Thyroglossal duct cyst
 Discussion of Thyroglossal duct cyst
- The thyroglossal duct cyst is the most common congenital neck mass, accounting for 70% of congenital neck anomalies, and the second most common benign neck mass, after benign lymphadenopathy.
- Thyroglossal duct cysts are located in the midline (75% of cases) or slightly off-midline (25%) in the anterior neck (they are always within 2 cm of the midline).
- Majority are infrahyoid in location.
- About 50% of patients present before 20 years of age, and a second group presents during young adulthood.
- A thyroglossal duct cyst usually manifests as an enlarging, painless midline mass in a pediatric or young adult patient.
- During its migration, the anlage of the thyroid gland is connected to the tongue by a narrow tubular structure, the thyroglossal duct.
- This duct normally involutes by the 8th–10th gestational week.
- The site of the original opening of the thyroglossal duct persists as the foramen cecum of the tongue, with the inferior end of the canal becoming the pyramidal lobe of the thyroid gland.
- If any portion of the thyroglossal duct persists, secretions from the epithelial lining (likely secondary to repeated local infection and inflammation) may give rise to cystic lesions.
- The duct is intimately associated with the developing hyoid bone, usually passing through it.
 Imaging Findings for Thyroglossal duct cyst
- US frequently shows a hypoechoic mass with a thin outer line either in the midline of the anterior neck close to the hyoid bone or paramedian within the strap muscles.
- Heterogeneity seen in the cyst is due to the proteinaceous content of the cyst rather than to inflammation or infection.
- At CT, thyroglossal duct cysts appear as well-circumscribed masses with thin walls.
- The cyst contents have a mucoid attenuation.
- Peripheral rim enhancement is observed after intravenous injection of contrast material.
- At MR imaging, an uncomplicated cyst has low signal intensity on T1-weighted images and high signal intensity on T2-weighted images.
- The wall of the cyst may enhance on T1-weighted images after intravenous injection of gadolinium.
Patient #2: Infected thyroglossal duct cyst
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 References for Thyroglossal duct cyst
- Kelly K. Koeller, Leonor Alamo, Carol F. Adair, and James G. Smirniotopoulos. From the Archives of the AFIP: Congenital Cystic Masses of the Neck: Radiologic-Pathologic Correlation. RadioGraphics 1999 19: 121-146.
- Jean-Yves Meuwly, Domenico Lepori, Nicolas Theumann, Pierre Schnyder, Ghazal Etechami, Judith Hohlfeld, and François Gudinchet. Multimodality Imaging Evaluation of the Pediatric Neck: Techniques and Spectrum of Findings. RadioGraphics 2005 25: 931-948.