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Anatomy of the skull
NEUROSURGICAL
Anatomy of the skull
Learning objectives
John Craven After reading this article you should be able to locate the: C surface marking of the pterion C site of injection when performing a lingual nerve block C site of injection when performing an inferior alveolar nerve block
Abstract The external bony characteristics of the skull are described in this article, with emphasis on surface anatomical features, bony landmarks and relationships to nervous and vascular structures. Common fractures are described, together with their associated complications and diagnostic features.
alveolar margins of the maxillae and mandible. The mental foramen of the mandible, in line with the supra- and infraorbital foramina, conveys the mental vessels and nerve.
Keywords external features; fractures; skull; surface markings
Lateral aspect (Figure 1) The zygomatic arch is formed by the zygomatic process of the squamous temporal bone and the temporal process of the zygomatic bone. The masseter muscle arises from the lower border and medial surface of the arch. The squamous part of the temporal bone extends upwards to articulate with the parietal bone. The temporal line curves upwards and backwards from the zygomatic process of the frontal bone across the parietal bone,
The skull, (a term which includes the mandible), is described viewed from above, from in front, from the side and from below.
Superior aspect The vault is crossed by three sutures. The coronal suture separates the frontal bone from the two parietal bones posteriorly (Figure 1). The midline sagittal suture separates the two parietal bones. Its junction with the coronal suture, the bregma, is incompletely ossified at birth and can be felt as a diamond-shaped deficiency known as the anterior fontanelle. This closes by about 18 months. The lambdoid suture separates the two parietal bones and the occipital bone posteriorly and meets the sagittal suture at the lambda. This, too, is not ossified at birth and presents as a small bony deficiency, the posterior fontanelle, which closes by the third to sixth month.
Lateral aspect of the skull Bregma
Anterior aspect (Figure 2)
Parietal bone
Temporal fossa
Temporal line
Greater wing of sphenoid
Lambdoid suture
Frontal bone
Lambda
Zygoma
The smooth convexity of the frontal bone lies above the openings of the orbital, nasal and oral cavities, forming the upper third of the facial skeleton e the maxillae and the mandible form the lower two-thirds. The supraorbital margin possesses a supraorbital notch or foramen in its inner third which transmits the supraorbital vessels and nerve. The lateral orbital margin is formed by the frontal and zygomatic bones; the medial margin by the frontal bone and the frontal process of the maxilla; the inferior margin by the maxillary bone medially and the zygomatic bone laterally. Above the supraorbital margins are the superciliary arches. The prominence of the cheek is produced by the zygomatic bone. About 1 cm below the orbit on the maxilla, in line with the supraorbital notch, is the infraorbital foramen, from which emerge the infraorbital vessels and nerve. The nasal aperture is bounded above by the nasal bones, and below and laterally by the maxillae. The opening of the oral cavity is surrounded by the
Glabella Nasal bone
Occipital
Mandible Maxilla Zygomatic arch Pterion
John Craven FRCS was formerly Consultant Surgeon at York District Hospital, York, UK. He is past chairman of the primary examiners of the Royal College of Surgeons of England. Conflicts of interest: none declared.
ANAESTHESIA AND INTENSIVE CARE MEDICINE 12:5
External acoustic meatus
Coronal suture
External occipital protuberance Squamous Mastoid Tympanic Styloid
Parts of temporal bone
The external acoustic meatus (opening) is surrounded by the squamous and the tympanic parts of the temporal bone
Figure 1
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Ó 2011 Elsevier Ltd. All rights reserved.
NEUROSURGICAL
and then down and forwards over the squamous temporal bone to end above the external acoustic meatus. Below the temporal line, deep to the zygomatic arch, is the temporal fossa, roofed by the temporal fascia attached to the temporal line and the zygomatic arch. Temporalis muscle arises from the inferior temporal line and the whole surface of the temporal fossa. The medial wall of the fossa is formed by the frontal, parietal, temporal and greater wing of the sphenoid bones. Their H-shaped union, the pterion, lies about 3.5 cm behind and 1.5 cm above the palpable frontozygomatic suture. Here the middle meningeal artery grooves the inner surface of the bone. A blow to the side of the head may fracture the thin bones of the pterion and rupture the middle meningeal vessels. The resulting extradural haematoma puts pressure on the underlying brain. Below the temporal fossa is the infratemporal fossa, limited medially by the lateral pterygoid plate, which communicates with the pterygopalatine fossa through the pterygomaxillary fissure and with the orbit through the inferior orbital fissure. The external acoustic meatus opens below the posterior zygomatic arch and the palpable mastoid process is prominent behind the meatus. To this is attached sternomastoid.
Anterior aspects of the skull showing foramina and their contents Frontal bone Supraorbital foramen (supraorbital N from ophthalmic division of fifth cranial N)
Frontozygomatic suture
Superior orbital fissure (third, fourth and sixth cranial Ns, nasociliary, lachrymal and frontal branches of fifth cranial N, orbital branch of middle meningeal A, ophthalmic veins, sympathetic fibres)
Parietal bone Greater wing of sphenoid Optic canal (second cranial N, ophthalmic A) Middle concha Inferior concha
Inferior orbital fissure (maxillary and zygomatic Ns, infraorbital vessels) Infraorbital foramen (infraorbital N from maxillary branch of fifth cranial N)
Inferior aspect (Figure 3)
Maxilla
Anteriorly is the hard palate, formed by the palatine processes of the maxillae in front of the horizontal plates of the palatine bones. It is bounded anterolaterally by the alveolar processes of the maxillae. Anteriorly a midline incisive foramen communicates with the nose and transmits the greater palatine arteries and nasopalatine nerves; on the posterolateral palate are the greater and lesser palatine foramina, which convey vessels and nerves of the same name. The posterior nasal apertures (choanae) open above the palate, bounded above by the body of the sphenoid bone, below by the horizontal plates of the palatine
Mandible
Nasal septum Mental foramen (mental N from mandibular branch of fifth cranial N)
N, nerve; A, artery
Figure 2
Inferior aspect of the skull showing foramina and their contents Maxilla
Incisive canal (nasopalatine N and greater palatine A) Vomer
Palate
Greater palatine foramen (greater palatine N and vessels)
Hamulus of the medial pterygoid plate Lateral pterygoid plate
Maxillary tuberosity
Foramen lacerum (filled with cartilage only) Foramen spinosum (middle meningeal A) Posterior nasal choanae
Carotid canal (internal carotid A, sympathetic fibres)
Foramen ovale (mandibular division of fifth cranial N)
Jugular foramen (internal jugular vein, ninth, tenth, eleventh cranial Ns)
Mandibular fossa Styloid process
Condyle
External acoustic meatus
Mastoid process
Stylomastoid foramen (seventh cranial N) Foramen magnum (spinal cord, ascending part of eleventh cranial N, spinal and vertebral As, branches of spinal Ns C1–C3)
Hypoglossal canal (twelfth cranial N) Inferior nuchal line Superior nuchal line External occipital protuberance N, nerve; A, artery
Figure 3
ANAESTHESIA AND INTENSIVE CARE MEDICINE 12:5
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NEUROSURGICAL
The mandible, medial aspect
Lateral pterygoid Temporalis Mandibular foramen Medial pterygoid
Position of the sublingual gland
Position of the submandibular gland
Genioglossus Geniohyoid
Mylohyoid
Diagastric
Figure 4
bones, and laterally by the medial pterygoid plates. The apertures are separated by the tiny, wedge-shaped midline vomer. From the medial pterygoid plate projects the hamulus which gives attachment to the pterygomandibular raphe. Behind the base of the lateral pterygoid process is the foramen ovale, which transmits the mandibular nerve; and posterolateral to the foramen is the spine of the sphenoid and the foramen spinosum, which transmits the middle meningeal artery. To the spine is attached the sphenomandibular ligament and lateral to the spine is the mandibular fossa, with which the mandibular condyle articulates. The petrous temporal bone lies between the occipital and sphenoid bones and contains the carotid canal, whose inferior opening lies behind the spine of the sphenoid. Posterolateral to the carotid opening is the jugular foramen, which transmits the internal jugular vein and the glossopharyngeal, vagus and accessory nerves. Posterolateral to the styloid process is the stylomastoid foramen, which transmits the facial nerve. The occipital bone contains the foramen magnum, bounded on each side by the occipital condyles, and a small foramen transmitting the hypoglossal nerve. Behind the foramen magnum are the superior and inferior nuchal lines, between which are attached the postvertebral muscles. In the middle of the superior line is the prominent and palpable external occipital protuberance.
ANAESTHESIA AND INTENSIVE CARE MEDICINE 12:5
The mandible (Figure 4) is formed by the midline union of its two halves each with a horizontal body joining with a vertical ramus at the palpable angle. The flat ramus bears two prominences superiorly; the coronoid process giving attachment to temporalis and the posterior condylar process articulates with the mandibular fossa of the temporal bone. Masseter is attached to the external surface of the ramus and in the centre of its medial surface is the mandibular foramen which conveys the inferior alveolar vessels and nerve. To the lower lip of the foramen is attached the sphenomandibular ligament. Palpation of this ligament helps to locate the inferior alveolar nerve. Medial pterygoid muscle is attached to the medial surface of the angle below the mandibular foramen. The body has a smooth inferior border and an upper alveolar border bearing sockets for the teeth. The mental foramen, conveying the mental vessels and nerve, lies on the lateral surface below the premolar teeth. The medial (inner), surface is ridged by the mylohyoid line, to which mylohyoid is attached, passing downwards and forwards to the midline. The lingual nerve lies close to the medial surface of the mandible just behind the last molar tooth. A
FURTHER READING Abrahams P, Craven J, Lumley J. Illustrated clinical anatomy. London: Hodder Arnold, 2005.
188
Ó 2011 Elsevier Ltd. All rights reserved.
Anatomy of the skull
Learning objectives
John Craven After reading this article you should be able to locate the: C surface marking of the pterion C site of injection when performing a lingual nerve block C site of injection when performing an inferior alveolar nerve block
Abstract The external bony characteristics of the skull are described in this article, with emphasis on surface anatomical features, bony landmarks and relationships to nervous and vascular structures. Common fractures are described, together with their associated complications and diagnostic features.
alveolar margins of the maxillae and mandible. The mental foramen of the mandible, in line with the supra- and infraorbital foramina, conveys the mental vessels and nerve.
Keywords external features; fractures; skull; surface markings
Lateral aspect (Figure 1) The zygomatic arch is formed by the zygomatic process of the squamous temporal bone and the temporal process of the zygomatic bone. The masseter muscle arises from the lower border and medial surface of the arch. The squamous part of the temporal bone extends upwards to articulate with the parietal bone. The temporal line curves upwards and backwards from the zygomatic process of the frontal bone across the parietal bone,
The skull, (a term which includes the mandible), is described viewed from above, from in front, from the side and from below.
Superior aspect The vault is crossed by three sutures. The coronal suture separates the frontal bone from the two parietal bones posteriorly (Figure 1). The midline sagittal suture separates the two parietal bones. Its junction with the coronal suture, the bregma, is incompletely ossified at birth and can be felt as a diamond-shaped deficiency known as the anterior fontanelle. This closes by about 18 months. The lambdoid suture separates the two parietal bones and the occipital bone posteriorly and meets the sagittal suture at the lambda. This, too, is not ossified at birth and presents as a small bony deficiency, the posterior fontanelle, which closes by the third to sixth month.
Lateral aspect of the skull Bregma
Anterior aspect (Figure 2)
Parietal bone
Temporal fossa
Temporal line
Greater wing of sphenoid
Lambdoid suture
Frontal bone
Lambda
Zygoma
The smooth convexity of the frontal bone lies above the openings of the orbital, nasal and oral cavities, forming the upper third of the facial skeleton e the maxillae and the mandible form the lower two-thirds. The supraorbital margin possesses a supraorbital notch or foramen in its inner third which transmits the supraorbital vessels and nerve. The lateral orbital margin is formed by the frontal and zygomatic bones; the medial margin by the frontal bone and the frontal process of the maxilla; the inferior margin by the maxillary bone medially and the zygomatic bone laterally. Above the supraorbital margins are the superciliary arches. The prominence of the cheek is produced by the zygomatic bone. About 1 cm below the orbit on the maxilla, in line with the supraorbital notch, is the infraorbital foramen, from which emerge the infraorbital vessels and nerve. The nasal aperture is bounded above by the nasal bones, and below and laterally by the maxillae. The opening of the oral cavity is surrounded by the
Glabella Nasal bone
Occipital
Mandible Maxilla Zygomatic arch Pterion
John Craven FRCS was formerly Consultant Surgeon at York District Hospital, York, UK. He is past chairman of the primary examiners of the Royal College of Surgeons of England. Conflicts of interest: none declared.
ANAESTHESIA AND INTENSIVE CARE MEDICINE 12:5
External acoustic meatus
Coronal suture
External occipital protuberance Squamous Mastoid Tympanic Styloid
Parts of temporal bone
The external acoustic meatus (opening) is surrounded by the squamous and the tympanic parts of the temporal bone
Figure 1
186
Ó 2011 Elsevier Ltd. All rights reserved.
NEUROSURGICAL
and then down and forwards over the squamous temporal bone to end above the external acoustic meatus. Below the temporal line, deep to the zygomatic arch, is the temporal fossa, roofed by the temporal fascia attached to the temporal line and the zygomatic arch. Temporalis muscle arises from the inferior temporal line and the whole surface of the temporal fossa. The medial wall of the fossa is formed by the frontal, parietal, temporal and greater wing of the sphenoid bones. Their H-shaped union, the pterion, lies about 3.5 cm behind and 1.5 cm above the palpable frontozygomatic suture. Here the middle meningeal artery grooves the inner surface of the bone. A blow to the side of the head may fracture the thin bones of the pterion and rupture the middle meningeal vessels. The resulting extradural haematoma puts pressure on the underlying brain. Below the temporal fossa is the infratemporal fossa, limited medially by the lateral pterygoid plate, which communicates with the pterygopalatine fossa through the pterygomaxillary fissure and with the orbit through the inferior orbital fissure. The external acoustic meatus opens below the posterior zygomatic arch and the palpable mastoid process is prominent behind the meatus. To this is attached sternomastoid.
Anterior aspects of the skull showing foramina and their contents Frontal bone Supraorbital foramen (supraorbital N from ophthalmic division of fifth cranial N)
Frontozygomatic suture
Superior orbital fissure (third, fourth and sixth cranial Ns, nasociliary, lachrymal and frontal branches of fifth cranial N, orbital branch of middle meningeal A, ophthalmic veins, sympathetic fibres)
Parietal bone Greater wing of sphenoid Optic canal (second cranial N, ophthalmic A) Middle concha Inferior concha
Inferior orbital fissure (maxillary and zygomatic Ns, infraorbital vessels) Infraorbital foramen (infraorbital N from maxillary branch of fifth cranial N)
Inferior aspect (Figure 3)
Maxilla
Anteriorly is the hard palate, formed by the palatine processes of the maxillae in front of the horizontal plates of the palatine bones. It is bounded anterolaterally by the alveolar processes of the maxillae. Anteriorly a midline incisive foramen communicates with the nose and transmits the greater palatine arteries and nasopalatine nerves; on the posterolateral palate are the greater and lesser palatine foramina, which convey vessels and nerves of the same name. The posterior nasal apertures (choanae) open above the palate, bounded above by the body of the sphenoid bone, below by the horizontal plates of the palatine
Mandible
Nasal septum Mental foramen (mental N from mandibular branch of fifth cranial N)
N, nerve; A, artery
Figure 2
Inferior aspect of the skull showing foramina and their contents Maxilla
Incisive canal (nasopalatine N and greater palatine A) Vomer
Palate
Greater palatine foramen (greater palatine N and vessels)
Hamulus of the medial pterygoid plate Lateral pterygoid plate
Maxillary tuberosity
Foramen lacerum (filled with cartilage only) Foramen spinosum (middle meningeal A) Posterior nasal choanae
Carotid canal (internal carotid A, sympathetic fibres)
Foramen ovale (mandibular division of fifth cranial N)
Jugular foramen (internal jugular vein, ninth, tenth, eleventh cranial Ns)
Mandibular fossa Styloid process
Condyle
External acoustic meatus
Mastoid process
Stylomastoid foramen (seventh cranial N) Foramen magnum (spinal cord, ascending part of eleventh cranial N, spinal and vertebral As, branches of spinal Ns C1–C3)
Hypoglossal canal (twelfth cranial N) Inferior nuchal line Superior nuchal line External occipital protuberance N, nerve; A, artery
Figure 3
ANAESTHESIA AND INTENSIVE CARE MEDICINE 12:5
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Ó 2011 Elsevier Ltd. All rights reserved.
NEUROSURGICAL
The mandible, medial aspect
Lateral pterygoid Temporalis Mandibular foramen Medial pterygoid
Position of the sublingual gland
Position of the submandibular gland
Genioglossus Geniohyoid
Mylohyoid
Diagastric
Figure 4
bones, and laterally by the medial pterygoid plates. The apertures are separated by the tiny, wedge-shaped midline vomer. From the medial pterygoid plate projects the hamulus which gives attachment to the pterygomandibular raphe. Behind the base of the lateral pterygoid process is the foramen ovale, which transmits the mandibular nerve; and posterolateral to the foramen is the spine of the sphenoid and the foramen spinosum, which transmits the middle meningeal artery. To the spine is attached the sphenomandibular ligament and lateral to the spine is the mandibular fossa, with which the mandibular condyle articulates. The petrous temporal bone lies between the occipital and sphenoid bones and contains the carotid canal, whose inferior opening lies behind the spine of the sphenoid. Posterolateral to the carotid opening is the jugular foramen, which transmits the internal jugular vein and the glossopharyngeal, vagus and accessory nerves. Posterolateral to the styloid process is the stylomastoid foramen, which transmits the facial nerve. The occipital bone contains the foramen magnum, bounded on each side by the occipital condyles, and a small foramen transmitting the hypoglossal nerve. Behind the foramen magnum are the superior and inferior nuchal lines, between which are attached the postvertebral muscles. In the middle of the superior line is the prominent and palpable external occipital protuberance.
ANAESTHESIA AND INTENSIVE CARE MEDICINE 12:5
The mandible (Figure 4) is formed by the midline union of its two halves each with a horizontal body joining with a vertical ramus at the palpable angle. The flat ramus bears two prominences superiorly; the coronoid process giving attachment to temporalis and the posterior condylar process articulates with the mandibular fossa of the temporal bone. Masseter is attached to the external surface of the ramus and in the centre of its medial surface is the mandibular foramen which conveys the inferior alveolar vessels and nerve. To the lower lip of the foramen is attached the sphenomandibular ligament. Palpation of this ligament helps to locate the inferior alveolar nerve. Medial pterygoid muscle is attached to the medial surface of the angle below the mandibular foramen. The body has a smooth inferior border and an upper alveolar border bearing sockets for the teeth. The mental foramen, conveying the mental vessels and nerve, lies on the lateral surface below the premolar teeth. The medial (inner), surface is ridged by the mylohyoid line, to which mylohyoid is attached, passing downwards and forwards to the midline. The lingual nerve lies close to the medial surface of the mandible just behind the last molar tooth. A
FURTHER READING Abrahams P, Craven J, Lumley J. Illustrated clinical anatomy. London: Hodder Arnold, 2005.
188
Ó 2011 Elsevier Ltd. All rights reserved.