Prenatal Craniofacial Development

Question 1

Morphogenesis of the face is a complex

3D process involving (4)

Answer 1

patterning,

outgrowth, fusion and moulding of tissues

Question 2

~— days, head & neck region comprises ~ half of embryo.

Answer 2

22days

Question 3

During 4th week, ventral mesoderm condenses into a series

of

Answer 3

segmented bilaterally paired, mesenchymal swellings

Question 4

pharyngeal (branchial) arches

> ultimately — pairs, arising in — order

Answer 4

5

cranial-caudal

Question 5

Initially, five prominences (tissue masses) surround the

stomodeum:

Answer 5

Øfrontonasal prominence
Øfirst arch (> mandibular process)
Ømaxillary process (delayed appearance)

Question 6

First (mandibular) arch
and maxillary processes
are both — structures

Answer 6

paired
> grow ventro-laterally
around the OM

Question 7

The majority of the growth and morphological change

in facial tissue masses is driven by the

Answer 7

invading cranial

neural crest-derived mesenchyme.

Question 8

Contrary to textbook literature, the paired first pharyngeal
arches only give rise to the

Answer 8

mandibular processes.

Question 9

Maxillary processes originate as

Answer 9

separate (delayed)

swellings rostral to the mandibular processes.

Question 10

Maxillary processes originate as separate (delayed)
swellings rostral to the mandibular processes.
> Invaded by distinct population of

Answer 10

late migrating CNCC

Question 11

Formation and invagination of nasal placodes (thickening

of ectoderm) in

Answer 11

Frontonasal Prominence (FNP)
•Induction and invagination of nasal placodes similar to
neural plate induction and invagination

Question 12

Two types of morphological processes for ‘joining’ tissues

Answer 12

merging

fusion

Question 13

1st: Merging

Answer 13

joining of two masses already partly in contact

Question 14

merging examples (2)

Answer 14

• Merging of Maxillary (MXP) & Lateral Nasal Processes (LNP)

* Medial merging of Mandibular Processes (MNP)

Question 15

2nd: Fusion

Answer 15

joining of two separate tissue masses

Question 16

fusion example

Answer 16

•Contact-dependent fusion between MNP and MXP/LNP

ØForms the primary palate and nares (nostrils)

Question 17

Secondary palate (future roof of mouth)
arises later from the medial aspects of the
MXPs >

Answer 17

palatal shelves

Question 18

After immigration of 
cranial neural crest cells, 
growth & morphogenesis 
of the face is controlled 
by

Answer 18

ongoing epithelial-

mesenchymal interactions

Question 19

Cranial neural crest cells (CNCC) primarily determine

Answer 19

facial form/shape

Question 20

The Ectoderm in Growth & Patterning

•defined boundaries of

Answer 20

expression in facial ectoderm

Question 21

skipped
Neural expression of Shh/Fgf8 precedes (and is
required for) the ectodermal expression: (3)

Answer 21

•juxta-positioned FGF8/SHH
» frontonasal ectoderm zone (FEZ)
•transplanted ectoderm retains FGF8/SHH pattern of
expression from originating tissue.
•Secreted factors from the FEZ can direct outgrowth of
the underlying CNCC and determines D-V pattern of the FNP
Øbut precise shape depends upon pattern
information inherent in the neural crest.

Question 22

A Dynamic Ectoderm (3)

Answer 22

support and direct outgrowth of the facial processes
guides differentiation of CNC
facilitating timely fusion of the facial processes

Question 23

interrelationship between the

Answer 23

CNC and ectoderm

Question 24

facilitating timely fusion of the facial processes

fusion establishes the

Answer 24

primary palate

goes on to form the alveolus and lip proper

Question 25

Third most common birth defect (~1 in 700 births worldwide)

Answer 25

Cleft lip +/- cleft primary palate

Question 26

Cleft lip +/- cleft primary palate | Embryological origin? (2)

Answer 26

ectodermal or CNCC

Question 27

Cleft lip +/- cleft primary palate | What else may be affected?

Question 28

Cleft lip +/- cleft primary palate What is impact on ongoing development of the face (2) and ultimately function (3)

Answer 28

growth, ossification feeding, breathing, oral hygiene

Question 29

The Secondary Palate (2)

Answer 29

•Palatal shelves (condensations of CNCC mesenchyme) •Secondary palate forms well after the primary palate/lip (10th week vs 7th week)

Question 30

Ossification of the secondary palate (osteoblasts derived from CNCC) begins just before

Answer 30

palatal development complete

Question 31

formation of the secondary palate (3)

Answer 31

1. Growth (either side of tongue) 2. Elevation & rotation 3. Medial growth & fusion at midline and with nasal septum

Question 32

cleft secondary palate prevalence

Answer 32

~1 in 1000 births world-wide

Question 33

cleft secondary palate can result from (3)

Answer 33

1) poor growth of shelves, 2) failed elevation, or 3) failed fusion

Question 34

Critical that tongue lowers to allow the shelves to rotate to a position

Answer 34

above the tongue

Question 35

--- (enlarged tongue) can provide a physical barrier to secondary palate closure

Answer 35

Macroglossia

Question 36

Small or retrognathic mandible also associated with

Answer 36

failed palatal fusion (Pierre-Robin sequence) | > Tongue forced backward and elevated

Question 37

Craniofacial cartilage first appears in the --- and | shortly thereafter in the (2)

Answer 37

mandible midface and cranial base

Question 38

Craniofacial cartilage first appears in the mandible and | shortly thereafter in the midface and cranial base (2)

Answer 38

> Provides structural support for shaping the growing head > Precedes ossification [NB: in the face, few cartilages are replaced by bone unlike the axial skeleton (ie. long bones)]

Question 39

•Cartilage of PA1 (Meckel’s cartilage) arises during

Answer 39

7th week (human) > forms template for the mandible. (E11.5 in mice)

Question 40

•PA1 also contributes to

Answer 40

two ear ossicles | > parts of malleus and incus (and ligaments)

Question 41

BUT, like most facial cartilages, most is not converted to ---.

Answer 41

bone

Question 42

Rather... parts ---, with caudal | aspects forming part of middle ear bones.

Answer 42

degenerate

Question 43

Development of the Ear is formed independent from

Answer 43

embryonic structures

Question 44

External and middle ear: (2)

Answer 44

* Derivatives of PA1 and PA2 * Intervening pharyngeal cleft * Pharyngeal pouch

Question 45

nner ear: | •Arises from

Answer 45

thickening of ectoderm (otic placode) dorsal to PA3 at level of hindbrain and subsequent invagination (otic pit)

Question 46

``` **Inner and outer ear malformations often associated with --- defects ```

Answer 46

mandibular

Question 47

Knowledge of the embryological origins of clinical presentations is important to appreciate the totality of the patient’s problem as it may: (3)

Answer 47

* merit additional clinical considerations * prompt more detailed assessment * impact treatment plans

Question 48

What might seem causally unrelated may in fact | be of clinical significance

Answer 48

> diagnosis