It is a cyst or congenital fistula. Thyroid develops from a blind hole of the tongue and in 6 weeks descends to the neck as an epithelial duct that eventually gets obturated and disappears. The thyroglossal cyst appears as a consequence of the incomplete reabsorption of the duct.
The congenital cyst is the most frequent. 50% of these cysts appear before the child becomes 10, and 65% of them before 20.
It is painless and looks like a lump just above Adam's apple and moves when the person swallows or puts their tongue out. It may get infected and then cause pain and burst creating a fistula (as it sometimes appears).
Up to 1% of the cases may become malignant.
The treatment is surgical. It requires a careful dissection of the cyst and its duct up to the base of the tongue, including the central part of the body of hyoid (cartilage) to prevent it from reappearing. 4% of the cases reappear due to an incomplete resection.
It is a congenital benign vascular (lymphatic system) tumour. These tumours are soft, multilobular and painless. They should be treated as soon as possible in order to prevent them from reappearing. The most common type is cystic hygroma.
Other neck midline cysts are:
The fetus, during the first stage of embryonic development, has gills. When there is an embryonic defect in the fusion of the branchial arches the child will develop a branchial cyst or fistula.
It is one of the most common congenital benign tumours that appear on the sides of the neck following the anterior edge of the sternocleidomastoid muscle, so it is a lateral cyst.
When they are of the first branchial arch (1-8%), they appear in the face (cleft palate, cleft lip) or related to the pinna.
The fistula of the first arch goes from the skin under the jaw, through the branches of the facial nerve and the parotid gland to the bottom of the ear canal.
The treatment is surgical and, since it touches the facial nerve, a parotidectomy incision must be practiced and the facial nerve must be located in order to protect it during the dissection of the fistula or the cyst.
The anomalies of the second, third and fourth arch result in a cyst or fistula on the line that goes from the ear to the sternum following the sternocleidomastoid muscle.
By far the most common are those related to the second arch. If the fistula is complete, it may reach the tonsil cavity. Those related to the third arch reach the thyroid membrane. Those related to the fourth arch end in the pyriform sinus and appear like low laterocervical abscesses or recurrent suppurative thyroiditis (infection of the thyroid gland). The latter have an innovative treatment that consists in locating through larynx microsurgery the orifice of the pyriform sinus and searing the tract through it, thus avoiding surgery.