This midline neck lump is a thyroglossal cyst. The thyroid gland appears as an epithelial proliferation in
the floor of the pharynx between the tuberculum impar and copula during the 4th week of development. In the
fully developed foetus this site is marked by the foramen caecum at the junction of the anterior 2/3 and the
posterior 1/3 of the tongue. From this site the thyroid gland descend anterior to the pharynx closely related to
the hyoid bone. It reaches it's final position in front of the tracheal cartilages during the 7th week of
development. During descent the gland remains connected to the base of the tongue by the thyroglossal duct that
later disappears in most individuals.
Several aberrations can occur in the development of the thyroid gland. A cystic remnant of the thyroglossal
duct can persist causing a thyroglossal cyst. These can be found at any site in the path of descent of the
thyroid gland but are usually found in close relationship to the hyoid bone. Rupture of thyroglossal cyst can
result in a thyroglossal sinus. These are often erroneously termed thyroglossal fistulae. A thyroglossal fistula
between the base of the tongue and neck skin due to persistence of the entire thyroglossal duct is very
uncommon. Failure of decent of all or part of the thyroid gland results in aberrant thyroid tissue most commonly
in the base of the tongue as a lingual thyroid. 75% of such patients have the entire gland in the aberrant site.
25% have some thyroid tissue at the normal location.
Over 40% of thyroglossal cysts appear in childhood. The remainder can occur at any stage in adult life
including old age. Despite their congenital origin they are rarely present at birth. Most are found close to, if
not always exactly in, the midline. Over 50% are closely associated with the hyoid bone. They usually present as
a painless midline neck lump. They may first become apparent when they become infected in which case sudden
onset of a painful, tender lump can be the presenting feature. They are often fluctuant but rarely
transilluminate. They can be easily moved from side to side but not up and down. The characteristic physical
sign that they display is elevation on protrusion of the tongue. This is not a sign seen with other thyroid
nodules. Histologically the cyst is lined by stratified squamous or ciliated pseudostratified columnar
epithelium. Thyroid or lymphoid tissue is frequently found in the cyst wall. The thyroid tissue is frequently
dysplastic with an increased risk of malignancy.
The classic operation described for a thyroglossal cyst is Sistrunk's Operation. With the neck extended a
transverse skin incision is made and platysma flaps elevated. These are retracted with a Joll's retractor. The
cyst and any associated tract are mobilised. The tract is dissected between the infrahyoid muscles up to the
hyoid bone. The central portion of the bone is excised. If necessary the tract is traced upwards in to the base
of the tongue. Failure to excise the central portion of the hyoid bone results in an increased risk of
Brewis C, Mahadevan M, Bailey C M, Drake D P. Investigation and treatment of thyroglossal cysts in
children. J R Soc Med 2000; 93: 18-21.
A not so recent paper
Sistrunk W E. The surgical treatment of cysts of the thyroglossal tract. Arch Surg 1920; 71:121-122.