall of the cyst/duct in 30-60% of cases.

Case report: 38-year-old female presented five months postpartum with symptoms of heat intolerance, palpitations and weight loss. Her bloods confirmed hyperthyroidism with a FT4 of 31.8 pmol/l (7.7-15), TSH of 0.01 mU/l (0.34-5.6), WBC-4.7x10⁹/l (4-11) and CRP- 1 mg/l (0-7.5). This was consistent with transient postpartum thyroiditis, followed by spontaneous recovery without the need for anti-thyroid medications. She had a family history of Grave’s disease, but her thyroid stimulating immunoglobulins and anti-TPO antibodies were normal. She also had a background history of a stable small 1 mm thyroglossal duct cyst (TGDC) noted on ultrasound in 2010. On examination she was noted to have nontender, firm upper midline neck swelling at site of the known TGDC, however she reported TGDC size increase corresponding with the onset of hyperthyroid symptoms. Neck ultrasound confirmed a thin wall cyst with viscous fluid content and increase in size from 17x12x1 mm in 2010 to 30x15x1 mm). Her thyroid was of normal size with features of thyroiditis. There was no solid component within the cyst and the enlargement of TGDC was presumed to be related to thyroiditis within the cyst wall. The cyst was managed conservatively as ultrasound did not show any suspicious solid components and there was no evidence of infection.

Discussion: Autoimmune thyroiditis and thyroid cancer (predominantly papillary) have been reported within the ectopic thyroid tissue in the TGDC wall. The prevalence of cancer within the excised TGDS is reported at 0.7-4%, but there is no data on prevalence of thyroiditis in excised TGDCs. Our case illustrates that TGDCs might enlarge significantly as part of the post-partum thyroiditis process. In our case, the main contributor to the enlargement, in the absence of solid component on ultrasound, was accumulation of fluid from the epithelium in response to the presumed inflammation of the thyroid tissue within cyst wall. This might explain, why the TGDC size did not regress to baseline with resolution of thyroiditis (last follow up 9 months post onset).