Thyroglossal duct

The most common congenital malformation in the neck

Pathophysiology

• Arise as a cystic expansion of a remnant of the thyroglossal duct tract, which has not completely obliterated, leaving behind epithelial duct cells
• Not usually clinically significant or even detectable; an autopsy study showed a 7% incidence of cyst, which is obviously far more common than it clinically comes to light
• Can occur anywhere along the thyroglossal duct tract, but 60% are between thyroid and hyoid
• Malignant transformation can occur
  • PTC is most common, followed by FTC and SCC

Presentation

• Presents as either mass or infection
• Classically move up and down with swallowing or protrusion of the tongue
• Mobile, soft, painless midline upper neck cystic structure

Investigation

• CT in adults or MRI in children
• NM thyroid study if ectopic thyroid tissue is suspected on CT
• FNA can be done to exclude thyroglossal duct cancer if clinically necessary based on imaging findings

Differential diagnosis

• Dermoid cyst
• Branchial cleft cyst
• Lipoma
• Ectopic thyroid

Management

• Infection
  • Manage with antibiotics then operate once infection has fully cleared
  • Incision and drainage if there is an abscess
• Uninfected
  • Remove all identified thyroglossal duct cysts (half become infected at some point, and 1-2% contain cancer, which is difficult to detect clinically)
• Non-surgical candidates
  • Percutaneous ethanol injection if cancer can be excluded based on imaging and FNA

Sistrunk procedure:

• Preparation:
• Principles:
  • En bloc resection of cyst and duct remnants, and part of hyoid if necessary
• Technique:
  • Elliptical transverse skin incision over sinus/cyst
  • Sub-platysmal flaps
  • Open midline raphe between straps
    • If there are chronic adhesions to surrounding tissues like straps, take a cuff to avoid leaving cyst behind
  • Dissect cyst and duct
    • Resect attachments to pyramidal lobe if present
    • Continue upwards until hyoid bone
  • Hyoid resection
    • Skeletonise the hyoid on location of planned cuts
    • Release infra-hyoid straps from underside for these areas
    • Clear posteriorly as well but don't enter pharynx
    • Divide just medial to lesser cornu on each side
    • Use bone cutters to excise this segment of bone, keeping it in continuity with the tract
  • Then grasp middle segment of cut hyoid with Allis and continue following up
  • Dissect to foramen caecum
    • May not be able to feel or see much above hyoid
    • Can have an assistant put a finger in the mouth and push the base of tongue
    • Ideally, ligate just below the foramen caecum
  • Haemostasis
  • Wash and leak test to exclude pharyngotomy
  • Small drain?
  • Reapproximate straps, platysma and skin
• Complications:
  • Lingual nerve injury
  • Recurrence
  • Hypothyroidism!