A lump /mass on the neck - Thyroglossal cyst

Thyroglossal cyst

Definition

An epithelium lined cyst found along the course of descent of the thyroid gland.

Aetiology

The thyroglossal duct is a tract of embryonic mesoderm that originates between the 1^st and 2^nd branchial pouches, represented by the foramen caecum of the tongue. It descends to a pretracheal site during development to form the thyroid gland. The duct normally disappears in the 6^th week; however if some tissue remains at any point along its course, it may develop into a cyst.

Association/risk factor

1-2% of cases are associated with lingual or ectopic thyroid tissue. Very rare, familial variants (mostly autosomal dominant in a prepubertal girl.)

Epidemiology

Present in children or adolescents, mean age of presentation is 5 years (but can vary from 4 months to 70 years). Three time more common than branchial cyst.

History

A swelling or lump is noticed in the midline of the anterior neck (90%; 10 % can be lateral , with 95% of these on the left side.)

Mostly asymptomatic, but in 5 % of cases there may be tenderness or rapid enlargement due to infection.

Examination

Midline smooth rounded swelling, typically between the thyroid notch and hyoid bone , although sometimes found in submental region.

Moves upwards on protrusion of the tongue and with swallowing.

Can usually be transilluminated.

Differential diagnosis includes, lymph nodes, epidermal inclusion ( dermoid cyst ), salivary duct abnormality or ectopic thyroid tissue.

Pathology

Thyroglossal cysts can occur at any point along the thyroglossal duct path; with 75% pre- hyoid.The lining is none keratinising stratified squamous, columnar or cuboidal epithelium with mucoid material filling the cyst.

Investigation

None may be necessary for euthyroid patient (normal thyroid level)

If the cyst is supra hypoid, thyroid function tests and isotopes (99mTc) shoud be carried out to exclude a lingual thyroid as its removal may render the patient hypothyroid.

Ultrasound or MRI scan: To differentiate from other structures (cysts have a high signal on T2 weighing).

Management

Any acute infection is treated with antibiotics.

Surgical: Excision is carried out with the Sistrunk procedure (removal of the cyst and any duct remnant along with the central portion of the hyoid bone). Rarely, the tract may extend up to the tongue, requiring the removal the small portion of the tongue.

Complication

Infection is the most common complication. Thyroglossal sinus or fistula may develop after infection and spontaneous rupture, after attempted drainage or incomplete excision. Carcinoma in a thryoglossal duct cyst has rarely been described.

Prognosis

Good, but even with good technique, reccurence rates are 7-8% , more commonly following infection.