Embryology of the Craniofacial Skeleton Flashcards
What are Neural Crest cells
- derived from ectoderm
- differentiate into mesenchymla cells
- arise in wk4 from infolding of neural tube migrate into head and neck region =>critical step for formaiton of branchial arches and facial processes
What is derived from the NCC?
- ocular structures
- melanocytes
- thyroid/adrenal gland
- CNS structures (glial cells, scwann cells, meninges)
- branchial arches
- facial processes
- cranial bones
- dental structures
What are disorders assocaited with NCC abnormalities?
NF
CHARGE
Albinism
What are the branchial arches and how/when do they form?
- building blocks of the craniofacial skeleton and soft tissues
- form as mesenchymal swellings along the foregut
- each arch contains 3 types of primitive tissue - endo/ecto/meso and NCC
- develop from wk 4-8
What strucutres are derived from 1st branchial cleft
EAC
What strucutres are derived from 1st branchial pouch
Middle ear
Eustachian tube
What strucutres are derived from 2nd brachial pouch
Palatine tonsils
TOnisllar fossa
What strucutres are derived from 3rd pouch
Inferior parathyroids
thymus
What strucutres are derived from 4th pouch
superior parathyroid
c-cells
What structures are derived from 1st branchial arch
- Mylohoid, Muscle of Mastication, Anterior belly digastric, TVP, TEnsor tympani
- Merckels cartilage = malleus, mandible template, sphenomandibular lig
- Quadrate cartilage = incus, greater wing sphenoid
- Artery degenerates
- CN5
What strucutres are derived from 2nd branchial arch
- Stapedius, Stylohyoid, Posterior belly digastric, facial expression muscles
- Reichart cartilage = stapes except footplate, hyoid lesser horn
- stapedial artery degen
- CN7
What structures are derived from 3rd branchial arch
- stylopharyngeus
- greater horn of hyoid
- carotid
- CN9
What strucutres are derived from 4th arch
- all muscles of pharynx except stylopharyngeus
- cricothyroid, cricopharyngeus, LVP
- thyroid cartilage
- right subclavian, Left aortic arch
- CNX, superior thyroid n
What structures are derived from 5ht arch
- all intrinsic muscles of larynx except cricothyroid
- arytenoids, cricoid, corniculate
- right and lef tpulmonary artery
- recurrent laryngeal n
What strucutres are derived from 6th arch
SCM, trapezius
CN 11
What are key developmental fusions of facial processes during wk 4-8
- Fusion of the MNP, LNP, & MxP →continuity between nose, upper lip, palate
- Merging of MNP + MxP →separation of oral & nasal cavities => palate
- Merging of the MNPs →philtrum + Cupid’s bow, nasal tip, premaxilla + primary palate + nasal septum
- LNPs →nasal alae
- Nasolacrimal groove =furrow separating LNP from MxP
- Merging of Paired MdP →lower jaw, lower lip, lower cheek & chin
- MxP →upper lip (excluding the philtrum) +upper cheek
- FNP →forehead, nasal dorsum + derivatives of MNP & LNP
How does the nose develop?
- ectodermal swelling on FNP = nasal placodes
- development of MNP LNP which grow anteriorly while placode remain stationalry - leading to invagination = pit
- Nasal dorsum derived from FNP
How do the facial bones develop
- MAINLY from MxP via IMO
- Except mandible from MdP via IMO
- and Condyles from MdP via EO
Which developmental phenotypes have defined failed fusions
- Tessier 7 - failure of development of 1st and 2nd branchial arches
- macrostomia - failure of fusion of the MxP and MdP
- Tessier 3 - failureo f fusion of MxP with LNP
What is the neurocranium and how does it develop
- Def: bones surrounding brain = including cranial vault bones and skull base
- Skull base - derived from NCC (anterior to sella turcica) and para-axial mesoderm (posterior to sella turcica
- forms by Endochondral ossification = cartilage templateis ossified
- bones of skull base include sphenoid, occiput, frontal, temporal, ethmoid
- Cranial vault - derived from NCC mesenchymal plates
- forms by Intramembranous ossification - dependent on underlying brain development
- bones of cranial vault include frontal, occiput, parietal
Which bones of the craniofacial skeleton develop from the MxP and MdP and via EO/IMO?
- MxP derivatives: maxilla, zygoma, vomer, palatine, temporal squamous portion - via IMO
- MxP derivative mandible - IMO
- MdP derivative - condyles - EO
How does the cranial vault grow
- Functional Matrix theory - underlying brain stiulate osteogenic growth at sutures - rapid grow relative to viscerocrnaium
- at bith 25% of adult size, age 2 75%, age 10 full adult size
- diploe devloped at age 3
How does skull base grow?
- via synchondroses (areas of cartilage/chondrocranium that do not ossify ) and remain growth centres - all surrouding/incolving sphenoid
What causes restriciton of AP growth in skull base as seen in bicoronal CS of apert/crouzon and schondroplasia?
premature fusion of synchondroses of skull base