What is a thyroglossal duct cyst in adults?

What is a Thyroglossal Duct Cyst in Adults?

A thyroglossal duct cyst (TDC) is a congenital midline neck mass that represents an embryologic remnant of the thyroid gland's descent during fetal development, and while most commonly diagnosed in childhood, it can present for the first time in adults as a painless or infected midline cervical swelling that requires surgical excision to prevent complications including infection and, rarely, malignant degeneration. 1, 2, 3

Clinical Presentation and Key Features

Location and Characteristics:

• TDCs typically present as midline neck masses, most commonly at or near the hyoid bone level, though they can occur anywhere along the thyroglossal duct tract from the tongue base to the suprasternal notch 1, 2, 4
• The classic diagnostic feature is upward movement of the mass with tongue protrusion or swallowing, distinguishing it from other neck masses 1, 3
• In adults, the most common presentation is an infected or painful mass rather than the asymptomatic swelling typical in children 1, 2

Age and Demographics:

• While present from birth, TDCs can remain asymptomatic until adulthood, with mean presentation age around 33-55 years in adult case series 2, 5
• There is a slight male predominance (M:F ratio approximately 1.1-1.4:1) 2, 5

Critical Diagnostic Considerations

Why This Matters in Adults:

• Midline neck masses in adults warrant special consideration because the differential diagnosis includes thyroglossal duct cyst, thyroglossal duct carcinoma, thyroid malignancy, or metastatic spread from laryngeal malignancy 6
• Unlike in children where TDCs are almost always benign, malignant degeneration is the most dreaded complication specific to adulthood, though it remains rare 2

Diagnostic Workup

Imaging:

• Ultrasound is the ideal initial investigation as it is readily accessible, inexpensive, and non-invasive, and can confirm the diagnosis in most cases 3, 5
• CT scan with contrast should be obtained for neck masses deemed at increased risk for malignancy, and has specific indications in adults to rule out malignancy 6, 7, 2
• MRI is the preferred modality for detailed characterization when distinguishing between benign and potentially malignant cystic lesions 7

Tissue Diagnosis:

• Fine needle aspiration (FNA) should be used as first-line histologic assessment for any adult with a cystic neck mass, though it has only moderate sensitivity (62%) for TDC diagnosis 7, 8, 5
• Cytomorphologic features include colloid (thick/fragmented or thin/watery), macrophages, lymphocytes, ciliated columnar epithelium, and rarely thyroid epithelium (only 11% of cases) 5
• FNA has a positive predictive value of only 69% for TDC, and many surgically confirmed TDCs are missed on prior FNA (61% false-negative rate in one series) 5
• If FNA is inadequate or benign but clinical suspicion remains high, ultrasound-guided repeat FNA or core biopsy should be attempted before open biopsy 7, 8

Common Pitfalls

Misdiagnosis Risk:

• TDCs can masquerade as other lesions including traumatic hematomas, particularly when presenting with hemorrhage 4
• Do not assume a midline cystic mass is benign without thorough evaluation, as malignant degeneration, though rare, is a specific adult complication 8, 2
• The differential diagnosis includes branchial cleft cyst, lymphoepithelial cyst, thyroid lesions, and lymphadenopathy 5

Infection Complications:

• Infection and abscess formation are frequent complications due to communication between the cyst and oral cavity with contamination by oral flora 1, 3
• An infected neck mass is the common presentation of TDC in adults, requiring appropriate diagnostic studies before definitive treatment 1

Treatment

Surgical Management:

• The Sistrunk procedure is the treatment of choice for TDC, involving excision of the cyst, the central portion of the hyoid bone, and the tract extending to the foramen cecum at the tongue base 1, 2, 3
• This procedure, developed in 1920, remains the gold standard to limit recurrence 1, 3
• For cases with malignant degeneration, total thyroidectomy with central neck dissection followed by radioactive iodine therapy is required 2

Timing:

• Surgical excision should be performed to prevent the risks of infection and malignant degeneration, which are specific complications in adulthood 2