Pharyngeal Arches

Question 1

name the derivatives of the 1st arch

Answer 1

• nerve:
  
  • CN V2/V3
• skeleton:
  
  • malleus, incus, sphenomandibular ligament, maxillary process, mandible
• muscles
  
  • lat. and med. pterygoid, temporalis, masseter, tensor veli palatini, tensor tympani, ant. digastric, mylohyoid (MAST MATT)

Question 2

name the derivatives of the 2nd arch

Answer 2

• nerve:
  
  • CN VII
• skeleton:
  
  • stapes, styloid process, stylohyoid ligament, hyoid bone (lesser horn and upper body)
• muscles
  
  • stapedius, stylohyoid, posterior digastric
• artery
  
  • stapedial (atrophies before birth)

Question 3

name the derivatives of the 3rd arch

Answer 3

• nerve
  
  • CN IX
• skeleton
  
  • hyoid bone (greater horn and lower body)
• muscles
  
  • stylopharyngeus
• artery
  
  • common and internal carotid

Question 4

name the derivatives of the 4th arch

Answer 4

• nerve
  
  • CN X, vagus superior laryngeal branch
• skeleton
  
  • thyroid, cricoid, artyenoid, corniculate, cuneiform cartilages
• muscles
  
  • constrictor muscles of the pharynx, levator veli palatini, cricothyroid
• artery
  
  • arch of the aorta, right subclavian

Question 5

name the derivatives of the 6th arch

Answer 5

• nerve
  
  • CN X, vagus recurrent laryngeal branch
• skeleton
  
  • thyroid, cricoid, arytenoid, corniculate, cuneiform cartilages
• muscles
  
  • intrinsic muscle of the larynx, striated muscles of the esophagus
• artery
  
  • ductus arteriosus, pulmonary arteries

Question 6

name the groove derivative of the 1st pouch

Answer 6

external acoustic meatus

Question 7

name the derivatives of the 1st pouch

Answer 7

tubotympanic recess, middle ear cavity, mastoid antrum

Question 8

name the derivatives of the 2nd pouch

Answer 8

palatine tonsils, tonsillar fossa

Question 9

name the derivatives of the 3rd pouch

Answer 9

thymus, inferior parathyroid glands

Question 10

name the derivatives of the 4th pouch

Answer 10

superior parathyroid glands, ultimobranchial body (parafollicular cells of thyroid)

Question 11

describe Treacher Collins syndrome

Answer 11

first arch syndrome

• failure of migration of neural crest cells into the 1st arch
• micrognathia
• ~50% cleft palate
• underdeveloped zygoma
• conductive hearing loss
• malformed pinna
• drooping lateral part of lower eyelid

Question 12

describe Pierre Robin sequence

Answer 12

• micrognathia or retrognathia
• glossoptosis (tongue in pharynx that causes airway obstruction)
• cleft palate
  
  • problems with feeding and respiratory distress

Question 13

describe the development of the ear

Answer 13

• ear develops at first high up in the neck from 6 auricular hillocks
  
  • 3 from 1st arch
  • 3 from 2nd arch
• malformation of their development can lead to auriculuar sinuses and cysts
• with the development of mandible it migrates to its definitive position

Question 14

Answer 14

radiograph with contrast of a complete fistula

Question 15

explain what is seen

Answer 15

CT of a cervical cyst (B) that is anterior to SCM (s)

Question 16

describe DiGeorge syndrome

Answer 16

• deletion in long arm of chr. 22
• faulty migration of neural crest cells
• mainly lack of 3rd and 4th pouch
• CATCH-22
  
  • cardiac abnormalities
  • abnormal face
  • thymic hypoplasia/aplasia
  • cleft palate
  • hypocalcemia (parathyroid underdeveloped/not dev.)

Question 17

describe the development of the thyroid gland

Answer 17

• develops as an epithelial proliferation in the floor of the pharynx
  
  • NOT a pouch structure
• the bi-lobed thyroid gland descends anterior to the developing foregut down to its adult position around C5-T1