craniofacial embryology- Ashok Ramadorai

FDS RCSEd (U.K.) FFDRCSIreland( Oral surg)

Embryoblasts differentiate to form the primary germ layers viz., Ectoderm and

Endoderm -14th dayMesoderm is formed by ectodermal

proliferation and differentiation-3rd week

Derivatives of germ layers

• Ectoderm-Cutaneous structures, skin & appendages, oral mucosa,enamel of teeth,neural structures CNS,PNS

• Mesoderm- CVS, Locomotor system, bones & muscles

• Endoderm- Lining (epithelium)of GIT, GUT, RS,

Early orofacial development

• Day 14- Oral development starts as thickening of the endoderm (prechordal plate) gives rise to Oropharyngeal membrane

• OPM- site of junction between ectoderm that forms the oral mucosa and endoderm that forms mucosa of the pharynx

• Stomadeum- a shallow depression the OPM forms the primitive mouth. Stomadeum forms the topographc centre for the development of face

Development of the face

• End of 4 weeks the stomadeum is bounded by 5 facial swellings consisting primarily of neural crest derived mesenchyme formed mainly by the 1st pair of pharyngeal arches

• FRONTONASAL PROCESS- upper border of the stomadeum

• MAXILLARY PROCESS - (2) Lateral • MANDIBULAR PROCESS-(2) caudal• The maxillary and mandibular processess are derived from

the first branchial arches.

• The facial process are demarcated by grooves in

the course of normal development become flattened out by the proliferative and migratory activity of the underlying mesenchyme and eventually contour the face.At this stage the OPM seperates the stomadeum from the developing pharynx. Day 28 OPM ruptures to establish continuity betweeen the ectodemally lined oral cavity and endodermally lined pharynx. Adult demarcation zone correlate in the 3rd molar

Week 5

• On both the FNP are local thickenings of the surface ectoderm , the nasal or olfactory placodes which form the olfactory epithelium and the lens.

• The nasal placodes sink into the underlying mesenchyme forming two blind ended nasal pits, primitive nasal cavity.Proliferation of the mesenchyme from the FNP around the nasal pits form the MEDIAL AND LATERAL NASAL PROCESSES.The nasal pits deepen to form anterior nares

NOSE

• Olfactory portion is formed by the Olfactory or nasal placodes.

• Growth of the medial and lateral nasal process- nasal pits- anterior nares

• Frontal prominence forms the bridge of the nose • Merged medial nasal process- Columella • Lateral nasal process- alae• Nasal septum- by the roof of the stomadeum

LIP

• The maxillary process grow medially and approach both the lateral and medial nasal process, but remain seperated from them by distinct grooves.

• Medial growth of the maxillary process pushes the medial nasal process towards the midline whereit fuses with its anatomical counterpart from the opposite side.

• The upper lip is formed from the maxillary process and medial nasal process.

Cont

• NASAL FIN is a sheet of epithelium present initially between the maxillary process and medial nasal process. The nasal fin soon degenerates allowing fusion of these process.Persistence of nasal fin –CLP

• Lowe lip is formed by the fusion of the two mandibular process.

• Maxillary and lateral nasal process is seperated initially by a deep furrow-naso optic furrow- epithelial groove fises and then - canalization – nasolacrimal duct

GLOBULAR PROCESS

• Fusion of the two medial nasal process form a single globular process

• tip of the nose, columella, Frenulum , Philtrum, the entire primary palate , part of the maxilla carrying the incisors

• Lateral nasal process form the alae of the nose.• CUPID’S BOW- Central tuberculum by the

globular process and lateral aspects from maxillary process.

SUMMARY

• 1. Frontonasal process- forehead, bridge of nose, medial and lateral nasal prominence

• 2. Maxillary process- Cheek, lateral portion of upper lip.

• 3. Medial nasal process- crest and tip of nose, philtrum of upper lip and also form the globular process and their derivatives

• 4. Lateral nasal process- Alae of nose• 5. Mandibular process- Lower lip

Cleft Lip

• Failure of the maxillary and medial nasal process to fuse, persistence of nasal fin between the maxillari and medial nasal process.

• MEDIAN CLEFT (HARELIP) –Incomplete fusion of the 2 medial nasal process in the midline( rare).This anomaly is accompanied by a deep groove bet R and L sides of the nose

• OBLIQUE cleft lip- Failure of the maxillary process to merge with its corresponding lateral nasal process.groove running between medial canthus of eye and ala of nose

Cause-CLP

• MULTIFACTORIAL- Genetic, environmental factors (anticonvulsants given during pregnancy viz., phenytoin, phenobarbitone.

• Cleft lip- MALE > FEMALE • 1:1000 live births, • Successive babies- 4%, 9%, 17%

CLP

• Cleft palate- female> male• Reason- female palatine shelves fuse

approximately I week LATER than males.• 2%, 7% 15%• I: 2500 births

DEVELOPMENTAL CYSTS

• Arise along the lines of facial and palatine clefts. Epithelial residues become trapped in the subjacent mesenchyme during merging and failure to degenerate by programmed cell death- epithelial rests persists- cyst formation

• NASOLABIAL CYSTS- where lateral nasal process and maxillary process meet.

• Median madibular cyst- midline of merging two mandibular arches.

• Globulomaxillary cysts- along the line of merging of globular an maxillary process.