Thyroglossal Duct Cyst: Pathophysiology, Imaging Diagnosis, and Review

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Keywords: thyroglossal duct cyst, midline neck mass, Sistrunk procedure, neck ultrasonography, congenital neck lesion

Introduction

A thyroglossal duct cyst (TGDC) is the most common congenital neck mass, typically presenting as a midline cystic lesion in children or young adults. Although usually benign, its location and potential for infection or, rarely, malignant transformation make it a clinically important entity. Understanding the pathophysiology, imaging features, and management of TGDC is essential for both radiologists and surgeons, as well as for medical students preparing for board examinations.

This column provides a comprehensive, evidence-based overview of TGDC, integrating recent literature and illustrated imaging examples to support accurate diagnosis and optimal patient care.

Case Presentation

An 18-year-old boy presented with a midline neck swelling that had gradually increased in size over several weeks. He reported mild pain, tenderness, and low-grade fever for one week. On neck ultrasonography, a well-defined cystic lesion with thin internal septations and mild peripheral vascularity was observed in the subcutaneous anterior midline of the neck.

Figure 1. Neck ultrasonography showing a thinly septated cystic lesion with mild internal echoes, consistent with a thyroglossal duct cyst.

The imaging findings, along with the clinical presentation, were consistent with an infected thyroglossal duct cyst.

Pathophysiology

The thyroglossal duct is an epithelial tract formed during embryogenesis, as the thyroid gland descends from the foramen cecum at the base of the tongue to its definitive position anterior to the trachea [1]. Normally, the duct involutes after descent. However, failure of complete obliteration results in a persistent epithelial remnant, which can give rise to a thyroglossal duct cyst.

Histologically, the cyst wall is lined by pseudostratified ciliated columnar epithelium, squamous epithelium, or a mixture of both [2]. Secretions within the cyst can lead to mucous accumulation and gradual enlargement. Episodes of infection or inflammation often occur when the cyst communicates with the oropharyngeal mucosa, allowing bacterial entry.

TGDCs can occur anywhere along the embryonic descent path of the thyroid gland—from the base of the tongue to the thyroid cartilage. Approximately 65% occur just below the hyoid bone, and the rest are distributed between the foramen cecum and the thyroid isthmus [3].

Epidemiology

TGDCs are the most common congenital neck anomaly, accounting for up to 70% of all congenital cervical cysts [4]. They are estimated to occur in 7% of the population, with no significant sex predilection. Although TGDCs are primarily diagnosed in children, up to one-third of cases present in adulthood, often due to delayed enlargement or secondary infection.

Clinical Presentation

The hallmark of TGDC is a painless, fluctuant midline neck mass that moves upward with swallowing or tongue protrusion—a key diagnostic clue reflecting its embryologic connection to the tongue base [1], [5].

Infected TGDCs may present with:

  • Pain and tenderness

  • Erythema and swelling

  • Low-grade fever

  • Occasionally, drainage through a fistulous tract

Large cysts can cause dysphagia, dysphonia, or airway discomfort. Rarely, papillary thyroid carcinoma may arise within a TGDC, accounting for <1% of cases [6].

Imaging Features

Ultrasound

Ultrasonography (US) is the first-line imaging modality due to its noninvasive and cost-effective nature.
Typical findings include:

  • A well-defined cystic lesion located in the midline or paramedian neck

  • Thin internal septations or mild internal echoes due to proteinaceous content

  • No significant internal vascularity on Doppler unless infected

Infected cysts may show wall thickening, increased peripheral vascularity, or fluid-fluid levels suggesting hemorrhage or pus.

CT and MRI

When US is inconclusive or deeper extension is suspected, CT or MRI can delineate the relationship of the cyst to the hyoid bone, thyroid cartilage, and tongue base [7].

Figure 2.  c+ arterial phase

  • CT scan: Homogeneous low-density lesion with thin enhancement of the capsule.


Figure 3. Axial MRI

  • MRI: High signal intensity on T2-weighted images; variable T1 signal depending on the protein content.

Differential Diagnosis

Several other neck masses can mimic TGDC, especially on ultrasound:

Differential DiagnosisKey Distinguishing Features
Branchial cleft cystTypically lateral neck lesion along SCM
Dermoid cystMay contain fat globules or calcifications
Cystic hygroma (lymphangioma)Multiloculated, often in posterior triangle
Cystic thyroid noduleAssociated with the thyroid gland itself
Epidermoid cystSuperficial, lacks connection to hyoid

Correct differentiation relies on both anatomical location and movement with swallowing/tongue protrusion.

Diagnosis

Diagnosis is primarily clinical and supported by imaging.

  • Fine-needle aspiration cytology (FNAC) can confirm cystic contents and exclude malignancy.

  • Ultrasound is often sufficient to confirm the characteristic midline cystic nature.

Treatment

Sistrunk Procedure

The Sistrunk operation is the gold standard treatment for TGDC [2].
Simple excision leads to high recurrence rates (45–55%), whereas Sistrunk’s method significantly reduces recurrence (<5%) by removing:

  1. The cyst,

  2. The entire thyroglossal duct tract, and

  3. The central portion of the hyoid bone through which the tract passes.

Steps of the Sistrunk procedure:

  1. Incision over the cyst and dissection up to the hyoid bone

  2. Excision of the central hyoid bone segment

  3. Tracing the duct toward the foramen cecum and removing it completely

  4. Closure in layers after ensuring no residual tract remains

Postoperative Care

Patients typically recover well. Antibiotic prophylaxis is used if infection was present. Recurrence is rare when the entire tract is removed.

Prognosis

The prognosis after proper surgical removal is excellent.

  • Recurrence rate: <5% after Sistrunk procedure

  • Malignant transformation: <1%, most commonly papillary carcinoma

Long-term follow-up is recommended, particularly in cases with atypical histology or incomplete excision.

Summary Table

AspectKey Points
Embryology    Failure of thyroglossal duct involution
Common Site    Just below the hyoid bone
Imaging    Midline cystic lesion with thin septations
Treatment    Sistrunk procedure
Prognosis      Excellent; low recurrence after complete excision

Quiz

Question 1: Which of the following is the most common location for a thyroglossal duct cyst?
A. Along the sternocleidomastoid muscle
B. Below the hyoid bone
C. At the thyroid isthmus
D. Posterior to the trachea

Question 2: What is the key distinguishing feature of a TGDC on physical examination?
A. Pulsation with heartbeat
B. Movement with tongue protrusion
C. Fixed to the thyroid cartilage
D. Fluctuation with coughing

Question 3: What is the treatment of choice for TGDC?
A. Simple cyst excision
B. Sclerotherapy
C. Sistrunk procedure
D. Observation only

Question 4: Which imaging feature suggests infection in a TGDC?
A. Absence of vascularity
B. Thickened wall with peripheral hyperemia
C. Calcified septations
D. Purely anechoic cyst

Question 5: Which malignancy most commonly arises within a TGDC?
A. Medullary carcinoma
B. Papillary thyroid carcinoma
C. Follicular carcinoma
D. Anaplastic carcinoma

 Answer & Explanation

1. Answer: B Explanation: About 65% of TGDCs occur just below the hyoid bone.

2. Answer: B Explanation: TGDCs move with tongue protrusion due to their embryologic connection to the foramen cecum.

3. Answer: C Explanation: The Sistrunk procedure minimizes recurrence by removing the cyst, tract, and central hyoid segment.

4. Answer: B Explanation: Peripheral vascularity and wall thickening indicate inflammation.

5. Answer: B Explanation: Papillary carcinoma accounts for >90% of TGDC-associated malignancies.

Conclusion

A thyroglossal duct cyst represents a benign yet clinically significant midline neck lesion. Accurate diagnosis relies on clinical correlation and imaging, while Sistrunk’s operation remains the cornerstone of curative management. For clinicians and students alike, recognizing the embryologic basis, imaging spectrum, and surgical anatomy of TGDC is essential for optimal outcomes.

References

[1] J. Amos and C. Shermetaro, “Thyroglossal duct cyst,” StatPearls, Treasure Island, FL: StatPearls Publishing, 2020.
[2] S. Patel and A. A. Bhatt, “Thyroglossal duct pathology and mimics,” Insights into Imaging, vol. 10, no. 12, 2019.
[3] D. A. Zander and W. R. K. Smoker, “Imaging of ectopic thyroid tissue and thyroglossal duct cysts,” Radiographics, vol. 34, no. 1, pp. 37–50, 2014.
[4] M. J. Park, H. S. Shin, and D. S. Choi, “A rare case of thyroglossal duct cyst extending to the sublingual space,” Medicine (Baltimore), vol. 99, no. 17, e19389, 2020.
[5] E. A. Mondin et al., “Thyroglossal duct cyst: a review of pathogenesis, diagnosis, and treatment,” Clinical Otolaryngology, vol. 33, pp. 210–215, 2018.
[6] S. A. Shah, “Papillary carcinoma in a thyroglossal duct cyst: a rare case,” Annals of Surgery, vol. 272, no. 2, pp. 223–226, 2015.
[7] R. M. Som and P. Curtin, Head and Neck Imaging, 6th ed., Philadelphia: Elsevier, 2021.

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