Prenatal development of cranial base
- 2. PRENATAL DEVELOPMENT OF CRANIAL BASE Dr. Manasa Ist MDS
- 3. CONTENTS • INTRODUCTION • BASIC GROWTH PRINCIPLES • GROWTH MOVEMENTS • ANATOMY OF NEUROCRANIUM • CRANIAL BASE ANATOMY • PRENATAL DEVELOPMENT OF THE SKULL BASE • TYPES OF OSSIFICATIONS
- 4. • SKULL BASE OSSIFICATION • CRANIAL BASE INTERRELATIONS CRANIOFACIAL DEVELOPMENT AND MALOCCLUSION • INFLUENCE OF CRANIAL BASE MORPHOLOGY ON ADJACENT STRUCTURES • CRANIAL BASE ABNORMALITIES • CONCLUSION • REFERENCES
- 5. INTRODUCTION • An understanding of the growth of the craniofacial complex has come to assume great importance in orthodontic. • The cranial base supports the brain and provides adaptation between the developing neurocranium and viscero cranium during growth.
- 6. • Located on a junction point between the cranium, midface and glenoid fossa, the cranial base plays a key role in craniofacial growth, helping to integrate spatially and functionally, different patterns of growth in various adjoining regions of the skull such as components of the brain, the nasal cavity, the oral cavity, and the pharynx.
- 7. • Depending on the fact that the maxilla is connected with the anterior part of the cranial base and the rotation of the mandible is influenced by the maxilla, a relationship can be found between the cranial base variations and sagittal malposition of the jaws.
- 8. Basic Growth Principles and its relevance in Neurocranial Growth • Cephalocaudal Growth • Scammon’s growth curve
- 9. • The cranial base, which from a functional point of view may be regarded as the border between brain and facial structure, is obliged, therefore, to develop in conformity with the different growth patterns of the brain ease and facial structure and, consequently,must follow two different growth rates, one along its internal surface and another along its external surface. “(Björk 1955)
- 10. Growth Movements • Drift • Displacement
- 11. Anatomy of the Neurocranium • Fastest growing area of the craniofacial skeleton at birth • The face and jaws are relatively underdeveloped . • The neurocranium can be subdivided into the cartilaginous part, which form base of the skull (or chondrocranium), and the membranous part, which form cranial vault (or Calvarium). (Sadler & Langman 2011; Jin et al. 2016)
- 12. Cranial Base Anatomy • The cranial base or cranial floor’s function is to support and protect the brain and spinal cord. • It articulates with the vertebral column, the mandible and the maxillary regions and forms a buffer area between the brain, face and pharyngeal region as these areas grow at different rates. • The Bones that constitutes the Cranial base is the Occipital bone, Sphenoid bone, Temporal bone, Ethmoid bone and Frontal bone.
- 13. • The internal surface of the cranial base is divided into anterior, middle and posterior cranial fossae due to the depressions caused by the lobes and intracranial contents. • The midsagittal section is divided into anterior and posterior sections. • The Anterior cranial base being from Sella to nasion and posterior cranial base being from Sella to basion.
- 15. Prenatal Development of the Skull Base The development of the skull base and calvaria goes through 3 major phases: I. The appearance of a mesenchymal anlage (the ectomeningeal capsule) II.Chondrification of this anlage by the development of multiple discreet cartilages that eventually fuse together. This happens only in bones that undergo Endochondral Ossification III.Ossification of this cartilage, or intramembraneously, from more than 100 ossification centres.
- 16. • There are 2 types of ossification: • Endochondral ossification • Mesenchyme or intramembranous ossification.
- 19. • During this process, the brain will become surrounded by the developing skull base as it meets the evolving calvaria. During foetal life, the bones of the calvaria are separated by attenuated connective tissue membrane that form the neonatal fibrous sutures and frontanelles.
- 20. i‐ Mesenchymal Anlagen • Development of the skull initiates in the fourth embryonic week, as the mesenchyme that surrounds the developing brain forms a capsule. • Mesenchymal tissue is derived from neural crest and occipital sclerotomes.
- 21. • The tissue condenses around the developing brain (basal portion will give rise to the cranial base, while the upper portion will give rise to the calvaria). • The cranial nerves, eyes, and blood vessels are already well underway in their development before the appearance of the ectomeningeal capsule, so the mesenchyme condenses around these pre‐existing structures, creating the primitive skull base foramina
- 22. • Origins of Mesenchyme: • The mesenchyme for the region anterior to the pituitary gland is derived from the neural crest • mesenchyme for the region posterior to the pituitary gland is of paraxial mesenchyme
- 23. • The ectomeninx capsule consists of 2 layers. • The inner layer ‐ will form the dura mater. • The outer layer has both chondrogenic and osteogenic properties and will form the cranial bones.
- 24. • This ectomeningeal mesenchyme will eventually produce 3 areas • The neurocranium or desmocranium (the future calvaria), which surrounds and protects the brain and is mainly ossified by intramembranous ossification the chondrocranium or skull base, which is ossified by endochondral ossification the viscerocranium, which will develop into the facial skeleton and is ossified by both intramembranous and endochondral ossification .
- 26. ii‐ Chondrification • Chondrification of the ectomeningeal capsule starts in the seventh embryonic week as cells within the ectomeningeal capsule differentiate into chondroblasts. Chondrification of the skull base proceeds from posterior to anterior. It begins to chondrify from 3 main pairs of cartilaginous precursors: • The Parachordal cartilage (posterior to the pituitary gland) • The Hypophyseal cartilages (lateral to the pituitary gland) and • The Prechordal cartilages (anterior to the pituitary gland)
- 28. Prechordal Cartilages • Laterally to Sella turcica, chondrification centres appear in the orbitosphenoid cartilages, which will develop into the lesser sphenoid wings. • The alisphenoid cartilages will form the greater sphenoid wings . • An anterolateral extension of the orbitosphenoid cartilage arises near the orbital portion of the developing frontal bone. This region, referred to as the sphenoet hmoidal cartilage, forms the roof of the orbit. • Anterior to the pituitary gland, the prechordal cartilages give rise to the nasal capsule (ectethmoid), which chondrifies in the second foetal month.
- 30. • The nasal capsule develops around the nasal sac and contributes to the format ion of the ethmoid bone, the nasal septum, and the inferior nasal turbinate. • The anterior prechordal region of the cranial base is derived from the neural crest, whereas the parachordal region is of mesodermal origin . • The boundary between these regions is marked by the future junction of the basisphenoid and the basioccipital bones (the spheno‐occipital synchondrosis).
- 32. • Although the skull base initially comprises discreet cartilaginous centres, by the end of the 8th foetal week, it has fused into a single perforated basal cartilaginous plate with the primitive neurovascular foramina. • The developing brain is now situated in a shallow recess in the chondrocrani um, and the central hypophyseal fossa is bounded by the presphenoid cartilage, which forms the tuberculum sellae anteriorly, and by the postsphenoid cartilage, which forms the dorsum sellae posteriorly.
- 33. Hypophyseal Cartilages • A foramen persists in the skull base for Rathke’s pouch to ascend from th underlying stomodeum, which will eventually form the anterior pituitary gland. • The cartilaginous area surrounding the foramen where the adenohypophy sis will develop gives rise to the Sella turcica and the posterior body of the sphenoid bone (Postsphenoid bone).
- 34. Parachordal Cartilage • It arises along the margins of the cranial end of the notochord and is derived from the occipital sclerotomes and the first cervical sclerotome (paraxial mesenchyme origin). • This sclerotome‐derived cartilage forms the boundaries of the foramen- magnum. It appears first at the base of the future occipital bone and then extends along the sides of the future foramen magnum. • It also provides the mesenchymal anlagen for the future basilar and condylar portions of the occipital bone.
- 35. • The otic capsules does not chondrify in humans, but fuses on either side with the parachordal cartilage to form a single mass, petromastoid cartilages. • Later ossification will give rise to the mastoid and petrous portions of the temporal bones
- 36. iii‐ Ossification • In the young foetus the entire cranial base from basion to nasion is a continuous sheet of cartilage. • In this cartilage, ossification centres for basioccipital, basisphenoid, and presphenoid bones appears in the first half of foetal life. • Fusion takes place between the presphenoid and basisphenoid centres shortly before birth
- 38. • The growth of the cranial base is highly uneven, in keeping with the highly irregular shape it develops to accommodate the undulating ventral surface of the brain. • The uneven growth of the parts of the brain is reflected in adaption of related parts of the cranial base as compartments or cranial fossae. • The diencephalon is the most precocious in growth, the telencephaln is next, and the rhombencephalon (with cerebellum) is slowest growth.
- 39. • The anterior and posterior parts of the cranial base, demarcated at the sella turcica, grow at different rates. • Between the 10th and 40th weeks post conception,the anterior cranial base increases its length and width sevenfold, but the posterior cranial base grows only fivefold. • Growth of the central ventral axis or the brain (the brain stem) and of the related body of the sphenoid &basioccipital bones is slow, providing a comparatively stable base.
- 40. • The anterior, middle, and posterior fossae of the cranial floor (related respectively to the frontal and temporal lobes of the cerebrum and to the cerebellum) expand enormously around this base, in keeping with the high rate of growth of these parts of the brain
- 41. ETHMOID BONE • The ethmoid bone ossifiesfrom3centres by endochondral ossification of cartilage from the nasal capsule. • One centre appears in the mesethmoid cartilage. • One centre appears in each ethmoid labyrinth in the cartilage of the nasal capsule.These labyrinthian centres appear during the fourth‐fifth foetal months, and ossification spreads from each labyrinth into the ethmoid turbinates. At birth ,the labyrinths are partially ossified
- 43. • The perpendicular plate ossifies from a median centre that appears in the first year of life. • The perpendicular plate fuses with the labyrinth in the second year of life.
- 44. • The cribriform plate is ossified from both the perpendicular plate and each ethmoid labyrinth. • The crista galli also ossifies in the second year. By 3 years of age, a single ethmoid bone is formed, and because the ethmoid cells begin to form during the third foetal month, these cells are present at birth.
- 45. Sphenoid bone: • The sphenoid bone comprises up to 19 intramembranous and endochondral ossification centres. • These centres can be grouped into 8 areas • the lesser wings • the greater wings • the pterygoid plates • and the presphenoid and postsphenoid centres of the body.
- 46. • Early in the eighth foetal week: the Alisphenoid and Hamulus are the first sphen oid elements to ossify. Initially, there is a suture between the Hamulus and the remaining medial pterygoid plate.
- 47. • Week 8: Endochondral ossification centres develop in the Alisphenoid cartilag es for the root of each greater sphenoid wing. • The remainder of each greater wing ossifies in membrane, and ossification then extends downward into the pterygoid plates. • Ossification centres appear in the Orbitosphenoid cartilages, which eventually become the lesser sphenoid wings. • Intramembranous ossification centres appear for the medial and lateral pterygoid plates. Each medial pterygoid plate also ossifies endochondrally from secondary cartilages in their Hamulus
- 49. • Month 4: A single median and 2 paired presphenoid ossification centres arise in the anterior tuberculum sellae region. • The postsphenoid portion of the sphenoid bone arises from 2 sets of paired centres in the postsphenoid or basisphenoid cartilage on either side of the upwardly projecting hypophyseal (Rathke’s) pouch.
- 50. • Near the cranial end of the basisphenoid, paired initially separate centres develop (the bones of Bertini). After birth, these will become incorporated into the sphenoid body; then, the sphenoid sinuses will eventually extend into these centres
- 51. • Development of the Optic Canal happens in 3 stages: • I. Formation of the cartilaginous optic foramen. • II. Ossification of the cartilaginous foramen . During the 12th‐17th foetal weeks, the cartilaginous optic foramen ossifies by first forming its lateral border.
- 52. • III.Transformation of the bony foramen into a bony canal. • canal begins to form during the fifth foetal month, but continues well into childhood.
- 53. • The Sella develops in 4 stages: • i.Chondrification . • ii. Prenatal ossification . • iii. Postnatal development of the planum sphenoidale . • iv. Posterior growth of the planum sphenoidale.
- 55. Cranial Base interrelations with craniofacial development and malocclusion • The cranial base or cranial floor’s function is to support and protect the brain and spinal cord. • It articulates with the vertebral column, the mandible and the maxillary regions. (Moyers 1988) • As such the growth and morphology of the Cranial Base should have an influence on these related structures.
- 56. Influence of Cranial Base morphology on adjacent structures • Bjork noted that the shape of the brain case varies considerably in relation to the shape of the cranial base (Björk 1955). • A flattening of the cranial base is usually accompanied by reduced height of the brain case, as measured from basion to bregma. On the other hand, the radius of the brain case, measured from Sella to bregma, is greater, whereas the radius from Sella to basion is greatly reduced. The posterior and median cranial fossae arc therefore raised in relation to the anterior one.
- 58. • Rotation of the brain case does not appear to cause any raising or lowering of the anterior cranial fossa. • This rotation of the bones of the brain case results in a rearward and upward displacement of the foramen magnum and causes the foramen angle to widen. • As the natural balance of the head on the spinal column depends on the location of the foramen magnum, a flattening of the cranial base usually will have the effect of tilting the face upward.(Björk 1955)
- 59. • The facial prognathism shows a reduction, as regards both the maxilla and the mandible, when the cranial base flattens out. • In retrognathic cases the cranial base is often found to by flattened with the effect that the head is carried with the face tilted upward
- 60. • Facial pattern is also associated with cranial base morphology • In Dolichocephalic individuals, the following is found • The brain is horizontally long and relatively narrow. This sets up a cranial base that is somewhat flatterthat is, the flexure between the middle cranial floor and the anterior cranial floor is more open. • It is also horizontally longer.
- 61. • These factors have several basic consequences for the pattern of the face. • First, the whole nasomaxillary complex is placed in a more protrusive position relative to the mandible because of the horizontally longer anterior and middle segments of the cranial floor. • Second, the whole nasomaxillary complex is lowered relative to the mandibular condyle. This causes a downward and backward rotation of the entire mandible.
- 62. • Third, the occlusal plane becomes rotated into a downwardinclined alignment. The two‐way forward placement of the maxilla and backward placement of the mandibular corpus results in a tendency toward mandibular retrusion, and the placement of the molars results in a tendency toward a Class II position. • The profile tends to be retrognathic. Because of the more open cranial base an gle and the resultant trajectory of the spinal cord into the cervical region, this t ype of face is associated with individuals having a greater tendency toward a so mewhat stooped posture and anterior inclination of the head and neck.
- 64. • For people with a Brachycephalic facial pattern the following is found: • Individuals with a brachycephalic head form have a rounder and wider brain. This sets up a cranial base that is more upright and has a more closed flexure, which decreases the effective horizontal dimension of the middle cranial fossa. • The result is a relative retrusion of the nasomaxilla and a more forward relative placement of the entire mandible. This causes a greater tendency toward a prognathic profile and a Class Ill molar relationship.
- 66. • The occlusal plane as well as the ramus of the mandible may be aligned upward, but various compensatory processes usually result in either a perpendicular or a downward‐inclined occlusal plane and slight backward rotation of the ramus. • Because of the more upright middle cranial fossa and the more vertical trajectoy of the spinal cord, individuals with all these various facial features also have a tendency for a more erect posture with the head in a more "military" (at braced attention) position.
- 68. Influence of Cranial Base morphology on malocclusion • The cranial base angle is measured at three points antero‐posteriorly. This measurement consists of two legs. The anterior leg, where the maxilla is attached, extends from S‐N. The posterior leg, where the mandible is attached, extends from S‐Ba. Therefore, any change in the cranial base angle can affect the relationships of the maxilla and mandible and influence the type of malocclusion.
- 70. • The posterior leg of the cranial base angle (BaSN) may be tipped anteriorly/ posteriorly, whereas the anterior leg may also be tipped up or down anteriorly by variation in either S or N vertically. • Furthermore, variable lengths may compensate for any cranial deflection,such as an acute posterior leg that places the mandible forward, and this action can be negated by a long posterior leg that places both the basion and mandible posteriorly and vice versa (Andria et al. 2004)
- 71. • The assessment of orthodontic anteroposterior skeletal discrepancy of the jaw s and arches should also account for the role of the cranial base (Hopkin et al. 1968). • The relationship of the cranial base with jaw position and classification of malo cclusion has subsequently been examined extensively.
- 72. • Scott proposed one of the main factors that influence facial prognathism is the opening of the cranial base angle. • This angle has a large individual variation, with a 5° standard deviation, and is markedly decreased in value from birth until the first year. • It is also considered one of the craniofacial constants as it changes little during growth from 5 to15 years (George 1978).
- 73. • Smaller linear and angular dimensions have been shown in class III patients, w hereas class II subjects demonstrate an increased cranial base angle that leads to a more posterior position of the mandible (Hopkin et al. 1968). • The anterior cranial base and the middle cranial fossa have also been reported to be longer in individuals with class II malocclusion (Cendekiawan et al. 2010) However, many studies have shown that the etiological relationship between the cranial base flexion and the type of malocclusion is not well supported.
- 74. • It therefore appears that the cranial base angle is not a pivotal factor in determi ning malocclusion. • Rather, the differential growth patterns and direction between the anterior crani al base and posterior cranial base imply that length and inclination of the cranial base are controlling factors of jaw position.
- 75. • Abnormalities of the posterior cranial base are related to mandibular prognathism , and those of the anterior cranial base to retrusive maxilla. • These relationships are probably explained by the glenoid fossa’s location in the posterior cranial base; an elongated cranial base would bring the glenoid fossa back and the mandible with it (Björk 1955)
- 76. • A compensating mechanism associated with cranial base flexure was first described by Anderson and Popovich,in a study showing that the angle between the posterior cranial base and the ramus of the mandible closes in a highly‐correl ated way to compensate for the opening of the cranial base flexure. • This phenomenon tends to maintain the angle between the ramus and the anteri or cranial base. Therefore, with a more obtuse cranial base angle, the mandible swings only slightly down and forward.
- 77. However, the difference between the anteroposterior positioning of the maxilla and mandible is partly due to variation in the size of the jaws, and partly due to variation in the length and flexure angle of the cranial base, which are associated with the both jaws.
- 78. Cranial base abnormalities • Due to the fact that the growth and development of the chondrocranium is under strong genetic control, it is subject to minimal environmental influence. • Conditions affecting defects in endochondral bone formation may be reflected in abnormal Cranial Base development. (Sperber et al. 2010)
- 79. • Evidence is accumulating to indicate that thecartilaginous cranial base is primarily involved in craniofacial anomalies; for example, the synchondroses of the skull base are completely fused at birth in patients with Crouzon syndrome and show early progressive fusion in Apert syndrome. Abnormal development of the Cranial base is of clinical importance because of the many vital structures that pass through the skull base.
- 80. • Cranial neuropathies can result from hypoplasia of skull base foramina • As seen with achondroplasia, a small skull base can cause hydrocephalus in infants and increased intracranial pressure in older children and adults.
- 81. • Deformity of the optic canals and superior orbital fissures may impair visual acuity by compression of the optic nerve or ocular motility by compression of cranial ner ves III, IV, and VI.(Tokumaru et al. 1996)
- 82. • Defective growth of cartilage will give rise to a shorter cranial base and an increased angulation due to the loss of the “flattening” effects of growth at the Spheno‐occipital Synchondrosis. • This will lead to a “dished in” middle 1/3 of the face and a bulging neurocranium • Premature closure of the synchondroses will lead to an underdeveloped middle 1/3 of the face, excessive cranial vaulting, exophthalmia and malocclusion (due to decreased space for maxillary teeth). (Sperber et al. 2010)
- 83. CONCLUSION • Knowing the basic growth and development of the Cranial Base and Calvaria is of great importance for the clinician. • By knowing the interactions of the various bones and structures that make up the craniofacial complex he can better come to a diagnosis and treatment plan for each patient, as well as know the underlying cause for the abnormality seen. • Using the knowledge gained from studying the growth changes of the craniofacia l region at different ages ,the clinician can know what patterns of development to expect at certain timeframes during treatment, thereby providing a more predictable treatment outcome
- 84. REFERENCES • Premkumar, S., 2011. Textbook of Craniofacial Growth • Proffit, W.R., Fields, H.W. & Sarver, D.M., 2013. Contemporary orthodontics • Som, P.M. & Naidich, T.P., 2013. Development of the Skull Base and Calvarium: An Overview of the Progression from Mesenchyme to Chondrification to Ossification • Thiesen, G. et al., 2013. Comparative analysis of the anterior and posterior le ngth and deflection angle of the cranial base, in individuals with facial Pattern I, II and III. Dental press journal of orthodontics.