BDS1_PharyngealArchesDev_2021.pdf

Craniofacial Development: Development of the pharyngeal arches Dr. Ana Angelova Volponi Objectives Identify the origin of different tissues derived from different germ layers. Describe the different tissue origins of the craniofacial area. Describe the development of pharyngeal arches, pouches and c...

Craniofacial Development: Development of the pharyngeal arches Dr. Ana Angelova Volponi Objectives Identify the origin of different tissues derived from different germ layers. Describe the different tissue origins of the craniofacial area. Describe the development of pharyngeal arches, pouches and clefts and associate their derivates to the embryonic development of the craniofacial region. Associate some pharyngeal arch defects with clinically presented anomalies and some syndromes. Review of embryology -Initially there are three germ layers Derivatives of the three germ-layers Germ layer Tissue-Types Ectoderm Epidermis, Nervous System Mesoderm Skeleton, Muscle, Dermis, Kidney, Gonads, Blood Endoderm e.g. Gut, Liver, Lungs, Thyroid, At the end of gastrulation ectoderm is the outermost layer of the embryo and endoderm the innermost layer, with mesoderm sandwiched between them. Fourth week of Embryonic development: Neural Folds meet superior to the neural groove and forms the NEURAL TUBE Neural folds also forms the cells of the neural crest: -migratory population of cells -multipotent -give rise to certain tissues in specific areas of head/face Embryo folds along this tube Anterior end of the neural tube rapidly expands to form the beginnings of forebrain, midbrain and hindbrain Also folds along the rostrocaudal axis Continued development of the somites The Neural Crest Epithelial-mesenchymal transformation NP E NC NC NC E NT The neural crest (NC) forms at the lateral edges of the neural plate (NP), at the boundary with the epidermis (E). Crest cells delaminate from the neural tube (NT) and migrate away. -The Anterior part of the neural tube expands greatly as forebrain, midbrain and hindbrain form. -Part of neural tube that forms hindbrain develops a series of eight bulgesRhombomeres -Lateral to the neural tube , the mesoderm partially segments to form seven somatomeres and fully segments caudally to form somites. - Migration of neural crest cells provides embryonic connective tissue needed for Craniofacial development. Neural crest cells migrate along specific pathways into the branchial arches The midbrain and rhombomeres 1 and 2 contribute to the face and the first branchial arch A Link between cranial and cardiac development: Neural crest cells Cranial neural crest cells and mesoderm are important for heart and artery development Structural: Conotruncal septum (partitioning of the outflow tract) Parasympathetic post-ganglionic neurons Needed for: Cardiac looping Remodelling of the aortic arches Secondary heart field development Contraction of heart Disorders: Persistent truncus arteriosus No divide into the pulmonary trunk and aorta. Transposition of the great vessels Narrowing of the orifice of the tricuspid valve of the heart. Tricuspid stenosis Double outlet right ventricle The aorta connects to the right ventricle (RV, the chamber of the heart that pumps oxygen-poor blood to the lungs), instead of to the left ventricle (LV, the chamber that normally pumps oxygen-rich blood to the body) Syndromes: DiGeorge syndrome, Charge syndrome Formation of the facial primordia PHARYNGEAL ARCHES Formation of the facial primordia -Development of Frontal Prominence forms the stomatodeum -Below this is the formation of the first branchial arch (mandibular) Yoshida et al. (2008) Mech. Dev. 125: 797-808 & Larsen’s Human Embryology Primitive stomatodeum forms as a wide, shallow depression in the developing face -limited by buccopharyngeal membrane PHARYNGEAL (BRANCHIAL) ARCHES and POUCHES Appear in 4th and 5th weeks of development Branchial arches consist of a ‘bar’ of mesenchymal tissue, lined on outside by ectoderm and inside by endoderm. Separated from each other by deep clefts on the outside and pouches on the inside. There are 5 arches numbered 1, 2, 3, 4 and 6. There is no 5th arch. These arches separate the stomatodeum from the developing heart The basic structure of each branchial arch is the same: Cartilage, nerve and artery Ectoderm Pharyngeal ARCH Basic structure Outside - ectoderm Endoderm Mesenchyme middle -mesenchyme (neural crest & mesoderm) Inside - endoderm Each arch has its own cranial nerve First arch For the skeletal component- fundamental importance! Located between the stomodeum and the first pharyngeal pouch; it shall give origin to the bones of the two lower thirds of the face. Within the first pharyngeal arch two different processes may be isolated: the maxillary and the mandibular process, respectively in a more dorsal and in a more anterior position, located laterally and inferiorly to the stomodeum. From the maxillary process derive the structures that constitute the maxilla and the palate: the maxillary bone, the premaxillary bone, the zygomatic bone and the squamous part of the temporal bone. Within the mandibular process is located the Meckel’s cartilage, which will disappear with development, with the exception of two small portions which will form the incus and the malleus. The mandibular bone will form by ossification of the mesenchymal tissue of the Meckel’s cartilage itself. Musculature of the 1st arch forms muscles of mastication. The nerve supply is from cranial nerve 5 (trigeminal). Second arch Hyoid arch, the cartilage forms the stapes, styloid process on the base of the skull, and lesser horns and upper part of the hyoid bone. Muscles are the functional group of ‘muscles of facial expression’ Nerve supply is from cranial nerve 7 (facial). Third arch Cartilage forms - greater horns and the lower part of the hyoid bone. Muscle - stylopharyngeus muscle. Nerve supply is via cranial nerve 9 (glossopharyngeal nerve). SUMMARY: Pharyngeal arch cartilages 1 1 2 Palatopterygoquadrate (maxillary prominence) Meckel’s cartilage (mandibular prominence) Reichert’s or hyoid cartilage Alisphenoid Malleus Incus 5 weeks Stapes Styloid process Stylohyoid ligament Greater cornu of hyoid Remnants of Meckel’s cartilage Thyroid cartilage Lesser cornu Of hyoid Cricoid cartilage Body of hyoid 20 weeks Pharyngeal arch muscle anlagen; origin is reflected in innervation Frontalis Temporalis Auricularis 5 weeks Buccinator Orbicularis oculi Masseter Stylohyoid Orbicularis oris Posterior belly of digastric Mylohyoid Stylopharyngeus Cricothyroid Anterior belly of digastric Middle constrictor of pharynx 20 weeks Platysma Inferior constrictor of pharynx Summary: Branchial/pharyngeal arches Arch Muscle (mesoderm) Cartilage (neural crest) Nerve 1st arch (maxilla and mandible) Muscles of mastication Meckels cartilage = malleus and incus CNV trigeminal 2nd arch (hyoid) Muscles of facial expression Stapes, styloid CNVII facial process, stylo-hyoid ligament and lesser horns of hyoid 3rd arch Stylopharyngeus Greater horns of hyoid CNIX glossopharyngeal 4th arch Constrictors of pharynx Cartilages of larynx = e.g. thyroid CNX superior laryngeal 6th arch Intrinsic muscles of the larynx Cartilages of larynx e.g. cricoid CNX recurrent laryngeal During the fifth and sixth weeks of embryonic development: - bilateral maxillary processes derived from first brachial arch fuse with the medial nasal process to form the upper lip, alveolus, and the primary palate. The lateral nasal process forms the alar (Alae) structures of the nose. The lower lip and jaw are formed by the mandibular processes. Palate Formation Pharyngeal Clefts Pharyngeal Pouches Development of Tongue Development of the palatal shelves The primary palate is formed by an extension of the intermaxillary process. The secondary palate forms from palatine shelves that grow medially from the maxillary prominences. Late 7th/8th week 10th week At the same time, growth of the nasal septum separates the left and right nasal chambers. Initially, the palatine shelves grow beneath the tongue (t) but soon move upwards to meet at the midline above the tongue. Here they fuse with each other and the nasal septum. The lower half of the palate undergoesossification, forming the hard palate. Fusion of the palatine shelves occurs 1 week earlier in male compared to female embryos. Cleft Palate Cleft palate occurs when the palatial shelves fail to fuse with each other during the 7th to 10 weeks of development. It is found in ~1/2000 life births (more often in females) and is often associated (50%) with cleft lip. Cleft palate may result from a variety of errors, including inadequate growth of the palatine shelves, failure of the shelves to elevate above the tongue, an excessively wide head, failure to fuse, and secondary rupture after fusion. It is found in a wide range of congenital syndromes affecting the head. Normally corrected surgically between 3-8 months of age. Types of clefts First Pharyngeal (Branchial) arch abnormalities Mandibulofacial dystostosis (Treacher-Collins syndrome) rare syndrome characterized by underdeveloped facial bones and a very small lower jaw and chin, called micrognathia. There is no angle between the neck and the chin. It is often associated to cleft palate. Acro-facial dysostosis: The forehead may be prominent. Bilateral mandibular hypoplasia with severe micrognathia and retrogenia which may be associated to severe respiratory distress is usually present. Cardiovascular anomalies and genitourinary anomalies may be associated Nager Syndrome ,.. CLINICAL FEATURES OF FIRST AND SECOND PHARYNGEAL ARCH SYNDROMES HEMIFACIAL MICROSOMIA (OTO-MANDIBULAR SYNDROME, OTO-MANDIBULAR DYSOSTOSIS), THE “OCULAR AURICULAR VERTEBRAL SPECTRUM” Hemifacial microsomia is characterized by a great variability in clinical manifestations. Only derivatives of the first branchial arch, or all derivatives of the second branchial arches may be involved. In the first case, the ramus, the mandibular condyle, the maxilla, the TMJ, the masticatory muscles, the oral commissure and the components of the ear which derive from the first branchial arch may be involved Where the structures originating from the second branchial arch are involved as well, the facial nerve may be affected, totally or partially, the segments of the ears which derive from the second arch. Mild form of HFM in which the structures originating from the first branchial arches are more involved: the ramus and mandibular condyle, the maxillary bone, the masticatory muscles. A macrostomia was present on the affected side. A preauricular tag was present, but the auricle is only mildly displaced and anteriorly rotated. https://pocketdentistry.com/clinical-features-of-first-and-second-branchial-arch-syndromes/ The muscular defects reduce the articular motion: opening, protrusion, and lateral movements are limited. When the patient opens the mouth, the mandible deviates towards the affected side, because of the absence of an adequate leverage on the affected condyle in its corresponding glenoid fossa. The difficulty of bringing the mandible towards the affected side is also related to both skeletal and muscular associated anomalies. Often times the temporal muscles and the masseter muscles are fused together and constitute a common muscular group, the temporo-masseter sling. Mimic musculature maybe normal or have severe defects, depending on how involved the facial nerve is. Some authors believe it to be involved in more than 45% of the cases Patient affected by HFM in which the structures originating from the first branchial arch as well as those from the second branchial arch are involved. The facial nerve is affected with a defect in the mimic musculature. Pharyngeal Clefts Pharyngeal pouches Pharyngeal Clefts Clefts are lined with ectoderm Only one forms a structure in the adult. First cleft between first and second arch forms the external auditory tube. First Pharyngeal cleft In 3rd month, ectoderm at bottom of cleft between 1st and 2nd arch proliferates. Forms solid epithelial plate of cells, ‘meatal plug’. 7th month, plug disintegrates. The other clefts are obliterated during development Lateral Tongue bud Median Tongue bud Lateral Cervical sinus Pharyngeal Clefts Copula Hypopharyngeal Eminence Entrance To oesophagus Hypopharyngeal Eminence Overgrows copula 2nd arch expands 29 days 32 days 42 days Remnants of the clefts can result in cysts Lateral Cervical cyst Cervical cyst With external fistulas Cervical cyst With internal Fistulas Cervical cyst With internal and External fistulas (most common 2nd pouch Derivative - tonsil) Sites of (a) aural and Cervical (b,c) cysts and fistula Cysts and fistula in (a) may damage facial nerve Sometimes a small sinus remains. Pharyngeal pouches Pouches are lined by endoderm They all form important structures in the adult. Various organs differentiate from the endoderm of these pouches: Pharyngeal Pouch 1 –develops into the auditory tube and middle ear cavity Pharyngeal Pouch 2 –forms numerous infoldings that become the crypts of the palatine tonsil Pharyngeal Pouch 3 –divides into a superior (or dorsal) and inferior (or ventral) portion: dorsal portion of pouch 3: forms the inferior parathyroid glands –the chief (or principal) and oxyphil cells are derived from the endodermal lining of the pouch ventral portion of pouch 3: forms the thymus –the epithelial reticular cells (including those that comprise the thymic or Hassall's corpuscles) are derived from the endodermal lining of the pouch. T-cell progenitors from the bone marrow infiltrate the cortex to establish the definitive thymus. Pharyngeal Pouch 4 –also divides into a superior (or dorsal) and inferior (or ventral) portion: dorsal portion of pouch 4: forms the superior parathyroid glands –the chief (or principal) and oxyphil cells are derived from the endodermal lining of the pouch ventral portion of pouch 4 - indicated as 5thPharyngeal Pouch: ultimobranchial body, which is incorporated into the thyroid. Form the parafollicular or C-cells of the thyroid. These secrete calcitonin regulating Ca2+ levels in the blood. Thyroglossal duct cyst Tongue Development: Multiple origins Foramen cecum Distal tongue buds Anterior 2/3 Tongue Foramen cecum Median tongue bud Terminal sulcus Palatine Tonsil Copula Epiglottis Hypopharyngeal eminence 4 weeks 5 weeks Posterior 1/3 tongue Distal tip of tongue Multiple innervation: 1st arch: cranial nerve V (trigeminal) (sensory receptors) 2nd arch: facial nerve VII (taste buds) 3rd arch: glossopharyngeal IX (sensory & taste buds) 4th arch: vagus nerve X Muscles: Occipital somites: hypoglossal nerve XII Head mesoderm: Vagus nerve X (palatoglossus muscle) 6 weeks (note attached to mandibular primordia) Mandibular Swelling Median sulcus Early 6th week Ankylogossia: Tongue Tie Reading: Larsen’s Human Embryology Langman’s Medical Embryology Sperber, Craniofacial Development