The skull

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10 The skull

Skull

The skull can be divided into 2 sections: the cranium and the face (Figs 10.1, 10.2 and 10.3).

Fig. 10.2 Position of bones of the skull (lateral aspect).

A–Frontal bone

B–Sphenoid bone (greater wing)

Fig. 10.3 Position of the bones of the skull (cranial cavity).

The floor of the cranial cavity is divided into three distinct sections:

1 – Anterior cranial fossa containing the frontal lobes of the brain.

2 – Middle cranial fossa containing the temporal lobes of the brain and the hypophysis cerebri (pituitary gland).

3 – Posterior cranial fossa containing cerebellum, pons and medulla oblongata.

The cranium is composed of the following bones:

The facial bones include:

Maxillae (2)

Mandible

Inferior nasal conchae (2)

Orbital cavity (Fig. 10.4)

Features of the orbital cavity

The orbital cavity contains the eyeball, its muscles, nerves and blood vessels, and the lacrimal gland.

Nasal cavity (Fig. 10.7)

Forms the upper part of the respiratory tract and is irregular in shape.

Fig. 10.7 Nasal cavity (sagittal section).

F–Horizontal plate of the palatine bone

G–Inferior meatus

H–Middle meatus

I–Spheno-ethmoidal recess

J–Sphenoidal sinus

K–Cribriform plate of the ethmoid bone.

Paranasal sinuses (Figs 10.8 and 10.9)

Consist of:

Fig. 10.8 Paranasal sinuses and associated structures (coronal section).

A – Ethmoidal sinuses

B – Maxillary sinus

C – Nasal cavity

D – Orbital cavity.

Fig. 10.9 Paranasal sinuses and associated structures (sagittal section).

1 –Frontal sinuses

2 –Spheno-ethmoidal recess

3 –Opening for the ethmoidal sinuses

4 –Opening for the maxillary sinuses

5 –Hard palate

6 –Inferior meatus

7 –Middle meatus

8 –Opening for ethmoidal sinuses

9 –Superior meatus

10–Sphenoidal sinuses

11–Sella turcica (hypophyseal fossa, pituitary fossa).

Maxillary sinuses (2)

Frontal sinuses (2)

Ethmoidal sinuses (3 groups)

Sphenoidal sinuses (2).

The sinuses are lined with mucous membrane, which is continuous with that of the nasal cavity.

Function

To lighten the skull.

To add resonance to the voice.

Sphenoidal sinuses (Fig. 10.9)

Shape

Cuboidal.

Position

In the body of the sphenoid bone below the sella turcica, hypophysis cerebri (pituitary gland) and the hypothalamus of the brain, above and behind the nasal cavity and the ethmoidal sinuses.

Communication (Fig. 10.9)

With the spheno-ethmoidal recess in the nasal cavity.

Radiographic appearances of the paranasal sinuses (Figs 10.10 to 10.18

)

Fig. 10.10 Nasal sinuses: occipito- mental projection.

1 – Orbit

2 – Nasal septum

3 – Maxillary antrium

4 – Zygoma

5 – Sphenoid sinus

6 – Infraorbital foramen

7 – Ethmoid air cells

8 – Frontal sinus.

(From Bryan 1996.)

Fig. 10.11 Radio- graphic projection of the nasal sinuses: occipitomental.

(From Bryan 1996.)

Fig. 10.12 Nasal sinuses: occipitofrontal projection.

1 – Superior orbital fissure

2 – Ethmoid air cells

3 – Petrous temporal bone

4 – Foramen rotundum

5 – Innominate line

6 – Frontal sinus.

(From Bryan 1996.)

Fig. 10.13 Radiographic projection of the nasal sinuses: 20° occipitofrontal.

(From Bryan 1996.)

Fig. 10.14 Nasal sinuses: lateral projection.

1 – Frontal sinuses

2 – Anterior margin of ethmoidal sinuses

3 – Maxillary sinuses

4 – Petrous temporal bones

5 – Sphenoidal sinuses

6 – Posterior margin of ethmoidal sinuses.

(From Bryan 1996.)

Fig. 10.15 Radiographic projection of the nasal sinuses: lateral.

F–Frontal sinus

E–Ethmoidal sinuses

M–Maxillary sinus

S–Sphenoidal sinuses.

(From Bryan 1996.)

Fig. 10.16 Nasal sinuses: submentovertical projection.

A – Nasal septum

B – Petrous temporal bone

C – Petrous temporal bone

D – Sphenoidal sinuses

E – Posterior ethmoidal sinuses.

(From Bryan 1996.)

Fig. 10.17 Radiographic projection of the nasal sinuses: submentovertical.

E – Ethmoidal sinuses

S – Sphenoidal sinus sinuses.

L – Left (Normal radiographic label).

(From Bryan 1996.)

Fig. 10.18 Sinuses: CT scan.

A – Maxillary sinus

B – Inferior concha

C – Middle concha

D – Posterior ethmoid air cells

E – Orbit and contents

F – Nasal septum.

Insight

Fluid can collect in the maxillary antrum, this will not be demonstrated unless a horizontal beam is used. Any angulation of the beam could give the appearance of thickening of the lining of the antrum rather than fluid.

Features of the skull (Figs 10.19 to 10.23)

Radiographic appearances of the skull (Figs 10.24 to 10.30)

Fig. 10.25 Cranial bones: 20° occipitofrontal projection.

1 – Crista galli

2 – Ethmoid air cells

3 – Mastoid air cells

4 – Floor of pituitary fossa

5 – Greater wing of sphenoid

6 – Superior orbital fissure

7 – Lesser wing of sphenoid

8 – Supraorbital margin

9 – Frontal sinus

10 – Sagittal suture.

(From Bryan 1996.)

Fig. 10.27 Cranial bones: submentovertical projection.

1 – Foramen ovale

2 – Foramen spinosum

3 – Head of mandible

4 – Anterior arch of atlas

5 – Foramen transversarium

6 – Transverse process of atlas

7 – Odontoid process

8 – External auditory meatus

9 – Pharynx

10 – Medial pterygoid plate

11 – Lateral pterygoid plate

12 – Anterior wall of middle cranial fossa

13 – Lateral wall of nasal cavity.

(From Bryan 1996.)

Fig. 10.29 CT scan at level of foramen magnum.

1 – Ethmoid air cells

2 – External auditory meatus

3 – Foramen magnum

4 – Petrous bone

5 – Condyle of mandible

6 – Temporomandibular joint

7 – Superior rectus muscle

8 – Globe

9 – Lens.

(From Bryan 1996.)

Fig. 10.31 Occipital bone (external surface).

A – Squamous part

B – Highest nuchal line

C – External occipital protuberance

D – Superior nuchal line

E – Inferior nuchal line

F – External occipital crest

K – Hypoglossal canal

L – Jugular notch

M – Condylar fossa

N – Foramen magnum.

Individual bones of the skull

Occipital bone (Fig. 10.31)

Fig. 10.19 Foramina in the base of the skull (internal aspect).

A – Optic canal, for the optic nerve and the ophthalmic artery.

B – Foramen rotundum, for the maxillary division of the trigeminal nerve.

C – Foramen ovale, for the mandibular division of the trigeminal nerve.

D – Foramen spinosum, for the middle meningeal artery.

E – Foramen magnum, for part of the medulla oblongata, the spinal roots of accessory nerves and the vertebral arteries.

F – Hypoglossal canal, for the hypoglossal nerve and the meningeal branch of the ascending pharyngeal artery.

G – Jugular foramen, for the internal jugular vein, the glossopharyngeal, vagus and accessory nerves and the inferior petrosal sinus.

H – Internal acoustic (auditory) meatus, for the facial and auditory nerves.

I – Foramen lacerum. The lower part is closed by fibrocartilage; the internal carotid artery crosses it (after entering by the carotid canal).

J – Cribriform plate, for the olfactory nerve filaments.

Carotid canal – lies on the external aspect, for the internal carotid artery.

Stylomastoid foramen – lies on the external aspect between the styloid and mastoid processes of the temporal bone, for the facial nerve.

Superior orbital fissure – concealed by the lesser wing of the sphenoid bone, for the oculomotor, trochlear and abducent nerves, ophthalmic division of the trigeminal nerve and the ophthalmic veins.

Fig. 10.20 Features of the skull (anterior aspect).

A–Sagittal suture

B–Coronal suture

C– Supraorbital notch (foramen)

D–Superior orbital fissure

E–Middle nasal concha

F–Vomer

G–Inferior nasal concha

H–Mental foramen

I–Zygomatic arch

J–Infraorbital foramen

K–Inferior orbital fissure

L–Optic canal.

Fig. 10.21 Features of the skull (lateral aspect).

F–Anterior nasal spine

G–Mental foramen

H–Symphysis menti

I–Angle of the mandible

J–Styloid process

K–External acoustic (auditory) meatus

L–Mastoid process

M–External occipital protuberance

N–Lambdoid suture

O–Squamosal suture.

Fig. 10.23 Features of the skull (cranial cavity).

A– Crista galli of the ethmoid bone

B– Cribriform plate of the ethmoid bone

C– Optic foramen

D– Tuberculum sellae of the sphenoid bone

E– Sella turcica (hypophyseal fossa, pituitary fossa) of the sphenoid bone

F– Foramen ovale

G– Foramen spinosum

H– Internal acoustic (auditory) meatus

I– Jugular foramen

J– Foramen magnum

K– Petrous portion of the temporal bone

L– Hypoglossal canal

M – Dorsum sellae

N– Foramen lacerum

O– Anterior clinoid process of the sphenoid bone

P– Foramen rotundum.

Type

Flat bone.

Position

Forms the posterior part of the base of the skull.

Articulations

The occipital condyles with the 1st cervical vertebra to form the atlanto-occipital joint.

The squamous part with the temporal bone and the parietal bones to form the lambdoid suture.

Main parts

The bone can be divided into 3 areas:

Squamous part

This lies posterior to the foramen magnum.

Internal surface –

concave, divided into 4 fossae by:

horizontal groove – for the transverse venous sinus; the tentorium cerebelli is attached to the edge of the groove.

sulcus for superior sagittal venous sinus – situated above the horizontal groove; the margins provide attachment for the falx cerebri

internal occipital crest – below the horizontal groove.

Internal occipital protuberance –

where the vertical grooves meet.

External surface –

convex.

External occipital crest –

midline structure from the foramen magnum to the external occipital protuberance.

External occipital protuberance –

midway between the foramen magnum and the superior aspect of the bone.

Superior nuchal lines –

run-laterally from the external occipital protuberance.

Highest nuchal lines –

faint lines above the superior nuchal lines.

Inferior nuchal lines –

below the superior nuchal lines, running laterally from the external occipital crest.

Basilar part

This lies anterior to the foramen magnum.

Pharyngeal tubercle –

lies on the inferior surface, 1 cm anterior to the foramen magnum, in the midline; provides attachment for the pharynx.

Clivus –

lies on the superior surface; runs upwards and forwards from the anterior border of the foramen magnum; forms attachment for the membrana tectoria and the apical ligament.

Ossification

Primary centres

Squamous part –

4 centres.

Lateral parts –

2 centres.

Basilar part –

1 centre.

Sphenoid bone (Figs 10.32 and 10.33)

Position

Forms part of the base of the skull, lying between the frontal, temporal and occipital bones.

Articulations

The greater wings with the temporal bone to form the sphenosquamosal suture.

With the vomer, ethmoid, occipital, frontal, zygomatic and palatine bones.

Main parts

The bone consists of a body, 2 pairs of wings and 2 pterygoid processes.

Body

Superior surface –

articulates with the ethmoid bone.

Optic canal (foramen) –

lateral part of the superior surface for the optic nerve.

Tuberculum sellae –

posterior to the optic canals, forming the anterior boundary of the sella turcica.

Sella turcica –

posterior to the tuberculum sellae; contains the hypophysis cerebri (pituitary gland).

Middle clinoid processes –

lateral projections on the tuberculum sellae.

Anterior clinoid processes –

lateral to the middle clinoid processes.

Dorsum sellae –

posterior part of the sella turcica.

Clivus –

posterior to the dorsum sellae and articulates with the clivus of the occipital bone.

Lateral surfaces –

junction of the body and greater wings.

Carotid sulcus –

above the lateral surfaces; carries the internal carotid artery and the cavernous venous sinus.

Anterior surface –

articulates with the ethmoid bone.

Sphenoidal crest –

on the anterior surface; forms part of the nasal septum.

Sphenoidal sinus –

in the body, see paranasal sinuses, pp. 207–210.

Sphenoidal conchae –

2 thin plates on the anterior aspect of the body.

Inferior surface –

has several processes:

sphenoidal rostrum – process in the midline; forms articulation with the vomer

vaginal processes – processes on either side of rostrum.

Greater wings

Two processes from the sides of the body.

Sphenosquamosal suture –

junction between the greater wings and the squamous part of the temporal bone.

Cerebral surface –

forms part of the middle cranial fossa; presents with 3 foramina:

foramen rotundum – on the antero-medial surface, for the maxillary nerve

foramen ovale – postero-lateral to the foramen rotundum, for the mandibular nerve and the accessory meningeal artery.

foramen spinosum – medial to the foramen ovale, for the middle meningeal artery and the meningeal branch of the mandibular nerve.

Orbital surface –

forms the posterior part of the lateral wall of the orbit.

Postero-lateral border of inferior orbital fissure –

formed by the inferior border of the orbital surface.

Lateral border of superior orbital fissure –

formed by the medial border of the orbital surface.

Anterior border of foramen lacerum –

formed by the posterior border of the junction of the greater wing with the body.

Position

Form the side and part of the base of the skull.

Articulations

Mandibular fossa with the head of mandible to form the temporomandibular joint.

The squamous part with the parietal bones to form the squamosal suture and with the occipital bones to form the lambdoid suture.

With the greater wings of sphenoid to form the sphenosquamosal suture.

With the zygomatic bone.

Main parts

The bone is formed by 3 parts:

Squamous part

Forms the upper anterior part of the bone.

Temporal surface –

forms part of the temporal fossa.

Zygoma –

articulates with the zygomatic bone and forms the mandibular fossa.

Mandibular fossa –

articulates with the articular disc of the temporomandibular joint. Its posterior aspect is non-articular.

Petromastoid part

This is formed by a mastoid and a petrous part.

Mastoid part –

forms posterior aspect of the bone:

mastoid process –

contains the mastoid air cells, which vary in size from person to person

mastoid notch –

on the medial aspect of the mastoid process.

Tympanic part

This lies in front of the mastoid process.

External acoustic (auditory) meatus –

mainly lies in the tympanic part; extends to the tympanic membrane, which forms the boundary of the middle ear.

Stylomastoid foramen –

between the mastoid and styloid processes and carries the stylomastoid artery and the facial nerve.

Styloid process –

lies anterior to the mastoid process and forms attachment for the stylohyoid ligament.

Middle ear

Lies between the external acoustic meatus and the inner ear; contains the

auditory ossicles:

Malleus –

hammer-shaped; is in contact with the tympanic membrane.

Incus –

anvil-shaped; lies between the malleus and the stapes.

Stapes –

stirrup-shaped; lies at the junction of the middle and inner ear.

Ossification

Squamous part –

1 centre.

Petromastoid part –

up to 14 centres.

Tympanic part –

1 centre.

Styloid process –

2 centres.

Radiographic appearances of the temporal bone (Figs 10.36, 10.37 and 10.38)

Parietal bones (Fig. 10.39)

Type

Irregular bones.

Fig. 10.36 Temporal bone: lateral oblique projection.

A– Mastoid antrum

B– Edge of sigmoid sulcus

C– Mastoid process

D– Jugular foramen

E– Posterior border of ramus of mandible

F– Head of mandible

G – Zygomatic arch

H– External auditory meatus

I– Tegmen tympani.

(From Bryan 1996.)

Fig. 10.37 Temporal bone: modified Stenver’s projection.

1 – Internal auditory canal

2 – Cochlea

3 – Vestibule

4 – Lateral semicircular canal

5 – Arcuate eminence

6 – Superior semicircular canal.

(From Bryan 1996.)

Fig. 10.38 CT scan through middle and internal ear.

A– Cochlea

B– Malleus and incus

C– Mastoid air cells

D– Posterior semicircular canal

E– Horizontal semicircular canal

F– Internal auditory canal

G – Sphenoid sinus.

(From Bryan 1996.)

Fig. 10.39 Left parietal bone (external surface).

G– Inferior temporal line

H– Lambda

I– Superior temporal line

J– Sagittal border.

Position

Form the sides and the roof of the cranium.

Articulations

With the sagittal border of the opposite parietal bone to form the sagittal suture.

With the frontal bone to form part of the coronal suture.

With the occipital bone to form part of the lambdoid suture.

With the sphenoid and temporal bones.

Main parts

Each bone has 2 surfaces, 4 borders and 4 angles.

External surface –

convex, and has 2 curved lines, the superior and inferior temporal lines.

Internal surface –

concave, and has a groove for the superior sagittal sinus and some depressions (granular foveolae) for the arachnoid granulations.

Sagittal border –

on the superior aspect.

Squamosal border –

on the inferior aspect; articulates with the sphenoid and temporal bones.

Frontal border –

on the anterior aspect.

Occipital border –

on the posterior aspect.

Sphenoidal angle –

at the junction of the squamosal and frontal borders; has a groove for the frontal branch of the middle meningeal vessels.

Occipital angle –

at the junction of the occipital and sagittal borders (and therefore at the junction of the sagittal and lambdoid sutures, which is called the lambda).

Mastoid angle –

at the junction of the occipital and squamosal borders.

Frontal angle –

at the junction of the sagittal and frontal borders (and therefore at the junction of the sagittal and coronal sutures, which is called the bregma).

Ossification

2 primary centres.

Frontal bone (Figs 10.40 and 10.41)

Position

Forms the front of the cranium, above the orbits.

Articulations

With the maxillae, zygomatic, nasal, lacrimal, ethmoid and sphenoid bones.

Main parts

External surface –

convex.

Supraorbital margins –

form the upper border of the orbits.

Supraorbital notch –

for the supraorbital vessels and nerves; may be a foramen.

Zygomatic process –

lateral end of the supraorbital margin; articulates with the zygomatic bone.

Nasal part –

between supraorbital margins.

Nasal spine –

forms the end of the nasal part; forms part of the nasal septum.

Nasal notches –

either side of the nasal spine; articulate with the nasal bones.

Superciliary arches –

above the supraorbital margins.

Glabella –

junction of the 2 superciliary arches.

Internal surface –

concave.

Vertical groove –

in the midline for the sagittal venous sinus.

Frontal crest –

edges of vertical groove for attachment for the falx cerebri.

Granular foveolae –

indentations for the arachnoid granulations.

Parietal margin –

articulates with the greater wing of the sphenoid bone.

Orbital plates –

concave; form the roof of the orbit.

Fossa for lacrimal gland –

antero-lateral aspect of the orbital plates.

Ethmoidal notch –

at the junction of the orbital plates; occupied by the cribriform plate of the ethmoid bone.

Frontal sinuses –

see paranasal sinuses, pp. 206–210.

Ossification

2 primary centres.

Ethmoid bone (Fig. 10.42)

Type

Irregular bone.

Fig. 10.42 Ethmoid bone (posterior aspect).

A– Crista galli

B– Ethmoidal labyrinth

H – Perpendicular plate

I– Superior concha

J– Cribriform plate.

Position

Behind the nasal bones, between the orbits.

Articulations

With the vomer, maxillae, and the frontal, palatine, lacrimal and sphenoid bones.

Main parts

The bone is formed by 2 plates and 2 labyrinths.

Cribriform plate

Lies in the ethmoid notch of the frontal bone and forms the roof of the nasal cavity.

Crista galli –

in the midline of the cribriform plate; forms attachment for the falx cerebri.

Foramina –

in the cribriform plate for the olfactory nerve filaments.

Perpendicular plate

In the midline of the cribriform plate; forms part of the nasal septum.

Ossification

Perpendicular plate –

1 centre.

Labyrinth –

1 centre per labyrinth.

Maxillae (Fig. 10.43)

Type

Irregular bones.

Fig. 10.43 Left maxilla (lateral aspect).

A– Frontal process

B– Infraorbital foramen

C– Anterior nasal spine

D– Canine eminence

E– Maxillary tuberosity

F– Zygomatic process

G – Orbital surface

H– Nasolacrimal groove.

Position

Form the whole of the upper jaw.

Articulations

With the opposite maxilla, the palatine, lacrimal, zygomatic, nasal, ethmoid and frontal bones, the inferior nasal conchae, vomer and the upper teeth.

Main parts

Each bone has a body and 4 processes.

Body –

pyramid-shaped and has 4 surfaces. It encloses the maxillary sinus.

Anterior surface –

directed forward and laterally.

Incisive fossa –

depression above the incisor teeth.

Canine fossa –

depression above the canine tooth.

Canine eminence –

between the 2 fossae.

Infraorbital foramen –

above the canine fossa; for the infraorbital vessels and nerves.

Anterior nasal spine –

a pointed process, at the junction of the 2 bodies. Infratemporal surface – convex; lies laterally.

Maxillary tuberosity –

lies on the posterior aspect of the roots of the 3rd molar tooth (upper eight).

Orbital surface –

forms part of the floor of the orbit.

Lacrimal notch –

on the medial border of the orbital surface.

Inferior orbital fissure –

anterior border is formed by the posterior border of the orbital surface.

Infraorbital canal –

continuation of the infraorbital foramen.

Nasal surface –

forms the wall of the nasal cavity.

Maxillary hiatus –

opening on the posterior part of the nasal surface; leads to the maxillary sinus.

Conchal crest –

an oblique ridge on the anterior aspect.

Zygomatic process –

articulates with the zygomatic bone.

Frontal process –

articulates with ethmoid, frontal, nasal and lacrimal bones; forms part of the lateral wall of the nasal cavity.

Alveolar process –

forms articulation with the teeth.

Palatine process –

forms part of the floor of the nasal cavity and therefore the roof of the mouth; along with the other palatine process forms three-quarters of the bony palate.

Nasal crest –

at the junction of the 2 maxillae, between which is a groove for articulation with the vomer.

Maxillary sinus –

see paranasal sinuses, pp. 205–210.

Ossification

3 centres.

Mandible (Figs 10.44 and 10.45)

Position

Forms the lower jaw.

Articulations

The head of mandible with the mandibular fossa of the temporal bone to form the temporomandibular joint.

With the lower teeth.

Main parts

The bone is formed by a body and 2 rami.

Ossification

Primary centres

Body –

2 centres.

Secondary centres

Ramus –

4 centres.

Articulations

Fibrous gomphose joints between the teeth and alveoli.

Dentition

Deciduous teeth

Children have a full dentition of 20 teeth: 2 incisors, 1 canine and 2 molars in each quadrant of the mouth.

Permanent teeth (Fig. 10.48)

Adults have a full dentition of 32 teeth: 2 incisors, 1 canine, 2 premolars and 3 molars in each quadrant.

Fig. 10.48 Permanent teeth – right upper and lower quadrants.

Dental formulae

In order to identify the different teeth in the mouth, a formula is used. Numbers are used to identify permanent teeth:

Letters are used to identify deciduous teeth:

INSIGHT

To identify an individual tooth, part of the grid and the tooth are given, e.g.

Upper right 1 would be

Lower left 4 would be

Radiographic appearances of the teeth (Figs 10.49 and 10.50)

Fig. 10.49 Teeth: intraoral projection.

A– Erupting sac

B– Apex of root

C– Lamina dura

D– Periodontal membrane

E– Pulp cavity

F– Enamel of crown

G – Radio-opaque filling.

(From Bryan 1996.)

Fig. 10.50 Teeth: orthopantomograph.

5 – Unerupted 3rd molars (bilateral)

Lacrimal bones

Type

Irregular bone.

Position

Lie on the medial wall of the orbits.

Articulation

With the maxillae, ethmoid and frontal bones and the inferior nasal conchae.

Ossification

1 primary centre.

Palatine bones

Type

Irregular bones.

Position

They lie in the posterior part of the nasal and oral cavities.

Articulations

With the maxillae, vomer, inferior nasal conchae, sphenoid and ethmoid bones and the other palatine bone.

Main parts

The bones are L-shaped and each has a horizontal and a vertical plate.

Perpendicular plate

Has 2 surfaces and 4 borders.

Nasal surface –

forms part of the inferior meatus of the nasal cavity and has 2 crests.

Conchal crest –

articulates with the inferior nasal concha.

Ethmoidal crest –

articulates with the middle nasal concha.

Middle meatus –

part of this lies between the 2 crests.

Maxillary surface –

articulates with the maxilla and (along with the anterior border of the perpendicular plate) forms part of the medial wall of the maxillary sinus.

Posterior border –

articulates with the sphenoid bone.

Superior border –

has 2 large processes.

orbital process – articulates with the maxilla and ethmoid; forms part of the floor of the orbit and the inferior orbital fissure.

sphenoidal process – articulates with the sphenoid bone; forms part of the roof and lateral wall of the nasal cavity.

Sphenopalatine notch –

lies between the 2 processes.

Pyramidal process –

lies at the junction of the horizontal and perpendicular plates; articulates with the maxilla and sphenoid bone.

Ossification

Perpendicular plate –

1 primary centre.

Zygomatic bones

Type

Irregular bones.

Position

Forms the bony cheek and part of the lateral walls and the floor of the orbit.

Articulations

With the maxilla, temporal, frontal and sphenoid bones.

Main parts

Each bone has 3 surfaces, 5 borders and 2 processes.

Ossification

1 primary centre.

Hyoid bone

Type

Irregular bone.

Position

Lies in the front of the neck, above the thyroid cartilage of the larynx at the root of the tongue.

Articulations

The bone is attached to the temporal bone by the stylohyoid ligament.

Main parts

Body –

convex.

Greater cornua –

project back laterally from the body.

Lesser cornua –

project upwards at the junction between the body and the greater cornua.

The bone gives attachment for muscles of the mouth, tongue and middle constrictor muscle of the pharynx.

Ossification

Primary centres

Body –

2 centres.

Greater cornua –

2 centres.

Lesser cornua –

2 centres.

Radiographic appearances of the facial bones (Figs 10.51, 10.52 and 10.53)

Temporomandibular joint (Fig. 10.54)

Type

Synovial condylar joint.

Fig. 10.54 Left tem- poromandibular joint (sagittal section)

A– Fibrocartilage

B– Synovial fluid

C– Articular disc

D– Lateral pterygoid ligament

J– External acoustic meatus

K– Venous plexus

L– Mandibular fossa

Fig. 10.51 Facial bones: occipitomental projection.

A– Nasal bones

B– Frontozygomatic suture

C– Zygomatic bone

D– Maxillary sinus

E– Coronoid process of mandible

F– Ramus of mandible

G– Angle of mandible

H– Petrous part of temporal bone

I– Mastoid air cells

J– Head of mandible

K– Zygomatic arch

L– Infraorbital foramen

M – Lesser wing of sphenoid

N– Nasal septum

O– Supraorbital margin

P– Frontal sinus.

(From Bryan 1996.)

Fig. 10.52 Facial bones: 30° occipitomental projection.

1 – Zygomatic arch

2 – Coronoid process

3 – Maxilla

4 – Infraorbital margin.

(From Bryan 1996.)

Fig. 10.53 Facial bones: lateral projection.

A– Frontal sinuses

B– Lateral margin or orbit

C– Zygomatic processes of maxillae

D– Anterior nasal spine

E– Hard palate

F– Mental tubercle

G– Base of mandible

H– Unerupted third molars

I– Posterior surface of maxilla

J– Maxillary sinuses

K– Cribriform plate of ethmoid bone

L– Orbital plates of frontal bone.

(From Bryan 1996.)

Bony articular surfaces

Articular tubercle and the anterior aspect of the mandibular fossa of the temporal bone above, with the condyle of the mandible below. The articular surfaces are covered with white fibrocartilage.

Fibrous capsule

Surrounds the joint; it is attached to the articular tubercle, and the circumference of the mandibular fossa and the neck of mandible. The capsule is loose above and tight below.

Synovial membrane

Lines the fibrous capsule. The membrane secretes synovial fluid, which lubricates the joint.

Supporting ligaments

Lateral (temporomandibular) ligament –

from the zygoma to the neck of the mandible.

Sphenomandibular ligament –

from the spine of the sphenoid to the lingula of the mandibular foramen.

Stylomandibular ligament –

from the styloid process to the angle and ramus of the mandible.

Intracapsular structure

Articular disc –

fibrous tissue, divides the joint cavity horizontally into 2 sections and is fused with the capsule.

Movements

Depression by the lateral pterygoid muscle.

Elevation by the temporalis, masseter and medial pterygoid muscles.

Protrusion by the lateral and medial pterygoid muscles.

Retraction by the temporalis muscle.

Lateral movement by the medial and lateral pterygoid muscles.

Blood supply

Superficial temporal and maxillary arteries.

Nerve supply

Branches of the mandibular nerve.

Radiographic appearances of the temporomandibular joint (Figs 10.55, 10.56, 10.57 and 10.58)

Fig. 10.55 Tem- poromandibular joint: lateral oblique projection with mouth closed.

A – Mandibular fossa of temporal bone

B – Head of mandible.

(From Bryan 1996.)

Fig. 10.56 Tem- poromandibular joint: lateral oblique projection with mouth open.

1 – Head of mandible

2 – Mandibular fossa of temporal bone.

(From Bryan 1996.)

Fig. 10.57 Temporo- mandibular joint mouth closed. MR scan.

(From Resnick Kransdorf, 2005.)

Fig. 10.58 Temporo- mandibular joint mouth open. MR scan.

(From Resnick Kransdorf, 2005.)

Fractures

Cranium

Either a hairline fracture or a depressed fracture.

Cause –

blow to the head; may result in a haematoma (subdural or extradural).

Example of treatment –

bed rest with regular neurological checks; depressed fractures may require elevating.

Zygomatic arch

Cause – blow to the cheek.

Example of treatment – depressed fracture is raised during open surgery as the fracture is then stable; no immobilisation is required.

Mandible(Fig. 10.59)

Insight

Due to the rigidity of the temporomandibular joints, a fracture of the mandible will always result in a second fracture of the mandible or a fracture dislocation of the temporomandibular joint on the opposite side. Think of a polo mint – it is impossible to break it in one place.

Fig. 10.59 Fractured mandible.

(From Sutton 1987.)

Always 2 fracture lines or a fracture dislocation. Most common sites are the lower premolar region (lower four region) and the opposite condylar neck, or both condylar necks.

Cause –

oblique blow to the jaw.

Example of treatment –

the maxilla and the mandible may be wired together.

Maxilla

The most common region, the lower orbital rim, tends to cause bleeding into the maxillary sinus, which can be demonstrated radiographically using a horizontal beam technique (blood in the sinus shows as an area of increased density).

Cause –

blow to the orbit.

Example of treatment –

reduction under general anaesthetic. Immobilisation by either wiring to the mandible or wire from the teeth to a metal rod attached to a head plaster.

Pathology

Hydrocephalus

Malformation of the medulla and 4th ventricle with blockage of the opening resulting in accumulation of cerebrospinal fluid and therefore enlarged ventricles. If not controlled the skull vault becomes enlarged.

Example of treatment –

either a drain is inserted between one or both of the ventricles and the cisterna magna, or a unidirectional valve is inserted between the ventricles and the vena cava or the right atrium.

Pituitary fossa (Fig. 10.60)

Enlargement may indicate an adenoma and therefore the cause of acromegaly, gigantism or Cushing’s disease.

Fig. 10.60 Acromegaly. Note the thickened cranium, prominent sinuses and supraorbital ridges and enlarged pituitary fossa.

(From Resnick Kransdorf, 2005.)

Diminished size may indicate atrophy of the pituitary gland and therefore a cause of amenorrhea.

Facial bones

Infection of the maxillary sinus may result in mucosal thickening or fluid in the cavity. This can be demonstrated with an occipitomental radiograph.

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The skull

Orbital cavity (Fig. 10.4)

Radiographic appearances of the orbital cavity (Figs 10.5 and 10.6)

Nasal cavity (Fig. 10.7)

Paranasal sinuses (Figs 10.8 and 10.9)

Maxillary sinuses (largest) (Fig. 10.8)

Communication (Fig. 10.9)

Frontal sinuses (Fig. 10.8)

Communication (Fig. 10.9)

Ethmoidal sinuses (Fig. 10.8)

Communication (Fig. 10.9)

Sphenoidal sinuses (Fig. 10.9)

Communication (Fig. 10.9)

Radiographic appearances of the paranasal sinuses (Figs 10.10 to 10.18

Features of the skull (Figs 10.19 to 10.23)

Radiographic appearances of the skull (Figs 10.24 to 10.30)

Occipital bone (Fig. 10.31)

Sphenoid bone (Figs 10.32 and 10.33)