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

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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)

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