Thyroid dysgenesis
Encyclopedia
Thyroid agenesis is a cause of congenital hypothyroidism
where the thyroid
is missing, ectopic, or severely underdeveloped.
It should not be confused with iodine deficiency
, or with other forms of congenital hypothyroidism
where the thyroid is present but not functioning correctly.
Congenital hypothyroidism caused by thyroid dysgenesis can be associated with PAX8
.
A completely ectopic thyroid gland may be located anywhere along the path of the descent of the thyroid during its embryological development, although it is most commonly located at the base of the tongue, just posterior to the foramen cecum of the tongue
. In this location, an aberrant or ectopic thyroid gland is known as a lingual thyroid. If the thyroid fails to descend to even higher degree, then the resulting final resting point of the thyroid gland may be high in the neck, such as just below the hyoid bone
.
Parts of ectopic thyroid tissue ("accessory thyroid tissue") can also occur, and arises from remnants of the thyroglossal duct
, and may appear anywhere along its original length. Accessory thyroid tissue may be functional, but is generally insufficient for normal function if the main thyroid gland is entirely removed.
Congenital hypothyroidism
Congenital hypothyroidism is a condition of thyroid hormone deficiency present at birth. Approximately 1 in 4000 newborn infants has a severe deficiency of thyroid function, while even more have mild or partial degrees. If untreated for several months after birth, severe congenital hypothyroidism...
where the thyroid
Thyroid
The thyroid gland or simply, the thyroid , in vertebrate anatomy, is one of the largest endocrine glands. The thyroid gland is found in the neck, below the thyroid cartilage...
is missing, ectopic, or severely underdeveloped.
It should not be confused with iodine deficiency
Iodine deficiency
Iodine is an essential trace element; the thyroid hormones thyroxine and triiodotyronine contain iodine. In areas where there is little iodine in the diet—typically remote inlandareas where no marine foods are eaten—iodine deficiency gives rise to...
, or with other forms of congenital hypothyroidism
Congenital hypothyroidism
Congenital hypothyroidism is a condition of thyroid hormone deficiency present at birth. Approximately 1 in 4000 newborn infants has a severe deficiency of thyroid function, while even more have mild or partial degrees. If untreated for several months after birth, severe congenital hypothyroidism...
where the thyroid is present but not functioning correctly.
Congenital hypothyroidism caused by thyroid dysgenesis can be associated with PAX8
PAX8
Paired box gene 8, also known as PAX8, is a protein which in humans is encoded by the PAX8 gene.- Function :This gene is a member of the paired box family of transcription factors. Members of this gene family typically encode proteins which contain a paired box domain, an octapeptide, and a...
.
Ectopic thyroid
An ectopic thyroid is a form of thyroid dysgenesis in which an entire or parts of the thyroid located in another part of the body than what is the usual case.A completely ectopic thyroid gland may be located anywhere along the path of the descent of the thyroid during its embryological development, although it is most commonly located at the base of the tongue, just posterior to the foramen cecum of the tongue
Foramen cecum (tongue)
The dorsum of the tongue is convex and marked by a median sulcus, which divides it into symmetrical halves; this sulcus ends behind, about 2.5 cm from the root of the organ, in a depression, the foramen cecum , from which a shallow groove, the sulcus terminalis, runs lateral and anterior on either...
. In this location, an aberrant or ectopic thyroid gland is known as a lingual thyroid. If the thyroid fails to descend to even higher degree, then the resulting final resting point of the thyroid gland may be high in the neck, such as just below the hyoid bone
Hyoid bone
The hyoid bone is a horseshoe-shaped bone situated in the anterior midline of the neck between the chin and the thyroid cartilage. At rest, it lies at the level of the base of the mandible in the front and the third cervical vertebra behind.Unlike other bones, the hyoid is only distantly...
.
Parts of ectopic thyroid tissue ("accessory thyroid tissue") can also occur, and arises from remnants of the thyroglossal duct
Thyroglossal duct
The thyroglossal duct is an embryological anatomical structure forming an open connection between the initial area of development of the thyroid gland and its final position....
, and may appear anywhere along its original length. Accessory thyroid tissue may be functional, but is generally insufficient for normal function if the main thyroid gland is entirely removed.