Head and Neck Embryology
Prenatal life Embryonic period (weeks 1-8) § § §
Most organ systems established Most congenital anomalies appear Major features of body form recognizable
Fetal period (weeks 9-40) §
Rapid growth and maturation of tissues and organs.
Embryonic period (Weeks 1-8)
1.
Week 1: Single cell progresses to a multicelled, hollow blastocyst embedded in endometrial stroma.
First stages of segmentation of fertilized ovum
Week 2: Bilaminar germ disc is formed with ectodermal and endodermal layers. § § §
Bilateral symmetry Anterior and posterior ends Dorsal and ventral surfaces
Week 3: Folding of the embryonic disc Trilaminar germ disc § Ectoderm § Mesoderm § Endoderm Ectoderm § Nervous System § Skin (epidermis and appendages) § Neural crest cells Mesoderm:
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Endoderm:
§ Bone
§
Connective Tissue (Dermis)
§ Cartilage
§
Dura
§ Muscles
§
Cardiovascular System (Heart, Vessels, Blood)
§ Gastrointestinal and Respiratory Lining § Digestive Organ Parenchyma
Notochord Formed from invaginating cells Neural folds §
Develop above the notochord, and fuse to form the neural tube. Neural crest cells §
§
Form intermediate layer between neural tube and surface ectoderm.
Week 4: •
Neural crest cells in the head infiltrate developing pharyngeal (branchial) arch structures, proliferate extensively, and differentiate into mesenchyme – Forming the majority of the facial structures.
28 days
28 days: 4 well-developed pairs of arches •
• •
Pharyngeal arch – Artery – Nerve – Cartilaginous bar – Muscle component Pharyngeal cleft: – External groove below each arch Pharyngeal pouch: – Internal outpouching of the primitive pharynx
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Weeks 4-7: Development of the Face
29 days
Theories: § §
Fusion of processes Mesodermal penetration
Prominences Frontonasal prominence § § § §
Frontal prominence Medial nasal prominences Lateral nasal prominences Nasal placodes -> pits
31 days
Maxillary prominences *paired Mandibular prominences *paired
8 weeks
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Maxillary Morphogenesis
75 days
Medial nasal prominence of frontonasal prominence fuses with maxillary prominence to form the nasal tip and columella, philtrum, lip, alveolus, and primary palate Nasal pits enlarge dorsally to become nasal cavities Lateral nasal prominences of frontonasal prominence become the ala, and are separated from the maxillary prominence by the nasolacrimal groove, which becomes nasolacrimal duct. Week 5-6: The primary palate (palate anterior to the incisive foramen) forms from the fusion of the medial nasal prominence of frontonasal prominence with the maxillary prominence.
Week 9-12: The secondary palate (hard and soft palate posterior to the incisive foramen) develops from internal projections of the bilateral maxillary prominences called lateral palantine processes. As the mandible develops the tongue drops and the palantine processes grow medially to fuse in the midline. They also fuse with the nasal septum and the primary palate. 5
Prominence Derivatives Frontonasal Prominence § §
Forehead Apex of Nose
Medial Nasal Prominences § § § § § §
Primary Palate Midmaxilla Midlip Philtrum Central Nose Septum
Maxillary Prominences § Secondary Palate § Lateral Maxilla § Lateral Lip Mandibular Prominences § § §
Mandible Lower Lip Lower Face
Lateral Nasal Prominences §
Nasal Alae
Failure of Development Cleft Lip §
Failure of fusion of the medial nasal process with the maxillary process
Full Thickness Defect: Bone, Mucosa, Muscle, Skin
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Cleft Palate §
Failure of fusion of the palatal processes of the two maxillary processes
Primary Palate Clefts Can involve lip, nostril sill, alveolus, and/or hard palate anterior to incisive foramen § Complete vs Incomplete § Unilateral vs Bilateral
Secondary Palate Clefts Hard palate posterior to incisive foramen and/or soft palate § Complete vs Incomplete § Unilateral vs Bilateral § Cleft Velum § Submucous Cleft
Veau Classification Veau I - cleft of the soft palate only Veau II - cleft of the soft and hard palates Veau III - a cleft of the soft and hard palates and a unilateral prepalatal cleft Veau IV - cleft of the soft and hard palates and a bilateral prepalatal cleft
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Classification 1. 2. 3. 4.
Lips Alveolus Hard palate Soft palate
Unilateral Incomplete Cleft Lip
Unilateral Complete Cleft Lip
Unilateral Complete Cleft Lip and Cleft Palate Palate
Bilateral Incomplete Cleft Lip
Bilateral Complete Cleft Lip
Cleft of Secondary Palate
Suggested Reading: Sperber G, Sperber S. (2009) Embryology of Orofacial Clefting. In: Losse J, Kirschner R: Comprehensive Cleft Care (pp. 3-20). McGraw-Hill Companies. Gosain A, Nacamuli R. (2007) Embryology of the Head and Neck. In: Thorne C, et al: Grabb and Smithʼs Plastic Surgery, 6th ed (pp. 171-190) Philadelphia: Lippincott Williams & Wilkins. Embryology. In Grey H and Lewis W: Grey’s Anatomy 12th Edition. Philadelphia: Lea & Febiger, 1918. New York, Bartleby.com, 2000. Available at: http://www.bartleby.com/107/
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