development of the skull e-learning

8/2/2019 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

development of the skull e-learning

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