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Hashimoto's Thyroiditis Within Ectopic Thyroid Gland Mimicking the Presentation Of thyroglossal Duct Cyst

A 9-year-old girl was referred for evaluation of an anterior neck mass that had been present for 6 weeks without significant change in size. On examination, a soft 3.5 × 2.5 cm infrahyoid midline mass was noted. The mass elevated with swallowing and was nontender to palpation. At initial presentation, an evaluation included a serum thyroid-stimulating hormone (TSH) that was noted to be normal (3.52 μ/mL; normal, 0.30 to 5.00 μ/mL). At the time of consultation, the TSH had increased to 11.25 μ/mL with a normal T4 level (8.2μg/dL, normal 4.5 to 12μg/dL). An ultrasound of the thyroid was interpreted as showing normal thyroid tissue in a pretracheal position. A presumptive diagnosis of thyroglossal duct cyst (TGDC) was made, and surgery was planned. At surgery, a limited midline neck exploration did not identify a normal thyroid gland. Frozen section biopsy specimens of the paramidline mass revealed chronic lymphocytic thyroiditis. Secondary to concerns that the mass might represent the patient’s principal functioning thyroid, the aberrant tissue was not removed. Postoperatively, antimicrosomal (72 u/mL; normal, < 0.30u/mL) and antithyroglobulin antibodies (40u/mL; normal < 1.0u/mL) were noted to be elevated. The findings were considered consistent with the diagnosis of Hashimoto’s thyroiditis. A thyroid scan with iodine-123 showed 3 rightsided foci of thyroid tissue with absence of left lobe activity. The largest of the foci, previously felt to be the TGDC, was noted to approximate the midline at the level of the superior thyroid bed. The remaining foci were located superior and lateral (see Fig 1). Postoperatively, the patient had persistently elevated TSH levels requiring the initiation of thyroxine supplementation.