Inferior view
421
72
RETPAHC
tip usually reaching a point medial to the posterior margin of the man- The inferior surface may be conveniently subdivided into anterior,
dibular ramus. The styloid process is very variably developed. Its length middle, posterior and lateral parts. The anterior part contains the hard
ranges from a few millimetres to a few centimetres and increases with palate and the dentition of the upper jaw, and lies at a lower level than
age (Krmpotić Nemanić et al 2009). the rest of the cranial base. The middle and posterior parts may be
The infratemporal fossa is an irregular, postmaxillary space deep to arbitrarily divided by a transverse plane passing through the anterior
the ramus of the mandible. It communicates with the upper temporal margin of the foramen magnum. The middle part is occupied mainly
fossa deep to the zygomatic arch. It is best visualized when the mandi- by the sphenoid bone, the apices of the petrous processes of the tem-
ble is removed but, for completeness, is considered here. Its roof is the poral bones, and the basilar part of the occipital bone. The lateral part
infratemporal surface of the greater wing of the sphenoid, the lateral contains the zygomatic arches, mandibular fossae, tympanic plates and
pterygoid plate lies medially, and the ramus of the mandible and styloid the styloid and mastoid processes. The posterior part lies in the midline
process lie laterally and posteriorly, respectively. The infratemporal and is formed almost exclusively from the occipital bone. Whereas the
fossa has no anatomical floor. Its anterior and medial walls are sepa- middle and posterior parts are directly related to the cranial cavity (the
rated above by the pterygomaxillary fissure lying between the lateral middle and posterior cranial fossae), the anterior part is some distance
pterygoid plate and the posterior wall of the maxilla. The infratemporal from the anterior cranial fossa, being separated from it by the nasal
fossa communicates with the pterygopalatine fossa through the ptery- cavities.
gomaxillary fissure.
ANTERIOR PART OF INFERIOR SURFACE
INFERIOR VIEW


The bony palate within the superior alveolar arch is formed by the pala-
With the mandible removed, the inferior surface of the skull extends tine processes of the maxillae anteriorly and the horizontal plates of
from the upper incisor teeth anteriorly to the superior nuchal lines of the palatine bones posteriorly, all meeting at a cruciform system of
the occipital bone posteriorly (Fig. 27.5). The region contains many of sutures (see Fig. 27.5). The median palatine suture runs anteroposteri-
the foramina through which structures enter and exit the cranial cavity. orly and divides the palate into right and left halves. This suture is
Posterior nasal spine Incisive foramen
Vomer, alae Median palatine suture
Palatine bone, pyramidal process Maxilla, palatine process
Maxilla, zygomatic process Transverse palatine suture
Pterygoid process, medial plate Palatine bone, horizontal plate
Pterygoid hamulus Zygomatic arch
Pterygoid process, lateral plate Greater palatine foramen
Inferior orbital fissure
Sphenoid, greater wing
Infratemporal crest
Temporal bone, zygomatic process
Pterygoid process, medial plate
Foramen lacerum
Foramen ovale
Foramen spinosum
Pharyngeal tubercle
Mandibular fossa
Articular tubercle
Spine of sphenoid Hypoglossal canal
Styloid process Carotid canal
Mastoid canal
External acoustic meatus
Jugular fossa
Stylomastoid foramen
Occipitomastoid suture
Jugular foramen
Mastoid process
Parietal bone
Mastoid notch
Occipital condyle
Foramen magnum
Condylar canal
Inferior nuchal line
Superior nuchal line
External occipital protuberance
Maxilla Palatine bone Sphenoid
Frontal bone Vomer Temporal bone
Parietal bone Zygomatic bone Occipital bone
Fig. 27.5 The external surface of the base of the adult skull. (With permission from Waschke J, Paulsen F (eds), Sobotta Atlas of Human Anatomy, 15th
ed, Elsevier, Urban & Fischer. Copyright 2013.)


ExTERnAl skull
422
4
nOITCEs
continuous with the intermaxillary suture between the maxillary central fissure and bears an infratemporal crest associated with the origin of
incisor teeth. The transverse palatine (palatomaxillary) sutures run the upper part of lateral pterygoid. The infraorbital and zygomatic
transversely across the palate between the maxillae and the palatine branches of the maxillary nerve and accompanying vessels pass through
bones. The palate is arched sagittally and transversely; its depth and the inferior orbital fissure. Laterally, the greater wing of the sphenoid
breadth are variable but are always greatest in the molar region. The articulates with the squamous part of the temporal bone.
incisive fossa lies behind the central incisor teeth, and the lateral inci- The medial aspect of the greater wing of the sphenoid presents a
sive foramina, through which incisive canals pass to the nasal cavity, lie crescent of foramina of which only the most posterior two, foramen
in its lateral walls. Median incisive foramina are present in some skulls ovale and foramen spinosum, can be viewed on the basal aspect. The
and open on to the anterior and posterior walls of the fossa. The incisive foramen ovale lies medial to the foramen spinosum and lateral to the
fossa transmits the nasopalatine nerve and the termination of the foramen lacerum on the infratemporal surface of the greater wing of
greater palatine vessels. When median incisive foramina occur, the left the sphenoid bone. It transmits the mandibular division of the trigemi-
nasopalatine nerve usually traverses the anterior foramen and the right nal nerve, the lesser petrosal nerve, the accessory meningeal branch of
nerve traverses the posterior foramen. The greater palatine foramen lies the maxillary artery and an emissary vein that connects the cavernous
near the lateral palatal border of the transverse palatine suture; a vas- venous sinus to the pterygoid venous plexus in the infratemporal fossa.
cular groove, deeper behind and shallower in front, leads forwards from Posterolaterally, the smaller and rounder foramen spinosum transmits


the foramen. The lesser palatine foramina, usually two, lie behind the the middle meningeal artery and a recurrent meningeal branch of the
greater palatine foramen and pierce the pyramidal process of the pala- mandibular nerve. The irregular spine of the sphenoid projects postero-
tine bone, which is wedged between the lower ends of the medial and lateral to the foramen spinosum. The medial surface of the spine is flat
lateral pterygoid plates. The palate is pierced by many other small and, with the adjoining posterior border of the greater wing of the
foramina and is marked by pits for palatine glands. Variably prominent sphenoid, forms the anterolateral wall of a groove that is completed
palatine crests extend medially from behind the greater palatine posteromedially by the petrous part of the temporal bone. This groove
foramina. The posterior border projects back as the posterior nasal contains the cartilaginous pharyngotympanic tube, which leads postero-
spine. In the adult, the alveolar arch normally bears a maximum of 16 laterally into the bony portion of the tube that lies within the petrous
sockets or alveoli for the teeth; the sockets vary in size and depth, and part of the temporal bone. Occasionally, the foramen ovale and foramen
some are single and some are subdivided by septa, according to the spinosum are confluent or the posterior edge of the foramen spinosum
morphology of the dental roots. may be defective. A small foramen, the sphenoidal emissary foramen
The nasal fossae lie above the hard palate and are separated by the (of Vesalius), is sometimes found between the foramen ovale and
nasal septum in the midline. The bony nasal septum is formed from scaphoid fossa. When present, it contains an emissary vein linking the
the perpendicular plate of the ethmoid superiorly and the vomer in- pterygoid venous plexus in the infratemporal fossa with the cavernous
feriorly. The upper border of the vomer approximates to the inferior sinus in the middle cranial fossa.
aspect of the body of the sphenoid, where it expands into an ala on The foramen lacerum is bounded in front by the body and adjoining


each side. The two posterior nasal apertures (choanae) are located at roots of the pterygoid process and greater wing of the sphenoid bone;
the end of the nasal fossae; they are separated by the free posterior posterolaterally, by the apex of the petrous part of the temporal bone;
border of the vomer, and bounded below by the posterior border of the and medially, by the basilar part of the occipital bone. Although nearly
horizontal plates of the palatine bones, above by the sphenoid and 1 cm long, it is not traversed by any major structure. The almost circular
laterally by the medial pterygoid plates. carotid canal lies behind and posterolateral to the foramen lacerum in
the petrous part of the temporal bone. The internal carotid artery enters
the skull through this foramen, ascends in the carotid canal, and turns
MIDDLE PART OF INFERIOR SURFACE anteromedially to reach the posterior wall of the foramen lacerum. It
ascends through the upper end of the foramen lacerum, accompanied
The middle part of the inferior surface is made up from the sphenoid, by venous and sympathetic nerve plexuses. Meningeal branches of the
petrous parts of the temporal bones and the basiocciput (see Fig. 27.5). ascending pharyngeal artery and emissary veins from the cavernous
It extends from the posterior nares anteriorly to an artificial line drawn sinus also traverse the foramen lacerum. In life, the lower part of the
transversely through the anterior margin of the foramen magnum pos- foramen lacerum is partially occluded by cartilaginous remnants of the
teriorly. In the adult, the body of the sphenoid fuses with the basi- embryological chondrocranium. The pterygoid canal can be seen on
occiput to form a midline bar of bone that extends posteriorly to the the base of the skull at the anterior margin of the foramen lacerum,
foramen magnum (internally, this is known as the clivus). The basi- above and between the pterygoid plates of the sphenoid bone. It leads


occiput bears a small midline pharyngeal tubercle, which gives attach- into the pterygopalatine fossa and transmits the nerve of the pterygoid
ment to the pharyngeal raphe, the highest attachment of the superior canal and accompanying blood vessels.
pharyngeal constrictor.
The petrous processes of the two temporal bones pass from the
lateral sides of the base of the skull and fill the triangular space between POSTERIOR PART OF INFERIOR SURFACE
the greater wing of the sphenoid anteriorly and the lateral margins of
the basiocciput posteriorly. Each petrous process meets the basilar part The posterior part of the inferior surface of the skull is predominantly
of the occipital bone at a petro-occipital junction, which is deficient formed by the occipital bone (see Fig. 27.5). Prominent features are the
posteriorly at the jugular foramen. The petrosphenoidal junction and foramen magnum and associated occipital condyles, jugular foramen,
the groove for the pharyngotympanic tube lie between the petrous mastoid notch and the squamous part of the occipital bone up to the
process and the infratemporal surface of the greater wing of the sphe- external occipital protuberance and the superior nuchal lines, hypoglos-
noid. The apex of the petrous process does not meet the spheno- sal canals (anterior condylar canals) and condylar canals (posterior
occipital synchondrosis; the deficit so produced is the foramen lacerum. condylar canals).
Pterygoid processes descend from the junction between the greater The foramen magnum lies in an anteromedian position and leads
wing and body of the sphenoid, separated by a pterygoid fossa. An- into the posterior cranial fossa. It is oval and wider behind, with its
teriorly, the plates are fused, except inferiorly, where they are separated greatest diameter being anteroposterior. It contains the lower end of the
by the pyramidal process of the palatine bone. Sutures are usually dis- medulla oblongata, meninges, cerebrospinal fluid, vertebral arteries


cernible at this site in young skulls. Laterally, the pterygoid plates are and veins, and the accessory nerves; the apical ligament of the dens and
separated from the posterior maxillary surface by the pterygomaxillary the tectorial membrane pass through it to attach to the internal basi-
fissure, which leads into the pterygopalatine fossa. The posterior border occiput. Anteriorly, the margin of the foramen magnum is slightly
of the medial pterygoid plate is sharp, and bears a small projection near overlapped by the occipital condyles, which project down to articulate
the midpoint, above which it is curved and attached to the pharyngeal with the superior articular facets on the lateral masses of the atlas. Each
end of the pharyngotympanic tube. Above, the medial pterygoid plate occipital condyle is oval in outline and orientated obliquely so that its
divides to enclose the scaphoid fossa. Below, it projects as a slender anterior end lies nearer the midline than its posterior end. It is markedly
pterygoid hamulus, which curves laterally and is grooved anteriorly by convex anteroposteriorly, less so transversely, and its medial aspect is
the tendon of tensor veli palatini. The pterygoid hamulus gives origin roughened by ligamentous attachments. The hypoglossal canal, directed
to the pterygomandibular raphe. The lateral pterygoid plate projects laterally and slightly forwards, traverses deep to each condyle and trans-
posterolaterally and its lateral surface forms the medial wall of the in- mits the hypoglossal nerve, a meningeal branch of the ascending pha-
fratemporal fossa. Superiorly and laterally, the pterygoid process is ryngeal artery and an emissary vein from the basilar plexus. A depression,
continuous with the infratemporal surface of the greater wing of the the condylar fossa, lies immediately posterior to the condyle and may
sphenoid bone, which forms part of the roof of the infratemporal fossa. contain a (posterior) condylar canal for an emissary vein from the


This surface forms the posterolateral border of the inferior orbital sigmoid sinus. This fossa accommodates the posterior margin of the


neonatal, paediatric and senescent anatomy
423
72
RETPAHC
atlas when the head is fully extended. A jugular process articulates with
JOINTS
the petrous part of the temporal bone lateral to each condyle and its
anterior free border forms the posterior boundary of the jugular
foramen. The general characteristics of cranial sutures and the detailed anatomy
Laterally, the occipital bone approximates with the petrous part of of the temporomandibular joint and the atlanto-occipital joints are
the temporal bone anteriorly at the petro-occipital junction, and the described in Chapter 5 and on page 541 and page 736, respectively.
mastoid process of the temporal bone more posteriorly at the occipito- Sutural bones are described below on page 425.
mastoid suture. The jugular foramen, a large, irregular hiatus, lies at the
posterior end of the petro-occipital junction between the jugular process
NEONATAL, PAEDIATRIC AND
of the occipital bone and the jugular fossa of the petrous part of the
temporal bone (see Fig. 37.1C) (Vogl and Bisdas 2009). A number of SENESCENT ANATOMY
important structures pass through this foramen: inferior petrosal sinus
(anterior); glossopharyngeal, vagus and accessory cranial nerves THE SKULL AT BIRTH
(middle); and internal jugular vein (posterior). A mastoid canaliculus
runs through the lateral wall of the jugular fossa and transmits the At birth, the calvaria is large in proportion to other skeletal parts, reflect-
auricular branch of the vagus nerve. The canaliculus for the tympanic ing precocious cerebral maturation. The facial region is relatively small
branch of the glossopharyngeal nerve lies on the ridge between the and constitutes only about one-eighth of the neonatal skull, whereas it
jugular fossa and the opening of the carotid canal. A small notch, constitutes about half of the adult skull (Fig. 27.6). Smallness of the
related to the inferior glossopharyngeal ganglion, may be found medi- face at birth is due mainly to the rudimentary stage of development of


ally, on the upper boundary of the jugular foramen (it is more easily the mandible and maxillae; the teeth are unerupted and the maxillae
identified internally). The orifice of the cochlear canaliculus may be are not yet pneumatized (invaded by air cells). The nose lies almost
found at the apex of the notch. entirely between the orbits, and the lower border of the nasal aperture
The squamous part of the occipital bone exhibits the external is only slightly lower in position than the orbital floors. Bones of the
occipital protuberance, supreme, superior and inferior nuchal lines, calvaria are unilaminar and lack diploë. Frontal and parietal tuberosi-
and the external occipital crest, all of which lie in the midline, poste- ties are prominent; in the frontal view, the greatest width occurs between
rior to the foramen magnum. The region is roughened for the attach- the parietal tuberosities. The glabella, superciliary arches and mastoid
ment of muscles whose primary function is extension of the skull at processes are not developed and the cranial base is relatively short and
the neck. narrow.
Ossification is incomplete, and many bones are still in several ele-
ments that are united by fibrous tissue or cartilage. The ‘os incisivum’
LATERAL PART OF INFERIOR SURFACE
is continuous with the maxilla; pre- and postsphenoids may have just
united, but the two halves of the frontal bone and the mandible, and
The lateral part of the inferior surface consists of the zygomatic arch
the squamous, lateral and basilar parts of the occipital bone, are all
and infratemporal fossa anteriorly and the mandibular fossa, tympanic
separate, as are the petromastoid and squamotympanic parts of the
plate and styloid and mastoid processes posteriorly (see Fig. 27.5). The
temporal bone. The fibrous membrane that forms the calvaria remains
anterior structures have been considered earlier in this chapter.
unossified at the six angles of the parietal bones, producing six fonta-
The mandibular fossa is a thin-walled, smooth, concave depression


nelles: two single midline (anterior and posterior) and two lateral pairs
in the temporal bone and is most easily inspected when the mandible
(sphenoidal/anterolateral and mastoid/posterolateral). The anterior
is removed. The zygomatic arch extends laterally in front of the fossa
fontanelle is the largest, measuring approximately 4 cm in anteropos-
and a distinct ridge, the articular eminence, lies anterior to the fossa.
terior and 2.5 cm in transverse dimensions. It occupies the junction
Three fissures can be distinguished behind the mandibular fossa. The
between the sagittal, coronal and frontal sutures and is rhomboid in
squamotympanic fissure extends from the spine of the sphenoid,
shape. The posterior fontanelle lies at the junction between the sagittal
between the mandibular fossa and the tympanic plate of the temporal
and lambdoid sutures and is triangular in shape. The sphenoidal (an-
bone, and curves up the anterior margin of the external acoustic meatus.
terolateral) and mastoid (posterolateral) fontanelles are small and
A thin wedge of bone forming the inferior margin of the tegmen
irregular in shape and lie at the sphenoidal and mastoid angles of the
tympani lies within the fissure and divides the squamotympanic fissure
parietal bones, respectively.
into petrotympanic and petrosquamous fissures. The petrotympanic
At birth, the orbits appear relatively large. The developing tooth
fissure transmits the chorda tympani branch of the facial nerve from
germs are generally contained within the alveolar crypts, although erup-
the intracranial cavity into the infratemporal fossa. The tympanic plate
tion of the upper central incisor teeth can occur prior to, or shortly after,
forms the floor of the external acoustic meatus.
birth. Temporal bones differ greatly from their adult form. The internal
The stylomastoid foramen lies between the mastoid and styloid
ear, tympanic cavity, auditory ossicles and mastoid antrum are all
processes on the lateral aspect of the temporal bone. It transmits the
almost adult in size, the tympanic plate is an incomplete ring that has


facial nerve and the stylomastoid artery. The distance from the styloid
usually started to fuse with the squamous part, and the mastoid process
process to the stylomastoid foramen decreases with age (Krmpotić
is absent. The external acoustic meatus is short, straight and wholly
Nemanić et al 2009). A groove, the mastoid notch, lies medial to the
cartilaginous. The external aspect of the tympanic membrane faces
mastoid process and gives origin to the posterior belly of digastric. A
more inferiorly than laterally, in accord with the basal cranial contour.
groove related to the occipital artery often lies medial to the mastoid
The stylomastoid foramen is exposed on the lateral surface of the skull,
notch. A mastoid foramen may be present near, or in, the occipitomas-
the styloid process has not yet commenced ossification, the mandibular
toid suture; when present, it transmits an emissary vein from the
fossa is flat and more lateral, and its articular tubercle is undeveloped.
sigmoid sinus. The external acoustic meatus lies in front of the mastoid
The paranasal sinuses are rudimentary or absent and only the maxillary
process. It is surrounded inferiorly by the tympanic plate, which partly
sinuses are usually identifiable.
ensheathes the base of the styloid process as the vaginal process.
The skull is moulded by slow compression during vaginal birth. That
part of the scalp that is more central in the birth canal is often tempo-
CRANIAL FOSSAE (ANTERIOR, rarily oedematous (caput succedaneum) as a result of interference with
venous return. Fontanelles and the openness and width of the sutures
MIDDLE, POSTERIOR)
allow bones of the cranial vault some overlap during the process of
birth; the skull is compressed in one plane with compensatory orthogo-
The cranial fossae are described in Chapter 28. nal elongation. These deformations disappear within the first week after
birth.
DISARTICULATED INDIVIDUAL BONES
POSTNATAL GROWTH
Individual bones are described in the appropriate chapters. The bones


of the facial skeleton and cranial vault are described in the chapters on Although postnatal growth of the calvaria (cranial vault) and facial
the face and scalp (Ch. 30), nose and paranasal sinuses (Ch. 33), exter- skeleton usually proceeds in a coordinated fashion, these regions
nal and middle ear (Ch. 37), and orbit (Ch. 41). The sphenoid and exhibit different rates and temporal periods of expression. In general,
mandible are described in the chapter on the infratemporal fossa early growth of the vault is largely influenced by cerebral maturation
(Ch. 32) and the occipital bone is described in the chapter on the back while growth of the facial skeleton responds to spatial requirement for
(Ch. 43). the development of the teeth and the muscles of mastication. Growth


External skull
423.e1
72
RETPAHC
Anterior fontanelle
Metopic suture
Coronal suture
F F
P P
Sphenoid fontanelle Squamous suture
Ts Ts
E
Anterior fontanelle Sagittal suture
Coronal suture
F P Posterior fontanelle
Lambdoid suture
Sphenoid fontanelle
Sp Ts O
Z
Mastoid fontanelle
F Squamous suture
Sagittal suture
P P
Posterior fontanelle
O
Lambdoid suture
Mastoid fontanelle
Ts Ts
G
Fig. 27.6, E–G, Normal three-dimensional calvarial anatomy. E, Frontal
aspect. F, Lateral aspect. G, Basal aspect; there is a linear fracture in
the right parietal bone (double arrows). Abbreviations: F, frontal bone;
O, occipital bone; P, parietal bone; Sp, sphenoid bone; Ts, temporal
bone, squamous portion. (E–G, With permission from Y. Pekcevik,
E. Hasbay, R. Pekcevik; Izmir/TR; Diagnostic value of three-dimensional
CT in pediatric calvarial pathologies, ECR 2013 / C-1263, EPOS™,
European Society of Radiology.)


ExTERnAl skull
424
4
nOITCEs
A B
Anterior fontanelle
Metopic suture Coronal suture Anterior fontanelle
Coronal suture
Frontal bone,
Frontal bone, frontal
frontal eminence
eminence
Sphenoidal
Maxilla, frontal
fontanelle
process Parietal bone,
Sphenoid, parietal
greater wing eminence
Nasal bone Supraorbital Zygomatic
foramen
bone Posterior
Sphenoid,
greater wing Temporal bone Piriform aperture fontanelle
Bony nasal Temporal bone,
Occipital bone,
septum squamous part
Zygomatic bone squamous part
Infraorbital foramen Mandible Lambdoid suture
Deciduous tooth Mandible Mastoid fontanelle
Tympanic ring
Mental foramen Temporal bone, petrous part
Occipital bone, lateral part
Maxilla Mandibular symphysis
C D
Mandible
Premaxilla Palatine bone, horizontal plate
Metopic suture
Maxilla, palatine process Vomer
Sphenoid, pterygoid process
Frontal bone,
Anterior
fontanelle squamous part Posterior nasal aperture Temporal bone,
Coronal suture petrous part
Tympanic part,
tympanic ring
Foramen magnum Temporal bone,
Occipital bone, squamous part
Parietal bone, lateral part Temporal bone,
petrous part
parietal
eminence Mastoid fontanelle
Sagittal Transverse occipital
suture suture, var.
Parietal bone
Occipital bone,
Posterior fontanelle squamous part
Occipital bone, squamous part
Posterior fontanelle
Vomer
Lacrimal bone Occipital bone, palatine bone Ethmoid
Frontal bone Maxilla, premaxilla Sphenoid
Parietal bone Zygomatic bone Nasal bone, temporal bone, mandible
Fig. 27.6 A–D, The neonatal skull. A, Frontal aspect. B, Lateral aspect. C, Superior aspect. D, Basal aspect. (A–D, With permission from Waschke J,
Paulsen F (eds), Sobotta Atlas of Human Anatomy, 15th ed, Elsevier, Urban & Fischer. Copyright 2013.)


of the cranial base is largely independent of both vault and facial devel- sagittal, sphenofrontal, sphenotemporal, occipitomastoid and petro-
opment, and therefore the three regions will be considered separately. occipital junctions, while growth in height is said to occur at the fronto-
(For further reading, see Belden (1998), Sgouros et al (1999), Scheuer zygomatic and squamosal sutures, pterion and asterion. During this
and Black (2000) and Sperber and Guttmann (2001).) period, fontanelles are closed by progressive ossification of the bones
around them, but separate isolated centres of ossification may develop
into sutural bones. The sphenoidal and posterior fontanelles close
Growth of the calvaria
within 2 or 3 months of birth and the mastoid fontanelles usually close
near the end of the first year. Wide variability in both the size and the
Growth of the calvaria is rapid during the first year and then continues timing of closure of the anterior fontanelle has been reported, but most
at a slower rate until the seventh year, when it has reached almost adult will have closed by the middle of the second year and almost all will
dimensions. For most of this period, expansion is largely concentric; have closed by 24 months (Pindrik et al 2014).
overall form is determined early in the first year and remains largely Early in the first years, the calvarial bones commence interlocking at
unaltered thereafter. However, the shape of the vault is not solely related sutural junctions. Further expansion is largely achieved by accretion and
to cerebral growth, but is also influenced by genetic factors that mani- absorption on external and internal bone surfaces, respectively. At the
fest in an extensive range of shapes and sizes that may be sufficient to same time the bones also thicken, although this is not a uniform
allow an evaluation of ethnic origin. During the first and early second process. At birth, the vault is unilaminar but the tabular structure with
years, growth occurs primarily through ossification at apposed margins intervening diploë is generally apparent soon thereafter. Thickening of
of bones (which possess an osteogenic layer), accompanied by some the vault and development of external muscular markings reflect the


accretion and absorption of bone at surfaces in order to adapt to con- influences of musculoskeletal maturation. The mastoid processes do
tinually altering curvatures. Growth in breadth is said to occur at the not usually develop until the second year and they are pneumatized in


neonatal, paediatric and senescent anatomy
425
72
RETPAHC
the sixth year (Scheuer and Black 2000). (For further reading about
craniofacial morphology in preterm infants, see Paulsson and Bonde-
mark 2009.)
Growth of the cranial base
Growth of the cranial base is largely responsible for cranial lengthening.
It occurs at the cartilaginous joints between the sphenoid and ethmoid
anteriorly, and especially between the sphenoid and occipital bones
posteriorly (Lieberman et al 2000). Most of the growth occurs during
the first five years of life (Sgouros et al 1999); it continues at the
spheno-occipital synchondrosis until mid-teenage years. The prolonged
period of continued expansion reflects a significant delaying mecha-
nism that allows the continued and relatively late eruption of the per-
A
manent dentition. There is some evidence that growth may cease at
about 15 years following eruption of the second molars, and this can
often lead to insufficient space for growth of the third molars. A puber-
tal growth spurt has been ascribed to both sexes; it tends to occur some
2 years earlier in females and is likely to continue until the eighteenth
year in the male. The anterior cranial base is significantly shorter in
extremely preterm infants (under 28 weeks) (Paulsson and Bondemark
2009).
Growth of the facial skeleton
Growth of the facial skeleton occurs over a longer time period than is
witnessed for the calvaria. The ethmoid and the orbital and upper nasal
cavities have almost completed growth by the seventh year. Orbital and
upper nasal growth is achieved by sutural accretion, with deposition of
bone preferentially occurring on the facial aspects of the sutural junc-
tions. The maxilla is carried downwards and forwards by expansion of
the orbits and nasal septum and by sutural growth, especially at the
fontanelles and zygomaticomaxillary and pterygomaxillary sutures. In
the first year, growth in width occurs at the symphysis menti and mid-
palatal, internasal and frontal sutures; such growth diminishes or even
ceases when the symphysis menti and frontal suture close during the


first few years, even though the mid-palatal suture persists until mature
years. Facial growth continues up to puberty and shows a period of
B
expansion that is linked to the growth spurt and hormonal influences
of secondary sexual alteration. After sutural growth, near the end of the
second year, expansion of the facial skeleton occurs by surface accretion Fig. 27.7 The hydrocephalic skull of a 25-year-old male showing
on the face, alveolar processes and palate, and resorption in the walls numerous sutural bones. A, Lateral view. B, Posterior view. (Courtesy of
the Museum of the Royal College of Surgeons of England, photograph by
of the maxillary sinuses, the upper surface of the hard palate and the
Mr J Carr.)
labial aspect of the alveolar process. Coordinated growth and diver-
gence of the pterygoid processes reflect deposition and resorption of
bone on appropriate surfaces.
Obliteration of the calvarial sutures progresses with age, starting expression of growth factors have been implicated in the aetiology of
between 20 and 30 years internally, and somewhat later on the exterior. premature fusion but the reasons are not fully understood. Premature
Closure times vary greatly. Obliteration usually begins in the coronal fusion may occur in one or more of the cranial sutures; when the sutures
or sagittal sutures and then extends into the lambdoid suture. The size around the cranial base are involved, severe limitation of facial bone
of the mandible and maxillae diminish following the loss of teeth and growth will occur. Metabolic disorders such as rickets and familial
consequent resorption of alveolar bone; this reduces the vertical depth hypophosphatasia can also result in synostosis. Raised intracranial pres-
of the face and increases the mandibular angles. sure with or without hydrocephalus, visual deterioration and mental
retardation may result. Scaphocephaly (sagittal craniosynostosis) is the
Sutural bones most common and leads to lengthening of the vault in an anteropos-
terior direction; it can also occur in conjunction with other sutures, e.g.
Crouzon’s syndrome. Coronal synostosis, either unilateral (plagioceph-
Additional ossification centres may occur in or near sutures, giving rise


aly) or bilateral (brachycephaly/oxycephaly), is the next most frequently
to isolated sutural bones (also called Wormian bones) (Bellary et al
seen and results in reduced anteroposterior development with marked
2013). Usually irregular in size and shape, and most frequent in the
supraorbital recession. When it is unilateral, the face develops asym-
lambdoid suture, they also occur at fontanelles, especially the posterior
metrically and is rotated away from the side with premature fusion.
fontanelle. They may represent a pre-interparietal element, a true inter-
Metopic craniosynostosis (trigonocephaly) and pansynostosis (turri-
parietal, or a composite. An isolated bone at the lambda is sometimes
cephaly), where both the coronal and sphenofrontal sutures are
referred to as an Inca bone or Goethe’s ossicle. One or more pterion
involved, are much less common.
ossicles or epipteric bones may appear between the sphenoidal angle
Craniofacial dysostosis syndromes, such as Crouzon’s, Apert’s,
of the parietal and the greater wing of the sphenoid; they vary greatly
Saethre–Chotzen, Pfeiffer’s and Carpenter’s, show varying degrees of
in size but are more or less symmetrical. Sutural bones usually have
calvarial synostoses that are usually accompanied by a significant lack
little morphological significance. However, they appear in great numbers
of growth in the midface. Early release of the calvarial synostoses does
in hydrocephalic skulls (Fig. 27.7), and they have therefore been linked
not result in normal facial growth, and a midfacial osteotomy at the Le
with rapid cranial expansion.
Fort III level is usually required later in life. When significant orbital
hypertelorism develops, a transcranial bipartitioning procedure is
Craniosynostosis
needed in order to bring the two orbits together.
Altered patterns of skull growth resulting in altered profiles can also
Sutural growth makes an important contribution to growth of the skull, be achieved deliberately by affecting sutural growth using binding and


especially during the first few years of life. Premature closure of sutures other pressure, as has been practised in certain cultures of the world
(craniosynostosis) leads to restriction of growth along the sutures, pro- (Fig. 27.8) (Tubbs et al 2006). The earliest known record of the practice
ducing morphological changes that may result in skull deformity is from Iraq and dates back to 45,000 BCE (Gerszten and Gerszten
(Sharma 2013). Biomechanical forces and genetically determined local 1995).


ExTERnAl skull
426
4
nOITCEs
over 80% accuracy in the adult. This is extremely encouraging, given
that research has shown that the correct sex can usually be predicted
from the adult living face with only 96% accuracy.
Generally speaking, the male skull is more robust and the female
more gracile, although there are obvious genetic, and therefore ethnic,
variations that must be considered when attempting to assign sex from
a skull. The female forehead is generally higher, more vertical and more
rounded than that of the male, with retention of the frontal eminences.
The male mandible is more robust and larger than that of the female;
it generally displays a greater height in the region of the symphysis
menti, the chin is squarer, the condyles are larger, the muscle attach-
ments are more pronounced and the gonial angle is generally less than
125°. A male skull has thicker and more rounded orbital margins,
pronounced supraorbital ridges, and often a well-defined glabella that
occupies the midline above the root of the nose. The temporal lines are
more pronounced in the male and the supramastoid crest generally
extends posterior to the external acoustic meatus.
Other sites of muscle attachment on the skull reflect the biomechani-
cal requirement to keep the more robust male head erect. They include
the mastoid process for sternocleidomastoid, which is generally more
robust in the male and more gracile in the female, and the nuchal lines,
especially the external occipital protuberance for the attachment of the
ligamentum nuchae. The cranial base in the male is generally more
robust and the bone is thicker, which means that this area of the skull
survives inhumation particularly well and is therefore of value in sex
identification from fragmentary remains.
Fig. 27.8 Intentional skull modification: characteristic elongation of the
cranial vault produced by head-binding of a newborn. (Courtesy of John
Langdon.)
AGE DETERMINATION
Age is a continuous variable; to establish chronological age from a skull
Congenital abnormalities affecting the skull
requires that structures change with age at a relatively constant and
predictable rate. The relationship between chronological age and skel-


A large number of malformations and anomalies affect the bones and etal maturity is closest in the juvenile years, and therefore greater accu-
associated soft tissue structures of the skull and are the result of a local- racy is achieved in the prediction of age from the juvenile than from
ized error of morphogenesis during embryological development. Many the adult skull.
are recognized patterns of malformation that are presumed to have the The neonatal skull has been described above. Examples of additional
same aetiology. They do not arise as the result of just one isolated error features that allow reliable age determination throughout the subadult
in morphogenesis and are described as syndromes; specific texts should years are: development of the nasal spine (by year 3), completion of
be consulted for further details. the hypoglossal canal (by year 4), formation of the foramen of Huschke
(by year 5), ossification of the dorsum sellae (by year 5), and fusion of
the different parts of the occipital bone (by year 7). The fontanelles are
IDENTIFICATION FROM THE SKULL
usually all closed by the middle of the second year; the posterolateral
is the first to close in the first 2 months after birth, and the anterior
There are many ways of identifying an individual; in physical and fontanelle is the last to close around the middle of the second year. The
forensic anthropology, the most important concern biological and per- mastoid process appears in the second year and the metopic suture
sonal identity (Wilkinson and Rynn 2012). Biological identity pertains between the two frontal bones is usually closed by the end of the first
to those features that allow an individual to be classified in relation to year. The spheno-occipital synchondrosis will fuse between 11 and 16
features present in other individuals, e.g. sex, age, ethnic origin and years in the female and 13 and 18 years in the male, while the vomer
stature, whereas personal identity establishes criteria that are character- and the ethmoid will fuse between 20 and 30 years of age. The last part
istic and discriminatory for a particular individual, e.g. DNA, finger- of the skull to show active age-related growth is the jugular growth plate,


prints and dental information. The skull is a useful source of information a small triangular area sited posterolateral to the jugular foramen in the
for the establishment of both biological and personal identity and is occipitotemporal suture. Fusion here does not begin until the third
probably the most studied region of the skeleton. The foundation of decade, and bilateral fusion may not be completed before the middle
this obsession has many historical roots, but fundamentally it has of the fourth decade; in a small proportion of individuals, the plate
arisen from the importance that humans place on the concept that the may remain unfused into the sixth decade. Closure of the cranial sutures
skull is the repository of ‘self’, and that it is the means by which inter- is age-related but the correlation is not strong and displays strong
personal communication is effected. Our face is our primary means of genetic variation. Thus, while it can be said that suture closure may
recognition and communication, and therefore it plays a pivotal role begin in the early part of the third decade, and it is likely that many of
in establishing and reconstructing the identity of an individual (Lahr the sutures will be obliterated with advancing age, it is not a reliable
1996). means of establishing the age of an individual. See Scheuer and Black
(2000) for further information on age determination from the juvenile
skeleton.
SEX DETERMINATION The most accurate means of determining age from the skull (of both
a living and a deceased individual) is by assessment of dental matur-
The determination of sex from a juvenile skull is notoriously unreliable. ation. Tooth development can be studied throughout the entire juvenile
While sexual differences have been detected in measurements of the age span (from the early embryo to the adolescent), and importantly,
mandible, orbits, tooth size and pattern of dental eruption, they do not dental age and chronological age have been shown to exhibit a stronger
reach a level of statistical discrimination that will allow accurate and correlation than skeletal and chronological age. Further, the teeth tend
reliable assessment. It is equally difficult to assign sex to the face of a to survive inhumation successfully and are remarkably resilient to fire
child because the faces of prepubertal boys and girls are comparable; and explosion, ensuring their value in forensic investigations.
perceivable sexual dimorphism is not generally manifest until second- The chronological pattern of dental maturation is well documented


ary sexual changes are completed. Growth in the female face ceases in and is an extremely important tool for age evaluation. Tooth develop-
advance of that of the male, and consequently, female sex-related char- ment can be separated into a number of well-defined stages: deciduous
acteristics are more paedomorphic. The defining characteristics of sex mineralization (crown and root), deciduous emergence and matur-
in an adult skull are therefore male in orientation and reflect the effects ation, deciduous root resorption, shedding of deciduous teeth, mineral-
of the increased mass of the muscles of mastication, which attach to ization (crown and root) of permanent dentition, emergence and
the mandible, and the muscles associated with maintaining the erect maturation of deciduous dentition, and attrition of permanent crowns.
head. It is reported that using the skull alone, sex can be predicted with These stages do not occur in a linear fashion; while some of the


Identification from the skull
427
72
RETPAHC
deciduous teeth are emerging, permanent teeth are already being of this rather heterogeneous group is generally represented by a broad
formed. For example, mineralization of the deciduous central incisor nasal aperture, well-developed supraorbital ridging and glabella, and a
commences around the fifteenth week post fertilization, and this is the wide palate with large teeth.
first tooth to emerge within the first 5 months after birth. All deciduous There is a current resurgence in research into ethnic determination
teeth are in occlusion by around 3 years of age. The first deciduous teeth that is largely centred on genetic markers, and consequently, skeletal
to be shed are generally the central and lateral incisors around 7 years indicators now play a significantly reduced role in this task (Gill and
of age, when the permanent incisors emerge. The last deciduous tooth Rhine 2004).
to be shed is generally the second molar in the tenth year. The first
permanent tooth to show mineralization is the first molar, which occurs
around the time of birth (sometimes earlier and sometimes later); it is FACIAL APPROXIMATION (RECONSTRUCTION)
also the first permanent tooth to emerge at around 6 years of age, and
it will reach occlusion by the end of the seventh year. The last perma- Once the biological identity of an individual has been established (i.e.
nent tooth to emerge is the third molar; the variability of this occur- sex, age, stature and ethnic origin), an attempt to establish personal
rence makes it of restricted value for age prediction. identity may be necessary, particularly in relation to a forensic investiga-
The time taken for a crown to form can be calculated from ground tion. Achieving a possible name for a victim is necessary before com-
sections with considerable accuracy by counting the number of daily parison of antemortem and postmortem data can be achieved and a
cross-striations from the neonatal line. For permanent teeth, the time positive identity established. One of the accepted ways to achieve this
taken for the crown to form can be calculated by counting the number is to reconstruct the face from the skull, thereby producing a facial
of the enamel striae and multiplying by the individual’s periodicity. approximation that can be released to the community or the public at


Patterns of mineralization, emergence and shedding may be supple- large in an attempt to identify the victim. Experts in this discipline
mented by analyses of tooth length, cementum apposition, secondary utilize the many variations in the skull to reconstruct individual pos-
dentine formation, incremental enamel lines, attrition rates, root trans- sible representations of the face from the material available. Biological
lucency and dentine transparency (Whittaker and MacDonald 1989). variation will dictate the appropriate data used for tissue thickness that
Chemical analysis of the stable isotopes of carbon, oxygen and nitrogen are applied to the skeletal scaffold.
from teeth can provide important information concerning the nature There are fundamentally two approaches to facial reconstruction.
of the diet of an individual, and is used in paleodiet analysis and in The first approach is computer reconstruction – the skull is usually
studies of pathophysiology and nutrition in archaeological and living scanned by a laser three-dimensional scanner and an ‘average’ virtual
human populations (Reitsema 2013). face is wrapped around the skeletal scaffold. This approach is largely
automated and requires limited training and expertise. It is rapid to
achieve and relatively inexpensive, but relies on a large data set to
DETERMINATION OF ETHNIC ORIGIN ensure that the ‘average’ face utilized is appropriate. The second
approach is modelled reconstruction – the skull is usually cast, and pegs
The determination of ethnic or genetic origin is particularly difficult to are inserted into the cast at the appropriate tissue depth requirements.
achieve, although it is something that both physical and forensic In the ‘American’ approach, a skin of clay is then moulded over the pegs
anthropologists are frequently asked to attempt. The traditional view of to approximate the face. In the ‘Manchester’ method, each sequential
ethnicity is that it is ‘one of the major zoological subdivisions of muscle and soft tissue layer is built up around the pegs before a clay
mankind, regarded as having a common origin and exhibiting a rela- skin is moulded over the underlying structures. The modelling approach
tively constant set of physical traits’ (Bamshad and Olson 2003). Clas- is clearly more dependent on experience, takes longer to achieve and is
sifying groups on this basis is rather restrictive and, in our migrant more costly.


modern world, somewhat artificial. It is still useful to be able to attempt There is great debate over which approach is the most accurate and,
to assign a ‘most likely’ genetic group, especially when dealing with as yet, no agreement has been reached. Most practitioners state that the
unidentified forensic remains, but there are significant areas of overlap process achieves an approximation of one of the potential faces for the
between the characteristics, and within any ethnic group there is often deceased and does not purport to reconstruct the actual face. The ration-
a full spectrum of representation. Yet we persist in classification on the ale is to produce an image that will jog the memory of the public and
basis of visual characteristics, and the area of the body that is most often provide some possible names that will allow comparison of antemor-
analysed in this way is the skull. tem and postmortem identity data.
Early anthropologists classified humans largely through geographi-
cal origins and recognized physical traits. The four traditional races of
humans were: Caucasoid, Negroid, Mongoloid and Australoid. The FACIAL SUPERIMPOSITION
Caucasoid race is geographically from Europe, North Africa, the Middle
East, the Indian subcontinent and parts of Central Asia. Classically, the Once a possible name has been derived, it may be necessary to compare
Caucasoid skull has a rounded to long shape (dolichocephalic) with a the skull with photographs of the suspected individual. In these circum-
narrow nasal aperture, moderately developed supraorbital ridging, a stances, an image of the skull is superimposed on to an image of the
prominent nasal spine, a steeple-shaped nasal root, little prognathism face of the missing person (Fig. 27.9). This relies on achieving a live
and a narrow interorbital distance. The forehead is steep, the chin is capture image of the skull so that it can be rotated and manipulated
prominent, the palate is long and narrow, the cheek bones are not into an identical position and to an identical size as the photograph.
overly prominent, and there is a tendency to maxillary protrusion or Features that do not change are lined up; a photograph that shows teeth
mandibular retrusion. The Negroid race is geographically represented is ideal because teeth can be lined up with the dentition on the skull.


by Saharan, sub-Saharan and West African groups. The typical Negroid The image of the skull and photograph can then be faded in and out;
skull is also long with a wide nasal aperture, strong alveolar prognath- if this is undertaken at speed, any discrepancies will show up on the
ism, low nasal root, guttering of the nasal aperture and a wide inter- image as distortion.
orbital distance. The forehead is rounder, the palate is wider and the
teeth are larger. The Mongoloid race is geographically represented by
groups in East Asia, South East Asia, Central Asia, the Americas, Green-
land, Inuit regions, Polynesia, South Asia and Eastern Europe. The
Bonus e-book images
typical Mongoloid skull is generally described as round with a nasal
aperture of medium width, well-developed and high cheek bones, mod-
erate prognathism, a tented nasal root, short nasal spine and shovel-
shaped incisors. The palate is foreshortened, the forehead is vertical, the Fig. 27.6 E–G, Normal three-dimensional calvarial anatomy.
nasal bridge is low and there is a tendency for a forward rotation of the E, Frontal aspect. F, Lateral aspect. G, Basal aspect; there is a
mandible. The Australoid race is geographically represented by Austral- linear fracture in the right parietal bone.
ian Aborigines, Maori, Pacific Islanders, Fijians and Papuans. The skull


ExTERnAl skull
428
4
nOITCEs
Fig. 27.9 Facial superimposition: a
live capture image of the skull has
been manipulated into the identical
position and size of the face in the
photograph. (Courtesy of Professor
Caroline Wilkinson and Professor Sue
Black, Centre for Anatomy and
Human Identification, University of
Dundee.)
A B
KEY REFERENCES
Bamshad M, Olson S 2003 Does race exist? Sci Am 289:78–85. This award-winning text was the first to address solely the subject of
A really excellent article that challenges our perspective on what race is and development of the juvenile skeleton. It has stood the test of time and a
what that actually means for our modern, diverse world. second edition has been requested.
Berkovitz BKB, Moxham BJ 1994 Color Atlas of the Skull. London: Tubbs RS, Salter EG, Oakes WJ 2006 Artificial deformation of the human
Mosby–Wolfe. skull: a review. Clin Anat 19:372–7.
An excellent atlas that gives a clear illustration of the different components An excellent review article that highlights the incredible plasticity of the
of the skull. human skull.
Gill GW, Rhine S 2004 Skeletal Attribution of Race: Methods for Forensic Whittaker DK, MacDonald DG 1989 A Colour Atlas of Forensic Dentistry.
Anthropology. New Mexico: Maxwell Museum of Anthropology. London: Wolfe.
The determination of ‘race’ is a highly controversial subject in the biological An exceptionally useful atlas that, although not recent, is an excellent
literature. This reference gives a good, balanced perspective of what can be baseline resource for dental anatomy.
achieved through the identification of ethnic/genetic ancestry.
Wilkinson C, Rynn C 2012 Craniofacial Identification. Cambridge: Cam-
Lahr MM 1996 The Evolution of Modern Human Diversity: A Study of bridge University Press.
Cranial Variation. Cambridge: Cambridge University Press. Forensic facial reconstruction is an area that requires an equal amount of
An excellent text when considering the extent of human variation and scientific and artistic talent. This text addresses this complex subject in an
diversity. approachable manner.
Scheuer L, Black S 2000 Developmental Juvenile Osteology. London: Aca-
demic Press.


External skull
428.e1
72
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REFERENCES
Bamshad M, Olson S 2003 Does race exist? Sci Am 289:78–85. Reitsema LJ 2013 Beyond diet reconstruction: stable isotope applications
A really excellent article that challenges our perspective on what race is and to human physiology, health, and nutrition. Am J Hum Biol 225:
what that actually means for our modern, diverse world. 445–56.
Belden CJ 1998 The skull base and calvaria. Adult and pediatric. Neuroimag- Scheuer L, Black S 2000 Developmental Juvenile Osteology. London: Aca-
ing Clin N Am 8:1–20. demic Press.
This award-winning text was the first to address solely the subject of
Bellary SS, Steinberg A, Mirzayan N et al 2013 Wormian bones: a review.
development of the juvenile skeleton. It has stood the test of time and a
Clin Anat 26:922–7.
second edition has been requested.
Berkovitz BKB, Moxham BJ 1994 Color Atlas of the Skull. London:
Mosby–Wolfe. Sgouros S, Natarajan K, Hockley AD et al 1999 Skull base growth in child-
An excellent atlas that gives a clear illustration of the different components hood. Pediatr Neurosurg 31:259–68.
of the skull. Sharma RK 2013 Craniosynostosis. Indian J Plast Surg 46:18–27.
Gerszten PC, Gerszten E 1995 Intentional cranial deformation: a disappear- Sperber GH, Guttmann GD, Sperber SM 2001 Craniofacial Development,
ing form of self-mutilation. Neurosurgery 37:374–81. 4th ed. Ontario: BC Decker.
Gill GW, Rhine S 2004 Skeletal Attribution of Race: Methods for Forensic Tubbs RS, Salter EG, Oakes WJ 2006 Artificial deformation of the human
Anthropology. New Mexico: Maxwell Museum of Anthropology. skull: a review. Clin Anat 19:372–7.
The determination of ‘race’ is a highly controversial subject in the biological An excellent review article that highlights the incredible plasticity of the


literature. This reference gives a good, balanced perspective of what can be human skull.
achieved through the identification of ethnic/genetic ancestry. Vogl TJ, Bisdas S 2009 Differential diagnosis of jugular foramen lesions.
Krmpotić Nemanić J, Vinter I, Ehrenfreund T et al 2009 Postnatal changes Skull Base 19:3–16.
in the styloid process, vagina processus styloidei, and stylomastoid Weinzweig J, Kirschner R, Farley A et al 2003 Metopic synostosis: defining
foramen in relation to the function of muscles originating from the the temporal sequence of normal suture fusion and differentiating it
styloid process. Surg Radiol Anat 31:43–8. from synostosis on the basis of computed tomography images. Plast
Lahr MM 1996 The Evolution of Modern Human Diversity: A Study of Reconstr Surg 112:1211–8.
Cranial Variation. Cambridge: Cambridge University Press. Whittaker DK, MacDonald DG 1989 A Colour Atlas of Forensic Dentistry.
An excellent text when considering the extent of human variation and London: Wolfe.
diversity. An exceptionally useful atlas that, although not recent, is an excellent
baseline resource for dental anatomy.
Lieberman DE, Pearson OM, Mowbray KM 2000 Basicranial influence on
overall cranial shape. J Hum Evol 38:291–315. Wilkinson C, Rynn C 2012 Craniofacial Identification. Cambridge: Cam-
Ma S, Baillie LJ, Stringer MD 2012 Reappraising the surface anatomy of the bridge University Press.
pterion and its relationship to the middle meningeal artery. Clin Anat Forensic facial reconstruction is an area that requires an equal amount of
25:330–9. scientific and artistic talent. This text addresses this complex subject in an
approachable manner.
Paulsson L, Bondemark L 2009 Craniofacial morphology in prematurely
born children. Angle Orthodontist 79:276–83.
Pindrik J, Ye X, Ji BG et al 2014 Anterior fontanelle closure and size in full-
term children based on head computed tomography. Clin Pediatr
(Phila) 53:1149–57.


CHAPTER
28
Intracranial region
The neurocranium (calvaria and cranial base) contains the brain, the parietal branches of the middle meningeal vessels; the grooves contain
intracranial portions of the cranial nerves, blood vessels, meninges and the openings of minute channels that admit perforating vessels to the
cerebrospinal fluid. Its walls are formed by parts of the frontal, ethmoid, haemopoietic marrow within the diploic bone. Impressions for cerebral
parietal, sphenoid, temporal and occipital bones. gyri are less distinct on the bones of the calvaria than they are on the
cranial base.
The falx cerebri, a dural partition that separates the two cerebral
INTERNAL SURFACE OF CALVARIA
hemispheres of the brain, is attached anteriorly to a backward-projecting
anteromedian frontal crest. The crest exhibits a groove that widens as
The internal surface of the calvaria is deeply concave. It includes most it passes back below the sagittal suture and becomes continuous with
of the frontal and parietal bones and the squamous part of the occipital the sagittal sulcus, which houses the superior sagittal sinus. Irregular
bone, variously united at the coronal, sagittal and lambdoid sutures depressions, granular foveolae, which become larger and more numer-
(Fig. 28.1). With increasing age, these sutures become obliterated by a ous with age, lie on either side of the sulcus and usually house arach-
gradual process that begins on their intracranial surfaces. Inconstant noid granulations.
foramina may occur in the parietal bones near the sagittal sulcus and
anterior to the lambdoid suture; they admit emissary veins associated
CRANIAL FOSSAE (ANTERIOR,
with the superior sagittal sinus. The internal surfaces of the frontal and
parietal bones are grooved by furrows that house the frontal and MIDDLE, POSTERIOR)
The base of the cranial cavity is divided into three distinct fossae: the
Groove for superior Bregma Coronal suture anterior, middle and posterior cranial fossae (Fig. 28.2). The floor of


sagittal sinus the anterior cranial fossa is at the highest level and the floor of the
Frontal crest Groove for anterior branch
posterior fossa is at the lowest.
of middle meningeal artery
Detailed descriptions of the microsurgical anatomy of each region
of the cranial base are beyond the scope of this book, and the interested
reader is directed in the first instance to Rhoton (2007).
ANTERIOR CRANIAL FOSSA
The anterior cranial fossa is formed by the frontal, ethmoid and sphe-
noid bones, and supports the frontal lobes of the cerebral hemispheres.
Its floor is composed of the orbital plate of the frontal bone, the cribri-
form plate and crista galli of the ethmoid bone, and the lesser wings,
jugum sphenoidale, and prechiasmatic sulcus of the sphenoid.
A perforated plate of bone, the cribriform plate of the ethmoid bone,
spreads across the midline between the orbital plates of the frontal bone
and is depressed below them, forming part of the roof of the nasal
cavity. Olfactory nerves pass from the nasal mucosa to the olfactory bulb
of the brain through numerous small foramina in the cribriform plate.
Anteriorly, a spur of bone, the crista galli, projects upwards between the
cerebral hemispheres and serves as an attachment for the falx cerebri.
A depression between the crista galli and the crest of the frontal bone
is crossed by the frontoethmoidal suture. It bears the foramen caecum,
which is usually a small blind-ended depression formed by the devel-
opmental involution of a dural diverticulum that extends through the
foramen caecum to the columella; in adults, it occasionally accommo-
dates a vein draining from the nasal mucosa to the superior sagittal
sinus. Failure of the foramen caecum to close may cause nasal dermoid
cysts and nasoethmoidal encephalocoeles in children.
The anterior ethmoidal nerve and vessels enter the cranial cavity
where the cribriform plate meets the orbital part of the frontal bone.
They then pass into the roof of the nasal cavity via a small foramen by
the side of the crista galli. The posterior ethmoidal canal, which trans-


mits the posterior ethmoidal nerve and vessels, opens at the junction
of the posterolateral corner of the cribriform plate and jugum sphenoi-
dale. The convex orbital plate of the frontal bone separates the brain
from the orbit and bears impressions of cerebral gyri and small grooves
for meningeal vessels. Posteriorly, it articulates with the anterior border
of the lesser wing of the sphenoid laterally and the jugum sphenoidale
medially. The jugum sphenoidale is a flat surface on the upper aspect
Lambda Sagittal suture Granular foveolae
Grooves for middle of the sphenoid bone that connects the two lesser wings, also known
meningeal artery Lambdoid suture as the planum sphenoidale. The limbus of the sphenoid bone is a
Fig. 28.1 The internal surface of the cranial vault. (With permission from prominent ridge on the body of the sphenoid that forms the posterior
Drake RL, Vogl AW, Mitchell A (eds), Gray’s Anatomy for Students, 2nd border of the jugum sphenoidale and the anterior border of the prechi-
ed, Elsevier, Churchill Livingstone. Copyright 2010.) asmatic sulcus. The latter is an osseous groove that runs transversely 429


IntracranIal regIon
430
4
noItceS
Frontal crest Fig. 28.2 The floor of cranial cavity showing the
cranial fossae. (Adapted with permission from
Crista galli
Waschke J, Paulsen F (eds), Sobotta Atlas of
Cribriform plate of ethmoid
Optic strut Jugum (planum) sphenoidale Human Anatomy, 15th ed, Elsevier, Urban &
Fischer, 2013.)
Middle clinoid Limbus of the sphenoid
Prechiasmatic sulcus
Anterior
Tuberculum sellae
cranial Optic canal
fossa
Anterior clinoid process
Superior orbital fissure
Foramen rotundum
Foramen ovale
Foramen lacerum;
sphenopetrosal fissure
Middle
cranial
fossa Foramen spinosum
Carotid canal,
internal aperture
Internal acoustic meatus
Jugular foramen
Posterior
cranial
fossa Hypoglossal canal
Foramen magnum
between the optic canals. The optic chiasma usually lies above the located within the sphenoidal air sinuses, which is why the most direct
prechiasmatic sulcus, while the medial orbital surface of the frontal surgical route to the pituitary fossa is the trans-sphenoidal approach.
lobes and olfactory tracts lie above the jugum sphenoidale (see Figs The anterior edge of the sella is formed by a bony prominence known
28.2; 28.9). as the tuberculum sellae, which continues anteriorly with the prechias-
The posterior boundary of the lesser wing forms the posterior matic sulcus; the posterior boundary presents a vertical pillar of bone,
boundary of the anterior cranial fossa; the medial end of the lesser wing the dorsum sellae. The superolateral angles of the dorsum are expanded
constitutes the anterior clinoid process. The lesser wing and the anterior as the posterior clinoid processes. A fold of dura, the diaphragma sellae,
clinoid process join the sphenoid body by two roots that are separated is attached to the anterior and posterior clinoid processes and roofs over


by the optic canal. The anterior root, broad and flat, forms the roof of the pituitary fossa. The cavernous sinus lies lateral to the pituitary fossa.
the optic canal and is continuous with the jugum sphenoidale, while The lateral wall of the body of the sphenoid contains a shallow carotid
the smaller and thicker posterior root, also known as the optic strut, sulcus related to the internal carotid artery as it ascends from the carotid
joins the body of the sphenoid bone at the lateral aspect of the posterior canal and runs through the cavernous sinus.
bank of the prechiasmatic sulcus or tuberculum sellae (see Fig. 28.2). Each anterior clinoid process covers the roof of the cavernous sinus
The optic strut of the anterior clinoid process separates the optic canal and the paraclinoidal segment of the internal carotid artery as it leaves
from the superior orbital fissure (Kerr et al 2012). Each optic canal the cavernous sinus and pierces the dura to enter the intradural space.
transmits the optic nerve and ophthalmic artery. The anterior clinoid process gives attachment to the anterior petrocli-
noidal ligament, which forms the free margin of the tentorium cere-
belli, and the interclinoidal ligament, which lies between the anterior
MIDDLE CRANIAL FOSSA and posterior clinoids. The middle clinoid process arises from the body
of the sphenoid bone at the anterolateral margin of the sella turcica
The middle cranial fossa is formed by the sphenoid and temporal bones and may be connected to the anterior clinoid process by a thin osseous
and supports the temporal lobes of the cerebral hemispheres. It is bar, formed by ossification of the caroticoclinoid ligament. The result-
bounded in front by the posterior aspect of the lesser and greater wings ing caroticoclinoid foramen or ring surrounds the paraclinoidal segment
of the sphenoid, behind by the superior border of the petrous part of of the internal carotid artery (Fernandez-Miranda et al 2012). While
the temporal bone, laterally by the squamous part of the temporal bone anterior and posterior clinoids are always present, middle clinoids are


and greater wing of the sphenoid, and medially by the lateral aspect of not constant. A recent study revealed that the middle clinoid process
the sphenoid body, including the carotid sulcus, sella turcica and was usually identifiable in fine-cut head computed tomogram–
dorsum sellae. angiogram scans, and sometimes had at least one caroticoclinoid ring.
The middle cranial fossa communicates with the orbits by the su- The greater wing of the sphenoid bone contains three consistent
perior orbital fissures, each bounded above by a lesser wing, below by foramina and other small variable foramina. The foramen rotundum,
a greater wing, and medially by the body of the sphenoid bone and situated just below the medial end of the superior orbital fissure, leads
optic strut. The fissures contain the oculomotor, trochlear and abducens forwards into the medial aspect of the inferior orbital fissure and opens
nerves, and the lacrimal, frontal and nasociliary branches of the oph- into the pterygopalatine fossa; it contains the maxillary nerve (second
thalmic division of the trigeminal nerve, together with filaments from division of trigeminal nerve).
the internal carotid plexus (sympathetic), the superior and inferior Behind the foramen rotundum is the foramen ovale, which transmits
ophthalmic veins, the orbital branch of the middle meningeal artery, the mandibular nerve (third division of trigeminal nerve). The foramen
and the recurrent branch of the lacrimal artery. spinosum lies just posterolateral to the foramen ovale and transmits
The central part of the cranial base, located between both middle the middle meningeal artery and veins; these vessels groove the floor
cranial fossae, is formed by the body of the sphenoid bone, which and lateral wall of the middle cranial fossa. The foramen ovale and
contains the sphenoidal sinuses. The body of the sphenoid bone is foramen spinosum open into the underlying infratemporal fossa. The
deeply concave and houses the pituitary gland (hypophysis); it is there- small foramen of Vesalius sometimes occurs in skulls and lies antero-


fore termed the pituitary (hypophysial) fossa, also known as the sella medial to the foramen ovale and lateral to the foramen rotundum; it
turcica because it resembles the shape of a Turkish saddle (Paluzzi et al transmits an emissary vein through which the cavernous sinus and
2012) (Videos 28.1–28.3). The face and floor of the sella turcica are pterygoid plexus communicate.


cranial fossae (anterior, middle, posterior)
431
82
retPaHc
The foramen lacerum is a misnomer because it is a gap, not a true POSTERIOR CRANIAL FOSSA
foramen, formed by the incomplete confluence of the petrosphenoidal
and petroclival fissures. It may therefore also be called the sphenopetro- The posterior cranial fossa is formed by the sphenoid, temporal and
clival synchondrosis. It lies posteromedial to the foramen ovale at the occipital bones, and contains the cerebellum, pons and medulla oblon-
transition between the carotid sulcus of the sphenoid bone and the gata. It is bounded in front by the dorsum sellae, posterior aspects of
petrous carotid canal, bounded laterally by the lingula of the sphenoid the body of the sphenoid bone, and the basilar (or clival) part of the
and the petrolingual ligament extending to the petrous apex. The lower occipital bone; behind by the squamous part of the occipital bone; and
portion of the foramen lacerum is filled with fibrocartilage extending laterally by the petrous and mastoid parts of the temporal bones and
from the pharyngotympanic tube and basopharyngeal fascia. The upper by the lateral (condylar) parts of the occipital bone.
portion of the foramen contains the laceral segment of the internal The most prominent feature in the floor of the posterior cranial
carotid artery and should be considered as the rostral extension of the fossa is the foramen magnum in the occipital bone. The medulla
petrous carotid canal (Tauber et al 1999). The only structures that enter oblongata exits the cranial cavity through the foramen magnum to
or exit the intracranial cavity through the foramen lacerum are the continue as the spinal cord (Ch. 20). The cerebellum is fully con-
pterygoid (Vidian) nerve and vessels, terminal branches of the ascend- tained within the posterior fossa. When the lower part of the cerebel-
ing pharyngeal artery and small emissary veins connecting the extra- lum, the tonsils, descend abnormally through the foramen magnum,


cranial pterygoid plexus with the intracranial cavernous sinus. they may cause compression of the medulla at the level of the
The superior border of the petrous part of the temporal bone sepa- foramen magnum, a condition called tonsillar herniation or Chiari
rates the middle and the posterior cranial fossae, and is grooved by the malformation.
superior petrosal sinus. The trigeminal impression, which accommo- The clivus is a sloping surface that extends from the sella turcica to
dates the trigeminal ganglion, is situated on the anterior surface of the the foramen magnum, and is formed successively by the dorsum sellae,
petrous part of the temporal bone near its apex. A smooth trigeminal the posterior part of the body of the sphenoid and the basilar (clival)
notch leads into the impression and lies on the upper border of the part of the occipital bone. The spheno-occipital synchondrosis is
petrous part, anteromedial to the groove for the superior petrosal evident on the clivus of a growing child but not in adults. The clivus is
sinus. At the level of the notch, the trigeminal nerve passes from the located at the centre of the posterior skull base and separates the
posterior to the middle cranial fossa, and separates the superior petro- nasopharynx from the posterior cranial fossa. Cranial chordomas are
sal sinus from the underlying bone. The petrosphenoidal ligament (of malignant tumours that histologically are reminiscent of embryonic
Gruber) lies at the anterior end of the trigeminal notch, attached to a notochordal tissue and typically arise within the clival bone (Fernandez-
minute bony spicule, the petrous tubercle (Iaconetta et al 2003). The Miranda et al 2014). The clivus reaches its final length at the age of 11
ligament runs in a superior, anterior and medial direction to attach to years in both sexes (Krmpotić-Nemanić et al 2005). On each side, the
the posterior and lateral aspect of the posterior clinoid. The abducens clivus is separated from the petrous part of the temporal bone by a


nerve bends sharply across the upper petrous border and medially over petro-occipital (or petroclival) fissure, filled by a thin plate of cartilage
the lateral edge of the dorsum sellae, and typically passes under the and extending from the foramen lacerum (extracranially) and cavern-
petrosphenoidal ligament to enter the cavernous sinus (Ozveren et al ous sinus (intracranially) to the jugular foramen. The intracranial
2002). This interdural space (between dural layers), limited superiorly margins of the fissure are grooved by the inferior petrosal sinus. Chon-
by the petrosphenoidal ligament, laterally by the petrous apex, and drosarcomas are malignant tumours composed of transformed cells
medially by the dorsum sellae, is known as Dorello’s canal (Ambekar that produce cartilage; their most common intracranial location is pre-
et al 2012). It is also defined as the petroclival venous confluence cisely the petroclival fissure.
because it is filled with blood from the adjacent venous sinuses, The jugular foramen is a large opening located between the temporal
namely: the inferior and superior petrosal, cavernous and basilar and occipital bones at the posterior end of the petro-occipital fissure,
plexus (Barges-Coll et al 2010). above and lateral to the foramen magnum. The lower border of the
Lateral to the trigeminal impression, a narrow groove passes postero- jugular foramen is smooth and is formed by the lateral part of the
laterally into the hiatus for the greater petrosal nerve (also known as occipital bone. The upper border is sharp and irregular, and is formed
the facial hiatus); the hiatus and groove for the lesser petrosal nerve lies by the petrous part of the temporal bone. It contains a notch, the intra-
even further laterally (Kakizawa et al 2007). Posterolateral to the facial jugular process, which divides the foramen into a large posterolateral
hiatus, a rounded arcuate eminence is produced by the underlying compartment, the sigmoid part, which receives the drainage of the


superior semicircular canal. A line bisecting the angle subtended by the sigmoid sinus; and a small anteromedial compartment, the petrosal
arcuate eminence and the greater petrosal nerve estimates the location part, which receives the drainage of the inferior petrosal sinus. The
of the roof of the internal acoustic meatus (internal auditory canal) in accessory, vagus and glossopharyngeal nerves course in the medial side
the middle fossa. The petrous segment of the internal carotid artery runs of the intrajugular process; they lie between the petrosal part (which
from the carotid foramen to the foramen lacerum within the carotid contains the inferior petrosal sinus accompanied by a meningeal branch
canal of the petrous part of the temporal bone. The greater petrosal of the ascending pharyngeal artery) and the sigmoid part (which con-
nerve travels above and parallel to the petrous carotid canal, which may tains the sigmoid sinus accompanied by a meningeal branch of the
be dehiscent. The osseous portion of the pharyngotympanic tube and occipital artery). The cochlear canaliculus or aqueduct, which contains
tensor tympani run parallel and just lateral to the petrous carotid canal the perilymphatic ‘duct’, is sited in the deepest part of the intrajugular
within the floor of the middle fossa. The cochlea is situated within the process. The jugular foramina are typically asymmetric: the right
petrous part of the temporal bone, just medial to the posterior aspect foramen is usually larger than the left, reflecting the right dominance
of the petrous carotid canal and anterior to the internal acoustic meatus of the sigmoid sinus and jugular vein.
and arcuate eminence. The portion of petrous bone that is limited The jugular tubercle is a rounded prominence located at the junc-
anteriorly by the mandibular nerve, laterally by the greater petrosal tion of the basilar and lateral parts of the occipital bone, just medial to
nerve, medially by the superior petrosal sinus, and posteriorly by the the jugular foramen. The accessory, vagus and glossopharyngeal nerves


internal acoustic meatus and cochlea is named the posteromedial or cross the posterior portion of the tubercle on their way to the jugular
Kawase’s triangle of the middle fossa. The surgical procedure known as foramen. The hypoglossal (anterior condylar) canal lies just inferior to
anterior petrosectomy consists of removal of this bone in order to access the jugular tubercle, superior to the occipital condyle, and medial to
the posterior fossa from the middle fossa approach (Kawase et al 1985) and below the lower border of the jugular foramen (Morera et al 2010).
(Ch. 38). It transmits the hypoglossal nerve and its recurrent branch, together
The lateral surface of the petrous part of the temporal bone is formed with the meningeal branch of the ascending pharyngeal artery and an
by the tegmen tympani, a thin osseous lamina that separates the emissary vein that links the (intracranial) basilar plexus with the
tympanic cavity (middle ear) from the middle fossa. Chronically ele- (extracranial) internal jugular vein. The canal may be divided by bony
vated intracranial pressure may cause erosion of the tegmen tympani septa for different rootlets of the hypoglossal nerve. The occipital con-
and spontaneous cerebrospinal fluid otorrhoea. The posterior part of dyles form the lateral (or condylar) part of the occipital bone, and they
the tegmen tympani forms the roof of the mastoid antrum, lateral to lie within the anterior and lateral aspect of the foramen magnum. On
the arcuate eminence, and is also called the tegmen mastoideum. In each side, their medial surface bears a tubercle that gives attachments
young skulls, a petrosquamous suture may be visible at the lateral limit to the alar ligaments of the odontoid process, and their inferior surface
of the tegmen tympani but it is obliterated in adults. The tegmen is convex and articulates with the upper surface of the lateral mass of


tympani then turns down as the lateral wall of the osseous portion of the atlas. The posterior condylar canal, when present, is located in the
the pharyngotympanic tube, and its lower border may appear in the extracranial surface behind and above each occipital condyle; its inter-
squamotympanic fissure. Lateral to the anterior part of the tegmen nal orifice is posterolateral to that of the hypoglossal canal and con-
tympani, the squamous part of the temporal bone is thinned over a tains the supracondylar vein and a meningeal branch of the occipital
small area that coincides with the deepest part of the mandibular fossa. artery.


IntracranIal regIon
432
4
noItceS
The posterior surface of the petrous part of the temporal bone forms general rule, the meningeal layer covers neural tissues, while the endos-
much of the anterolateral wall of the posterior cranial fossa. It contains teal layer adheres to the osseous structures. These layers are united
the internal acoustic meatus, which lies anterosuperior to the jugular except where they separate to enclose the venous sinuses that drain
foramen, and transmits the facial and vestibulocochlear nerves, the blood from the brain. There is little histological difference between
nervus intermedius and labyrinthine vessels. A small subarcuate fossa the endosteal and meningeal layers. Both contain fibroblasts, and the
lined with dura mater lies posteriorly between the internal acoustic endosteal layer also contains osteoblasts. Focal calcification may occur
meatus and the opening of the vestibular aqueduct, and houses the in the falx cerebri and near the superior sagittal sinus.
saccus and ductus endolymphaticus and a small artery and vein. The The endosteal layer of dura adheres to the internal surfaces of the
suprameatal tubercle is a bony prominence located superiorly between cranial bones, particularly at the sutures and the cranial base, and
the internal acoustic meatus and the petrous ridge (Seoane and Rhoton around the foramen magnum. Fibrous bands pass from the dura into
1999). the bones, and it is difficult to remove the dura from the suture lines
The mastoid part of the temporal bone lies behind the petrous part in young skulls. However, as the suture lines fuse, the dura becomes
of the temporal bone in the lateral wall of the posterior cranial fossa. separated from them. The endosteal layer of the dura is continuous with
Anteriorly, it is grooved by a wide sigmoid sulcus that runs forwards the pericranium through the cranial sutures and foramina and with the
and downwards, then downwards and medially, and finally forwards to orbital periosteum through the superior orbital fissure. The meningeal


the jugular foramen; it contains the sigmoid sinus. Superiorly, where layer provides tubular sheaths for the cranial nerves as they pass out
the groove touches the mastoid angle of the parietal bone, it becomes through the cranial foramina, and these sheaths fuse with the epineur-
continuous with a groove that transmits the transverse sinus, and then ium as the nerves emerge from the skull. The dural sheath of the optic
crosses the parietomastoid suture and descends behind the mastoid nerve is continuous with the ocular sclera. The dura fuses with the
antrum. A mastoid foramen, which transmits an emissary vein from the adventitia of major vessels, such as the internal carotid and vertebral
sigmoid sinus and a meningeal branch of the occipital artery, may be arteries, at sites where they pierce it to enter the cranial cavity.
sited here. The lowest part of the sigmoid sulcus crosses the occipito- The inner, meningeal, layer of dura is closely applied to the arach-
mastoid suture and grooves the jugular process of the occipital bone. noid over the surface of the brain. However, the two membranes are
The right sigmoid sulcus is usually larger than the left. physically joined only at sites where veins pass from the brain into
The squamous part of the occipital bone displays a median internal venous sinuses, e.g. the superior sagittal sinus.
occipital crest. This runs posteriorly from the foramen magnum to an
internal occipital protuberance, gives attachment to the falx cerebelli, extradural haematoma
and may be grooved by the occipital sinus. The internal occipital pro- The anatomical organization of the dura, and its relationships to the
tuberance is close to the confluence of the sinuses. It is grooved bilater- major venous sinuses, sutures and blood vessels, are clinically signifi-
ally by the transverse sinuses, which curve laterally with an upward cant. Separation of the dura from the cranial bones requires significant
convexity to the mastoid angles of the parietal bones. The groove for force, and consequently happens when high-pressure arterial bleeding


the transverse sinus is usually deeper on the right, where it is generally takes place into the extradural or epidural space. This can result from
a continuation of the superior sagittal sinus, while on the left it is fre- damage to any meningeal vessel, commonly following skull fracture.
quently a continuation of the straight sinus. On both sides, the trans- The classic site for such injury is along the course of the middle menin-
verse sulcus is continuous with the sigmoid sulcus. Below the transverse geal artery, where a direct blow causing a fracture of the temporal and/
sulcus, the internal occipital crest separates two shallow fossae that or parietal bones can rupture the artery and cause rapid collection of
house the cerebellar hemispheres. The posterior clinoid process and blood into the extradural space. An extradural haematoma therefore
the margins of the grooves for the transverse and superior petrosal acts as a rapidly expanding intracranial mass lesion that causes acute
sinuses all provide anchorage for the attached margin of the tentorium brain compression and displacement; it is a classic medical emergency
cerebelli. that requires immediate diagnosis and surgery through a craniotomy
for epidural blood clot evacuation and coagulation of the ruptured
vessel (see Fig. 28.12).
MENINGES
Dural partitions
Three concentric membranes, the meninges, envelop the brain and
spinal cord. They provide support and protection for the delicate tissues The meningeal layer of the dura is reflected inwards to form four septa,
they surround. The individual layers, in order from outside to inside, namely: the falx cerebri, falx cerebelli, diaphragma sellae and tentorium
are the dura mater (pachymeninx), arachnoid mater and pia mater. The cerebelli, which partially divide the cranial cavity into compartments.
dura is an opaque, tough, fibrous coat that incompletely divides the
cranial cavity into compartments and accommodates the dural venous Falx cerebri
sinuses. The arachnoid is much thinner than the dura and is mostly The falx cerebri is a strong, crescent-shaped sheet that lies in the sagittal
translucent. It loosely surrounds the brain, cranial nerves and vessels, plane and occupies the longitudinal fissure between the two cerebral


spanning fissures and sulci. The pia mater is a transparent, microscopi- hemispheres (Fig. 28.3). The crescent is narrow in front, where the falx
cally thin membrane that follows the contours of the brain and is is fixed to the crista galli, and broad behind, where it blends with the
closely adherent to its surface. tentorium cerebelli; the straight sinus runs along this line of attachment
The dura is separated from the arachnoid by a narrow subdural to the tentorium (see Fig. 28.3). The anterior part of the falx is thin and
space. The arachnoid is separated from the pia by the subarachnoid may have a number of irregular perforations. Its convex upper margin
space, which varies greatly in depth; the larger expanses are termed is attached to the internal cranial surface on each side of the midline,
subarachnoid cisterns. The subarachnoid space contains cerebrospinal as far back as the internal occipital protuberance. The superior sagittal
fluid (CSF), which is secreted by the choroid plexuses of the cerebro- sinus runs in a cranial groove within the dura along this margin; the
ventricular system. CSF circulates within the subarachnoid space and is falx is attached to the lips of this groove. The lower edge of the falx is
reabsorbed into the venous system through arachnoid villi and granul- free and concave, and contains the inferior sagittal sinus.
ations associated with the dural venous sinuses.
Cranial and spinal meninges are continuous through the foramen Falx cerebelli
magnum. The cranial meninges are described in this section and the The falx cerebelli is a small midline fold of dura mater that lies below
spinal meninges are described on page 764. the tentorium cerebelli and projects forwards into the posterior cerebel-
lar notch between the cerebellar hemispheres. Its base is directed
upwards and is attached to the posterior part of the inferior surface of
DURA MATER
the tentorium cerebelli in the midline. Its posterior margin contains the
occipital sinus and is attached to the internal occipital crest. The lower


Dura mater is thick, dense and fibrous. It is predominantly acellular, apex of the falx cerebelli frequently divides into two small folds, which
and consists mainly of densely packed fascicles of collagen fibres disappear at the sides of the foramen magnum.
arranged in laminae. The fascicles run in different directions in adjacent
laminae, producing a lattice-like appearance that is particularly obvious Diaphragma sellae
in the tentorium cerebelli and around the defects or perforations that The diaphragma sellae is a small, circular, horizontal sheet of dura
sometimes occur in the anterior portion of the falx cerebri. mater. It forms a roof over the sella turcica and covers the pituitary
The cranial dura, which lines the cranial cavity, differs from the gland. The infundibulum (also known as pituitary stalk) passes into the
spinal dura mainly in its relationship to the surrounding bones. It has pituitary fossa through a central opening in the diaphragma. There is
an inner, or meningeal, layer and an outer, or endosteal, layer. As a wide individual variation in the size of this opening. The diaphragma


Meninges
433
82
retPaHc
A Sigmoid sinus B Great cerebral vein Inferior anastomotic Superior sagittal sinus
vein (of Labbé)
Straight sinus Falx cerebri
Superior petrosal sinus
Inferior sagittal sinus
Superior sagittal sinus Basilar sinus
Sphenoparietal
sinus
Straight sinus
Confluence of sinuses
Great cerebral vein
Inferior petrosal sinus
Right transverse sinus
Sigmoid sinus
Superior petrosal sinus
Cavernous sinus
Transverse sinus Dorsum sellae
Ophthalmic vein
Inferior anastomotic Superior petrosal Anterior petroclinoidal
Pterygoid plexus of veins vein (of Labbé) sinus ligament
Intercavernous sinus Tentorium cerebelli Tentorial incisure
Fig. 28.3 A, The cerebral dura mater, its reflections and associated major venous sinuses. B, An anatomical dissection of a silicon-injected specimen.
(A, Adapted from Drake RL, Vogl AW, Mitchell A (eds), Gray’s Anatomy for Students, 2nd ed, Elsevier, Churchill Livingstone. Copyright 2010.)
sellae is an important landmark structure in pituitary surgery because the cavernous sinus, where it is pierced by the internal carotid artery.
large pituitary tumours extend above it and may adopt a characteristic The interclinoidal ligament, between the anterior and posterior clinoid
dumbbell shape. A trans-sphenoidal approach is currently the preferred processes, forms the medial limit of the roof of the cavernous sinus and
option for accessing pituitary tumours, irrespective of whether there is continues medially with the diaphragma sellae. At, or just below, the
suprasellar extension beyond the diaphragma sellae. opening in the diaphragma for the pituitary stalk, the dura of the dia-
phragma and the suprasellar arachnoid blend with each other and with
Tentorium cerebelli the capsule of the pituitary gland; the subarachnoid space does not
The shape of the tentorium cerebelli (see Fig. 28.3B) is reminiscent of extend into the sella turcica.
a single-poled tent, from which its name is derived. It lies between the
transtentorial coning


cerebellum and the occipital lobes of the cerebral hemispheres, and
divides the cranial cavity into supratentorial and infratentorial compart- Normally, the arrangement of dural partitions such as the falx cerebri
ments, which contain the forebrain and hindbrain, respectively. Its and tentorium cerebelli may help to stabilize the brain within the
concave anterior edge is free and separated from the dorsum sellae of cranial cavity. However, when there is focal brain swelling or a focal
the sphenoid bone by a large curved hiatus, the tentorial incisure or space-occupying lesion within the brain or cranial cavity, mass effect
notch, which is filled by the midbrain and the anterior part of the and raised intracranial pressure may cause the brain to herniate under
superior aspect of the cerebellar vermis. The convex outer limit of the the falx cerebri or, more significantly, through the tentorial incisure. In
tentorium is attached posteriorly to the lips of the transverse sulci of this case, the medial temporal lobe, and particularly the uncus, will
the occipital bone and to the posterior inferior angles of the parietal compress the oculomotor nerve, midbrain and the posterior cerebral
bones, where it encloses the transverse sinuses. Laterally, it is attached arteries. This life-threatening event and neurosurgical emergency,
to the superior borders of the petrous parts of the temporal bones, occurring in patients with supratentorial space-occupying lesions, is
where it contains the superior petrosal sinuses. On each side, near the known as transtentorial uncal herniation. Similarly, space-occupying
apex of the petrous temporal bone, the lower layer of the tentorium is lesions in the smaller infratentorial compartment may cause upward
evaginated anterolaterally under the superior petrosal sinus to form a herniation of the cerebellar vermis through the tentorial hiatus
recess, Meckel’s cave, between the endosteal and meningeal layers in the (upward transtentorial herniation) or downward herniation of the cer-
middle cranial fossa. The cave is entered by the posterior root of the ebellar tonsils through the foramen magnum (tonsillar herniation)


trigeminal nerve and contains cerebrospinal fluid and the trigeminal (see Fig. 21.20); these neurosurgical emergencies require a suboccipital
ganglion; the evaginated meningeal layer fuses in front with the anterior craniectomy.
part of the ganglion.
Innervation of the cranial dura mater
The arrangement of the dura mater in the central part of the middle
cranial fossa is complex. The tentorium forms the medial part of the
floor of the middle cranial fossa. On both sides, the rim of the tentorial The innervation of the cranial dura mater is derived mainly from the
incisure is attached to the apex of the petrous temporal bone and three divisions of the trigeminal nerve, the second and third cervical
continues forwards as a ridge of dura, known as the anterior petrocli- spinal nerves, and the cervical sympathetic trunk (Fig. 28.4). Less well-
noidal ligament, to attach to the anterior clinoid process. This ligament established meningeal branches have been described arising from the
marks the junction of the roof and the lateral wall of the cavernous vagus and hypoglossal nerves, and possibly from the facial and glos-
sinus. The periphery of the tentorium cerebelli (attached to the superior sopharyngeal nerves.
border of the petrous temporal bone), crosses under the free border of In the anterior cranial fossa, the dura is innervated by meningeal
the tentorial incisure at the apex of the petrous temporal bone, and branches of the anterior and posterior ethmoidal nerves and anterior
continues forwards to the posterior clinoid process as a rounded ridge filaments of the meningeal rami of the maxillary (nervus meningeus
of the dura mater known as the posterior petroclinoidal ligament. The medius) and mandibular (nervus spinosus) divisions of the trigeminal
dural extension between the anterior and posterior petroclinoidal liga- nerve. Nervi meningeus medius and spinosus are, however, largely dis-
ments forms the roof of the cavernous sinus. On either side, it is pierced tributed to the dura of the middle cranial fossa, which also receives fila-


superiorly by the oculomotor nerve and behind by the trochlear nerve, ments from the trigeminal ganglion. The nervus spinosus re-enters the
which proceed anteroinferiorly into the lateral wall of the cavernous cranium through the foramen spinosum with the middle meningeal
sinus. artery, and divides into anterior and posterior branches that accompany
In the anteromedial part of the middle cranial fossa, the dura ascends the main divisions of the artery and supply the dura mater in the middle
as the lateral wall of the cavernous sinus, reaches the ridge produced by cranial fossa and, to a lesser extent, the anterior fossa and calvarium.
the anterior petroclinoidal ligament, and runs medially as the roof of The anterior branch communicates with the meningeal branch of the


IntracranIal regIon
434
4
noItceS
A B
Anterior meningeal branches
of ethmoidal nerve
Anterior ethmoidal
Tentorial nerve Meningeal branch
nerve
(meningeal branches of maxillary nerve
Infundibulum
of ophthalmic nerve)
Anterior clinoid process
Posterior ethmoidal
Anterior meningeal nerve
branches of anterior
ethmoidal nerve
Ophthalmic
Maxillary Divisions of trigeminal nerve
Mandibular Meningeal branches of C2 fibres distributed
mandibular nerve by vagus nerve
(including nervus spinosus) C2, C3 C by2 , h C yp3 o f gib lore ss s ad l is nt eri rb vu eted
Tentorial nerve
(recurrent meningeal branch To floor of posterior cranial fossa
of ophthalmic nerve)
Area innervated by ophthalmic nerve (V1) Area innervated by mandibular nerve (V3)
Area innervated by maxillary nerve (V2) Area innervated by cervical spinal nerves (C2, C3)
Fig. 28.4 The innervation of the cranial meninges.
maxillary nerve; the posterior branch also supplies the mucous lining tation, peaking at term and subsequently decreasing during the first year
of the mastoid air cells. The nervus spinosus contains sympathetic of postnatal life (Davidson et al 2012).
postganglionic fibres from the middle meningeal plexus. The nervus
tentorii, a recurrent branch of the intracranial portion of the ophthal-
Dural venous sinuses
mic division of the trigeminal, supplies the supratentorial falx cerebri
and the tentorium cerebelli. Intraoperative mechanical stimulation of
the falx may trigger the trigeminocardiac reflex (Bauer et al 2005). The Dural venous sinuses form a complex network of venous channels that
dura in the posterior cranial fossa is innervated by ascending meningeal drain blood from the brain and cranial bones (see Figs 28.3, 19.11; Figs