1 osteology of cranial bones rt(67) dr. rahul tiwari

05/02/2023 12:14 AMRT/OSTEOLOGY OF CRANIAL BONES/63

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OSTEOLOGY OF CRANIAL BONES

PRESENTED BYDr. RAHUL TIWARI

1ST YEAR MDS - PG StudentDEPT. OF ORAL & MAXILLOFACIAL SURGERY

SIBAR INSTITUTE OF DENTAL SCIENCES

GOOD AFTERNOON


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CONTENTS INTRODUCTION CRANIAL BONES

EMBRYOLOGY ANATOMY VARIATIONS

APPLIED CLINICAL ASPECTS SURFACE ANATOMY AND ITS IMPORTANCE DEVELOPMENTAL DISTURBANCES

CONCLUSION


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INTRODUCTION Osteology- The branch of anatomy that

studies the bones of the skeleton. Cranial- Of or relating to the cranium

which encloses the brain. Bones- Rigid connective tissue that

makes up the skeleton. Skeleton- The hard structure (bones and

cartilages) that provides a frame for the body.


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EMBRYOLOGY Cranium is formed from:

● Paraxial mesoderm ● Neural crest

Cranium development occurs in Neurocranium forms the bones of the cranial base and cranial vault

and can be divided into membranous neurocranium and cartilaginous neurocranium

Bony cranium is formed by either of 2 mechanisms: ● Intramembranous ossification ● Endochondral ossification


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MEMBRANOUS NEUROCRANIUMGerm Layer

Portions of Neurocranium

Adult Structure

Ossification

Neural crest

Main portion of the roof and lateral sides of the cranial vault

Frontal bone

Squamous portion ofthe temporal bone

Intramembranous

Paraxialmesoderm

Main portion of the roof and lateral sides of the cranial vault

Parietal bone

Occipital bone(intraparietal portion)

Intramembranous


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CARTILAGINOUS NEUROCRANIUM

Germ Layer

Portions of Neurocranium

Adult Structure Ossification

Neural crest

Prechordal

Anterior to the sella turcica

Ethmoid

Sphenoid

Endochondral

Paraxialmesoderm

Chordal

Posterior to the sella turcica

Petrous portion of the temporal bone

Mastoid process of thetemporal bone

Occipital bone

Endochondral


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INTRAMEMBRANOUS OSSIFICATION Intramembranous or endesmal

ossification occurs in the connective tissue of the primary (membrane) bones.

The future bones are first formed as connective tissue membranes, that are replaced with bony tissue They include certain flat bones of the skull and some of the irregular bones.

The osteoblasts migrate to the membranes and deposit bony matrix around themselves.

As a result of osteoblastic activity appear

points (centers) or nuclei of ossification.


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ENDOCHONDRAL OSSIFICATIONEndochondral or enchondral ossification involves the replacement of hyaline cartilage with bony tissue. Most of the bones of the skeleton are formed in this manner


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ENDOCHONDRAL OSSIFICATION


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THE PRIMORDIAL CARTILAGES OF THE CHONDROCRANIUM AND THEIR DERIVATIVES


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MEMBRANE BONES AT 9 & 12 WEEKS

Brown-Pharyngeal arch mesenchyme for viscerocranium

Red- Head mesenchyme for neurocranium

Blue- Cartilage from pharyngeal arches for viscerocranium and neck cartilages.

Purple- Cartilage from somite sclerotomes and neural crest anteriorly for base of neurocranium.

Brown & red- Intramembranous ossification

Purple & blue- Endochondral ossification


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SKULL OF NEWBORN

Fontanelle Time of Closure

Anterior fontanelle (bregma) 4–26 months Posterior fontanelle (lambda) 1–2 months

Sphenoidal fontanelle (pterion) 2–3 months Mastoid fontanelle (asterion) 12–18 months


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POSTNATAL GROWTH Growth of the vault is rapid during the

first year and then slower to the seventh.

Growth in breadth occurs at the sagittal, sphenofrontal, sphenotemporal and occipitomastoid sutures and petro-occipital cartilaginous joints.

Growth in height occurs at the frontozygomatic, pterion and asterion.


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POSTNATAL GROWTH During this period fontanelles are closed by

ossification of the bones around them, but separate centres may convert them into sutural bones.

At birth the vault is unilaminar. Tables and intervening diploe appear about the fourth year, with maximal differentiation at about 35 years, when diploic veins are prominent in radiograms.

Growth ceases by 15 yrs in male and 17.5 yrs in males


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THE SECTIONAL ANATOMY OF THE SKULL

Figure 7.4a


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CALVARIA

Frontal bone - 1

Parietal bone - 2

Temporal bone - 2

Occipital bone - 1

Sphenoid bone - 1

Ethmoid bone - 1

-Unpaired bones:

frontal bone, ethmoid bone, sphenoid bone, occipital bone

-Paired bones:

temporal bone parietal bone


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ARTICULATION


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ARTICULATIONS. NO.

Bone Single

Paired

Articulates with

1 Frontal X Parietal, sphenoid, zygomatic, maxilla, ethmoid, nasal, lacrimal

2 Parietal X Frontal, parietal, temporal, occipital, sphenoid

3 Temporal

X Parietal, occipital, sphenoid, zygomatic, mandible

4 Occipital X Parietal, temporal, sphenoid, and atlas (C1)

5 Sphenoid

X Frontal, parietal, temporal, occipital, zygomatic, maxilla, ethmoid,palatine, vomer

6 Ethmoid X Frontal, sphenoid, maxilla, palatine, vomer, nasal, lacrimal, inferiornasal concha


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FRONTAL BONE


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FRONTAL BONE


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FRONTAL BONE


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Characteristics Part

sOssification

Comments

Contains the frontal & paranasal sinusesHas two primary centers that ossify alongfrontal suture (metopic) in the 2nd yearHelps form the foramencecum, which allows passage of an emissaryvein that connects to the superior sagittal sinus There is 1 frontal bone

Squamous part

For all 3 parts: intramembranous

The largest part of the frontal boneForms the majority of the foreheadForms the supraorbital margin and the superciliary arch. The zygomatic process of the frontal bone extends from the posterior part of supraorbital marginArachnoid foveae—depressionscaused by arachnoid granulationsthat push on the Dura mater,causing bone resorption on theendocranial surface

Orbital part

Forms the roof of the orbit and floor of the anterior cranial fossa

Nasal part

The trochlea of the orbit articulateswith the orbital portionArticulates with the nasal bonesand the frontal process of themaxilla to form the root of the nose


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OCCIPITAL BONE


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sOssification

Comments

Forms the posterior part of the cranial vault articulates with the atlas The squamous andlateral portionsnormally ossifytogether by year 4 The basilar portion unites to this sectionat year 6There is 1 occipital Bone

Squamous portion

Intramembranous

Articulates with the temporal and parietal bonesArticulates with the largest portion of the occipital bone Located posterior and superior to foramen magnumHas the external occipital protuberance (more pronouncedin males) Has the superior and the inferior nuchal linesHas grooves on the internal surface for 3 of the sinuses forming the confluence of the sinuses (the superior sagittal andthe right and left transverse sinuses)The depression superior to the transverse sinus is for the occipital lobes of the brain The depression inferior to the transverse sinus is for the Cerebellum

Lateral portion

Endochondral

Articulates with the temporal Bone Is the portion lateral to the foramen magnum Has the occipital condyles that articulate with the atlasContains the hypoglossal canal Forms a portion of the jugular foramen

Basilar portion

Endochondral

Articulates with the petrous part of the temporal and the sphenoid bones Is the portion immediately anterior to the foramen magnum Pharyngeal tubercle is part of the basilar portion that provides attachment for the superior Constrictor Internal surface of the basilar portion is called the clivus, and part of the brainstem lies against it


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SPHENOID BONE


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SPHENOID BONE


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SPHENOID BONE


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SPHENOID BONECharacteristics

Parts

Ossification

Comments

Forms the majority of the middle portion of the cranial base & fossa contains the sphenoid paranasal sinus. There is 1 sphenoid bone

Body

Endochondral ossification

The center of the sphenoidAnterior portion of the body helps form part of the nasal cavitySuperior part of the body, known as the sella turcica, is saddle shaped and possesses the anterior and posterior clinoid processes Hypophyseal fossa, the deepest part of the sella turcica, houses the pituitary gland Dorsum sellae is a square-shaped part of the bone that lies posterior to the sella turcica Clivus is the portion that slopes posterior to the body contains the sphenoidparanasal sinuses Lateral portion of the body iscovered by the cavernous sinusOptic canal is found in the body ofthe sphenoid


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Pterygoid process

Intramembranous ossification

Arises from the inferior surface of the body.There are 2 pterygoid processes, Each has a:● Lateral pterygoid plate ● Medial pterygoid plate Pterygoid hamulus extends from the medial pterygoid plate Two canals are associated with the pterygoid process: ●Pterygoid canal ● Pharyngeal canal

Lesser wing

Endochondral ossification

Extends laterally and anteriorly from the superior portion of thesphenoid body Separated from the greater wing bythe superior orbital fissure

Greater wing

Endochondral and intramembranous ossification

Extends laterally and anteriorly from the posterior portion of the body of the sphenoidEndocranial portion helps form a large part of the middle cranial fossaLateral portion is the infratemporal surfaceAnterior portion lies in the orbitContains 3 foramina:● Foramen spinosum● Foramen rotundum● Foramen ovale


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THE ETHMOID

Figure 7.9


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ETHMOID BONE


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ETHMOID BONE


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ETHMOID BONE


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ETHMOID BONE


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Ossification

Comments

A porous bone that forms the major portion of the middle part of the face between the orbits Helps form the orbit, nasal cavity, nasal septum, andanterior cranial fossa There is 1 ethmoid bone

Perpendicular plate

Endochondral

A flat plate that descends from the cribriform plate to form part of the nasal septumArticulates with the vomerInferiorly

Cribriform plate

A horizontal bone that forms thesuperior surface of the ethmoidContains numerous foramina forthe olfactory nerveCrista galli is a vertical plate that extends superiorly from thecribriform plate providing attachment for the falx cerebri of the meninges Associated with a small foramen cecum


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ETHMOID BONEEthmoid labyrinth

The largest part of the ethmoid Bone Descends inferiorly from the cribriform plate Ethmoid paranasal sinuses are located within the ethmoid Labyrinth Ethmoid labyrinth forms 2 major structures within the nasal cavity: ● Superior nasal concha● Middle nasal concha Ethmoid bulla is the large elevation of bone located by the middle ethmoid paranasal sinusesUncinate process is a curved piece of bone Between the uncinate process and the ethmoid bulla is the hiatus semilunaris


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THE TEMPORAL BONES

Figure 7.7


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TEMPORAL BONE


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TEMPORAL BONE


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TEMPORAL BONE


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Characteristics

Parts

Ossification

Comments

Squamous part

Intramembranous

The largest portion of the bone Three portions to the squamous part: ● Temporal● Zygomatic process● Glenoid fossaTemporal portion is the thin large area on the squamous part of the temporalOn the internal surface of the temporal portion lies a groove for the middle meningeal a. The zygomatic process extends laterally and anteriorly from the squamous portion; it articulates with the temporal process of thezygomatic bone to make the zygomatic archGlenoid fossa is inferior and medial to the zygomatic process; it articulates with the mandibular condyle, forming the temporomandibular joint

Tympanic part

Intramembranous

A plate of bone forming the anterior, posterior, and inferior portions of the external acoustic meatusAnterior part forms the posteriorportion of the glenoid fossa


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Petrous part

Endochondral

Forms the solid portion of bone The auditory and vestibular apparatuses are located within the petrous part Helps to separate the temporal and the occipital lobes of the brain It extends anteriorly and medially The medial part articulates with the sphenoid bone to form the foramen lacerum Internal acoustic meatus is observed on the medial side of the petrous part Carotid canal lies on the inferior part of the petrous part Petrotympanic fissure lies between the petrous part of the temporal bone and the tympanic part of the temporal bone On the medial portion of the petrous part lie grooves for the superior and inferior petrosal Sinuses On the posterior inferior surface of the petrous part lies the jugular fossa Between the jugular fossa and the carotid canal is the tympanic Canaliculus The mastoid process extends posteriorly and has large mastoid air cell

Styloid process

Endochondral

A projection from the temporal boneThe stylomastoid foramen lies posterior to this process


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PARIETAL BONE


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PARIETAL BONE


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Characteristics

Parts Ossification Comments

Forms the majority ofthe cranial vaultProvides the attachment of the temporalis muscle. The four corners of the parietal are not ossified at birth and give rise to the fontanelles .There are 2 parietal bones.

Has 4 angles: ●Frontal— located at bregma● Sphenoid—located at pterion ● Occipital—, located at the lambda● Mastoid—located atasterion

Intramembranous

Relatively square, forming the roof and sides of cranial vaultEndocranial surface is filledwith grooves made by middle meningeal arterySigmoid sulcus is a groovecaused by the beginning of the transverse sinus located at mastoid angle


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SUTURAL / WORMIAN BONES Additional ossificatory

centres may occur in or near sutures, giving rise to isolated sutural bones.

Usually irregular in size and shape, and most frequent in the lambdoid suture, they sometimes occur at fontanelles, especially the posterior.

An isolated bone at the lambda is sometimes seen called the Inca bone or Goethe's ossicle.

Seen in great number in hydrocephallic skulls.


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SURFACE ANATOMY


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CHILD V/S ADULT SKULL


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AGE DETERMINATION Development of the nasal spine (by year 3) Completion of the hypoglossal canal (by

year 4) Formation of the foramen of Huschke (by

year 5), Ossification of the dorsum sellae (by year

5) Fusion of the different parts of the occipital

bone (by year 7). The fontanelles are usually all closed by

the middle of the second year.


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AGE DETERMINATION The posterolateral is the first to close in

the first two months after birth, and the anterior fontanelle is the last to close around the middle of the second year

The mastoid process appears in the second year and the metopic suture between the two frontal bones will close by year 4.

The spheno-occipital synchondrosis will fuse between 11 and 16 years in the female and 13 and 18 years in the male


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AGE DETERMINATION The vomer and the ethmoid will fuse

between 20 and 30 years of age. The last part of the skull to show active age-

related growth is the jugular growth plate, a small triangular area sited posterolateral to the jugular foramen in the occipitotemporal suture.

Fusion here does not begin until 22 years of age, and bilateral fusion may not be completed before 34 years

In a small proportion of individuals, the plate may remain unfused beyond 50 years


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SEXUAL VARIATIONMALE-

Robust Chin is more square Gonial angle less than 125 Condyles are larger More rounded and thick orbital margins The adult male cranium has 11% larger

cranial capacity than females, The male cranium tends to have thicker

bones. The muscle origins and insertions more

marked , e.g. the temporal and nuchal lines

The frontal sinuses are larger, as are the glabella and the superciliary arches

The external occipital protuberance and the mastoid processes are more prominent

Well defined glabella

FEMALE-

Gracile

Forehead – higher, Vertical , rounded than male

Retention of frontal eminence

Diagnosis of sex is most accurately assessed using multivariate statistical techniques such as discriminant function analysis.


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GEOGRAPHIC VARIATION African cranium are broader, with taller

upper faces, more inferiorly positioned nasal regions, and more prognathic mandibular and maxillary arches than crania from other parts of the globe.

European skulls tend to be narrow. They share many cranial similarities with American Indians

Asian skulls are typically wide (brachycephalic)

Australian are often characterized by narrow skulls (dolichocephaly)


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CONGENITAL ANOMALIES AFFECTING THE SKULL

Hemifacial microsomia (Goldenhar syndrome)-

The mastoid process shows degrees of hypoplasia.

Often there is frontal bossing. Ten percent of cases are bilateral, but

invariably one side is more severely affected.

Absence of the external auditory meatus is common.


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MANDIBULOFACIAL DYSOSTOSIS Teacher Collins syndrome Clinically the skull vault appears

normal, but on imaging it is seen that the supraorbital ridges are poorly developed.

Despite normal sutural development there may be increased digital markings on the inner table.

The mastoid processes are not pneumatized and may be sclerotic.


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CRANIOSYNOSTOSIS Occur as a result of small brain size or failure of

the development of fibrous bands between the sutures.

Metabolic disorders such as rickets and familial hypophosphatasia.

Raised intracranial pressure, visual deterioration and mental retardation may result.

Sagittal craniosynostosis occurs in conjunction with other sutures, e.g. Crouzon's syndrome.

Premature fusion of the coronal suture results in reduced anteroposterior development with marked supraorbital recession.


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Brachycephaly -- Short head

-- Coronal suture Scaphocephaly -- Keel-

shaped head -- Sagittal suture

Plagiocephaly -- Asymmetric head -- Unilateral coronal, Unilateral lambdoid

Trigonocephaly -- Triangular-shaped head -- Metopic suture

Acrocephaly -- Pointed head- Coronal/lambdoid suture


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Dolichocephaly -- Long head -- Sagittal

suture

Oxycephaly -- Tower-shaped head- Coronal / lambdoid or all sutures

Turricephaly -- Tower-shaped head -- Coronal suture

Kleeblattschädel -- Clover-leaf skull -- Multiple but not all sutures


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SYNDROMES ASSOCIATED- CROUZON'S, APERT Premature fusion of the coronal suture

characterizes cases of ACROCEPHALOSYNDACTYLY (APERT’S SYNDROME)

Early synostosis of the coronal ,sagittal, and lambdoid sutures occurs in craniofacial dysostosis (CROUZON’S SYNDROME)


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CONCLUSION

JUST AS THE CLINICIAN NEEDS THE MEDICAL

HISTORY TO MAKE A LOGICAL DIAGNOSIS,

SO TO THE ANATOMY IS ESSENTIAL FOR A

LOGICAL EXPLANATION OF ANY STRUCTURAL

AND FUNCTIONAL IMBALANCES IF IT DO

OCCURS


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REFERENCES 1. Churchill Livingstone - Gray's Anatomy–

Textbook of human anatomy - 40th Edition 2. F Netters -Head and Neck Anatomy for

Dentistry- 2nd edition. 3. McMinn’s -Color Atlas of Head and Neck

Anatomy- 3rd Edition. 4. James L. Hiatt, Leslie P. Gartner - Head and

Neck Anatomy- -4th edition. 5. Keith L. Moore- Clinically Oriented Anatomy-

6th Edition. 6. Geoffrey H. Sperber – Craniofacial

Development.


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THANK YOU FOR YOUR KIND ATTENTION AND ACTIVE PARTICIPATION


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Landmark Shape Location Pterion (G. wing) Junction of greater wing of sphenoid, squamous

temporal, frontal, and parietal bones; overlies course of anterior division of middle meningeal artery

Lambda (G. the letter L) Point on calvaria at junction of lambdoid and sagittal sutures

Bregma (G. forepart of head) Point on calvaria at junction of coronal and sagittal sutures

Vertex (L. whirl, whorl) Superior point of neurocranium, in middle with cranium oriented in anatomical (orbitomeatal or Frankfort) plane

Asterion (G. asterios, starry) Star shaped; located at junction of three sutures: parietomastoid, occipitomastoid, and lambdoid

Glabella (L. smooth, hairless) Smooth prominence; most marked in males; on frontal bones superior to root of nose; most anterior projecting part of forehead

Inion (G. back of head) Most prominent point of external occipital protuberance

Nasion (L. nose) Point on cranium where frontonasal and internasal sutures meet


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Foramina/Apertures Contents

Anterior cranial fossa Foramen cecum Nasal emissary vein (1% of population) Cribriform foramina in cribriform plate Axons of olfactory cells in olfactory epithelium that form

olfactory nerves Anterior and posterior ethmoidal foramina Vessels and nerves with same namesMiddle cranial fossa Optic canals Optic nerves (CN II) and ophthalmic arteries Superior orbital fissure Ophthalmic veins; ophthalmic nerve (CN V1); CN III, IV, and VI; and

sympathetic fibers Foramen rotundum Maxillary nerve (CN V2) Foramen ovale Mandibular nerve (CN V3) and accessory meningeal artery Foramen spinosum Middle meningeal artery and vein and meningeal branch of CN V3 Foramen laceruma Deep petrosal nerve and some meningeal arterial branches and small veins Groove or hiatus of greater petrosal nerve Greater petrosal nerve and petrosal branch of middle

meningeal arteryPosterior cranial fossa Foramen magnum Medulla and meninges, vertebral arteries, CN XI, dural veins, anterior and

posterior spinal arteries Jugular foramen CN IX, X, and XI; superior bulb of internal jugular vein; inferior petrosal and sigmoid

sinuses; and meningeal branches of ascending pharyngeal and occipital arteries Hypoglossal canal Hypoglossal nerve (CN XII) Condylar canal Emissary vein that passes from sigmoid sinus to vertebral veins in neck Mastoid foramen Mastoid emissary vein from sigmoid sinus and meningeal branch of occipital

artery artery The internal carotid artery and its accompanying sympathetic and venous plexuses actually pass horizontally across (rather than vertically through) the area of the foramen lacerum, an artifact of dry crania, which is closed by cartilage in life.


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1 osteology of cranial bones rt(67) dr. rahul tiwari

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