Thyroid gland

General Information:

• Begins in the floor of the pharynx as an invagination at the foramen cecum.
• Descends inferiorly to its final position alongside the larynx.
• May be connected to the foramen cecum by the thyroglossal duct (which normally atrophies and disappears, remnants may persist and form cysts).
• Divided into 2 lateral lobes connected by an isthmus, from which a pyramidal lobe sometimes develops.
• Follicular cells are derived from the endoderm, parafollicular cells are derived from the ultimobranchial body.

Pharyngeal Pouch Abnormalities

Ectopic thyroid

• Thyroid tissue in an aberrant location.
• Often the only thyroid tissue in the affected person.
• Susceptiblscated at the base of the tongue (lingual thyroid).
• Common locations include:

1. Lingual thyroid.
2. Sublingual thyroid.
3. Thyroglossal duct remnant.
4. Anterior mediastinum.
5. Prelaryngeal.
6. Intralingual.
7. Intratracheal.

Pharyngeal Arch Abnormalities

PIERRE ROBIN

• First reported as a condition characterized by micrognathia, cleft palate, and glossoptosis.
• Now includes any condition with a series of anomalies caused by events initiated by a single malformation.
• In this micrognathia, the inferior dental arch is posterior to the superior arch.
• The clefting may affect the hard and the soft palate.
• Glossoptosis (posterior displacement of the tongue) may cause airway obstruction or apnea.
• The mandible usually grows fairly quickly during childhood.
• Multiple surgeries typically needed to correct the cleft palate and to aid speech development in children.

TREACHER COLLINS 

• A hereditary condition affecting the head and neck.
• caused by haploinsufficiency of the gene TCOF1 (Treacher Collins-Franceschetti syndrome 1) which is officially known as Treacle Ribosome Biogenesis Factor 1.
• The gene product is the treacle protein, which contributes to development of cartilage and bone of the face.
• Children of an affected parent have a 50% risk of having the syndrome.
• Clinical manifestations include:

1. Downslanting eyes.
2. Incomplete orbits.
3. Notching of the lower eyelids.
4. Hypoplastic mandible.
5. Hypoplastic zygomatic bones (malar hypoplasia).
6. Underdeveloped or malformed ears or "sideburns," or both, are prominent.

• Common associated problems include:

1. Hearing loss.
2. Eating/breathing difficulties.
3. Cleft palate.

DIGEORGE SYNDROME

• A rare condition caused by a deletion on chromosome22, characterized by a wide array of clinical manifestations.
• possible explanation: proper development is dependent on migration of neural crest cells to the area of the pharyngeal pouches.
• A lthough researchers decribed the syndrome as abnormal development of the 3rd and 4th pharyngeal pouches, defects involving the 1st to the 6th pouches have been observed.
• Thus, the affected individual is born without a thymus and parathyroid glands.
• Possible associated problems include:

1. Congenital heart defects (such as tetralogy of Fallot, right infundibular stenosis, truncus arteriosus, aberrant left subclavian artery, and ventricular septal defect).
2. Facial defects (such as cleft palate, microstomia, downslanting eyes, low-set ears, or hypertelorism).
3. Increased vulnerability to infections (due to impaired immune system from the loss of T cells associated with absence or hypoplasia of the thymus).