Head and Neck Embryology

Question 1

Ectoderm

Answer 1

nervous system, skin (epidermis and appendages), neural crest cells and derivatives

Question 2

Mesoderm

Answer 2

bone, cartilage, muscles, connective tissue (dermis), dura mater, heart, vessels, blood, reproductive organs, genitourinary system

Question 3

Endoderm

Answer 3

GI and respiratory lining, digestive organ parenchyma

Question 4

Neural crest cells

Answer 4

Ectodermal origin; pluripotent; migrate along cleavage planes, differentiate into connective, muscle, nervous, endocrine, and pigmentary tissues, induce differentiation of the tissue they invade

Question 5

Pharyngeal (branchial) arches (definition and origin, not specific derivations)

Answer 5

from migrating NCCs and surrounding pharyngeal endoderm and mesoderm; different from somites; separated by pharyngeal grooves on the external surface and pharyngeal pouches on the internal surface; grooves and pouches are separated by mesoderm; each arch has nervous, arterial, muscular and bony components

Question 6

Somites

Answer 6

mesodermal swellings around the neural tube

Question 7

Pharyngeal/Branchial Arch I

Answer 7

N: CN V
A: Maxillary artery
B: Greater wing of sphenoid, malleus, maxilla, zygomatic, temporal (squamous), mandible
M: Muscles of mastication, anterior digastric, mylohyoid, tensor tympani, tensor veli palatini
Ear: forms anterior hillocks (tragus, root of helix, superior helix)

Question 8

Pharyngeal/Branchial Arch II

Answer 8

N: CN VII
A: Stapedial artery (corticotympanic)
B: Stapes, styloid process, stylohyoid ligament, lesser horn and upper body of horn
M: Muscles of facial expression, posterior digastric, stylohyoid, stapedius
Ear: posterior hillocks (antitragus, antihelix and lobule)

Question 9

Pharyngeal/Branchial Arch III

Answer 9

N: CN IX
A: Common carotid, proximal internal carotid
B: Greater horns and lower body of hyoid
M: Stylopharyngeus

Question 10

Pharyngeal/Branchial Arch IV/VI

Answer 10

N: CN X
A: Aortic arch, right subclavian, origin of pulmonary arteries, ductus arteriosus
B: laryngeal cartilages
M: Pharyngeal constrictors, levator veli palatini, palatoglossus, striated upper esophageal muscles, laryngeal muscles

Question 11

Pharyngeal Groove(Cleft) I

Answer 11

becomes external auditory canal, mesoderm becomes tympanic membrane

Question 12

Pharyngeal Groove II-IV

Answer 12

operculum flap grows downward from arch II and fuses below cleft IV to create cervical sinus
Anomalies from groove II are the most common

Question 13

Pharyngeal grooves (clefts)

Answer 13

Failure to obliterate can lead to cysts (sealed in neck), sinuses (end in blind sac) or fistulas (connect with pharynx; often detected in the second decade of life and palpable at the anterior border of the SCM

Question 14

Pharyngeal Pouch I

Answer 14

Internal auditory canal

Question 15

Pharyngeal Pouch II

Answer 15

Palatine tonsil

Question 16

Pharyngeal Pouch III

Answer 16

inferior parathyroid and thymus

Question 17

Pharyngeal Pouch IV

Answer 17

Superior parathyroid (migrates above pouch III)

Question 18

Pharyngeal Pouch V

Answer 18

Ultimobranchial body (thyroid C cells)

Question 19

Intramembranous ossification

Answer 19

cartilaginous precursors resorb; mesenchymal cells directly differentiate into osteoblasts without cartilaginous intermediate

Question 20

Endochondral ossification

Answer 20

cartilaginous template is directly and gradually replaced with a bony matrix

Question 21

Neurocranium

Answer 21

portion of the skull encasing and protecting the brain

Question 22

Membranous neurocranium

Answer 22

forms via intramembranous ossification of neural crest origin, includes paired frontal, squamosal, and parietal bones, and upper occipital bone

Question 23

Cartilaginous neurocranium

Answer 23

forms via endochondral ossification of mesodermal origin, includes sphenoid and ethmoid bones, mastoid and petrous temporal bone, and the base of the occipital bone

Question 24

Viscerocranium

Answer 24

bones of the facial skeleton; forms via intramembranous ossification of pharyngeal arch I, except for Meckel’s cartilage (which forms the malleus and mandibular condyles)

Question 25

Craniosynostosis

Answer 25

sutures fuse prematurely, associated with FGFR and TGFßR and TWIST and Wnt pathways

Question 26

Virchow's Law (of skull)

Answer 26

After suture fusion, growth proceeds parallel to suture instead of perpendicular

Question 27

Five Prominences of the Face

Answer 27

Frontonasal (1), Maxillary (2), Mandibular (2)

Question 28

Frontonasal prominence

Answer 28

pulled ventrally and caudally, forming the forehead, nasal dorsum (apex), and medial and lateral nasal prominences

Question 29

Maxillary prominence

Answer 29

Migrate medially to form the secondary palate, lateral maxilla, and lateral lip

Question 30

Tessier number 3

Answer 30

Oblique facial cleft; Failure of fusion of the junction with the lateral nasal prominences forms the nasolacrimal groove and nasolacrimal duct system

Question 31

Mandibular prominence

Answer 31

Forms mandible, lower lip, and lower face

Question 32

Prominent growth factors and signaling pathways

Answer 32

TGFß, BMP, FGF, IRF, Wnt, FOXe1

Question 33

Teratogens affecting Sonic Hedgehog Pathway

Answer 33

retinoids, alcohol, drugs that affect cholesterol synthesis and transport

Question 34

Stomodeum

Answer 34

primitive mouth forms at 3-4 weeks from invagination of the ectoderm around the buccopharyngeal membrane

Question 35

Unilateral cleft lips

Answer 35

result from failure of fusion of the medial nasal prominence and a maxillary prominence

Question 36

Tessier Cleft 7

Answer 36

Cleft at the lateral oral commissure, results from failure of fusion of the maxillary and mandibular prominences

Question 37

Tessier Cleft 0

Answer 37

median cleft lips are rare and result from failure of the medial nasal prominences to fuse

Question 38

Tessier Cleft ?

Answer 38

central defects of the lower lip and chin result from failure of the mandibular processes to fuse

Question 39

Primary Palate and Cleft

Answer 39

5-6 weeks, medial nasal prominences come together to form the primary palate, midmaxilla, and septum; cleft results from failure of fusion of the medial and lateral palatine processes

Question 40

Secondary Palate and Cleft

Answer 40

9-12 weeks, lateral palatine shelves initially hang vertically but assume a horizontal position as the tongue drops with mandibular growth; right palate drops first, which explains higher incidence of cleft palate on the left side; cleft results from failure of fusion of the lateral palatine process with the nasal septum

Question 41

Incisive foramen

Answer 41

Lies between the primary and secondary palate

Question 42

Epstein pearls

Answer 42

along the median raphe or junction of the hard/soft palates result from cystic degeneration of epithelial lining at edges

Question 43

Nasopalatine duct cysts

Answer 43

at the incisive foramen result from epithelial entrapment at the junction of developing primary/secondary palates

Question 44

Thyroid

Answer 44

from endodermal proliferation at foramen cecum of tongue, descends with a trailing diverticulum to final position distal to cricoid cartilage

Question 45

Thyroglossal duct cysts

Answer 45

may form anywhere along the path of the thyroid, presenting as painless midline (or near midline) neck mass, may rupture and result in sinus or fistula formation; treat with sistrunk procedure (removal of cyst and central hyoid bone)

Question 46

Lingual thyroids

Answer 46

result from failure of thyroid descent

Question 47

Anterior 2/3 of tongue

Answer 47

Originates from pharyngeal arch I and is innervated by lingual nerve CN V3

Question 48

Posterior 1/3 of tongue

Answer 48

Originates from arches III and IV (these overtake arch II) and is innervated by CN IX and X

Question 49

Tongue muscles

Answer 49

Arise largely from occipital myotomes (CN XII) except for palatoglossus (CN X)

Question 50

External Ear

Answer 50

Forms at interface between pharyngeal arches I and II

Question 51

Arch I

Answer 51

Forms anterior hillocks (tragus, root of helix, and superior helix)

Question 52

Arch II

Answer 52

Forms three posterior hillocks (antitragus, antihelix, lobule)

Question 53

Groove I

Answer 53

lies between arches I and II and forms external auditory canal

Question 54

Medial nasal prominence

Answer 54

Primary palate, midmaxilla, midlip, philtrum, central nose, and septum

Question 55

Lateral nasal prominence

Answer 55

Nasal ala