Head and Neck Embryology

R. Dale Reynolds

University of Texas at Houston

Plastic and Reconstructive Surgery

Branchial and Pharyngeal Arches

Fourth week Neural crest cells

– Most skeletal and connective tissue in H&N

Numbered cranial caudal Four well-defined pairs visible externally Fifth and sixth rudimentary Separated by grooves

Branchial and Pharyngeal Arches

First = Mandibular– Mandibular Prominence jaw– Maxillary Prominence maxilla/zyg/temp

Second = Hyoid

Branchial and Pharyngeal Arches

Fate– Typical arch contains

• Aortic arch

• Cartilaginous rod (skeleton of arch)

• Muscular component

• Nerve

Branchial and Pharyngeal Arches

Pharyngeal Pouches

First– Tubotympanic recess tympanic membrane– Connects with pharynx eustachian tube

Second– Palatine tonsil, tonsillar fossa

Third– Inferior parathyroid gland– Thymus

Pharyngeal Pouches

Fourth– Superior parathyroid gland– Ultimobranchial body fuses with thyroid– Parafollicular C cells calcitonin

Fifth– Rudimentary

Pharyngeal Pouches

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

Branchial or Pharyngeal Grooves

Branchial or Pharyngeal Membranes

Only one pair contribute to adult structures First tympanic membrane

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

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 infant’s neck, bilateral in 10%

– Internal branchial sinuses: Rare, persistent second pouch, open into intratonsillar cleft

Branchial and Pharyngeal Anomalies Branchial Fistula

– Connection between intratonsillar cleft and neck

– Runs between internal and external carotids

– Persistent second groove and second pouch

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

Branchial and Pharyngeal Anomalies

Branchial Vestiges– Cartilaginous or bony

remnants

– Usually anterior to inferior third of sternocleidomastoid

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

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

Branchial and Pharyngeal Anomalies

Accessory Thymic Tissue– Isolated portion of

thymic tissue may persist

– Often in close association with inferior parathyroid gland

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

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

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

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

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

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)

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

Tongue

Taste buds– Most are filiform

papillae and are sensitive to touch

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 (Hanhart’s syndrome)

Bifid or Cleft Tongue (Glossochisis)

– Incomplete fusion of distal tongue buds deep median sulcus

Ear 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

Microtia– 1:6000-8000 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

– Arnold’s (X) concha / posterior auditory canal (referred oropharyngeal pain)

Ear

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

Face Mandible forms first Nasal placodes nasal

pits Six auricular hillocks

ear Epithelial cord canalizes

in nasolacrimal groove nasolacrimal duct– Atresia if canalization fails

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)

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

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)

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

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

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)

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

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

Palate

Secondary Palate– Nasal septum develops

from downgrowths of merged medial nasal prominences

– Fusion between nasal septum and palatine processes proceeds anteriorly to posteriorly

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

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

Palate

Secondary Palate– Small nasopalatine

canal persists between premaxilla and palatine processes as incisive foramen (openings for incisive canals)

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

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

Clefts

– Lip• 1:1000 births, 70% male,

• Caucasion>Asian>Hispanic>AA

• Notches on vermilion border to alveolar maxilla

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 (Simonart’s band) joins parts of incomplete cleft lip

Unilateral cleft lip

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

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

Clefts

– Palate• +/- lip in 1:2500 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

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

Craniofacial clefts

1.4-5.1:100,000 Numbered 0-14 (sum=14)

– 0-7 are facial

– 8-14 are cranial Number 7 is least rare

(1:5600) =hemifacial microsomia (hypoplasia of mandibular ramus, hypoplasia of midface, others) associated with Goldenhar syndrome

Bilateral 6,7,8 is complete form of Treacher-Collins

Others

Facial clefts

Macrostomia

Microstomia

Nasal

Single nostril

Bifid nose

Absence

END