Growth of the skull vault and base
- Introduction
- Anatomical Reminder
- Embryological Reminder
- Skull Vault Growth
- Growth of the base of the skull proper
- Increase in length of the base of the skull
- Increase in width of the base of the skull
- Influence of Skull Base Growth on the Face
- Conclusion
- Introduction :
The skeleton of the head is made up of a bony box: the skull . At its antero-inferior end is attached a bony mass: the face . The junction between the two is ensured by the base of the skull which occupies a key position.
The growth of the skull base is a complex phenomenon that can be influenced by multiple factors, it is related to the growth of the brain and the play of the sutures, partly causing the growth of the face.
- Anatomical reminder
The skull is an ovoid bony box with a large posterior end enclosing the brain. It is the only part of the skeleton where the 2 types of ossifications coexist:
- Membranous ossification affects most of the vault and face.
- Enchondral ossification mainly affects the base. It occurs spontaneously.
Growth of the arch and base occurs mainly during the first two years of life and then more slowly until the age of 7 years.
So the skull is presented in 2 parts:
- An upper part: the vault or the cranial cap;
- A lower part: the base of the skull.
We are talking about the cranium which contains the brain:
The vault of the skull or calvaria: which has a protective role, is formed by:
- The vertical part of the frontal in front.
- The parietals and the scale of the temporals on the sides.
- The upper part of the occipital behind.
This vault presents on the median line and from front to back the metopic suture then the sagittal suture.
On the sides, the fronto-parietal or coronal suture and the parieto-occipital or lambdoid suture.
The junction of the sagittal suture with the frontoparietal suture constitutes the “Bregma” point.
The meeting of the parieto-occipital and sagittal sutures constitutes the “Lambda” point.
The base of the skull: Is divided into three parts : from front to back, we distinguish
- The anterior floor consists of the ethmoid in front, and the sphenoid in the center and laterally (the basi-sphenoid and the sphenoid wings). On each side, we notice the significant and irregular relief of the roof of the orbits. The sella turcica is in the center of the sphenoid.
- The middle floor constituted by the upper face of the rock or petrous bone which contains the organs of hearing (middle ear and inner ear).
- The posterior floor, or posterior fossa , is formed in front by the basi-sphenoid, and laterally by the posterior face of the petrous bone. The occipital scale closes the cranial cavity behind, leaving a large exit orifice, the occipital foramen.
The bones of the base of the skull are flat bones that have two faces :
- An internal or endocranial face .
- An external or exocranial face.
These flat bones are connected by sagittal and transverse sutures ;
- Sagittal sutures:
- metopic suture which then divides into two paths
- synchondrosis separating the lesser and greater wings of the sphenoid
- anterior intra-occipital synchondrosis
- Transverse sutures:
- ethmoidosphenoidal synchondrosis
- inter or intra-sphenoidal synchondrosis
- spheno-occipital synchondrosis
- posterior intra-occipital synchondrosis.
- Embryological reminder:
The skull is made up of two large parts:
- the neurocranium which protects the brain
- the viscero-cranium which forms the facial skeleton
In the human embryo, the earliest manifestation of skull formation is the concentration of mesenchyme around the dorsal cord in the hindbrain during the fifth and sixth weeks.
This mesenchymal formation is made up of two elements:
– above the neural tube cranial cap or vault
– below a plate which forms the base of the skull.
At the seventh week , the skull begins to become cartilaginous, this cartilaginous rudiment called chondrocranium forms in the region of the future sphenoid and extends into the occipital and optic region and also forward into the chondroethmoid . It encapsulates the sensory expressions of the brain and forms a cartilaginous mask.
It is within this cartilaginous model that bony centers will appear :
- body, the lesser wings and part of the greater wings of the sphenoid.
- the petrous part of the temporal bone
- the basilar and exoccipital part of the occipital
- ethmoid
- lower horn
In addition, the mesenchymal membrane bones intended to form the roof of the cranium (the upper and vertical part of the frontal bone, the parietals, the squama of the temporal bones, the upper part of the occipital) are acquired.
They make up the upper wall and sides of the skull. As well as the bones of the face and jaws.
They never turn into cartilage and bone forms directly in the membranous tissue.
- Growth of the skull vault:
Its ossification is membranous and development occurs partly within the framework of brain development. Indeed, the increase in the size of the brain tends to separate the sutures of the vault of the skull which respond by apposition at the level of the edges of the cranial bones, and by external apposition and of course internal resorption accompanying brain growth and this up to 6 years.
Growth at the sutures (mentioned above) persists even in adolescents and does not permanently close until adulthood (the metopic suture closes around 3 years of age ).
Two medians:
- The anterior fontanelle or bregmatic fontanelle fuses around the age of 2 years.
- The posterior fontanelle or lambdatic fontanelle fuses around the age of 2 months.
Four sides:
- Two anterior lateral fontanelles or pteric fontanelles fuse together around the age of 2 to 3 months.
- two posterior lateral fontanelles or asterisk fontanelles fuse together around the age of 2 years.
- In young children , the volume of the cranium is greater than that of the facial mass, due to the rapid growth of the brain. The mode of growth is centrifugal.
This will be achieved through sutural growth and peiosteal growth.
- sutural growth and fontanelles:
The bones of the cranial vault are separated by bands of connective tissue called membranous sutures or syndesmoses which will allow the growth and union of the various skeletal parts, in parallel with the increase in the volume of the brain:
- Metopic: between the frontal hemi.
- Coronal or fronto-parietal.
- Sagittal or interparietal.
- Lambdoid or parieto-occipital
- Sphenotemporal.
- Temporo parietal.
- Occipitotemporal.
According to VIRCHOW’s law 1851 , each suture allows the growth of the arch in the direction perpendicular to the suture concerned.
Transverse growth : occurs through the activity of the metopic and sagittal sutures.
Antero-posterior growth: occurs through the coronal suture in front and the lambdoid suture behind.
Vertical growth : more important than antero-posterior growth, it is achieved through the entire sutural system.
Chronology of fontanelle closure:
Lambda : 2 months
Pteryon: 3-6 months
Bregma: 6-18 months
Asterion : 25-30 years (Disacorn)
Sutural growth is catch-up growth, essential for brain development. It is secondary to growth stimulators, the encephalon, the main functional matrix of the skull vault.
- Peiosteal remodeling growth:
Indeed, the increase in brain size tends to separate the sutures of the skull vault which respond with remodeling growth.
For ENLOW, remodeling growth occurs concomitantly with sutural growth, which is still active up to 7 years of age .
It is done through a process of apposition on the exocranial surfaces and resorption on the endocranial surfaces.
The formation of the cranial sinus is also due to phenomena of external apposition and internal resorption.
So the vault is subject to two constraints, one internal which is the growth of the brain, the other external, the pericranial musculature.
Remodeling growth also allows the bone to move and increase its thickness while maintaining its own morphology.
It is under the influence of conformators : muscles, the brain, the vascular and nervous elements and the dura mater aponeuroses.
Muscular action gradually shapes the surface of the skull and gives rise to protuberances that do not exist in the newborn.
Pathological growth of the skull vault :
- Anencephaly is characterized by a complete absence of the cranial vault.
- Hemibrain atrophy corresponds to normal development of one hemibrain.
- Microcephaly.
- Hydocephaly: hypersecretion of cerebrospinal fluid
- The intentional distortions of certain populations.
- Craniostenosis
Conclusion: the growth of the skull vault is carried out by the connective tissue and the sutures, the ossification centers here have no action.
Its study appears very important in the assessment of the etiopathogenesis of maxillary malformations encountered in ODF.
- Growth of the base of the skull itself:
The growth of the base of the skull is essentially cartilaginous . It is related to the growth of the brain, and practically influenced by the size of the latter on the one hand and on the other hand by the play of the sutures which play an important role in the anteroposterior and lateral growth, while the increase in thickness seems to be carried out only by appositions .
- Increase in length of the base of the skull:
- Changes due to sutures:
- Ethmoid-sphenoidal synchondrosis
- Inter or intrasphenoidal synchondrosis
- Spheno-occipital synchondrosis
- Basi-exo-occipital synchondrosis or posterior intra-occipital synchondrosis
This sutural growth is predominant especially during the first years of life in relation to the growth of the brain .
As a result of the rapid closure of these anterior sutures, the dimension of the internal face of the frontal to the sella turcica is established very early .
Modifications remain possible in the posterior part of the base of the skull, between the sella turcica and the occipital hole, this part being oblique downwards and backwards, a displacement directed in this direction is detectable at the level of the glenoid cavity and therefore of the lower maxilla.
- Modification by apposition and resorption:
The growth in length by this process is small, it is observed mainly on the anterior surface of the frontal, which leads to the formation of the brow and orbital arches.
Resorption occurs on either side of the midline into the mass of bone and produces the frontal sinuses.
The result is that the child’s bulging forehead becomes flatter and more receding in adults.
The external orbital processes and temporal crests develop by apposition.
Finally, we note slight modifications at the level of the occipital scale.
- Increase in width of the base of the skull:
- Changes due to sutures:
The growth in width of the base of the skull only occurs during the first year of life , it occurs through the longitudinally oriented sutures :
metopic syndesmosis: it separates the 2 halves of the frontal at birth, divides into two parallel paths from the blind hole, each continuing with a synchondrosis separating the body of the small and large wings of the sphenoid, the anterior torn hole and the anterior intra-occipital synchondrosis. From the 1st year the small and large wings of the sphenoid fuse to the body of the sphenoid. The metopic suture remains more or less active until 2 years.
- Anterior intraoccipital synchondrosis disappears around the age of 5 years.
- The cribriform plate of the ethmoid bone ossifies around 3 years of age.
- Modification by apposition and resorption :
There is an apposition on the external face of the base of the skull and a concomitant resorption of its internal face in order to respond to the intense growth of the brain.
- Construction of the mastoid processes
- CAE Training
- Formation of the glenoid cavities.
- INFLUENCE OF SKULL BASE GROWTH ON THE FACE:
– the maxilla in its anterior part
– the mandible in the posterior and lateral part, via the ATM.
It is from this that the face will be constructed and developed.
Its growth influences the relationship between the two maxillae
The movement of one bone would induce the movement of the other bones under a primary directive force (SUTHERLAND and his successors).
The important element is the integration of this individual mobility into the overall movement of the cranial puzzle, to achieve a state of balance between the different skeletal parts which is driven by the large flexion mechanism of the base of the skull.
The architectural balance always evolves in the direction of a flexion of the base of the skull to more or less advanced degrees.
The sphenoid bone is the inductive element of all craniofacial biomechanics.
For DELAIRE , it is the “building ground of the face”.
Lengths of the craniofacial and craniospinal fields participate in the determination of skeletal cl. II and cl. III.
DESHAYES according to the degree of flexion of the base of the skull (corresponds to the angular variation around the spheno-occipital synchondrosis):
- hypoflexion promotes skeletal cl. II
- hyperflexion promotes skeletal cl. III
- CONCLUSION :
The growth of the base of the skull is the subject of numerous studies, which have shown that the process is based on interactions between several elements.
To understand how craniofacial growth remains harmonious or deteriorates, it is necessary to know the course of the phenomenon of flexion of the base of the skull and its influence on facial architecture.
Growth of the skull vault and base
Deep cavities may require root canal treatment.
Dental veneers correct chipped or discolored teeth.
Misaligned teeth can cause uneven wear.
Dental implants preserve the bone structure of the jaw.
Fluoride mouthwashes help prevent cavities.
Decayed baby teeth can affect the position of permanent teeth.
An electric toothbrush cleans hard-to-reach areas more effectively.