Thyroglossal Duct Cyst: Definition, Diagnosis, and Management
A thyroglossal duct cyst (TGDC) is a congenital neck anomaly that forms due to failure of the thyroglossal duct to involute during embryonic development, typically presenting as a painless midline neck mass that moves with swallowing or tongue protrusion.
Embryology and Anatomy
- The thyroglossal duct forms during embryonic development as the thyroid gland descends from the foramen cecum at the base of the tongue to its final position in the anterior neck
- When portions of this duct fail to involute completely, they can form cystic structures anywhere along the path of descent
- Most commonly located in the midline of the neck, often at or below the level of the hyoid bone 1
- Can also occur in the suprahyoid or infrahyoid regions, and occasionally laterally
Clinical Presentation
- Most common congenital cervical abnormality 1
- Typically presents as a painless, mobile, midline neck mass
- Size usually ranges from 1.5-2.4 cm, though can be larger (up to 8-9 cm in rare cases) 2
- Often moves upward with tongue protrusion or swallowing due to its attachment to the hyoid bone
- May become infected, causing pain, redness, and rapid enlargement
- Can occasionally cause dysphagia or mild dyspnea if large 2
- Affects all age groups, though most commonly diagnosed in childhood or early adulthood
Diagnostic Features
Clinical Examination
- Mobile, smooth, non-tender midline neck mass
- Movement with swallowing or tongue protrusion is pathognomonic
- Location typically at or near the hyoid bone
Imaging
- Ultrasound is the ideal initial investigation due to its accessibility, low cost, and non-invasive nature 3
- CT or MRI may be used for further characterization:
- Well-defined cystic lesion
- May contain homogeneous fluid
- No solid components in uncomplicated cases
- Located in the midline or slightly off-midline
Fine Needle Aspiration (FNA)
- Can be used for confirmation but has moderate sensitivity (62%) 4
- Typical findings include:
- Colloid material (thick/fragmented or thin/watery)
- Macrophages and inflammatory cells
- Ciliated columnar epithelium or squamous epithelium
- Thyroid epithelium rarely present (11% of cases) 4
Differential Diagnosis
- Branchial cleft cyst (typically lateral in location)
- Dermoid cyst
- Thyroid nodule or ectopic thyroid tissue
- Lymphadenopathy
- Lipoma
- Lymphoepithelial cyst 4
Management
Surgical Treatment
- The Sistrunk procedure remains the standard of care and most effective treatment for thyroglossal duct cysts 1, 5
- This procedure involves:
- En bloc excision of the cyst
- Removal of the central portion of the hyoid bone
- Excision of a core of tissue from the hyoid bone to the foramen cecum at the base of the tongue
- The complete Sistrunk procedure reduces recurrence rates from approximately 50% to 3-5% 5
Alternative Treatments
- Sclerotherapy with agents like OK-432 has been described as an alternative in select cases 3
- Simple aspiration or incomplete excision is associated with high recurrence rates and is not recommended
Important Considerations
- Malignant degeneration is rare (approximately 0.7% of cases) but should be considered, especially in adults 1
- Preoperative imaging should evaluate for the presence of normal thyroid tissue to rule out ectopic thyroid, which would contraindicate removal
- Recurrence is most commonly due to incomplete excision, particularly failure to remove the central portion of the hyoid bone and tract extending to the tongue base
- Infection prior to surgery may increase the technical difficulty of the procedure and the risk of recurrence
Classification in Imaging
- In oncological imaging systems like ONCO-RADS, thyroglossal duct cysts are classified under "Other findings, including anatomic variations" in the neck region 6
- They are considered benign developmental anomalies rather than neoplastic lesions
Proper diagnosis and complete surgical excision using the Sistrunk procedure provides excellent outcomes with low recurrence rates for patients with thyroglossal duct cysts.