Head & Neck Embryology with Dr. Sultan Al-Zyoud

Embryonic Development

• The development of the head and neck begins in the 4th and 5th week of gestation
• Growth of mesenchymal tissue in the cranial region results in the formation of arches separated by clefts, known as pharyngeal arches and pharyngeal clefts

Pharyngeal Arches

• Initially, there are four pharyngeal arches, separated by pharyngeal clefts
• Only the 1st cleft gives rise to a permanent structure in the adult, the external auditory meatus
• The 2nd, 3rd, and 4th clefts form temporary cervical sinuses that are later obliterated by the rapidly proliferating 2nd pharyngeal arch

Pharyngeal Pouches

• Pharyngeal pouches separate pharyngeal arches on the inner (endodermal) surface
• There are five pairs of pouches, but only four give rise to structures in the adult

Face Development

• The external human face develops between the 4th and 6th week of embryonic development
• The development of the face is completed by the 6th week
• An oropharyngeal membrane appears at the site of the future face during week 3 of embryonic development
• The oropharyngeal membrane breaks down to form the future oral cavity by the 4th week

Palate Development

• The palate begins to develop between the 6th and 8th week
• The maxillary prominences expand medially to give rise to the palatal shelves
• The palatal shelves fuse with each other in the horizontal plane and with the nasal septum in the vertical plane to form the secondary palate
• The development of the palate is completed by the 12th week

Tongue Development

• The tongue begins development in the 4th week of gestation
• The tongue is derived from pharyngeal arches 1-4 (forms the mucosa of the tongue) and the occipital somites (forms the musculature of the tongue)
• A process of sculpting apoptosis releases the tongue from the floor of the oral cavity, leaving the lingual frenulum to anchor the tongue in the mouth

Cranial Nerve Development

• The nuclei of all cranial nerves are present by week 4
• All cranial nerves arise from the hindbrain except olfactory and optic
• Motor nuclei derived from rhombomeres produced by neuroepithelium gives rise to motor nuclei of cranial nerves 4, 5, 6, 7, 9, 10, 11, and 12
• Cranial nerve sensory ganglia originate from neural crest cells and ectodermal placodes

Clinical Relevance

• Cleft lip and cleft palate occur when the medial nasal prominence and maxillary prominence fail to fuse
• Branchial cysts occur when pharyngeal clefts are not obliterated by the 2nd pharyngeal arch
• Thyroglossal duct is an epithelialized tract that connects the thyroid gland to the foramen cecum of the tongue