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Cranial Vault

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									     Pre and Post Natal Development of the
                 Cranial Vault

Introduction
Conventionally, the craniofacial region is divided into 4 major regions, in order to
better understand growth.

These regions are:-
   1. The Cranial Vault
   2. The Cranial Base
   3. The Naso-maxillary complex
   4. The Mandible

The growth of each region is further divided into:-
   1. Pre natal
   2. Post natal

To understand how the growth occurs we need to pay attention to the following
aspects:-
   1. The sites and location of growth.
   2. The type of growth.
   3. The determinant and controlling factors.



Anatomy of the Cranial Vault – In Brief
Synonyms –
   1. Calvaria, and not Calvarium
   2. Cranial vault
   3. Desmocranium
   4. Calva
The skull may be viewed from different angles:-
   1. Above – Norma Verticalis
   2. Below – Norma Basalis
   3. Side – Norma Lateralis
   4. Behind – Norma occipitalis
   5. Front – Norma frontalis
The cranial vault spans from the superciliary ridges and glabella of the frontal
bone, upto and including the squamous occioital bone. It also includes part of the
squamous temporal bone, laterally.

When seen from above:-




The vault is roughly ellipsoid, with the greatest width at its occipital end. The
bones that make up the vault are-
The frontal bone – It forms the forehead. It passes back to meet the two parietal
bones at he coronal suture.
At birth, a suture is seen between the 2 halves of the frontal bone – the frontal or
metopic suture. It usually closes early in life, but may persist into adulthood in 10-
15% of cases.

The parietal bones form most of the cranial vault. They articulate in the midline at
the saggital suture.

Posteriorly, the parietal bones articulate with the occipital bone at the lambdoid
suture (named after the Greek letter ‘lambda’, which it resembles in shape).

Laterally, the parietal bones extend upto the greater wing of the sphenoid –
anteriorly, and squamous temporal bone- posteriorly.

The junction of the coronal and saggital suture is known as the ‘bregma’ and
The junction of the lambdoid and saggital suture is known as the ‘lambda’.

Also, there is a parietal eminence on each side and a frontal eminence anteriorly.

The vault is covered by the SCALP which has 5 layers-
Skin, subcutaneous tissue, aponeurosis of the occupito-frontalis, loose areolar
tissue, and pericranium.




                            Pre-natal Growth
The cranial vault is a derivative of the mesenchyme, which is initially arranged in
the form of a capsular membrane around the developing brain.

The membrane has 2 parts:-
     Endomeninx- derived from neural crest cells
     Ectomeninx – derived from neural crest cells and paraxial mesoderm.

The ectomeninx deferentiates into :-
             Inner dura mater
             Outer superficial membrane with osteogenic properties

The part of the superificial membrane which is over the dome of the brain ossifies
intramembranously and forms the vault.
The part that is below the brain, ossifies endochondrally and forms the cranial
base.

The endomeninx differentiates into:-
            Piamater
            Arachnoid.


During their development, the 2 layers (ectomeninx and endomeninx) remain in
close apposition, except in areas where the venous sinuses will develop. The
duramater shows distinctly organized fiber bundles, which later develop into the
various folds – falx cerebri, falx cerebelli and tentorium cerebelli.

These bands also, to an extent , control the shape of the brain, which would
expand as a perfect sphere if it were not for them.

Sites of ossification                     Sites of the future bones.

Type of Ossification                      Intra membranous.

Controlling factors                       Brain
Endomeninx gives rise to the following bones –
Mesoderm – frontal, parietal, sphenoid, petrous temporal and occipital.
Neural crest – lachrymal, nasal, squamous temporal, zygomatic, maxilla &
mandible.

The individual bones form from various primary and secondary ossification
centers.

Frontal bone
        Single primary center in the region of the superciliary arch. This appears in
     th
the 8 week of intrauterine life.
3 secondary ossification centres appear in the zygomatic process, nasal spine and
trochlear fossae.

Parietal bones
       1 primary center each in the region of parietal eminence. These do not fuse
with each other, and a saggital fontanelle remains between them, at birth.

Occipital bones
       Squamous portion ossifies intramembranously – primary center appearing
just above the supranuchal lines.

Squamous part of tempral bone
     Single ossification center appearing at eht root of the zygoma.

Tympanic ring of the temporal bone
     4 centres on the lateral wall of the tympanum.

Also, the development of sutural bones occurs if any unusual ossification sites
develop. Most centers of ossification appear during the 7th or 8th week intrauterine,
but ossification is not complete until after birth. Appart from fontanelles, the
sutures themselves are wide, with syndesmotic articulations.

The fontanelles are named according to ther relation with the parietal bones-
Anterior, posterior, 2 – antero-lateral, 2 – postero-lateral.

These close at varied times between 2 months after birth (post. And ant.lateral)
and 2 years (ant. And post.lateral).
Sutures continue to ossify until they fuse, sometime in adult life.

Van Limbourgh poses 3 questions in relation to control of morphogenesis
(prenatal growth)of the skull –

   1. Is there a relationship between development of the skull and presence of
      primordial of other organs?
   2. How is endochongral and intramembranous growth coordinated?
   3. How is growth of the skull and growth of other organs coordinated?


3 major controlling factors come to mind:-

   1. Intrinsic Genetic factors – or direct hereditary influence of genes
   2. Epigenetic factors – indirect genetic control through intermediary action on
      the associated structures (eye, brain etc)
   3. Environmental factors

Earlier a totally genetic influence was thought to control the cranial differentiation.
                                            Intrinsic Genetic control

                                            Local epigenetic factors
             Cranial                        General epigenetic factors
         differentiation
                                            Local Environmental factors

                                            General Environmental factors
But various observations have served to swing the pendulum more in favor of
epigenetic influences.
Example – If the primordial of the eye does not develop, usually, the orbits do not
develop. The number of orbits that develop correlates with the number of eyes that
develop.

   -   If no brain develops, no cranial vault develops (anencephaly).

Generally accepted –
   Role of genetics to a small extent.
   More acceptance to local epigenetics.
   Also consideration of general epigenetics and local and general
      environmental factors.
                                      Intrinsic Genetic control

                                      Local epigenetic factors

           Cranial                    General epigenetic factors
       differentiation
                                      Local Environmental factors

                                      General Environmental factors



             Post Natal Growth of the Cranial Vault

   1. Growth of the skull vault is closely related to growth of the brain.
   2. Due to rapid growth of the CNS up to the 5th year of life, it is seen that the
      calvaria is relatively bigger at birth than in adulthood. This reflects the
      cephalocaudal gradient of growth.
   3. There is a different explanation of growth of the vault according to different
      theories of growth. In order to understand the site of growth of the cranial
      vault, the type of growth and controlling factors, it is important of look at
      some of the theories of growth and how different theories have interpreted
      cranial growth in different ways.

Theories of growth and how they relate to the growth of the cranial
vault.


   1. Sutural growth theory
            Sicher said that skull growth was genetically deremined. That
            growth occurred at the dutures. Local factors, like muscle activity
            had only a mild effect.

   2. Scott’s Theory
             Scott gave importance to cartilage growth. He said that cartilage had
             inherent growth potential and sutures grew in response to
             cartilaginous growth.
             Therefore, sutures respond to growth at synchondrosis and to
             environmental factors.

   3. Moss’ FMH
            Moss postulated the role of functional matrices which are formed by
            non osseous tissue. Hence, this is an example of epigenetic control
            and environmental control.


Combination of the Theories

Sicher claimed that the growth was under intrinsic genetic control, but from the
work of Moss, we know that this is not a direct control, but epigenetic control.
Hydrocephaly, microcephaly and anencephaly are testimony to this.

What Scott’s exoeriments showed, is that cartilages are not responcive to pressure
or tension, but intramembranous bone is. Therefore one could deduce that as the
synchondroses grow, there is tension created at the sutures, and bone deposition
occurs. This view is supported by others – Sarnat, Burdi, Baume,, Petrovic etc.
This also explains why growth of the cranial base is influenced less by brain
growth as compared to the cranial vault.

We are familiar with Moss’ explanation for control of none growth ny brain
growth. He expecially based his theory on the fact that in the synostosis
syndromes, though the craniu cannot grow, the brain continues to grow. The
growth is deen in many ways – example, bulging of the eyes.




But it is interesting to see that if growth were to be explained entirely on the basis
of the FMH, in hydrocephaly or anenchphaly, even the cranial base would be
relatively large or small, as the growing brain would exert equal force in all
directions.

                                   V A    U L T




                                      Brain



                                         B A S E


But what is seen, is that the cranual base remainls more or less normal. (Burdi,
Van Limborgh, Sarnat, Latham, Baume, Petrovic & others.)

Thus there is some support for Scott’s theory, that cartilage growth is under
genetic control.

So the modern view should be a rational amalgamation of these theories. This has
been summarized by Van Limborgh as under:-

   1.   Intrinsic control of growth is exhibited at the synchondroses.
   2.   The intrinsic control of sutural growth is less
   3.   The Synchondroses should be considered as growth centres.
   4.   Sutural growth is controlled, in part, by growth at the synchondroses.
   5. Some amount of periosteal growth also takes place in the cranial vault, this
      is controlled epigenetically.
   6. Growth of the cranial vault is also controlled, to some extent by local
      environmental factors (muscle forces inclusive).

                                        Intrinsic Genetic control
        Chondrocranial
           Growth
                                        Local epigenetic factors


                                        General epigenetic factors



         Desmocranial                   Local Environmental factors
           Growth

                                        General Environmental factors




                         Growth of the Cranial Vault
Growth of the cranial vault is directly influenced by pressure from the
neurocranial capsule.




As the brain expands the cranial vault bones are separated, at the sutures and the
resulting space is closed by proliferation of connective tissue at the suture and its
subsequent ossification. BUT the bones are NOT PUSHED outwards.

Each bone is enmeshed in a stroma, which is continuous with the meninges and
skin. Hence, as the brain grows, this connective tissue stroma separates the bones
at the sutures.
Another change taking place is periosteal growth. In general, deposition occurs
both, at the inner table and outer table of the bones of the vault, and resorption
occurs at the endosteal surface. The effect is twofold:-

   1. To flatten the bones.
             At birth, the bones are quite curved. The remodeling serves to flatten
             the bones and hence arrange them along a bigger arc. There may be
             certain areas of reversal of the resorption – deposition pattern
             mentioned earlier, in order to achieve this.




   2. This also helps to increase the thickness of the bones.
             At birth the bones are thin and lack the spongy diploë between the
             inner and outer table.
             According to Sicher, the thickening is not uniform, as the inner table
             is influenced by the growth of the brain, while the outer table is
             influenced by mechanical force, especially of muscles in the
             supraorbital, otic and mastoid regions.

Another response to functional stresses is the development of the frontal
sinus(Benninghoff). As the thickness of the bone increases, the supraorbital ridges
develop due to more thickening of the outer table. Then, the spongy bone between
the inner ans outer table is slowly filled in by the developing sinus.

90% of the cranial vault growth of completed by the age of 5 – 6 years, as has
been shown by Davenport. This is in accordance with Scammons curve for brain
growth as well as the cephalocaudal gradient.




                           Clinical Implications
   1. Synostosis Syndromes
           These syndromes result from early closure of the sutures between
the cranial and facial bones. Ti is obvious that, since growth occurs at the
sutures, cranial growth will be extremely limited.
           Apart from limited cranial growth, maxillary growth is also limited
due to synostosis of the circum-maxillary sutures. The orbits are bulging – due
to a combination of increased intracranial pressure and underdevelopment of
the maxilla.
           Treatment – Surgery to release sutures

2. Hydrocephaly, Microcephaly and Anencephaly
          Change in the size of the vault due to increased CSF or absence of
   the brain.




                        Microcephaly

3. Herniation of the dura into the nose.
           For some time, the dura covering the forebrain and the ectoderm
remain in contact at the surface, I the region of the anterior neuropore. When
the frontonasal process bends ventrally, the dura lies near the future frontonasal
process. Then, the nasal capsule forms around it. A midline canal is formed,
which later develops into the foramen caecum, when the dura separates from
the ectoderm. The foramen caecum, then closes. If this fails to happen, it
leaves an are from where the dura can herniated into the nasal cavity. It can
also lead to the formation of dermoid cysts, sinus, or encephalocele.
4. Distortion of the head during birth which is possible due to the presence of
   Fontanelles.




5. Development of the outer superstructure of the vault due to muscular forces
   esp mastoid, temporal and nuchal line, coronid process etc. Direct
   dependence on muscular activity.
6. Abnormal external forces, as applied by headboards etc to attain bizarre
   shapes of the cranium. This was done by some primitive tribes.
7. In various conditions – cretinism, progeria, trisomy 21, cleidocranial
   dysostosis – there is delayed ossification of the frontal suture, and anterior
   fontanelles remain open into adult life. It results in a brachycephalic skull
   and ‘bossed’ forehead, and highly curved frontal and parietal bones and
   hypertelorism.




                                References:

 Craniofacial Embryology
                   -G.H.SPERBER

 Essencials Of Facial Growth
                   -D.H.ENLOW

 Anatomy –Gray
 Abnormalities Of Cleidocranial Disostosis – Kreiborg,bjork& Skeiller
  (Ajo May; 1981 )


 Cranial Base Growth For Dutch Boys & Girls – M.Herneberke,b.P.
  Andersen (Ajo November; 1994 )

 Contemporary orthodontics
                  W.R.PROFFIT

								
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