Embryology

Question 1

Abnormal ear shape or size

Answer 1

Microtia

Question 2

Agenesis of the ear

Answer 2

Anotia

Question 3

What are some causes of congenital neurosensory deafness?

Answer 3

• Abnormal development of cochlea, cranial nerve VIII or brain stem
• Rubella in first trimester will damage the organ of Corti in 30% of case

Question 4

What are some causes of congenital conduction deafness?

Answer 4

• Persistent meatal plug; seen in first arch syndrome
• Fixation of footplate of stapes
• Malleus and incus often involved in first arch syndrome

Question 5

Rare disorders where one or both eyes are small and absent.

Answer 5

Anopthalmia and microphthalmia

Question 6

Defective closure of the choroid or optic fissure.

Postioned in the infero-nasal quadrant, reflective of the location of the optic fissure during fetal development.

Answer 6

Congenital coloboma.

Question 7

Cloudy cornea from abnormally high intraocular
pressure usually due to malformed drainage apparatus. Genetic mutations
account for ~85% of cases. May also result from rubella infection.

Answer 7

Congenital glaucoma

Question 8

Cloudy or opaque lens. May be inherited, caused by rubella virus or a result of congenital galactosemia.

Answer 8

Congenital cataracts

Question 9

Surrounds the developing foregut. It is the source of mesenchymal tissue that will form the head & neck, face, palate & nasal cavity structures. Pouches are evaginations on this inside of this.

Answer 9

Pharyngeal apparatus

Question 10

What is formed from Meckel’s cartilage, all First Arch derivatives?

Answer 10

• Mandible
• Malleus
• Incus
• Spine of the sphenoid
• Sphenomandibular ligament

Question 11

First arch syndrome caused by deficiency of neural crest cells migrating into the arch. Results in mandibulofacial dystosis, abnormal first arch structures. Hypoplasia of upper and lower jaw. Conductive hearing loss.

Answer 11

Treacher Collins Syndrome

Question 12

First Arch Syndrome. Micrognathia + large posteriorly placed tongue resulting in airway obstruction.

Answer 12

Pierre Robin Sydrome

Question 13

What is formed from Reicherts cartilage?

Answer 13

• Stapes
• Styloid process
• Stylohyoid ligament
• Lesser cornu

Question 14

What is derived from the first pharyngeal pouch?

Answer 14

• Auditory tube (epithelial lining)
• Tympanic or middle ear cavity (epithelial lining)
• Mastoid air cells

Question 15

What is derived from the second pharyngeal pouch?

Answer 15

Palatine tonsils (epithelial component)

Question 16

What is derived from the third pharyngeal pouch?

Answer 16

• Thymus (ventral)
• Inferior parathyroid glands (dorsal); these have the farthest to travel, thus there terminal location is highly variable. Tough to locate surgically.

Question 17

What is derived from the fourth pharyngeal pouch?

Answer 17

• Superior parathyroid glands (dorsal)

- Ultimobranchial bodies (ventral) AKA parafollicular cells of the thyroid.

Question 18

Genetic and/or environmental micro deletion of Chr. 22q11.2 No thymus or parathyroids.
“CATCH 22” – a partial list of symptoms
Cardiac abnormality
Abnormal facies
Thymic hypoplasia
Cleft palate
Hypocalcemia
22 - deletion/abnormality of chromosome 22
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Answer 18

DiGeorge Syndrome.

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Question 19

What pharyngeal membrane (separates pouches from clefts) is the only one that persists?

Answer 19

1st membrane becomes the tympanic membrane.

Question 20

What are the muscles and nerve associated with the first pharyngeal arch?

Answer 20

Trigeminal nerve

• Muscles of mastication
• Tensor tympani
• Tensor veli palatini
• Mylohyoid
• Anterior belly of digastric

*Meckel’s cartilage

Question 21

What are the muscles and nerve associated with the second pharyngeal arch?

Answer 21

Facial nerve

• Muscles of facial expression
• Posterior belly of digastric
• Stylohyoid
• Stapedius

*Reichert’s cartilage

Question 22

What are the muscles and nerve associated with the third pharyngeal arch?

Answer 22

Glossopharyngeal nerve

-Stylopharyngeus

Question 23

What are the muscles and nerve associated with the 4th and 6th pharyngeal arch?

Answer 23

Vagus nerve

4th arch: Superior Laryngeal Nerve

• Muscles of the soft palate (except tensor veli palatini)
• Muscles of the pharynx (except stylopharyngeus)
• Cricothyroid
• Cricopharyngeus

6th arch: Recurrent branch of the laryngeal nerve

• Intrinsic muscles of the larynx (except cricothyroid)
• Striated (upper) muscles of esophagus

Question 24

What is derived from the first cleft?

Answer 24

External auditory meatus (epithelial lining)

Question 25

What happens to the 2nd, 3rd, and 4th clefts?

Answer 25

They normally disappear; lateral cervical (branchial) cyst or fistula occurs when it persists

Question 26

What pharyngeal arch is the tongue derived from?

Answer 26

Arches 1-4. This is why you get the innervations of Trigeminal, Facial, Glossopharyngeal, and superior branch of laryngeal nerve (vagus).