The skull

10 The skull



Chapter contents



Skull


Orbital cavity


Nasal cavity


Paranasal sinuses


Maxillary sinuses

Frontal sinuses

Ethmoidal sinuses

Sphenoidal sinuses

Features of the skull


Individual bones of the skull


Occipital bone

Sphenoid bone

Temporal bone

Parietal bones

Frontal bone

Ethmoid bone

Maxillae

Mandible

Teeth

Pathology

Inferior nasal conchae

Lacrimal bones

Nasal bones

Vomer

Palatine bones

Zygomatic bones

Hyoid bone

Temporomandibular joint


Fractures

Pathology 253


Skull


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


image

Fig. 10.1 Position of the bones of the skull (anterior aspect).


A–Frontal bone


B–Parietal bone


C–Greater wing of sphenoid bone


D–Temporal bone


E–Nasal bone


F–Ethmoid bone


G–Maxilla


H–Zygomatic bone


I–Maxilla


J–Mandible


K–Inferior nasal concha


L–Vomer


M–Zygomatic bone


N–Lacrimal bone


O–Palatine bone


P–Greater wing of sphenoid bone


Q–Lesser wing of sphenoid bone.


image

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


A–Frontal bone


B–Sphenoid bone (greater wing)


C–Lacrimal bone


D–Ethmoid bone


E–Nasal bone


F–Zygomatic bone


G–Maxilla


H–Mandible


I–Temporal bone


J–Occipital bone


K–Parietal bone.


image

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


A – Frontal bone


B – Ethmoid bone


C – Sphenoid bone


D – Temporal bone


E – Parietal bone


F – Occipital bone.


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:



image Occipital bone


image Sphenoid bone


image Temporal bones (2)


image Parietal bones (2)


image Frontal bone


image Ethmoid bone.


The facial bones include:



image Maxillae (2)


image Mandible


image Inferior nasal conchae (2)


image Lacrimal bones (2)


image Nasal bones (2)


image Vomer


image Palatine bones (2)


image Zygomatic bones (2).



Orbital cavity (Fig. 10.4)




Bones forming the orbital cavity




Sphenoid bone –

the greater and lesser wings.


image

Fig. 10.4 Bones forming the left orbit (anterior aspect).


A–Ethmoid bone


B–Lacrimal bone


C–Palatine bone


D–Maxilla


E–Zygomatic bone


F–Sphenoid bone


G–Frontal bone.


Structures associated with the left orbit – anterior aspect


1 – Optic canal (foramen)


2 – Inferior orbital fissure


3 – Superior orbital fissure


4 – Supraorbital foramen (notch).



Zygomatic bone –

orbital surface and border.



Ethmoid bone –

orbital plate.



Palatine bone –

orbital process.



Frontal bone –

supraorbital margin and the orbital plate.



Lacrimal bone –

orbital surface.



Maxilla –

orbital surface.



Features of the orbital cavity


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




Superior orbital fissure –

transmits the oculomotor, trochlear and abducent nerves, ophthalmic division of the trigeminal nerve and the ophthalmic veins.



Inferior orbital fissure –

transmits the maxillary nerve.



Supraorbital foramen (notch) –

transmits the supraorbital vessels and nerves.



Optic foramen –

opening of the optic canal.



Optic canal –

transmits the optic nerve and the ophthalmic artery.



Infraorbital groove –

contains the infraorbital nerve before it passes through the infraorbital canal to the infraorbital foramen.



Lacrimal groove –

in which the lacrimal sac is situated.



Nasolacrimal canal –

carries the nasolacrimal duct from the lacrimal gland to the nasal cavity.



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



image

Fig. 10.5 Optic foramen: right oblique projection.


A–Supraorbital margin


B–Optic foramen


C–Petrous temporal bone


D–Petrous temporal bone


E–Posterior ethmoidal sinuses


F–Lesser wing of sphenoid


G–Frontal sinus.


(From Bryan 1996.)


image

Fig. 10.6 CT scan through orbits.


1 – Pterygoid


2 – Sphenoid bone


3 – Medial rectus muscle


4 – Optic nerve


5 – Lateral rectus muscle


6 – Globe


7 – Lens.


(From Bryan 1996.)



Nasal cavity (Fig. 10.7)


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


image

Fig. 10.7 Nasal cavity (sagittal section).


A–Nasal bone


B–Superior concha


C–Middle concha


D–Inferior concha


E–Maxilla


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.




Roof


Formed by:


Nasal septum of the frontal and nasal bones.


Cribriform plate of the ethmoid bone.


Body of the sphenoid bone.



Floor


Forms the division between the oral and nasal cavities. Formed by:


Palatine process of the maxilla.


Horizontal plate of the palatine bone.



Medial wall


Referred to as the nasal septum. Formed by:


Vomer.


Perpendicular plate of the ethmoid bone.


Septal cartilage.



Lateral wall


Irregular as it forms the 3 nasal conchae. Formed by:


Nasal surface of the maxilla.


Perpendicular plate of the palatine bone.


Ethmoidal labyrinth.


Inferior nasal concha.



Conchae




Superior nasal concha –

projection from the ethmoid bone.



Middle nasal concha –

part of the ethmoid bone.



Inferior nasal concha –

a separate bone.



Spheno-ethmoidal recess


Above and behind the superior concha.


Communicates with the sphenoidal sinus.



Superior meatus


Forms attachment for the superior nasal concha.


Communicates with the posterior ethmoidal sinuses.



Middle meatus


Lies between the middle and inferior nasal conchae.


Communicates with the anterior ethmoidal sinuses, the middle ethmoidal sinuses, the frontal sinus and the maxillary sinus.



Inferior meatus


Lies below the inferior nasal concha.


Communicates with the orbit via the nasolacrimal canal.



Paranasal sinuses (Figs 10.8 and 10.9)


Consist of:


image

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


A – Ethmoidal sinuses


B – Maxillary sinus


C – Nasal cavity


D – Orbital cavity.


image

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.



Maxillary sinuses (largest) (Fig. 10.8)



Shape


Pyramidal cavities.



Position


They lie on either side of the nasal cavity, below the orbits.



Structure




Base –

formed by the lateral wall of the nasal cavity.



Apex –

projects into the zygomatic process of the maxilla.



Floor –

formed by the alveolar process of the maxilla.



Roof –

formed by the floor of the orbit.



Communication (Fig. 10.9)


With the middle meatus of the nasal cavity via the antral ostium.



Frontal sinuses (Fig. 10.8)



Shape


Irregular.



Position


In the midline above the nasal cavity and the orbits, in front of the anterior cranial fossa, behind the superciliary arches.



Structure


Vary in size and shape from person to person. Are divided from each other by a septum, near the midline.



Communication (Fig. 10.9)


With the middle meatus of the nose via the frontonasal canal or ethmoidal infundibulum.



Ethmoidal sinuses (Fig. 10.8)



Shape


Numerous small cavities, irregular in shape.



Position


Situated between the medial wall of the orbit and the nasal cavity, in the ethmoidal labyrinth, below the anterior cranial fossa.



Structure


Divided into 3 groups: anterior, middle and posterior.




Orbital plate –

forms the boundary between the sinus and the medial wall of the orbit.



Medial plate –

forms the boundary between the sinus and the lateral wall of the nasal cavity.



Communication (Fig. 10.9)




Anterior and middle groups –

via the spheno-ethmoidal recess above the superior conchae of the nasal cavity.



Posterior group –

with the superior meatus of the nasal cavity.



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


)


image

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.)


image

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


F–Frontal sinus


R–Right orbit


L–Left orbit


M–Maxillary sinus


S–Sphenoid sinuses.


(From Bryan 1996.)


image

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.)


image

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


F–Frontal sinus


e–Ethmoidal sinuses


R–Right orbit


L–Left orbit


M–Maxillary sinus


(From Bryan 1996.)


image

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.)


image

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.)


image

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.)


image

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.)


image

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)



image

Fig. 10.24 Cranial bones: occipitofrontal projection.


A– Coronal suture


B– Frontal sinus


C– Petrous part of temporal bone


D– Ethmoidal sinuses


E– Head of mandible


F– Coronoid process


G– Angle of mandible


H– Body of mandible


I– Mandibular canal


J– Inferior nasal concha


K– Maxillary sinus


L– Ethmoid bone in nasal cavity


M – Mastoid air cells


N– Supraorbital margin


O– Squamous part of temporal bone


P– Frontal bone


Q– Parietal bone


R– Sagittal suture


S– Lambdoid suture.


(From Bryan 1996.)


image

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.)


image

Fig. 10.26 Cranial bones: lateral projection.


A– Parietal bones


B– Lambdoid suture


C– Occipital bone


D– External occipital protuberance


E– Mastoid air cells


F– Petrous part of temporal bones


G– Mastoid process


H– Hard palate


I– Maxillary sinuses


J– Orbital cavities


K– Sphenoidal sinuses


L– Glabella


M – Frontal sinuses


N– Anterior clinoid processes


O– Frontal bone


P– Groove for middle meningeal artery


Q– Coronal suture


R– Sella turcica


S– Dorsum sellae


T– Channels of diploic vein.


(From Bryan 1996.)


image

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.)


image

Fig. 10.28 Diagram of submentovertical projection.


A– Incisor tooth


B– Maxillary sinus


C– Angle of mandible


D– Foramen ovale


E– Head of mandible


F– External auditory meatus


G – Mastoid air cells


H– Cervical spine


I– Posterior arch of atlas


J– Odontoid process


K– Foramen transversarium


L– Internal auditory meatus


M – Foramen lacerum


N– Foramen spinosum


O– Sphenoid sinus


P– Ethmoid sinus


Q– Zygomatic arch.


image

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.)


image

Fig. 10.30 Cranial bones: 30° fronto-occipital projection.


A – Lambdoid suture


B – Occipital bone


C – Occipital crest


D – Foramen magnum


E – Mastoid air cells


F – Internal auditory meatus


G – Dorsum sellae


H – Inferior orbital fissure


I – Zygomatic arch


J – Ramus of mandible


K – Roof of maxillary sinus


L – Mastoid process


M – Cochlea


N – Semicircular canals


O – Temporal bone


P – Transverse sulcus


Q – Parietal bone


R – Sagittal suture.


(From Bryan 1996.)


image

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


G – Condylar canal


H – Jugular process


I – Condyle


J – Basilar part


K – Hypoglossal canal


L – Jugular notch


M – Condylar fossa


N – Foramen magnum.



Individual bones of the skull



Occipital bone (Fig. 10.31)



image

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.


image

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.


image

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


A–Coronal suture


B–Glabella


C–Nasion


D–Temporal fossa


E–Zygomatic arch


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.


image

Fig. 10.22 Features of the skull (inferior aspect).


A–Palatine process of the maxilla


B–Zygomatic arch


C–Vomer


D–Foramen ovale


E–Foramen spinosum


F–Styloid process


G–External acoustic (auditory) meatus


H–Stylomastoid foramen


I–Foramen magnum


J–External occipital crest


K–Inferior nuchal line


L–Condylar canal


M–Mastoid process


N–Occipital condyle


O–Jugular foramen


P–Carotid canal


Q–Foramen lacerum


R–Palatine bone.


image

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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Jun 19, 2016 | Posted by in MUSCULOSKELETAL MEDICINE | Comments Off on The skull

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