Embryology · Head and neck: pharyngeal arches

Thyroglossal duct cyst and ectopic thyroid !

Malformation

A lump in the middle of the neck, near the hyoid bone, that rises on swallowing. It is left over from the path the thyroid took on its way down.

Updated 2026-11-01

See it in 3D: Thyroid gland · Hyoid bone · Tongue · Thyroid cartilage

What it is

The thyroglossal duct cyst is the commonest congenital neck anomaly. It forms when part of the duct that linked the thyroid to the tongue fails to disappear. It is always in or very near the midline, almost always beside the hyoid. Ectopic thyroid is the reverse case: the gland stops along the way, most often at the base of the tongue.

Key facts

Standard treatment: the Sistrunk operation, which removes the cyst, the tract and the central hyoid; it cuts recurrence to about 5%.
Removing an ectopic thyroid that was the only gland leaves the patient hypothyroid, which is why a normal thyroid is confirmed first.

Embryological cause

The thyroid primordium descends from the foramen cecum, tied to the tongue by the thyroglossal duct.
The duct should disappear by about week 10; if an epithelium-lined segment persists, it secretes and forms a cyst.
The duct passes in front of, through or behind the hyoid, which forms later: hence the cyst's close link to this bone.
Ectopic thyroid: descent stops; the base of the tongue (lingual thyroid) is the commonest site.

How it presents

Painless, mobile midline mass at or just below the hyoid; also at the base of the tongue or beside the thyroid cartilage.
Rises on swallowing and on sticking out the tongue, because it is tethered to the hyoid and tongue.
Usually appears in childhood (before age 10), often after a respiratory infection enlarges or infects it.
It can become infected and open onto the skin as a fistula.
Rarely (under 1%) it contains carcinoma, almost always papillary.
Lingual thyroid: a mass at the base of the tongue with dysphagia or hypothyroidism; it may be the only thyroid tissue.

Diagnosis

Neck ultrasound first: it shows the cyst and confirms whether a normal thyroid is in place.
Thyroid function tests; scintigraphy if ectopic thyroid is suspected.
Differential diagnosis: dermoid cyst, lymph node and branchial cyst (the latter is lateral).

Test yourself

Think of the answer, then tap the question to see it.

Why does a thyroglossal cyst rise when the tongue is stuck out?

Because it is a remnant of the duct that tied the thyroid to the tongue and is fixed to the hyoid.

Which test is done before surgery, and why?

Ultrasound, to see the cyst and confirm that normal thyroid tissue is present in the neck.

Why does the Sistrunk operation remove the central hyoid?

Because the duct tract runs with the hyoid and leaving it greatly raises recurrence.

What is the commonest site of ectopic thyroid?

The base of the tongue (lingual thyroid), next to the foramen cecum.

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See it in 3D

The structures of Durgical's 3D anatomy where it is found.

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Educational content on embryonic development; not a guide to prenatal diagnosis or to medicines in pregnancy and no substitute for a health professional's advice. No doses are given.

Sources: Thyroglossal Duct Cyst - StatPearls - NCBI Bookshelf (StatPearls Publishing (NCBI Bookshelf), 2025); Langman's Medical Embryology, 13th ed., ch. 17: Head and Neck (Wolters Kluwer, 2015).

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