Head and Neck Embryology

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Head and Neck Embryology

• R. Dale Reynolds
• University of Texas at Houston
• Plastic and Reconstructive Surgery

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Branchial and Pharyngeal Arches

• Fourth week
• Neural crest cells
• Most skeletal and connective tissue in HN
• Numbered cranial ? caudal
• Four well-defined pairs visible externally
• Fifth and sixth rudimentary
• Separated by grooves

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Branchial and Pharyngeal Arches

• First Mandibular
• Mandibular Prominence ? jaw
• Maxillary Prominence ? maxilla/zyg/temp
• Second Hyoid

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Branchial and Pharyngeal Arches

• Fate
• Typical arch contains
• Aortic arch
• Cartilaginous rod (skeleton of arch)
• Muscular component
• Nerve

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Branchial and Pharyngeal Arches
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Pharyngeal Pouches

• First
• Tubotympanic recess ? tympanic membrane
• Connects with pharynx ? eustachian tube
• Second
• Palatine tonsil, tonsillar fossa
• Third
• Inferior parathyroid gland
• Thymus

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Pharyngeal Pouches

• Fourth
• Superior parathyroid gland
• Ultimobranchial body fuses with thyroid
• Parafollicular C cells ? calcitonin
• Fifth
• Rudimentary

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Pharyngeal Pouches
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Branchial or Pharyngeal Grooves

• Four on each side
• Separate branchial or pharyngeal arches
• First ? External acoustic meatus
• Others lie in depression (cervical sinus) which
  obliterates

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Branchial or Pharyngeal Grooves
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Branchial or Pharyngeal Membranes

• Only one pair contribute to adult structures
• First ? tympanic membrane

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Branchial and Pharyngeal Anomalies

• Congenital Auricular Sinuses and Cysts
• Small sinuses (pits) and cysts commonly found in
  a triangular area of skin anterior to the ear
• May be remnant of branchial or pharyngeal groove

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Branchial and Pharyngeal Anomalies

• Branchial Sinuses
• Lateral cervical Uncommon, open externally
  (neck), failure of second groove or cervical
  sinus to obliterate
• External branchial sinuses Mucous d/c from
  infants neck, bilateral in 10
• Internal branchial sinuses Rare, persistent
  second pouch, open into intratonsillar cleft

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Branchial and Pharyngeal Anomalies

• Branchial Fistula
• Connection between intratonsillar cleft and neck
• Runs between internal and external carotids
• Persistent second groove and second pouch

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Branchial and Pharyngeal Anomalies

• Branchial Cysts
• Develop along anterior border of
  sternocleidomastoid
• Most inferior to angle of mandible
• Often present in adulthood
• Remnants of cervical sinus and/or second groove

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Branchial and Pharyngeal Anomalies

• Branchial Vestiges
• Cartilaginous or bony remnants
• Usually anterior to inferior third of
  sternocleidomastoid

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Branchial and Pharyngeal Anomalies

• First Arch Syndrome
• First branchial or pharyngeal arch
• Treacher Collins syndrome
• Malar hypoplasia, down-slanting of palpebral
  fissures, lower eyelid colobomas, ear
  deformations
• Pierre Robin syndrome
• Hypoplasia of the mandible, cleft palate, and
  defects of the eye and ear

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Branchial and Pharyngeal Anomalies

• DiGeorge Syndrome (Congenital Thymic and
  Parathyroid Aplasia)
• Failure of third and fourth pouches to
  differentiate into thymus and parathyroid glands
• Hypoparathyroidism
• Increased incidence of infections
• Shortened philtrum
• Low-set notched ears
• Nasal clefts
• Thyroid hypoplasia
• Cardiac anomalies

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Branchial and Pharyngeal Anomalies

• Accessory Thymic Tissue
• Isolated portion of thymic tissue may persist
• Often in close association with inferior
  parathyroid gland

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Branchial and Pharyngeal Anomalies

• Ectopic Parathyroid Gland
• Variable in number (2-6) and location
• Superior more constant than inferior
• Thyroid to thorax
• Absence of Parathroid Gland

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Thyroid Gland

• Begins as thickening in the floor of the pharynx
• Forms an outpouching (thyroid diverticulum)
• Descends into neck passing ventral to hyoid bone
  and laryngeal cartilages
• Connected to tongue by thryoglossal duct at
  foramen cecum

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Thyroid Gland

• Isthmus connects right and left lobes
• Thyroglossal duct degenerates
• Blind pit marks the foramen cecum
• Pyramidal lobe extends superiorly from the
  isthmus in fifty per cent

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Thyroid Anomalies

• Thyroglossal Duct Cysts and Sinuses
• May form anywhere along the course followed by
  the thyroglossal duct
• Most seen by 5 yo
• Asymptomatic unless infected
• Midline, painless, moveable neck mass
• Sinuses are open, cysts are closed

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Thyroid Anomalies

• Ectopic Thyroid Gland
• Lingual thyroid
• Result of failure to descend
• Often only thyroid tissue present
• Accessory thyroid tissue
• Tongue
• Neck, superior or lateral to thyroid

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Tongue

• General
• Merged distal tongue buds ? anterior 2/3
• Copula and hypobranchial eminence ? posterior 1/3
• Terminal sulcus divides anterior and posterior
• Taste buds
• Most are filiform papillae and are sensitive to
  touch
• Muscles
• Supplied by XII except for palatoglossus (X)

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Tongue

• Nerves
• Sensory for anterior 2/3 is from V3 (lingual)
• Chorda tympani (VII) taste buds for anterior 2/3
  (except for vallate papillae supplied by IX)
• IX supplies posterior 1/3
• X (Superior Laryngeal) supplies area around
  epiglottis

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Tongue

• Taste buds
• Most are filiform papillae and are sensitive to
  touch

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Tongue Anomalies

• Lingual cysts and Fistulas
• Persistence of thyroglossal duct open to foramen
  cecum
• Ankyloglosia (Tongue-Tie)
• Short frenulum to tip, stretches with time
• Macroglossia
• Usually from muscular hypertrophy or lymphangioma

• Microglossia
• Associate with micrognathia and limb defects
  (Hanharts syndrome)
• Bifid or Cleft Tongue (Glossochisis)
• Incomplete fusion of distal tongue buds ? deep
  median sulcus

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Ear

• Microtia
• 16000-8000 births
• Associated with hemifacial microsomia
• Nerves
• Great auricular (C2, C3) ? lower lateral/lower
  cranial
• Auriculotemporal (V3) ? superolateral/ anterior
  and superior external auditory canal
• Lesser occipital ? superior cranial
• Arnolds (X) ?concha / posterior auditory canal
  (referred oropharyngeal pain)

• Three anterior hillocks of the first branchial
  arch form the tragus, helical crus, and superior
  helix
• Three posterior hillocks of the second branchial
  arch form the antihelix, antitragus, and lobule
• First branchial groove forms external auditory
  meatus

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Ear
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Face

• Stomodeum is primitive mouth
• Five facial primordia appear as prominences
  around stomodeum
• Single fronto(?forehead)nasal? most of
  nose(except septum/alae) prominence ? optic
  vesicles ? eyes
• Paired maxillary prominences ? lateral upper lip,
  most of maxilla, secondary palate
• Paired mandibular prominences ? chin, lower lip,
  lower cheek

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Face

• Mandible forms first
• Nasal placodes ? nasal pits
• Six auricular hillocks ? ear
• Epithelial cord canalizes in nasolacrimal groove
  ? nasolacrimal duct
• Atresia if canalization fails

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Face

• Lateral nasal prominence ? nasal alae
• Medial nasal prominences merge ? intermaxillary
  segment ? philtrum of lip, premaxilla (gum),
  primary palate, nasal septum
• Second arch ? muscles of facial expression (VII)
• First arch ? muscles of mastication (V)

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Face

• Labiogingival lamina ? lips and gingivae, lingual
  frenulum
• Changes
• Early fetal period Flat nose and underdeveloped
  mandible
• Enlarging brain Prominent forehead, medial
  movement of eyes and external ears rise

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Nasal Cavities

• Nasal placodes ? nasal pits ? deepening ? nasal
  sacs
• Oronasal membrane separates the oral cavity from
  the nasal sacs
• Membrane ruptures ? primitive chonae (opening b/w
  nasal cavity and nasopharynx)

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Nasal Cavities

• Olfactory system
• Ectodermal epithelium in the roof of each nasal
  cavity ? specialized ? olfactory epithelium
• Some epithelial cells ? olfactory receptors
  (axons become olfactory nerve) and grow into
  bulbs of the brain

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Nasal Cavities

• Paranasal sinuses
• From outgrowths of nasal cavity walls ? pneumatic
  (air-filled) extensions of the nasal cavities in
  adjacent bones
• Original openings of the outgrowths persist as
  the orifices of the adult sinuses
• Most are rudimentary in newborns
• Frontal sinuses are visible by seven
• Sphenoidal sinuses usually evident by two
• Vomeronasal cartilage ? narrow cartilage strips
  between the inferior edge of the cartilage of
  nasal septum and vomer

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Palate

• Palatogenesis from 5th 12th week
• Primary Palate
• Median palatine process begins to develop from
  deep intermaxillary segment of maxilla
• Primary palate forms the premaxillary part of
  the maxilla
• Represents a small part of the adult hard palate
  (anterior to the incisive foramen that lodges the
  incisor teeth)

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Palate

• Secondary Palate
• Primordium of hard and soft palates that extend
  posteriorly from the incisive foramen
• Shelf-like structures called lateral palatine
  processes (palatine shelves) project
  inferiomedially on each side of the tongue

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Palate

• Secondary Palate
• Shelves elongate and ascend to a horizontal
  position superior to the tongue
• Shelves fuse in a median plane with nasal septum
  and posterior primary palate
• Elevation to the horizontal position is thought
  to be caused by the intrinsic shelf elevating
  force by hydration of hyaluronic acid in the
  shelves

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Palate

• Secondary Palate
• Nasal septum develops from downgrowths of merged
  medial nasal prominences
• Fusion between nasal septum and palatine
  processes proceeds anteriorly to posteriorly

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Palate

• Secondary Palate
• Bone develops in primary palate forming the
  premaxillary part of the maxilla which lodges
  between the incisor teeth
• Bone extends from the maxillae and palatine bones
  in to the lateral palatine processes to form the
  hard palate

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Palate

• Secondary Palate
• Posterior aspects do not ossify
• Extend posteriorly beyond nasal septum and fuse
  to form the soft palate and uvula
• Palatine raphe permanently indicates the line of
  fusion of the lateral palatine processes

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Palate

• Secondary Palate
• Small nasopalatine canal persists between
  premaxilla and palatine processes as incisive
  foramen (openings for incisive canals)

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Clefts

• Lip and palate
• Upper lip and anterior maxilla with or without
  hard and soft palate
• Hard and soft palate
• Complete posterior (to incisive foramen) palate
• Anterior cleft anomalies
• Cleft lip, with or without a cleft of the
  alveolar part of the maxilla
• Result from deficiency of mesenchyme in the
  maxillary prominences and intermaxillary segment

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Clefts

• Posterior cleft anomalies
• Clefts of secondary or posterior palate that
  extend through the soft and hard palate to the
  incisive foramen
• Caused by defective development of the secondary
  palate and result from the growth distortions of
  the lateral palatine processes (shelves) which
  prevent their medial migration and fusion

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Clefts

• Lip
• 11000 births, 70 male,
• CaucasiongtAsiangtHispanicgtAA
• Notches on vermilion border to alveolar maxilla

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Clefts

• Unilateral
• Failure of maxillary prominence on affected side
  to unite with merged medial nasal prominences
• Consequence of failure of mesenchymal masses to
  merge and the mesenchyme to proliferate and
  smooth out the overlying epithelium
• Results in persistent labial groove
• Epithelium in the labial groove stretches and
  tissues of the floor breakdown
• Lip is divided into medial and lateral parts
• Bridge of tissue (Simonarts band) joins parts of
  incomplete cleft lip

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Unilateral cleft lip
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Clefts

• Bilateral
• Failure of mesenchymal masses in the maxillary
  prominences to met and unite with the merged
  medial nasal prominences
• Epithelium in both labial grooves becomes
  stretched and breaks down
• May have varying degrees of defects on each side
• When there is a complete bilateral cleft of the
  lip and alveolar part of the maxilla, the
  intermaxillary segment hangs free and projects
  anteriorly
• These defects are deforming because of loss of
  continuity with the orbicularis oris muscle which
  purses the lips

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Clefts

• Median (rare)
• Upper
• Mesenchymal deficiency causing partial or
  complete failure of medial nasal prominences to
  merge and form the intermaxillary segment
• Characteristic of the Mohr syndrome
• Lower
• Failure of mesenchymal masses in the mandibular
  prominences to merge completely and smooth out
  the embryonic cleft between them

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Clefts

• Palate
• /- lip in 12500 births, females
• Uvula, soft/hard palate, lip, alveolar maxilla
• Failure of mesenchymal masses in lateral palatine
  processes (shelves) to fuse with each other, the
  nasal septum and posterior margin of the median
  palatine process

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Clefts

• Palate (divided by incisive foramen)
• Anterior
• Failure of mesenchymal masses in lateral palatine
  masses to fuse with primary palate
• Posterior
• Failure of mesenchymal masses in lateral palatine
  masses to fuse with nasal septum
• Both
• Failure of mesenchymal masses in lateral palatine
  masses to fuse with each other, primary palate or
  nasal septum

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Craniofacial clefts

• 1.4-5.1100,000
• Numbered 0-14 (sum14)
• 0-7 are facial
• 8-14 are cranial
• Number 7 is least rare (15600) hemifacial
  microsomia (hypoplasia of mandibular ramus,
  hypoplasia of midface, others) associated with
  Goldenhar syndrome
• Bilateral 6,7,8 is complete form of
  Treacher-Collins

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Others

• Facial clefts
• Macrostomia
• Microstomia
• Nasal
• Single nostril
• Bifid nose
• Absence

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