Key Facts

Definition：Thyroglossal duct cyst (TGDC) is remnant of thyroglossal duct found between foramen cecum of tongue base and thyroid bed of infrahyoid neck.

Classic imaging appearance：Cystic neck mass with thin rim of peripheral enhancement, located in midline.Can occur in tongue base, at hyoid bone,or embedded in infrahyoid strap muscles.The more inferior the TGDC, the more paramedian.Most common congenital neck lesion and 90% of nonodontogenic congenital cysts.

Presents as asymptomatic midline or paramedian neck mass.

Imaging Findings

General features：(1)Best imaging clue is midline cystic neck mass embedded in infrahyoid strap muscles ("claw sign").(2)TGDC is shown as benignappearing, cystic neck mass, and wall may enhance if infected.Location is important key to diagnosis.(3)Above hyoid bone, occurs at base of tongue or within posterior floor of mouth.At level of hyoid bone, found in midline abutting hyoid.May project into pre－epiglottic space.In infrahyoid neck,embedded in strap muscles.(4)Carcinoma is associated with TGDC (＜1%).Differentiated thyroid Ca (85% papillary carcinoma).

CT findings：(1)Low－density mass,occasionally septated.(2)If associated thy roid carcinoma, solid eccentric mass, without calcification.(3)Associated with cyst.

MR findings：(1)Hypointensity on T1WI and hyperintensity on T2WI; (2)No enhancement (unless infected).

Ultrasound Findings：Anechoic midline neck mass in close association with hyoid.

Imaging recommendations：TGDC in children have a classic clinical presentation.Sonography to confirm normal thyroid gland.CT or MR more than adequate to task of defining nature and extent.Recommended if cyst is suprahyoid in location, if there is question about diagnosis, if mass is infected or recurrent, or when there is suspicion of associated carcinoma.

Nuclear scintigraphy only if unable to identify normal thyroid gland.

Differential Diagnosis: Anterior Neck Mass

(1)Lingual or sublingual thyroid：Ectopic thyroidal tissue will enhance and appear solid on CT/MR.(2)Lymphadenopathy：Usually multiple,paramedian,non－cystic unless necrotic.(3)Dermoid of the tongue：Dermoid will be fat density on CT, hyperintense on enhanced T1WI.(4)Mixed laryngocele：Laryngocele can be traced back to laryngeal origin.Laryngocele will not be em bedded within strap muscles.(5)Malignant necrotic node, anterior neck (Delphian chain) may be difficult to differentiate necrotic node from infected TGDC.

Pathology-Genetics

Familial cases are rare, and usually autosomal dominant.Thyroid developmental anomalies often occur in the same family, including TGDC, agenesis,ectopia, pyramidal lobe.

Embryology-Anatomy

Thyroglossal duct originates near foramen cecum.Descends through base of tongue, floor of mouth, around or through hyoid bone area, anterior to strap muscles, to the final position in thyroid bed anterior to thyroid or cricoid cartilage.

Fig 1 a)Axial T2WI and b)axial T1WI reveal a thyroglossal duct cyst (arrow)in the region of midline.c)Sagittal T2WI demonstrates a cyst(arrow)adjacent to hyoid bone.Fig 2 This drawing depicts the tract of the thyroglossal duct as it passes from the cephald foramen cecum (arrow) to the distal thyroid bed.The tract passes close to the mid－h(huán)yoid bone (open arrow).In the infrahyoid neck, the thyroglossal duct cyst fades off midline to a paramedian location.

Etiology-Pathogenesis

Failure of involution of thyroglossal duct and persistent secretion of epithelial cells lining duct result in TGDC.TGDC can occur anywhere along route of descent.Ectopic thyroid tissue can also occur anywhere along this course.

Epidemiology

TGDC is most common congenital neck mass.Female＞Male if hereditary form.

Gross Pathologic,Surgical Features

Smooth, benign－appearing cyst, usually with a tract to the hyoid bone ± the foramen cecum.

Microscopic Features

Cyst lined by respiratory or squamous epithelium.

Small deposits of thyroid tissue commonly associated.

Clinical Issues

Presentation：(1)Principal presenting symptom：midline neck mass.(2)Other presenting symptoms：recurrent,soft,mobile,asymptomatic,midline or slightly paramedian neck mass.(3)Often has a history of recurrent, intermittent neck swelling,or multiple prior incision and drainage procedures.(4)Age of presentation：＜10 years (90%); 10% are 20－35 year olds.(5)Physical examination：when TGDC surrounds hyoid bone, it moves with tongue movement.

Natural History

Recurrent, intermittent swelling of mass, usually following a minor upper respiratory infection.

Treatment & Prognosis

Complete surgical resection, termed a sistrunk procedure.Entire cyst and midline portion of hyoid bone is resected and tract to foramen cecum dissected free, to prevent recurrence.Sistrunk procedure decreases recurrence rate from 4% to 50%.Excellent with complete surgical resection.Recurrences (incomplete resection) often complicated, lateral.

醫(yī)學(xué)詞匯注釋與簡要講解

thyroglossal duct cyst 甲狀舌管囊腫

foramen cecum 盲孔

hyoid bone 舌骨

odontogenic 牙源性的

infrahyoid strap muscles 舌骨下帶肌

pre－epiglottic 前會厭

nuclear scintigraphyh 核素閃爍成像

lingual 舌的

sublingual 舌下的

lymphadenopathy 淋巴結(jié)病變

dermoid 皮樣囊腫

laryngocele 喉膨出; 喉囊腫

autosomal dominant 常染色體顯性

agenesis 缺如

ectopia 異位

pyramidal lobe 錐狀葉

cricoid cartilage 環(huán)狀軟骨

epithelial cells 上皮細胞

respiratory epithelium 呼吸上皮

squamous epithelium 鱗狀上皮