## Pharyngeal (Branchial) structures [@Afshar_2013; @Carlson_2014; @Hopper_2014; @Moore_2016; @Sadler_2015; @Tepper_2010] ### Pharyngeal arches > 6 arches form from migrating neural crest cells (pluripotent ectoderm) that invade and induce the differentiation of surrounding pharyngeal endoderm and mesoderm to form characteristic structures - Pharyngeal clefts (grooves) separate each arch on the **external** surface - Pharyngeal pouches separate each arch on the **internal** surface - Grooves and clefts are separated by mesoderm - Arch V only exist transiently during development.[@Larsen_1993] ![[Pasted image 20250112114857.png | Cartilaginous and bony structures corresponding to each pharyngeal arch]] ![[Pasted image 20250112114859.png | Table: Each pharyngeal arch has 4 main derivatives (nervous, arterial, bony, and muscular) (bold structures are usually tested on written examinations) ]] ### Pharyngeal clefts (grooves) ![[Pasted image 20250112130544.png | (Blue is ectoderm; dark red is mesoderm; yellow is endoderm)]] - Groove I: Becomes the external auditory canal. The mesoderm becomes the tympanic membrane. - Grooves II–IV: Operculum flap grows downward from arch II and fuses below cleft IV to create the cervical sinus - When the cervical sinus does not obliterate, it can become a cleft cyst, sinus, or fistula - These anomalies are often detected in the second decade of life - Cleft II anomalies (most common) run under the middle/ lower SCM, over the glossopharyngeal nerve (arch III), and toward the tonsillar fossa between the external and internal carotid arteries (i.e., over the internal carotid artery and stylopharyngeus muscle from arch III) - Cleft III anomalies run under the internal carotid artery (i.e., below structures of arch III) ### Pharyngeal pouches - Pouch I: Internal auditory canal - Pouch II: Palatine tonsil - Pouch III: Inferior parathyroid and thymus - Pouch IV: Superior parathyroid (pouch III migrates below IV) - Pouch V: Ultimobranchial body (thyroid C cells) ## Cranium ^[@Afshar_2013; @Carlson_2014; @Rice_2009] - Neurocranium: Portion of skull encasing and protecting the brain - Membranous neurocranium → forms via intramembranous ossification of neural crest origin - Includes paired frontal, squamous temporal bone, and parietal bones, and upper occipital bone - Cartilaginous neurocranium → Forms via endochondral ossification of mesodermal origin - Includes sphenoid and ethmoid bones, mastoid and petrous temporal bone, and the base of the occipital bone - Viscerocranium: Bones of facial skeleton - Forms primarily via intramembranous ossification of pharyngeal arch I - Meckel's cartilage forms the malleus and the mandibular condyles - **Growth** - **Cranial vault grows in response to brain growth** (d/t glial and csf changes)^[Sgouros S, Goldin JH, Hockley AD, Wake MJ, Natarajan K. Intracranial volume change in childhood. _J Neurosurg_. 1999;91(4):610-616. doi:[10.3171/jns.1999.91.4.0610](https://doi.org/10.3171/jns.1999.91.4.0610)] - 1 yr: triple - 2 yr: quadruple - 3 yr: 85% adult - 6-10 yr: ~adult size - Bone growth through perpendicular sutural and radial appositional growth (resorption at the inner surface to deposit in the other surface) - **Virchow's law**: After suture fusion, growth proceeds parallel to suture instead of perpendicular - [[Craniosynostosis]]: Sutures fuse prematurely, often in utero - Timeline for **fontanelle closure** and **suture fusion**: - 3-6 mo: posterior fontanelle - 9-12 mo: anterior fontanelle - 6-8 mo: metopic suture - 22 yr: sagittal suture - 24 yr: coronal suture - 26 yr: lambdoidal suture - ![[Pasted image 20250112134617.png]] ## Face ![[Pasted image 20250118160131.png]] (A, Week 5. B, Week 6. C, Week 7.) - The face develops from 5 prominences: 1. Frontonasal prominence - Form: forehead, nasal dorsum, and medial and lateral nasal prominences - Pulled ventrally and caudally - Nasal placodes at lateral aspect of frontonasal complex develop into depressed nasal pits, and eventually form the nares - Diverticula of lateral nasal walls extend into bones to form **sinuses** - **maxillary** at 3 months’ gestation, **ethmoid** at 5 months’ gestation - **sphenoid** 5 months postnatally, **frontal** 2–6 years postnatally - ![[Pasted image 20250118162242.png | 250]] 2. Medial nasal prominence - Form: primary palate, midmaxilla, midlip, philtrum, central nose, and septum 3. Lateral nasal prominence - Form: nasal alae 4. Maxillary prominences - Form: secondary palate, lateral maxilla, and lateral lip - Medial migration compresses the medial nasal prominences into one, separating the nasal pits and stomodeum (later, nasal and oral cavities) - Junction with the lateral nasal prominences forms the nasolacrimal groove and nasolacrimal duct system - Failure of fusion produces an oblique facial cleft (Tessier number 3) 5. Mandibular prominences - Form: mandible, lower lip, and lower face ## Mouth - **Stomodeum**: Primitive mouth forms at 3–4 weeks from invagination of ectoderm around buccopharyngeal membrane ## Palate ## Tongue ## External Ear ## Thyroid ## References Afshar, M., Brugmann, S., & Helms, J. (2013). Embryology of the craniofacial complex. In P. Neligan, R. J. Warren, & A. Van Beek (Eds.), _Plastic surgery_ (3rd ed). Elsevier Saunders. Carlson, B. M. (2014). _Human embryology and developmental biology_ (5th ed). Elsevier/Saunders. Hopper, R. (2014). Cleft lip and palate: embryology, principles, and treatment. In C. Thorne, K. C. Chung, A. Gosain, G. C. Guntner, & B. J. Mehrara (Eds.), _Grabb and Smith’s plastic surgery: editor-in-chief, Charles H. Thorne ; editors, Kevin C. Chung, Arun Gosain, Geoffrey C. Gurtner, Babak Joseph Mehrara, J. Peter Rubin, Scott L. Spear_ (Seventh edition). Wolters Kluwer/Lippincott Williams & Wilkins Health. Larsen, W. J. (1993). _Human embryology_. Churchill Livingstone. Moore, K. L., Persaud, T. V. N., & Torchia, M. G. (2016). _The developing human: clinically oriented embryology_ (10th edition). Elsevier. Rice, D. (2009). Craniofacial genetics and dysmorphology. In B. Guyuron, S. Eriksson, & J. Persing (Eds.), _Plastic surgery_ (1st edition). Saunders/Elsevier. Sadler, T. W. (2015). _Langman’s medical embryology_ (13th edition). Wolters Kluwer. Tepper, O., & Warren, S. (2010). Craniofacial embryology. In F. Weinzweig (Ed.), _Plastic Surgery Secrets Plus_ (2nd ed). 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