Thyroglossal duct cyst
Thyroglossal duct cyst (TGDC) is the most common congenital neck cyst. It is typically located in the midline.
Demographics and clinical presentation
They typically present during childhood (90% before the age of 10), or remain asymptomatic until they become infected, in which case they can present at any time.
Presentation is therefore either as a rounded swelling or if infected as a red warm painful lump.
Location
The cysts can occur anywhere along the course of the thyroglossal duct, although infrahyoid location is most common.
- suprahyoid : 20 - 25 % (less common in adults ~ 5%)
- at the level of hyoid bone : 15 - 50 %
- infrahyoid : 25 - 65 %
Typically they are located in the midline (~ 65 %) with those off-midline characteristically tucked next to the thyroid cartilage.
Pathology
Thyroglossal duct cysts are epithelial lined cysts. They result from failure of normal developmental obliteration of the thyroglossal duct during development, and can thus occur anywhere along the course of the duct.
The epithelial lining of the cyst varies with location. Those that form near the tongue are lined by stratified squamous epithelium. The more common cysts located in the neck are lined by cells similar to thyroidal acinar epithelium. Malignancies do occur but are rare, seen in less than 1% of cysts. When they do occur they are most frequently papillary thyroid carcinoma.
Radiographic features
Ultrasound
Unless infected, they are painless, fluctuant masses which spread the strap muscles.The fluid is usually anechoic, but may contain debris. In adults in particular, they may be complex heterogeneous masses. The walls are usually thin, without internal vascularity.
If there is associated infection, there may be surrounding inflammatory changes.
CT
Thin walled, smooth, well defined homogeneously attenuating lesion at an anterior midline or para-midline location. The generally accepted rule is that they should be within 2 cm of the midline. May demonstrate slight rim enhancement. The sternocleidomastoid is typically displaced posteriorly or posterolaterally.
Treatment and prognosis
Complete resection of the cyst and duct up to the foramen caecum is curative. The Sistrunk procedure includes resection of the middle third of the hyoid bone.
Differential diagnoses
- branchial cleft cyst : three times less common, and usually well away from the midline
- delphian node adenopathy
- epidermoid cyst
- thyroid cyst or thyroid neoplasm
- laryngocoele
- ranula
- parathyroid adenoma
