- Anterior midline well-defined cystic mass, may contain thyroid tissue
- Small risk of malignant transformation usually to papillary thyroid carcinoma
Description
Thyroglossal duct cysts (TGDC) are the most common congenital cervical cystic anomalies, arising from persistent epithelial remnants of the thyroglossal duct, the embryologic tract through which the thyroid gland descends from the tongue base to the neck. These cysts can present at any age but are most frequently diagnosed in children and young adults. It can occur anywhere along the path of the thyroglossal duct but is most commonly found near the hyoid bone. These cysts can become infected or form fistulas, leading to secondary complications. The term “thyroglossal” is derived from “thyro,” referring to the thyroid gland, and “glossal,” referring to the tongue.
Pathogenesis
During embryogenesis, the thyroid gland descends from the foramen cecum at the base of the tongue to its final pretracheal position, creating the thyroglossal duct. This duct usually degenerates and disappears by the 10th week of gestation. Incomplete obliteration can result in epithelial remnants that form cysts. The cyst can be lined by columnar or squamous epithelium and may contain thyroid tissue. Infection or inflammation of these cysts can lead to symptomatic presentation.
Subtypes
- Infrahyoid (most common): Located below the hyoid bone.
- Suprahyoid: Located above the hyoid bone.
- Intralingual: Located within the tongue.
- Suprasternal: Located above the sternum.
Epidemiology, Risk Factors & Associations
- Age: Most common in children (60% of cases present before age 10).
- Gender: Slightly more common in males.
- Risk Factors:
- Family history of congenital neck anomalies.
- Infections that may exacerbate cyst formation or symptoms.
- Associations:Ectopic thyroid tissue (often found within the cyst).
Clinical Features
- Painless, midline neck mass that elevates with swallowing and tongue protrusion.
- May become infected, leading to tenderness, erythema, and purulent discharge from a sinus tract.
- Rarely, dysphagia or dyspnoea if the cyst is large.
Complications
- Infection is the most common complication, which can lead to the formation of a draining sinus.
- Risk of malignant transformation: Approximately 1%, most commonly to papillary thyroid carcinoma.
- Fistula formation following infection or rupture.
Pathological Features
Histopathology
- Macroscopic: Smooth, cystic mass.
- Microscopic: Cyst lined by columnar or squamous epithelium, with possible thyroid tissue in the cyst wall.
Serology
- Typically not diagnostic; may use thyroid function tests if ectopic thyroid tissue is suspected.
Biochemistry
- Not typically relevant for diagnosis.
Radiological Features
General Features
- Firstline Investigation: Ultrasound.
- Gold Standard Imaging Protocol: Ultrasound for initial assessment, with possible CT or MRI for further delineation.
- Typically appears as a well-defined, anechoic or hypoechoic cyst near the hyoid bone.
- No calcifications are typically seen. Calcification within the cyst may represent previous infection or potentially carcinoma.
US
- B-mode: Well-defined anechoic or hypoechoic cyst with posterior acoustic shadowing. May show internal debris or septations if infected.
- Colour: Hyperaemia suggests infection.
CT
- Non-contrast: Well-defined cystic lesion, typically midline.
- C+ Arterial/Venous: Enhancement of the cyst wall if infected or inflamed.
MRI
- T1: Variable T1 signal reflecting proteinaceous content.
- T2: Hyperintense, indicating fluid content. Perilesional soft-tissue oedema suggests inflammation.
- T1 Gad+: Enhancement of the cyst wall may represent infection or inflammation. Solid components raise suspicion for malignant transformation (rare).
Grading and Staging
Not applicable for benign cysts; if malignant transformation occurs, use thyroid cancer staging systems.
Diagnosis
- Clinical examination revealing a midline neck mass that moves with swallowing and tongue protrusion.
- Confirmatory imaging with ultrasound showing a well-defined cystic structure.
Differential Diagnosis
- Branchial cleft cyst: Typically located laterally, often presenting with fistulae.
- Dermoid cyst: Can be midline but does not move with swallowing.
- Lymphadenopathy: Often multiple nodes, firm, associated with systemic symptoms.
- Thyroid nodule: Typically located within the thyroid gland, not along the thyroglossal tract.
Management
- Referral to paediatric surgery or ENT specialist.
- Surgical excision (Sistrunk procedure) including the central portion of the hyoid bone to prevent recurrence.
- Antibiotics if infection is present.
Memory Aid
“TONGUE”
- T: Thyroid tissue (small risk of thyroid carcinoma)
- O: Oval shape
- N: Near hyoid bone (infrahyoid most common)
- G: Gross movement with swallowing
- U: Ultrasound first
- E: Excision (Sistrunk procedure)