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1、Female,67y painless mass in the anterior neck for one week,Thyroglossal duct cyst,The thyroid gland, which is the first endocrine gland to develop in the human embryo, initially appears in the floor of the pharynx. From this point, the thyroid descends to its normal adult position. The thyroglossal
2、duct is a canal that connects the tongue to the thyroid during its descent in the embryo. While this duct normally atrophies, remnants of the duct may persist as cysts along its course. Up to 62% of these ducts contain ectopic thyroid tissue.,Thyroglossal duct cysts may arise during the fifth week o
3、f embryonic life after the descent of the thyroid gland from the base of the tongue to its position in the neck The cyst can be located anywhere from the foramen caecum (base of tongue) to the suprasternal region: 25% occur in the suprahyoid region, 15% at the level of the hyoid and 65% below the le
4、vel of the hyoid bone. When it occurs above the hyoid bone it is often in a midline location. If infrahyoid, the cyst can be midline or slightly off-midline in location,Pathway of the thyroglossal duct. Drawing shows a lateral view of the embryologic thyroglossal duct from the foramen cecum through
5、the developing hyoid bone to the pyramidal lobe of the thyroid. If the duct fails to involute completely, a thyroglossal duct cyst may result, with 80% of these lesions being at or below the level of the hyoid bone.,The thyroglossal duct cyst is the most common congenital neck mass, accounting for 7
6、0% of congenital neck anomalies, and the second most common benign neck mass, after benign lymphadenopathy. About 50% of patients present before 20 years of age, with a second group of patients presenting in young adulthood.Rare cases of hereditary thyroglossal duct cysts have been reported; typical
7、ly, these cysts have an autosomal dominant pattern of transmission and occur in prepubertal girls.,There is no sex predominance. 65% of patients present before the age of 30. The composition of the cyst is thick mucous material lined with secreting columnar or squamous epithelium. The cyst is surrou
8、nded by a thick fibrous capsule.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. Of those in a paramedian location, most will occur on the left for reasons that are not well understood.,T
9、he cyst presents as a fluctuating and painless cervical mass unless it becomes infected. The mass moves with the protrusion of the tongue. The most frequent complication is the formation of a fistula, usually after trauma or infection. About 1% of thyroglossal duct abnormalities are associated with
10、thyroid carcinoma arising from ectopic rests of thyroid tissue within the duct and not from the duct itself. The presence of a carcinoma within a thyroglossal duct cyst is rarely suspected preoperatively,Radiologic Features,On CT scans, a thyroglossal duct cyst usually appears as a smooth, well-circ
11、umscribed mass anywhere along the vertical course of the vestigial thyroglossal duct. The mass has a thin wall and homogeneous attenuation, the values of which correspond to those of fluid (1018 HU). Elevated attenuation values of the fluid cyst reflect its increased protein content and generally co
12、rrelate with a history of prior infections. Although thyroglossal duct cysts are usually unilocular, septations may be seen occasionally. Peripheral rim enhancement is usually observed on contrast-enhanced scans,An uncomplicated thyroglossal duct cyst has low signal intensity on T1-weighted images a
13、nd is hyperintense on T2-weighted images, findings that reflect its fluid content. The rim will be nonenhancing unless inflammation is present. In case of infection or hemorrhage, a thick irregular rim may be visualized, and the signal intensity of the fluid becomes variable from the presence of pro
14、teinaceous debris,Thyroglossal duct cyst in a 41-year-old man. Axial contrast-enhanced CT scans show a cystic mass in the anterior midline of the neck just above and at the level of the hyoid bone. Axial T1-weighted MR image at the thyrohyoid membrane level shows hyperintensity of the mass, a findin
15、g suggestive of proteinaceous content or hemorrhage.,Differential Diagnosis,Dermoid cyst cystic hygroma branchial cyst lipoma laryngocele,Dermoid cysts appear as moderately thin-walled, unilocular masses, located in the submandibular or sublingual space. On CT scans, the central cavity is usually fi
16、lled with a homogeneous, hypoattenuating (018 HU) fluid material. It may appear to be filled with “marbles,“ due to the coalescence of fat into small nodules within the fluid matrix . This “sack-of-marbles“ appearance is virtually pathognomonic for a dermoid cyst in this location.,A cystic hygroma i
17、s the most common form of lymphangioma . In children, the most common location is the posterior cervical space, followed by the oral cavity. In adults, cystic hygromas are more commonly seen in the sublingual, submandibular, and parotid spaces . On CT images, cystic hygromas tend to appear as poorly circumscribed, multiloculated, hypoattenuated masses. They typically have characteristic homogeneous fluid attenuation .,
