Thyroglossal cyst

Section: Head and neck Curriculum: Curriculum, page 43

Definition

• Congenital epithelial cyst of thyroglossal tract remnants
• Midline neck lump in the anterior neck

Epidemiology

• Most common congenital neck cyst
• 7% of pop
• M=F
• Mainly infrahyoid - 60%

Relevant Embryology

• Week 3 thyroid commences development
• Median outgrowth from primitive pharynx (foramen caecum)
• Located at junction of ant ⅔ and post ⅓ tongue
• Thyroid descends in ant neck, anterior to hyoid and closely associated
• Week 7 it reaches the pretracheal position
• Thyroglossal duct (narrow tubular structure) follows thyroid down
• Connects foramen caecum to thyroid gland
• Distal part of it becomes the pyramidal lobe in 50% of people
• Week 10 usually the duct involutes

Pathology

• Failure of thyroglossal duct involution → Normally week 10
• Epithelial lining can secrete - causing inflammation and cyst formation

Classification

• Suprahyoid - 15%
• Level of hyoid 25%
• Infrahyoid - 60%

Clinical

• Asymptomatic
• Midline neck swelling
• Elevates with tongue protrusion
• Can be associated with infection/inflammation
• In context of URTI
• 1% risk of thyroid malignancy (papillary)

Investigations

• USS - good for cyst, not for relationship with hyoid bone
• CT/MRI - gives info about relationship with hyoid bone
• (?semantics as hyoid will come out anyways)
• TFT/USS/thryoid scan to ID ectopic thyroid tissue prior to sistrunk

Thyroid Ectopia

• 50% of pts with thyroglossal cyst have ectopic thyroid tissue
• Ectopic thyroid tissue most commonly
  • LINGUAL then
  • Thyroglossal cyst
• Can have associated hypothyroidism
  • Should be corrected pre-surgery
  • Identified by doing TFTs, USS and thyroid scan
  • Need to plan for this as if it is hyper/hypofunctioning and not responsive to medical therapy or has associated malignancy - needs resection too

Differential diagnosis

Central neck lump

• Congenital
  • Branchial cleft cyst
  • Dermoid Cyst
  • Cutaneous cysts
  • Epidermoid cyst
  • Thymic cyst
  • Ranula (plunging)
    • Pseudocyst in floor of mouth
    • Painless, blue and fluid filled
    • Obstruction of sublingual gland duct
    • Plunging if descending over edge of mylohyoid into submandibular space
    • Transoral sublingual gland excision or marsupialization and packing
• Inflammatory
  • LN
  • Bacterial
  • Viral
  • Parasitic
• Neoplastic
  • Benign
    • Thyroid nodule
    • Salivary gland cyst
  • Malignant
    • Primary
      • Thyroid cancer
      • Salivary gland tumour
    • Secondary
      • Lymphoma
      • SCC
      • Melanoma

Management

• Treat infection - abx and settle (oral flora) (communicates with tongue)
  • Augmentin
• Avoid I+D at all costs as it makes subsequent surgery very difficult
• Surgery
  • Sistrunk procedure
    • What is it
      • Thyroglossal cyst, duct and partial hyoid resection (pyramidal lobe)
    • When
      • Once infection has settled down
    • Rationale
      • Operate on all
      • Get recurrent infection
      • Particularly if they’ve had one bout already
      • Risk of malignancy
    • Goals
      • Complete excision of thyroglossal duct tract up to base of tongue
      • Superior and posterior to hyoid bone
    • Procedure
      • Setup - GA/IVabx, supine, shoulder roll, head ring, stand on right
      • Steps
        • Transverse incision over cyst
        • Subplatysmal flaps
        • Dissect cyst
        • Identify thyroglossal duct (posterosuperior to cysts)
        • Follow and mobilise duct until hyoid bone is reached
        • Divide muscle on sup and inf aspects of hyoid bone (diathermy)
        • Transect central hyoid bone with cutter 1-1.5cm
        • Continue duct dissection to floor of mouth
        • Depress tongue with hand in mouth to help
        • Ligate and transect duct at foramen caecum with vicryl
        • Layered absorbable closure