Thyroglossal duct cyst is a congenital cystic lesion that develops from the failure of obliteration of the thyroglossal duct, the embryologic migration pathway of the thyroid gland. It is typically located in the midline or paramedian position, with the infrahyoid location being the most common site. It is the most frequent cause of midline neck cystic lesions and is usually diagnosed in childhood or young adulthood. Movement with swallowing and tongue protrusion is a characteristic clinical finding.
Age Range
5-30
Peak Age
15
Gender
Equal
Prevalence
Uncommon
During embryologic development, the thyroid gland migrates from the foramen cecum at the base of the tongue to the anterior neck, forming the thyroglossal duct along this pathway. Normally, this duct obliterates by the 5th-10th gestational week; however, if complete closure fails, a cyst develops from duct remnants. The cyst fills with mucous or serous fluid secreted by the duct epithelium and progressively enlarges. The close anatomic relationship with the hyoid bone exists because the thyroglossal duct courses around the hyoid bone — this is why the Sistrunk operation includes removal of the central portion of the hyoid bone. On ultrasonography, the cyst typically appears as a thin-walled anechoic structure; however, internal echoes and wall thickening may be seen with infection or hemorrhage. On CT and MRI, the embedding of the cyst within the strap muscles and its relationship to the hyoid bone are important distinguishing features from dermoid cysts and lymphatic malformations.
Anechoic cystic lesion in the midline or paramedian anterior neck at or just below the hyoid bone level, embedded within strap muscles. Cranial movement with swallowing and tongue protrusion on clinical examination is pathognomonic — this finding reflects the connection of the thyroglossal duct to the foramen cecum.
Thin-walled, anechoic cystic lesion in the midline or slightly paramedian position of the anterior neck. It demonstrates well-defined posterior acoustic enhancement. The cyst wall is smooth and thin, without internal echoes in uncomplicated cases. It is closely related to and embedded within the surrounding strap muscles.
Report Sentence
A thin-walled, anechoic cystic lesion is seen in the anterior midline neck at/below the hyoid bone level, embedded within the strap muscles, demonstrating posterior acoustic enhancement. Findings are consistent with a thyroglossal duct cyst.
In an infected thyroglossal duct cyst, diffuse or dependent internal echoes, wall thickening, and a hypoechoic halo representing surrounding soft tissue edema are seen. The cyst is no longer anechoic; gravity-dependent movement of internal debris can be demonstrated on dynamic assessment.
Report Sentence
Newly developed internal echoes, wall thickening, and surrounding soft tissue edema are seen in a previously known midline cystic lesion; findings are consistent with an infected thyroglossal duct cyst.
The thyroglossal duct cyst is avascular with no Doppler signal within the cyst. In uncomplicated cysts, no significantly increased vascularity is expected in surrounding tissues. In infected cysts, increased vascularity may be seen in the cyst wall and pericystic tissues; however, the cyst interior remains avascular.
Report Sentence
The cystic lesion is avascular on Doppler examination; no significant increased vascularity is seen in the cyst wall or surrounding tissues. Findings are consistent with an uncomplicated cystic lesion.
On non-contrast CT, a well-defined, homogeneously hypodense (0-20 HU) cystic lesion in the midline or paramedian anterior neck. It is embedded within the strap muscles (sternohyoid and sternothyroid). In the infrahyoid location, it shows close relationship with the hyoid bone. The cyst wall is thin and not conspicuous on non-contrast examination. In infected cysts, increased density (20-40 HU) and stranding in surrounding fat planes may be seen.
Report Sentence
A well-defined, homogeneously hypodense (__ HU) cystic lesion is seen in the anterior midline neck in the infrahyoid position, embedded within the strap muscles. The lesion shows close proximity to the hyoid bone. Findings are consistent with a thyroglossal duct cyst.
On contrast-enhanced CT, thin, smooth wall enhancement is seen; however, no solid component or mural nodule is present. The cyst contents do not enhance and remain homogeneously hypodense. In infected cysts, wall thickening and prominent rim enhancement are seen; inflammatory changes in surrounding soft tissues may be present.
Report Sentence
On contrast-enhanced series, thin smooth wall enhancement is seen without solid component or mural nodule. The cyst contents show no enhancement.
On T2-weighted sequences, the cyst shows markedly hyperintense signal (fluid signal). The surrounding strap muscles with iso- to hypointense signal create clear contrast with the cyst. The relationship between the hyoid bone and cyst is optimally evaluated on axial and sagittal planes on MRI. If suprahyoid extension is present, the extension of the duct toward the foramen cecum ('tail sign') may be visible. In infected cysts, T2 signal may become heterogeneous and edema (increased T2 signal) is seen in surrounding soft tissues.
Report Sentence
On T2-weighted sequences, a markedly hyperintense cystic lesion is seen in the anterior midline neck related to the hyoid bone, embedded within the strap muscles. Suprahyoid duct extension is present/not identified.
On T1-weighted sequences, the uncomplicated cyst shows low to intermediate signal intensity (fluid-like). In cases of proteinaceous content or hemorrhage, T1 signal may increase (may become hyperintense). This signal variation reflects the complication status of the cyst and is a feature to note in differentiation from dermoid cysts (T1 hyperintense due to fat content).
Report Sentence
On T1-weighted sequences, the cystic lesion shows low/intermediate/high signal intensity. No signal loss is seen on fat-suppression sequences — inconsistent with dermoid cyst.
Criteria
Location below the hyoid bone — most common type (65%). Usually midline, located between or within the strap muscles. Develops along the segment between the thyroid gland and hyoid bone.
Distinct Features
May show direct relationship with thyroid gland; sometimes extends into thyroid parenchyma (intrathyroid type). Close proximity to the thyroid gland and embedded structure within strap muscles on US is characteristic. CT/MRI shows cystic lesion just below the hyoid bone.
Criteria
Location above the hyoid bone (20%). May be located in the submandibular region or base of tongue. Close to the foramen cecum, sublingual location is also possible.
Distinct Features
May mimic base of tongue lesions — differential diagnosis with ranula, dermoid cyst, and lingual thyroid is important. MRI sagittal plane evaluates relationship with foramen cecum. Suprahyoid cysts are usually paramedian (slightly lateral to exact midline).
Criteria
Location at the hyoid bone level (15%). The cyst may be adherent to the anterior or posterior surface of the hyoid bone or related to duct remnants passing through the bone.
Distinct Features
Intimate relationship with hyoid bone — most critical location for Sistrunk operation. The cyst may extend behind the hyoid bone or pass through it. CT best evaluates the relationship between bone and cyst. At this location, removal of the central portion of the hyoid bone (Sistrunk procedure) during surgery reduces recurrence risk.
Criteria
Secondary infection of thyroglossal duct cyst at any location. Clinically presents with pain, erythema, swelling, and fever. Often triggered following upper respiratory tract infection.
Distinct Features
Internal echoes, wall thickening, surrounding edema on US. Rim enhancement, surrounding fat stranding on CT. Infected cyst must be clinically differentiated from abscess. Surgery should be planned 6-8 weeks after infection is controlled (high complication risk with acute-phase surgery).
Distinguishing Feature
Thyroid simple cyst is located WITHIN the thyroid parenchyma surrounded by thyroid tissue. Thyroglossal duct cyst is located in the midline, between strap muscles, OUTSIDE the thyroid gland. Location differentiation is easily made on US.
Distinguishing Feature
Dermoid cyst shows hyperintense signal on T1 due to fat content and signal loss on fat-suppression sequences. Thyroglossal duct cyst shows low signal on T1 (if not proteinaceous). Dermoid cyst is also usually in submental location, more superficially located, and has no relationship with strap muscles.
Distinguishing Feature
Lymphatic malformation (cystic hygroma) is typically in the lateral neck, posterior triangle, and shows multiloculated cystic structure. Thyroglossal duct cyst is midline and unilocular. Fluid-fluid levels between septa and septal enhancement may be seen in lymphatic malformation. Additionally, lymphatic malformation may infiltrate surrounding structures, while thyroglossal duct cyst is well-circumscribed.
Distinguishing Feature
Colloid nodule is located WITHIN the thyroid gland and typically shows 'comet-tail' artifact (colloid crystals). Thyroglossal duct cyst is midline, outside the thyroid, between strap muscles, and does not show comet-tail artifact. Colloid nodule may have thick internal echoes and irregular wall structure, while simple thyroglossal cyst is anechoic.
Urgency
routineManagement
surgicalBiopsy
Not NeededFollow-up
specialist-referralThyroglossal duct cyst is a benign congenital lesion with low malignancy risk (<1% — usually papillary thyroid carcinoma). Treatment is the Sistrunk operation (excision of cyst + duct + central hyoid bone + tissue up to the foramen cecum). The Sistrunk procedure reduces recurrence from 50% to <5% compared to simple cyst excision. Normal thyroid gland presence should be confirmed on US before surgery (rare ectopic thyroid possibility). In infected cysts, antibiotic therapy and drainage if needed first, followed by elective surgery 6-8 weeks later. Biopsy is generally not needed; however, FNA should be considered for malignancy exclusion if a solid component is present.
Thyroglossal duct cyst is benign but has risk of infection and rare papillary carcinoma (<1%). Surgical treatment is the Sistrunk procedure (cyst + hyoid body + tract). Recurrence rate is high with simple cystectomy. Presence of normal thyroid gland should be confirmed by US before surgery.