Development of the Skull E-learning
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Transcript of Development of the Skull E-learning
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Development of The Skull
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Development of The Skull
The skull bones develop from loosely organized embryonic C.T.that surrounds the brain (Mesenchyme)
2 bone formation mechanisms:
1. Intramembranous Ossification:
mesenchyme
bone(flat bones)
2. Endochondral Ossification
mesenchyme cartilage bone(long bones, cranial base)
The development of the skull starts during fetal period (Prenatal),however it continues after birth (Postnatal) until adulthood
(16-18y)
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Intramembranous Ossification
Mesenchyme condenses & become highly vascularized
Mesenchymal cellsosteoblasts
Osteoblasts start to deposit bone matrix
trabeculae
Osteoblasts trapped in the matrix they secretosteocytes
As growth continue, trabeculae become interconnected
to formWoven bone
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Endochondral Ossification
Mesenchyme turns into cartilaginous model
Centers of ossification appear within the cartilage &
start to spread out
Within these ossification areas:
chondrocytes enlarge
matrix become calcified
cells die
Perichondrium becomes periosteum
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Formation & Prenatal Development ofThe Skull
Prenatal skull consists of:
- Neurocranium (brain case)
Membranous part: formed by ?, Cranial vaultCartilaginous part: formed by ?, Cranial base
- Viscerocranium (facial sk.)
Memebranous: Jaw bones & Zygoma
Cartilaginous: ear ossicles, mandibular condyle
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Membranous Neurocranium
develops by intramembranous ossification to form C.V.
Includes cranial vault bones (Calvaria):
-Frontal
- Parietal
- Sq. of Temporal
- Sq. of Occipital
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Cartilaginous Neurocranium
Formed by fusion of several cartilages that develops later into thecranial base by endochondral ossification
Includes cranial base bones:
- Basilar occipital bone
- Petrous temporal bone
- Sphenoid bone
- Ethmoid bone
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Prenatal Cranial Base Cartilages
Several cartilages formed around the age of ?
& fuse together to form the cartilaginous cranial base(Chondrocranium) at the age around ?
Later on:
chondrocranium cartilages ossified to form bony cranial base
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Chondrocranium Cartilages
Parachordal (basal) cartilage
basilar occipital
Hypophysial cartilage
forms around hypophysis (?)
body of ?
Trabeculae Carnii
body of ?
Ala Orbitalis
lesser wing of sphenoidOtic Capsule
petrous & mastoid part oftemporal bone
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Membranous Viscerocranium
Formed by intramembranous ossification
Includes:
Maxillary bones
Zygomatic bones
Nasal bone
Mandible (Except?)
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Cartilaginous Viscerocranium
Formed by endochondral ossification
Includes:
Middle ear ossicles
Styloid process of temporal
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Postnatal Period
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Newborn Skull
Characteristics
Round & its bonse are thin
Large in proportion to the rest ofthe body
Large cranium relative to face
Small size jaws
Calvaria bones are separated by
C.T. membranous areas(Fonatanelles)
Absence of air sinuses
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Postnatal Growth of The cranium
Contains 6 fontanelle areas:permit the cranium to enlarge in order to accommodate the
growing brain
The in calvaria size is greatest during first ?? of life
most head growth is accomplished by expansion along suturelines & fontanelles. Thereafter, the skull grows by internalresorption and external replacement.
Skull continues to in capacity until adulthood (16-18y)
In facial height coincides with the growth of alveolar processes& eruption of deciduous teeth
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Cranial Fontanelles
6 unossified membranous areas
Anterior fontanelle:
2 frontal & 2 parietal
Posterior fontanelle:2 parietal & occipital
2 Anterolateral (Sphenoid):
F, P, T, & S
2 Posterolateral (Mastoid):
P, T, & Occip.
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Clinical:
Developmental Abnormalitiesof The Skull
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Acrania
Failure of the cranial vault to develop
(Absence of Calvaria)
Associated with
Anencephaly (absence of the brain)
~1/1000 birth
Incompatible with life
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Microcephaly
Small size calvaria with normal size face
Infant has a small underdeveloped brain (Microencephaly)
mental retardation
Causes:
Genetic
Environmental:viral infection in utero (?)
Ionizing radiation
Alcohol abuse
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Craniosynostosis
Several kinds of skull deformities result from premature closure ofone of the skull sutures
Males than females
Types: (depend on which suture closes)Scaphcephaly: (~50%)
premature closure of sagittal suture
Oxycephaly (Turricephaly):
premature closure of ? Suture
Plagiocephaly:
premature closure of coronal or lambdoid
suture on one side
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Scaphocephaly
Premature closure of sagittal suture
long, narrow, wedge-shaped skull
~ 50% of cases
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Oxycephaly (Turricephaly)
Premature closure of coronalsuture
High, tower-like skull
~ 30% of craniosynostosis
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Plagiocephaly
Premature closure of coronal orlambdoid suture on one side
Twisted, asymmetrical skull
- Genetic Factors
Enviromental Factor:
sleeping position
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Positional Plagiocephaly
A positional deformity that developsduring infant sleeping in the sameposition most of the time
It is primarily a cosmetic issue
However, 10-15% intracranial Pr.The sooner the problem is addressedthe better the outcome
Rx.:alternate sleeping position
5-6 months orthotic management
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Cloverleaf Skull
Premature closure of all threesutures together (S, P, & L)
Cranial vault growth ceased
However, the cranial basecontinue to grow in size
Most common characteristic ofThanatophoric Dwarfism type II
Due to mutation in FGFR3