The thyroid gland develops from endodermal cells in the floor of the pharynx. It begins as a diverticulum on the dorsum of the tongue, which elongates to form the thyroglossal duct. The duct extends downward in front of the hyoid and thyroid cartilage, where it divides into two parts that form the thyroid lobes. The ultimobranchial body contributes parafollicular cells to the thyroid gland. The thyroglossal duct degenerates from the foramen cecum on the tongue down to the hyoid bone. Persistence of parts of the duct can lead to congenital anomalies like lingual thyroid or thyroglossal cysts.

1. Development of Thyroid Gland
• It is developed from endodermal cells of floor of
pharynx (area of developing tongue).
• It begins a diverticulum at dorsum of tongue
between tuberculum impar and hypobranchial
eminence.
• Elongation of thyroid diverticulum to form thyro-
glossal duct. It elongates downwards infront hyoid
and thyroid cartilage where it ends by dividing into
2 parts.
• Ultimobranchial body gives parafollicular cells to
thyroid gland. Dr. Sherif Fahmy

2. Dr. Sherif Fahmy
Foramen
cecum
Thyroglossal
diverticulum
Developing anterior
2/3 of tongue

3. Dr. Sherif
Fahmy
Thyroglossal
duct
Thyroid
gland
Developing
anterior 2/3 of
tongue

4. Dr. Sherif
Fahmy
Foramen
cecum
Degenerating
thyro-glossal
duct
Hyoid bone
Thyroid
cartilage
Levator glandulae
thyroidae
Pyramidal lobe
Lobe of
thyroid gland

5. Fate of Thyro-glossal Duct
• Upper end of the duct remains as foramen cecum
on dorsum of tongue.
• The duct degenerates from foramen cecum and
hyoid bone.
• The duct from the hyoid to divisions of the duct
form levator glandulae thyroidae and may be
pyramidal lobe.
• Divisions of the duct form lobes of thyroid gland
with isthmus inbetween.
• Ultimobranchial body forms parafollicular cells of
the gland.

6. Congenital Anomalies
• Thyroid agenesis: Failure of its formation.
• Lingual thyroid: Failure of thyroid descend.
• Aberrant thyroid (Retrosternal goiter): over-
descend of thyroid gland in the thorax.
• Thyroglossal cyst: It is persistence of a part of
the thyroglossal duct.
• Thyroglossal fistula: Thyroglossal duct opens
to skin.
Dr. Sherif Fahmy

7. Dr. Sherif
Fahmy

8. Dr. Sherif
Fahmy