Download The skull

Radiologic Anatomy of
the Skull
Assistant prof.
Dr. Haider Najim Aubaid
F.B.M.S., D.M.R.D
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RADIOLOGIST IS….A GOOD ANATOMIST AND GOOD PATHOLOGIST!!
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The skull
Very complex structure, composed of more than 20 bones.
We should be familiar with the 4 standard projections, even though
they are no longer routinely practiced.
The standard projections are:
I. The lateral view,
2. The PA view.
3. The Towne's view
4. The basal view
Skull X-rays are now relatively unimportant in the
diagnosis of cerebral tumors and other cerebral
lesions.
They remain essential in the investigation of :
-lesions affecting the bony skull, including fractures,
-bony tumors (both primary and secondary),
-and inflammatory lesions.
In addition to the standard views, extra projections to
define specific anatomical landmarks may be required.
The special views in general use include:
1. Optic foramen
2. Sinuses
3. Mastoids
4. Petrous bones
5. Coned pituitary fossa.

The skull can be divided into two
portions:
 The neural skull is made up
of 6 bones: frontal, parietal,
temporal, occipital, sphenoid
and ethmoid.
 The facial skull comprises 8
different bones.
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The sutures
 Readily recognized on films of the adult skull and their
serrated appearances are illustrated.
 The serrations visualized lie on the outer table: the suture is
linear on the inner table but this is not identified except
occasionally.
 The serrated suture should help to differentiate it from a
fracture.
Neonatal
&
growing
skull
What infantile skull differs from adult?
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What infantile skull differs from adult?
• At birth there may be overlapping of the cranial bones
due to moulding; this disappears over several days.
• The diploic space is not developed,
• Vascular markings are not visible
• The sinuses are not aerated.
• The sutures are straight lines
• Wormian bones may be seen.
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What infantile skull differs from adult?
• The skull vault is approximately 8 times the size of the
facial bones on the lateral skull radiograph.
• The fontanelles are open
– Posterior fontanelle closes by 6-8 months
– Anterior fontanelle is usually closed by 15-18 months
– Two pairs of lateral fontanelles close in the 2nd or 3rd month.
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Growing skull
• By 2 years of age,
– Sutures start to assume the serrated appearance of the adult sutures
– the diploic space has begun to develop
– middle meningeal and convolutional markings start to appear.
• The convolutional markings may be very prominent, but become less so after the
age of 10 years and eventually disappear in early adulthood.
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Growing skull
• The fastest period of growth of the skull vault is the first year,
and adult proportions are almost attained by the age of 7 years.
• Sutures are wide and prominent but by 6 months the sutures
have narrowed to 3 mm or less. They are essentially fused in
the second decade, but complete bony fusion occurs in the
third decade.
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Correlated anatomic and
radiographic considerations of the
internal aspect of cranial cavity:
For anatomical purposes, the basal portion of the skull is divided
into three fossae.
on Lat. XR, step-like higher ant, lowest post.
Anterior CF:
 space above the orbital roofs, anterior to
the ridge formed by the greater and lesser
wings of the sphenoid.
 It contains the frontal lobes and the
olfactory bulbs and tracts.
 Dorsum sellae and ACP form posterior
boundary centrally.
Middle CF:
Lower level than Ant CF, (resembles bird with outstretched wings).
 It contains the temporal lobe.
 should not be confused with the temporal fossa, which is the extracranial space
deep to the zygomatic arch.
 lies posteroinferior to the sphenoid ridge.
Middle CF
 It’s bounded
– laterally mainly by squamous temporal bone (but also by
small parts of greater wing of sphenoid and parietal)
– posteroinferiorly by the petrous ridge.
Middle CF, is
bounded
– laterally mainly by squamous temporal bone (but also by
small parts of greater wing of sphenoid and parietal)
– posteroinferiorly by the petrous ridge.
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• Mid-portion ( formed by body of sphenoid) is elevated above lateral parts &
contains sella turcica, optic foramina united by chiasmaticus groove & carotid
grooves.
• Carotid groove begins posterolaterally at foramen lacerum & ends medial to ACP.
• Cavernous sinus lie on each side of this groove& ICA is embedded in this sinus.
Important foramina in middle CF:
 Optic,
 sup orbital fissure,
 rotundum,
 lacerum,
 ovale
• Three of them are oriented along an oblique line in the greater
sphenoidal wing from anteromedial behind the superior orbital
fissure to posterolateral mnemonic:"rotos" foramen
• rotundum ovale spinosum
The posterior cranial fossa
 Lower level than Middle CF.
 This comprises all the space below the tentorium or tentorial
hiatus and above the foramen magnum.
The posterior cranial fossa It is bounded
• Anteriorly by the clivus in the midline,
• by the posterior surface of the petrous
bone on each side,
• and elsewhere by the occipital bone.
• Superolaterally :
in the midline the apex of the tentorium
lies almost at the level of the pineal.
NOTE:
• Marked variations in the shape of the tentorium (e.g.
the straight sinus can be almost vertical or nearly
• It contains the
–
–
–
–
–
Pons and medulla oblongata,
cerebellum,
fourth ventricle,
lower cranial nerves
vertebro-basilar arterial tree.
Important landmarks:
1-Basisphenoid suture: lie between basilar part of
occipital bone (basiocciput), basilar portion of
sphenoid. It is open at birth and may remain so for
several years.
2-IAM at anterior wall of post CF, short canal in petrous
bone separated laterally by thin bone from inner ear.
The base of the skull is perforated by a
number of foramina and canals
Vascular markings
1-Meningeal markings
easily recognized by their constant position and course,
increase gradually in size from above downwards, (like a river).
2-Supraorbital and middle temporal arteries
occasionally associated with vascular grooves on outer surface
of the skull (can be mistaken for fractures).
Pacchionian impressions
 produced on the inner table by the pacchionian bodies
 appear as relative translucencies suggesting small
bone defects..
 most numerous in the parasagittal region but may be
seen in other sites, particularly around the torcular,
Significance?
 where they can simulate pathological bone defects
due to metastases.
Frontal view
Lateral view
Computed Tomography
 The contrast or brightness ("window" or "level," respectively) of
these images can be adjusted to highlight particular tissues.
 Brain parenchymal detail (brain windows)
 images visualize bony detail (bone windows).
 Cortical bone appears white.
 Air within the paranasal sinuses & mastoid air cells appears black.
 Cerebral white matter appears slightly darker than gray matter.
The nasal bones
The paired nasal bones are attached to each other and
to the nasal spine of the frontal bone.
They are grooved on their deep surface by one or more
anterior ethmoidal nerves.
These vertically oriented grooves can be seen on a
radiograph and should not be mistaken for fractures
The zygoma
the malar bone.
It articulates
with the frontal, maxillary
and temporal bones at
the zygomaticofrontal,
zygomaticomaxillary
&zygomaticotemporal
sutures.
Yellow arrow: Frontozygomatic suture
Orange arrows: Zygomaticofacial canal
Red arrows: Zygomaticomaxillary suture
Sella turcica:
-on intracranial aspect of body of sphenoid bone,
Consisted of:
• Dorsum sellae :
• TC (Tuberculum sellae)
• Hypophyseal fossa :
Sella turcica:
• Dorsum sellae (DS) thin square plate ends
superolaterally with PCP (posterior clinoid
processes).
• Tuberculum sellae TC : at
anterosuperior aspect of sella
– just anterior to it is the groove of optic
chiasm
– just beneath & medial to it on each side is
Optic foramina
• Hypophyseal fossa :
•
•
basal concavity of the sella, houses the pituitary
gland.
appears as dense curved line on lat. XR (double
contour??)
Dimensions:
Normal pituitary fossa as shown in a lateral
skull film can vary considerably in size.
Length=11 -16 mm and a
depth = 8-12 mm
However, the question of the upper limit of
normal remains largely subjective overlaps the
pathological.
• Lateral XR:
• Towne's: DS & PCP in F. magnum. ACP is
usually can be seen.
• PA: TS & ACP (but poor details).
The temporal bone
1-squamous portion.
2-mastoid portion:
3-Petrous portion:
The temporal bone
1-squamous portion; lateral, (calvarium).
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The temporal bone
2-mastoid portion: formed from both squamous & petrous
portions at petrosoquamous suture be careful not to
confuse with #.
Mastoid foramen (perforate mastoid process).
Transverse sinus runs on inner surface.
Mastoid Air cells:
• three groups (anterosuperior, middle & apical),
• open all in mastoid antrum which communicates with
upper part of tympanic cavity (Epitympanic recess)
The temporal bone
3-Petrous portion: pyramid with 3 surfaces
(2 within cranial cavity & 1 surface downward at base
of skull).
3-Petrous portion:
1) Posteromedial surface:
1) IAM (7th &8th n) 1cm long, anterolateral course. Posterior
crest is porus acousticus.
2) Vestibular duct (anteromedial course).
2) Anteriosuperior surface:
1) impression for semilunar ganglia of 5th n. (near apex)
2) arcuate eminence (under which is SSC),
3) tegmen tympani (laterally) thin bony roof over tympanic
cavity.
3) Basilar surface:
carotid canal, jugular fossa, stylomastoid process & foramen.
Note:
Medial & posterior wall of tympanic cavity is sometimes described
as 4th surface of petrous.
Tympanic cavity or middle ear :
~2-4x15mm space,
-Consisted of three
portions:
1. Middle (Mesotympanum),
2. Upper (eiptympanum or
attic) ,
–
posterosuperiorly with mastoid
antrum through Aditus)
3. Lower (hypotympanum)
–
Anteroinferiorly with Eustachian
tube
Relation:
• Anteroinferiorly : ICA., & jugular V..
• Medially , tow fenestra (oval &round windows) in contact
with inner ear (one with cochlea, one with vestibule)
Medially: Structures are from above to below:
-anterior part of superior SSC,
-canal containing facial nerve,
-below &posteriorly is the oval window , anteriorly the promontory at the
lowest turn of cochlea. Posterior to promontory is round window.
• Below the floor of middle ear cavity, is jugular bulb.
• Above middle ear cavity is dura matter of middle cranial fossa
separated by tegmen.
-3 ossicles (malleus, incus, stapes),
Incus
Malleus
Stapes
This stirrup-shaped bone
ossicle is the smallest and
lightest bone of the human
body
Inner ear:
 contains the bony labyrinth (filled by perilymph) within it is
the membranous labyrinth (filled with endolymph fluid).
Bony L: three
portions:
1-anteriorly snail-like
cochlea
2-In the middle is
vestibule
3-Posteriorly the 3
semicircular canals
Inner ear:
• Directed anteromedial with cochlea anterior.
Inner ear:
The cochlear duct coiled for two and half turns
around its bony modiolus.
In cross section bony cochlea appears triangular
shape in each turn.
• External auditory meatus:
The outer part of the canal is cartilaginous and the medial two
thirds is bony.
• Eustachian tube:
posterior third of the adult tube is osseous and the anterior two
thirds is composed of membrane and cartilage
Plain radiography of the temporal bone
• Plain mastoid views are now almost entirely
obsolete except for postoperative assessment
of the position of a cochlear implant a
electrode array in inner ear.
• For this , either the Stenver's or the perorbital
view may be used.
Oblique posteroanterior (Stenver's) view
•
•
Whole length of the petrous bone is demonstrated by
placing it parallel to the X-ray film.
A radiograph in Stenver's position should
demonstrate:
1.
2.
3.
4.
5.
6.
petrous tip and
internal auditory meatus (IAM),
semicircular canals (superior and lateral),
middle ear cleft,
mastoid antrum and the
mastoid process
Perorbital view
• best view of the IAM if tomography is unavailable;
• The petrous pyramids and IAM are projected through the
orbits
– Occipito-frontal: the petrous ridges should be completely superimposed within the
orbit, with their upper borders coincident with the upper third of the orbit.
– OF10°↓: the petrous ridges appear in the middle third of the orbit.
– OF15°↓: the petrous ridges appear in the lower third of the orbit.
– OF20°↓: the petrous ridges appear just below the inferior orbital margin.
CT anatomy
Axial sections
Axial sections:
1-just below the external auditory meatus show the
basal turn of cochlea and round window niche:
2-midmodiolar sections show the individual coils of the
cochlea and incudostapedial region;
3-Sections at the level of the vestibule
– best show the IAM.
– head of the malleus
– body and short process of incus
The three parts of the facial nerve canal can be
identified, base plane is least satisfactory for the
descending portion, which is seen in cross-section
behind the middle ear cavity.
Coronal sections
-level of the vestibule shows
– internal auditory meatus
– stapes
– oval window.
-Further back still, the pyramidal eminence is shown
between facial recess and sinus tympani.
Coronal sections
Normal intracranial calcification: regarded as physiological
can occur at
1. Pineal (60% of adults)
2. Habenular commissure (30%)
3. Choroid plexuses.
4. Dura
(falx (7%), tentorium, Dural plaques , frequently parasagittal)
5. Ligaments: petroclinoid (12%) and interclinoid
7. Pacchionian bodies
8. Basal ganglia and dentate nuclei
9. Pituitary gland (rare)
10- Diaphragm sellae
11. Lens
-LATERAL VIEW
1.Chamberlain line = line between posterior pole of hard
palate + opisthion (= posterior margin of foramen
magnum) tip of odontoid process usually lies below /
tangent to Chamberlain line tip of odontoid process
may lie up to 1 ± 6.6 mm above the Chamberlain line
2.McGregor line = line between posterior pole of hard
palate + most caudal portion of occipital squamosal
surface substitute to Chamberlain line if opisthion not
visible tip of odontoid <5 mm above this line
3.Craniovertebral angle = clivus-canal angle =angle
formed by line along posterior surface of axis body
and odontoid process + basilar line ranges from 150°
in flexion to 180° in extension ventral spinal cord
compression may occur at <150°
4.Welcher basal angle =formed by nasion-tuberculum
line and tuberculum-basion line angle averages 132°
(should be <140°)
5.McRae line = line between anterior lip (= basion) to
posterior lip (= opisthion) of foramen magnum tip of
odontoid below this line -
Never mind, you have excuse !
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