Pharyngeal arches (branchial arches) provide nerve, artery, bone and muscle to the craniofacial development. This article explores arches, pouches and grooves.
Ectoderm, endoderm and mesoderm form pharyngeal arches that develop into maxillary, mandibular, frontonasal prominences.
I, II, III, IV, and VI paired arches each contain nerve, artery, muscle, and bone. The 1st and 2nd arches are the most important in facial development.
Grooves and Pouches
Arches are connected by internal pouches and external grooves (also called clefts).
During the 4th-8th week of gestation from frontonasal process, paired maxillary and mandibular processes
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Overview of Pharyngeal Arches
Ectoderm, mesoderm and endoderm form paired pharyngeal arches (I, II, III, IV, VI) that give rise to maxillary, mandibular and frontonasal processes.
There are 6 paired pharyngeal arches containing neural crest cell derivatives: nerve, artery, bone, muscle. These arches are formed by:
- Ectoderm: nerves, skin, pluripotent neural crest cells.
- Endoderm: GI and respiratory lining.
- Mesoderm: bone, cartilage, muscles, vessels.
6 paired pharyngeal arches each contain nerve, artery, bone/cartilage, and muscle. This can be linked to specific congenital conditions.
1st Pharyngeal (Mandibular) Arch
- Nerve: Trigeminal
- Artery: Maxillary
- Bone: mandible, maxilla, greater sphenoid, malleus, squamous temporal.
- Muscle: mastication, tensor veli palitini, tensor tympani, anterior digastric, mylohyoid.
- Syndromes: Treacher Collins, Pierre Robin, Stickler Syndrome.
2nd Pharyngeal (Hyoid) Arch
- Nerve: Facial Nerve
- Artery: Stapedial (corticotympanic artery)
- Bone/Cartilage: Stapes, upper body of hyoid, lesser cornu, styloid process
- Muscle: facial expression, posterior digastric, stapedius, stylohyoid
- Syndrome: Mobius Syndrome (bilateral facial nerve absence).
The second pharyngeal arch also contains Reichert's cartilage.
3rd Pharyngeal Arch
- Nerve: glossopharyngeal nerve, taste to the posterior 1/3rd of the tongue
- Artery: common carotid artery and proximal portion of internal carotid artery
- Bone/Cartilage: lower body and greater horn of the hyoid.
- Muscle: stylopharyngeus
- Syndrome: Velocardiofacial (DiGeorge) syndrome
The third pharyngeal arch also develops the thymus and inferior III parathyroids. This explains thymus hypoplasia and hypocalcaemia in patients with DiGeorge syndrome.
4th Pharyngeal Arch
- Nerve: superior laryngeal branch of the vagus.
- Artery: proximal subclavian artery (right), aortic arch (left)
- Bone/Cartilage: laryngeal cartilages
- Muscles: pharynx constrictors, levator veli palatini, cricothyroid.
6th Pharyngeal Arch
- Nerve: recurrent laryngeal branch of vagus, diffuse sensory innervation
- Artery: proximal pulmonary arteries (right), ductus arteriosus (left)
- Bone/Cartilage: laryngeal cartilages
- Muscles: intrinsic muscles of the larynx (except for cricothyroid)
Pharyngeal Pouches and Grooves
Arches are connected by internal pouches and external grooves. They form specific aspects of the craniofacial skeleton.
Pharyngeal pouches are internal connections between the arches. Each pouch helps develop specific areas of the head and neck region.
- 1st pouch forms middle ear, internal auditory canal, and Eustachian tube.
- 2nd pouch forms palatine tonsils.
- 3rd pouch forms inferior parathyroids and thymus.
- 4th pouch forms superior parathyroids.
- 5th pouch forms parafollicular cells of the thyroid
Pharyngeal grooves (clefts) are external connections between the arches.
- 1st cleft forms the external auditory canal and tympanic membrane.
- 2nd-4th clefts form the sinus of His, which will normally become involuted
Branchial Cleft Cysts
Branchial cysts emerge due to failure of obliteration of the sinus. The most common type is a 2nd brachial cyst at the anterior border of the sternocleidomastoid muscle.
Failure to obliterate these branchial grooves/clefts can result in "branchial cleft cysts". These can relate to the first and secondary branchial clefts.
1st Branchial Cleft Cyst
There are typically 2 different types:
- Type I: near the external auditory canal, posteroinferior to tragus, or in the parotid.
- Type 2: at the angle of the mandible and may involve the submandibular gland.
2nd Branchial Cleft Cyst
These are much more common than 1st branchial cleft cysts and are usually found on the anterior aspect of the sternocleidomastoid muscle. Other locations can include:
- Between the internal and external carotid arteries
- Over the glossopharyngeal nerve
- In the palatine tonsil.
3rd Branchial Cleft Cyst
These are very rare and can occur
- Deep to the sternocleidomastoid muscle
- Pyriform Sinus
- Deep to the internal carotid artery
Please note, branchial cysts are different to fistulas in various different ways. These include:
- It can open between the hyoid bone and the suprasternal notch
- It can travel from the anterior sternocleidomastoid border to the upper pole of the ipsilateral tonsil fossa.
- The majority are diagnosed by 5 years.
- Associated with recurrent mucoid discharge or upper respiratory tract infections.
During the 4th-8th week of gestation from frontonasal process, paired maxillary and mandibular processes.
The face develops during the 4th-8th week of gestation from 5 processes:
- Paired maxillary processes arising from 1st branchial arch.
- Paired mandibular process arising from 1st branchial arch.
- Frontonasal process arising from mesoderm proliferation.
The mandibular prominences arise from 1st branchial arch and contain Meckel's cartilage, which is adjacent to the marginal mandibular nerve. The majority of this cartilage is resorbed, except for:
- Posterior cartilage remnants form the malleus
- Adjacent mesenchyme forms the mandible.
The maxillary prominences also arise from the 1st branchial arch. It contains the quadrate cartilage and helps form:
- Secondary palate
- Maxilla and premaxilla
- Squamous portion of the temporal bone
- Incus and greater wing of the sphenoid.
- Nasolacrimal duct system
The frontonasal prominences are independent of the branchial arteries. They are formed by a proliferating mesoderm that develops into paired placodes.
- Medial placode forms the medial nasal process, which forms midline structures (primary palate, philtrum, cupid bow, premaxilla, nasal tip and septum).
- Lateral placode forms the lateral nasal process, which forms the nasal alae.
Specific conditions arise due to the failure of fusion of the following two structures:
- Cleft Lip: unilateral medial nasal process with maxillary process.
- Bilateral Cleft Lip: bilateral medial nasal process with maxillary process.
- Cleft Palate: medial and lateral palatine processes.
- Median Cleft Lip: midline fusion of median nasal prominences
- Tessier 3-6: lateral nasal processes and maxillary process at the alar groove.
- Tessier 7: maxillary and mandibular processes
- Tessier 0: median nasal prominences in the midline
- Tessier 30: failure of the fusion of the mandibular prominences.
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