THYROGLOSSAL DUCT CYST
The thyroid gland begins developing about day 24 of gestation on the floor of the pharynx in the midline between the 1st and 2nd branchial arches.
As the embryo elongates and the tongue grows, the thyroid descends from its location at the base of the tongue. The thyroid remains connected to the
tongue by the fibrous thyroglossal duct, and the indentation which develops at the base of the tongue by the downward growth of the thyroid is called
the foramen cecum. The thyroid reaches its normal final location in the lower neck by seven weeks of gestational age. The foramen cecum persists as the
proximal remnant of the thyroglossal duct at the base of the tongue. A middle or pyramidal lobe of the thyroid persists as the distal remnant of the
thyroglossal duct in about 50% of the population. The path of thyroid migration extends from the base of the tongue through the region of future hyoid
bone just above the thyroid cartilage, and down the anterior neck. Rests of thyroid tissue may remain anywhere along the path of migration, and resulting
cysts may form anywhere along that path. Less often, a cyst can form within the base of the tongue causing difficulty swallowing. Rarely the thyroid fails
to migrate and a lingual thyroid results. This should always be removed as complications are frequent but thyroid replacement is easy and safe.
The typical thyroglossal cyst occurs just anterior to the hyoid bone high in the midline anterior neck. It may remain quiescent for years before suddenly
enlarging or becoming infected. It is not unusual for a previously unsuspected mass suddenly to enlarge to marble size or greater and then shrink with
time and antibiotics to a tiny but palpable mass. An abscessed thyroglossal cyst should be incised and drained, then resected at least six months later,
after the inflammation has resolved. Recurrent infection during the intervening time should be immediately treated with antibiotics.
Years ago, Dr. Sistrunk noted that resecting the center portion of the hyoid bone along with the cyst greatly reduced the risk of recurrence, and the
procedure in which both the cyst and the bone are removed bears his name. Recurrence is also common if the cyst had previously been infected, even if the
infection had been adequately treated. Removal of an uninfected thyroglossal cyst is generally recommended at the time of diagnosis or as soon thereafter
as is reasonable. It is performed as an outpatient procedure and is remarkably well tolerated.
The differential diagnosis of midline upper anterior cervical masses is short. Lymphadenopathy rarely occurs directly in the midline. Epidermal inclusion
cysts may occur anywhere on the body, and if one occurs in this location it might be mistaken for a thyroglossal cyst. Ultrasonography is not helpful.