Neurosurgical

The skullJohn craven

AbstractThe 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.

Keywords external features; fractures; skull; surface markings

The skull is described viewed from above, from in front, from the side and from below.

Superior aspectThe vault is crossed by three sutures. The coronal suture sepa-rates 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 incom-pletely ossified at birth and can be felt as a diamond-shaped defi-ciency known as the anterior fontanelle. This closes at 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 at 3–6 months.

Anterior aspect (Figure 2)The smooth convexity of the frontal bone lies above the open-ings of the orbital, nasal and oral cavities. The supraorbital mar-gin 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. One centimetre 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

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.

aNaesTHesia aND iNTeNsiVe care MeDiciNe 9:5 181

the maxillae. The opening of the oral cavity is surrounded by the alveolar margins of the maxillae and mandible. The mental foramen on the mandible, in line with the supra- and infraorbital foramina, conveys the mental vessels and nerve.

Lateral aspect (Figure 1)The zygomatic arch is formed by the zygomatic process of the squamous temporal bone and the temporal process of the zygo-matic bone. The temporal line curves upwards and backwards from the zygomatic process of the frontal bone across the pari-etal bone, and then down and forwards over the squamous tem-poral 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. The medial wall of the fossa is formed by the frontal, parietal, temporal and greater wing of the sphe-noid 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.

Below the temporal fossa is the infratemporal fossa, limited medially by the lateral pterygoid plate, which communicates with the pterygopalatine fossa through the pterygomaxillary fis-sure and with the orbit through the inferior orbital fissure. The

Lateral aspect of the skull

The external acoustic meatus (opening) is surrounded by the squamous and

the tympanic parts of the temporal bone

Bregma

Coronal suture

Temporal fossa

Greater wing

of sphenoid

Zygoma

Frontal bone

Glabella

Nasal

bone

Mandible

Maxilla

Zygomatic arch

Pterion

External acoustic meatus

Parietal bone

Temporal line

Squamous

Mastoid

Tympanic

Styloid

Parts of

temporal

bone

External

occipital

protuberance

Occipital

Lambdoid

suture

Lambda

Figure 1

© 2008 elsevier ltd. all rights reserved.

Neurosurgical

external acoustic meatus opens below the posterior zygomatic arch and the palpable mastoid process is prominent behind the meatus.

Inferior aspect (Figure 3)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 max-illae. Anteriorly a midline incisive foramen communicates with the nose and transmits the greater palatine arteries and nasopala-tine 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 bones. The apertures are separated by the tiny, wedge-shaped midline vomer. From the medial pterygoid plate projects the hamulus, which gives attach-ment to the pterygomandibular raphe. Behind the base of the lat-eral 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 sphenoman-dibular ligament and lateral to the spine is the mandibular fossa, with which the mandibular condyle articulates. The petrous tem-poral 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 trans-mits 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.

Anterior aspects of the skull showing foraminaand their contents

Frontal bone

N, nerve; A, artery

Supraorbital foramen (supraorbital N from ophthalmic division of fifth cranial N)

Superior orbital fissure (third, forth and sixth cranial Ns, nasociliary, lachrymal and frontal branches of fifth cranial N, orbital branch of middle meningeal A, ophthalmic veins, sympathetic fibres)

Inferior orbital fissure (maxillary and zygomatic Ns, infraorbital vessels)

Infraorbital foramen (infraorbital N from maxillary branch of fifth cranial N)

Nasal septum

Mental foramen(mental N from mandibular

branch of fifth cranial N)

Parietalbone

Greater wingof sphenoid

Optic canal(second cranial

N, ophthalmic A)

Middle concha

Inferior concha

Maxilla

Mandible

Frontozygomaticsuture

Figure 2

Inferior aspect of the skull showing foramina and their contents

Incisive canal (nasopalatine N and greater palatine A)

Vomer

Maxilla

Palate

Hamulus of the medial pterygoid plate

Lateral pterygoid plate

Foramen lacerum (filled with cartilage only)

Foramen spinosum (middle meningeal A)

Carotid canal (internal carotid A,

sympathetic fibres)

Jugular foramen (internal jugular vein,

ninth, tenth, eleventh cranial Ns)

Mastoid process

Condyle

Foramen magnum (spinal cord, ascending

part of eleventh cranial N, spinal and

vertebral As, branches of spinal Ns C1–C3)

Greater palatine foramen

(greater palatine N and vessels)

Maxillary tuberosity

Posterior nasal choanae

Foramen ovale (mandibular division

of fifth cranial N)

Mandibular fossa

Styloid process

External acoustic meatus

Stylomastoid foramen (seventh cranial N)

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 9:5 182 © 2008 elsevier ltd. all rights reserved.

Neurosurgical

Posterior aspectBehind 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.

Skull fracturesHard blows to the cranium result in fractures that usually radiate out from the site of impact in rather straight lines. A severe blow, such as from a hammer or a bullet, may cause a depressed frac-ture in which several pieces of skull detach inwards to be driven into the brain and these will require surgical elevation. A blow to the side of the head may fracture the thin bones of the pterion and rupture the middle meningeal vessels which lie outside of the dural covering. The resulting extradural haematoma will put pressure on the underlying brain.

aNaesTHesia aND iNTeNsiVe care MeDiciNe 9:5 18

Blows to the face may result in:• fractures of the maxilla and damage to the infraorbital nerve,

producing sensory loss over the cheek• fractures of the zygomatic bone, which may be marked by

painful limitation of movement of the temporomandibular joint

• fractures of the orbital floor, which may produce diplopia• fractures of the base of the skull if they involve the cribriform

plate or temporal bone may cause cerebrospinal fluid and/or blood leaks from the ears or nose. ◆

FurTher reAdIng

abrahams P, craven J, lumley J. illustrated clinical anatomy. london:

Hodder arnold, 2005.

3 © 2008 elsevier ltd. all rights reserved.