Thyroglossal Cyst

Fig.1: Thyroglossal duct cyst in typical siteThe thyroid gland is the first of the body's endocrine glands to develop, beginning in the third week of gestation, even before the nervous system has begun development. It develops at the base of the tongue, at an area called the foramen caecum, and descends in front of the pharyngeal gut along the thyroglossal tract. During this migration the thyroid is still connected to the tongue via the thyroglossal duct. This tubular duct later solidifies and subsequently obliterates entirely.

Further descent of the thyroid gland carries it anterior (in front) to the hyoid bone and, subsequently, anterior to the cartilages of the larynx (voicebox). As the thyroid gland descends, it forms its adult shape, with an isthmus connecting the two lateral lobes (see Anatomy).

The thyroid gland tissues merge and migrate to their final location, in front of the trachea (windpipe) by day 45-50. 

If the thyroglossal duct fails to obliterate completely the remnant can present as a thyroglossal duct cyst (Fig. 1). While half of these generally midline cystic masses are located at or just below the level of the hyoid bone (a small horseshoe-shaped bone that floats in the neck muscles under the tongue), they may be located anywhere from the thyroid cartilage right up to the base of the tongue.

Presentation

Fig.2: Thyroglossal cyst resting on the top of the thyroid cartilage in the midlineThyroglossal cysts usually present with a palpable (able to be felt) asymptomatic midline neck mass at or below the level of the hyoid bone, above the thyroid cartilage (Adam's apple) (Fig. 2). The neck lump is most often in the midline, although often may present slightly off the midline to one side or the other. They may present in childhood (less than 50%) or later in life, usually as a young adult below the age of 20 years.

Characteristically on examination, they move up when the tongue is protruded, reflecting the attachment of these cysts to the base of the tongue by the thyroglossal tract. Some patients have neck or throat pain, or dysphagia (difficulty swallowing), but usually most patients are just concerned by the lump in their neck and have no other symptoms. 

Fig.3: Infected thyroglossal cystIf the cyst becomes complicated the presentation may be different. If the cyst ruptures, it may form a thyroglossal duct sinus or a thyroglossal duct fistula that exits through the overlying skin. Typically there is a midline opening on the skin that discharges mucus.

The cyst may become infected, presenting with redness and swelling (Fig. 3), and there is a small risk of a malignant thyroid tumour (PTC) arising in the wall of the cyst.

Investigation

Usually the diagnosis is made by clinical examination alone, but ultrasound can help to confirm the clinical suspicion, showing a cystic (fluid-filled) structure around the hyoid bone (Fig. 4). FNA (fine needle biopsy) is not required for these patients.

Fig.4: Ultrasound of a thyroglossal cyst (arrowed), lying close to the hyoid bone, with a tract heading superiorly (to the left)Treatment

Fig.6: Typical thyroglossal cyst with the hyoid remnant (at the top of picture) removed at Sistrunk procedureManagement of thyroglossal duct cyst is surgical removal by an operation called Sistrunk's procedure, named after Dr. Walter Ellis Sistrunk who described the procedure in 1920. This involves an incision over the cyst itself, removal of the cyst and all of the accompanying thyroglossal duct up to the base of the tongue (Figs 5 & 6).

Fig.5: Sistrunk operation to remove the (collapsed) cyst (arrowed) and part of the hyoid bone above itThe important thing about this operation is that the thyroglossal duct goes either just above, just below, or right through the hyoid bone. This means that the central part of the hyoid bone must also be removed, because of this firm attachment. This will minimise the risk of recurrence. 

Because of the risk of infection and rupture, which makes a successful operation more difficult and the cyst prone to recurrence, it is best to just get on and remove the cyst once the diagnosis is made.