Pathology

1. Thyroglossal cyst
   • Persistance of the thyroglossal tract (marks development of the descent of the thyroid)
   • at 4th week, thyroid appears as midline diverticulum and decends ventrally to the pharynx between the developing 2nd arch as a duct
   • Origin of the tract can persist as a midline dimple (foramen caecum) at the junction of the valate and filiform papillae of the tongue
2. Epidermiology
   • Rare
   • Worldwide distribution
   • Equally common in men and women
   • Rarely present at birth - 40% present in first decade and even present late in 9th decade
3. Pathological features
   • Lined by stratified squamous / ciliated pseudostratified columnar epithelium
   • May also contain thyroid or lymphoid tissue (which can undergo malignant change) - if malignancy occurs, usually of the thyroid papillary type

Approach

• As for neck examination

1. Inspect
   • Site of lump - 75% midline, 25% either a little to the side
   • Smooth, rounded
   • Associated thyroglossal sinus with seropurulent discharge (follows rupture or incision of a thyroglossal cyst)
   • Scars
2. Protrusion of the tongue
   • As patient to open mouth and stick tongue out as far as possible
   • If moves on protrusion, likely to be a thyroglossal cyst (cyst related to base of tongue by a patent / fibrous tract which runs through the central portion of the hyoid bone)
   • Lump from the thyroid does not move on protrusion of the tongue
3. Swallowing
   • Place glass of water in patients hands
   • Ask them to sip, hold, then swallow
   • If moves on swallowing, likely to originate from thyroid gland (due to pull of superior constrictor, and the fact that the thyroid lies within the pre-tracheal fascia)
4. Palpate (from the back)
   • Repeat protrusion and swallowing gently palpating cyst from heind to ensure diagnosis is correct

Completion

1. History
   • Concentrate on how lump affects life

Differential diagnosis

1. Thyroid nodules / masses / pyramidal lobe
2. Enlarged lymph nodes
3. Dermoid / epidermoid
4. Subhyoid bursae

Complications:

1. Infection
2. Thyroglossal sinus (from rupture of the cyst)
3. Maligancy (papillary thyroid cancer) 

Treatment of thyroglossal cyst

1. Surgical (Sistrunk operation) excision
   • Inject patent tract with dye at start of operation
   • Excise cyst and the tract which runs throught the central portion of the hyoid bone (which is also excised)
   • May have to dissect up to the foramen caecum
   • If central portion of the hyoid bone not excised. high incidence of recurrence