19 - Embryology of the Head and Neck II

Question 1

What is the location of the pituitary gland and what is it’s embryological origin?

Answer 1

• Sits in hypophyseal fossa of sella turcica in sphenoid bone

- Anterior: from ectoderm Rathke’s pouch so endocrine

- Posterior: from neuroectoderm infundibulum so neuroendocrine

Question 2

How does the pituitary gland form embryologically?

Answer 2

• Downward outgrowth of forebrain (infundibulum) to the roof of the pharynx
• Invagination of ectoderm at stomatodeum (Rathke’s) which grows dorsally towards forebrain
• Sphenoid bone ossifies and pinches off the Rathke’s pouch so it can join with the infundibulum, which is still connected to the forebrain by a stalk

Question 3

What are the two structures being pointed to on the tongue?

Answer 3

Foramen cecum: remnant of where the thyroid gland developed from

Sulcus terminalis: separates the two boundaries of the tongue

Question 4

How does the tongue form embryologically?

Answer 4

• Develops around the same time as the soft palate and recieves contributions from all 6 arches (6 insignificant)
• 2 lateral lingual swellings (arch 1) and 3 lingual swellings arches 1 to 4
• Lateral lingual swellings overgrow tuberculum impar and third arch overgrows cupola of 2nd arch
• Cell degeneration at floor of oral cavity leaving lingual frenulum so tongue can move freely

Question 5

What is the sensory innervation of the tongue and how does this relate to it’s embryological origin?

Answer 5

Mucosa of anterior 2/3: V and IX as from arch 1 and 3

Posterior 1/3: IX and X as from arch 3 and 4

Taste buds: special sensory from VII (chorda tympani)

Question 6

What is the motor innervation to the tongue and where does it come from embryologically?

Answer 6

XII - Hypoglossal

Occipital somites all migrate to the tongue to innervate intrinsic and extrinsic muscles

Question 7

Where does the primordium of the thyroid gland form?

Answer 7

Between the tuberculum impar and the cupola in an area called the foramen cecum so thyroid depends on tongue to develop

Question 8

How does the thyroid gland form embryologically?

Answer 8

• Gland differentiates and bifurcates as it descends so bilobed diverticulum joined by isthmus
• During descent thyroid remains connected to tongue by thyroglossal duct which degenerates at final positon

Question 9

What abnormalities can arise during the embryological development of the thyroid gland?

Answer 9

• Pyramidal lobe: 50% of population have third lobe as thyroglossal duct persists

- Thyroglossal cysts/fistula

- Ectopic thyroid tissue

Question 10

What embryonic structures contribute to the development of the face?

Answer 10

• FNP and 1st/2nd pharyngeal arches

Question 11

In general terms how does a cleft lip and palate form?

Answer 11

• Faliure of fusion of median nasal prominence from FNP and maxillary prominence
• Failure of palate shelves to form

Question 12

What is the importance of neural crest cells in the development of the face?

Answer 12

They populate the cartilage bars to make up the skeleton of the face, they are susceptible to alcohol and can lost in the body when migrating

Question 13

What is Treacher Collins Syndrome? (first arch syndrome)

Answer 13

• Failure of neural crest cells to populate 1st PA
• Defect in development of eyes, ears, mandible and palate
• Hypoplasia of mandible and maxilla with low set ears
• Autosomal dominant insufficiency of treacle involved in neural crest cell migration

Question 14

What is DiGeorge syndrome?

Answer 14

• Thymic aplasia and absence of parathyroid glands
• CATCH 22 deletion
• Disruption of 3rd and 4th PA
• Difficulty regulating Ca levels and infections

Question 15

What is CHARGE syndrome?

Answer 15

• CHD7 mutation that is normally needed for production of multipotent neural crest cells