Midline neck mass in a toddler: not every thyroglossal cyst should be excised
A 3-year-old boy is brought for a midline neck swelling present since birth. It is 2.2 cm, smooth, non-tender, and moves upward when he swallows and when he protrudes his tongue. He is thriving, with no dysphagia, stridor, or hoarseness. His TSH is 2.1 mIU/L and free T4 is normal. Ultrasound reports a 2.2 cm midline cystic-solid lesion at the hyoid level and an empty thyroid fossa; no normal thyroid tissue is seen in the usual pretracheal location. His parents are anxious for excision because a relative had a thyroglossal duct cyst removed. There is no history of infection or discharge. Examination shows a soft, mobile mass; the overlying skin is normal. The child is otherwise healthy and has no developmental delay.
1. What is the differential diagnosis, and what imaging should be done before any surgery?
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The differential includes thyroglossal duct cyst, ectopic thyroid, dermoid cyst, and enlarged midline lymph node. The key finding is the ultrasound report of an empty thyroid fossa, which raises the possibility that the mass is the child's only functioning thyroid tissue. Before any excision, obtain a radionuclide scan with Tc-99m pertechnetate or I-123 to confirm whether the mass concentrates tracer and whether there is orthotopic thyroid tissue. Ultrasound alone cannot prove function. CT is unnecessary and adds radiation. If the scan shows ectopic thyroid as the only thyroid tissue, the diagnosis changes from a cyst to ectopic thyroid, and excision would render the child hypothyroid.
2. If the scan confirms ectopic thyroid as the only functioning thyroid tissue, how should you manage the mass and why?
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Do not excise the mass. If it is the only functioning thyroid tissue, removal causes permanent hypothyroidism and requires lifelong levothyroxine; surgery is reserved for obstruction, rapid growth, or suspicious features. Monitor growth, TSH, and free T4 every 6-12 months. If the mass causes compressive symptoms, levothyroxine suppression can be tried, but it is controversial; surgery would then be a last resort with careful counseling. If the scan shows normal orthotopic thyroid and a non-functioning midline cyst, the diagnosis is thyroglossal duct cyst, and Sistrunk procedure is appropriate after treating any infection.
3. What would you tell the parents about recurrence and hypothyroidism after a Sistrunk procedure if the mass were a thyroglossal duct cyst?
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After Sistrunk, recurrence is about 3-5% and is higher if the central hyoid body is not removed or if there is a ramus remnant. Hypothyroidism is uncommon if the thyroid is normal, but the parents should know that removal of an ectopic thyroid would cause it. I would explain that surgery is planned only after the scan confirms the diagnosis, that the scar is cosmetic, and that follow-up includes wound check, thyroid function if there was any concern, and monitoring for recurrence. If the mass recurs, imaging and repeat surgery may be needed.