Development of Face and palate

Development of Face - Commencement

• Begins at week 4 of development

• Development is centered around

stomodeum (primitive mouth), which is:

- an external depression of surface

ectoderm beneath rostral brain vesicle

- Its floor is occupied by oro-pharyngeal

or bucco-pharyngeal membrane

- Oropharyngeal membrane marks

external limit of the foregut

Stomodeum - boundaries

• 5 initial primordia from neural crest

mesenchyme surround stomodeum

• One median, and 2 pairs of bilateral

prominences

1. Single frontonasal prominence

(FNP)

– composed of the tissue that

surrounds the forebrain

– forms forehead, dorsum and apex of

the nose

2. paired maxillary

prominences

– Will form upper cheek, and

upper lip

3. paired mandibular

prominences

– Will form lower cheek, chin, and

lower lip

Caudal boundary of stomodeum

• Caudal limit of

stomodeum is

formed by

pericardium of the

developing heart

• In later

development heart

descends into

thorax

How Prominences Arise

• Recall that ectomesenchyme forms mostly

from neural crest cells, and paraxial mesoderm

• In specific locations of the head and neck

region, ectomesenchyme proliferates to raise

the surface ectoderm

• Localized proliferation results from specific

GDFs that facilitate ectodermal-mesenchymal

interactions

• The raised structures are called processes/

prominences

OLFACTORY PLACODES (OP)

• Earliest change in FNP occurs

with bilateral thickening of

ectoderm to form olfactory

placodes

• Localized thickenings are also

called nasal placodes

• Ectoderm of placodes will line

the nasal cavities

• Placodes are pushed medially as

development proceeds

Development of the Nose (1)

• During week 5 the nasal

placodes invaginate becoming

nasal pits

• Horseshoe-shaped

prominences or ridges

develop around (invaginations

of the) nasal pits

When nasal pits deepen, the

horseshoe-shaped ridges

become more prominent

• Ridge on outer edge of each

nasal pit is called lateral nasal

prominence (LNP)

• Ridge on inner edge of each

nasal pit is called medial nasal

prominence (MNP)
Maxillary processes grow larger

and medially

• They push medial nasal processes

(MNPs) towards each other in the

midline where they will fuse

• In doing so, a groove b/n each

MNP and Maxillary (blue arrows)

process is overgrown

• Hence, maxillary process merges

with MNP on either side

Development of Nose (4)

• Lower part of fused MNPs forms

philtrum

• Philtrum forms medial part of upper

lip

• Lateral parts of upper lip forms from

maxillary processes

• Lateral nasal processes, pushed up

by medially advancing maxillary

processes form alae (sides) of nose

Arhinia

• Arhinia is congenital partial or complete

absence of nose at birth

• Extremely rare condition

• Generally classified as a craniofacial

abnormality

• Occurs with varying degrees of severity

• May require surgical insertion of a

tracheostomy tube to facilitate breathing

Formation of the mouth

• The external opening of mouth

(commissure) is formed by fusion of lateral

edges of maxillary and mandibular

prominences (arrows)

• Excessive fusion results in microstomia –

smaller than normal oral commissure

• Failure or sub-optimal fusion results in

macrostomia – wider than normal oral

commissure

Development of face

• Developing orbits (lens

placode) appear in angle b/n

FNP and maxillary process

on either side (blue arrows in

diagram)

• Mandibular processes (lower

green in diagram) merge in midline

to form lower lip, chin, and

mandible

Labiogingival lamina

• At first ectoderm and underlying

mesenchyme of lips are attached

• Lips are free by ectodermal ingrowth

(known as labiogingival lamina) into

mesenchyme of gums

• Labiogingival lamina later

degenerates to separate lips from the

gums

• Midline remnant of labiogingival

lamina forms labial frenulum

Development of face

• Forehead formed by upper

broader part of FNP

• Cheeks formed by broader

maxillary processes and upper

part of mandibular process

• Bridge of nose formed by

middle narrow part of FNP

• Crest and tip of nose formed

by compressed upper part of

MNP

Oronasal Membrane

• An oronasal membrane forming floor of

nasal pit at first separates (nasal pit) from

pharynx

• The oronasal membrane breaks down to

allow continuity between the nasal pit and

the common oral and nasal cavities

Oropharyngeal Membrane

• At first floor of stomodeum is formed by

oropharyngeal or buccopharyngeal

membrane, which separates the primitive

mouth from pharynx

• Towards end of week 4, oropharyngeal

membrane breaks down to allow

continuity b/n stomodeum and pharynx

Development of Palate

• The MNPs contribute the tissues that

will form the anterior part of the palate,

the primary palate

• The four maxillary incisors develop

within the primary palate

The secondary palatal

processes originate as

horizontal shelves from

maxillary prominences on

either side

Secondary palatal processes grow

towards each other in midline (yellow

arrows in diagram)

• When they meet, there is fusion

with each other, the nasal septum,

and the primary palate

• Posterior extensions of secondary

palatal processes form the uvula

Malformations of face

• The most frequently occurring

congenital malformation of the face is

cleft in the lip and/or palate

• Occurs with 300+ different varieties

• Arises from failure or incomplete fusion

of prominences or processes involved in

formation of the face and/or palate

Clefts of lips or palate

• Median (1) –failure of fusion between free

edges of philtrum

• Unilateral or bilateral(2) cleft lip –failure of

fusion between maxillary and medial nasal

process on either or both side(s)

• Oblique facial cleft –imperfect fusion

between maxillary and lateral nasal process

• Cleft palate may occur alone or in

conjunction with cleft lip

Cleft Lip & Palate

• Cleft lip and palate develop between the 4th and 8th week of gestation and is

dominated by changes resulting in the formation of the nose.

• Palatal development occurs between the 7th and 12th week of gestation and

is divided into the formation of the primary palate (prolabium), premaxilla and

cartilaginous septum) and formation of the secondary palate (hard and soft

palate).

• 300+ different abnormalities

• different cleft forms and extent

• upper lip and ant. maxilla

• hard and soft palate

Kabuki Syndrome

• A rare (about 350 cases worldwide) genetic syndrome

• Gives a dysmorphic face: unusual eyes, large and low ears,

depressed nasal tip, arched eyebrows, cleft lip and palate.

• The main feature is mental retardation and major postnatal

growth retardation, skeletal abnormalities, unusual

dermatoglyphic (lines that form patterns on the skin, palms and

soles) patterns and a range of other multisystem disorders

Fetal Alcohol Spectrum Disorders

(FASD)

• Exposure to alcohol in early development (week 3+)

• Characterized by facial and neurological abnormalities

• Variable degrees of severity

Lowered ears, small face, mild

mental retardation

– Microcephaly - leads to small

head circumference.

– Short Palpebral fissure - opening

of eye.

– Epicanthal folds - fold of skin at

inside of corner of eye.

Flat midface

• Low nasal bridge

• Indistinct Philtrum - vertical grooves

between nose and mouth

• Thin upper lip

• Micrognathia - small lower jaw

Exposure of embryos in vitro

to ethanol simulates

premature differentiation of

prechondrogenic mesenchyme

of the facial primordia (1999)

Anomalies of face - Excessive Vitamin A

• Retinoic Acid- present in skin ointments and some

vitamin A supplements first identified as 1988 associated

with facial developmental abnormalities

• Use of 13-cis-retinoic acid by women

during pregnancy can result in anomalies such as cleft

palate, absent or abnormally small ears, heart defects,

and thymus abnormalities called teratogenic effect

First Arch Syndrome

• There are 2 major types of first arch syndrome,

• Treacher Collins (mandibulofacial dysostosis)

• The typical physical features include:

- downward slanting eyes,

- a small lower jaw,

- malformed or absent ears.

Pierre Robin syndrome

- marked by a very small lower jaw (micrognathia).

- The tongue tends to fall back and downward

(glossoptosis)

- There is cleft soft palate.