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Session 2 – The Cranium and Brain
1) Demonstrate on a skull and in radiographs the following bones – frontal, parietal, temporal (squamous,
petrous and mastoid process), ethmoid, sphenoid (body and wings) and occipital
Frontal Bone
Parietal Bone
Sphenoid Bone
(wing)
Occipital Bone
Nasal Bone
Zygoma
Temporal Bone
Mastoid Process
Maxilla
Styloid Process
Mandible
Anterior Cranial Fossa
Ethmoid bone (cribriform plate)
Lesser wing of sphenoid
Greater wing of sphenoid
Middle Cranial Fossa
Petrous of Temporal Bone
Foramen Magnum
Posterior Cranial Fossa
2) Identify both on the brain and in x-ray, CT and MR images the following – ventricles, cerebral hemispheres,
thalamus, hypothalamus, internal capsule, basal ganglia, brainstem, optic chiasm and pituitary
1
Lateral ventricle [may be cut through twice in horizontal or
coronal plane]
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
Third ventricle [may look like a hole or a slit in coronal and
horizontal plane, depending on angle of section]
Fourth ventricle
Aqueduct
Corpus callosum [may be cut through twice in horizontal
plane]
Frontal lobe
Occipital lobe
Parietal lobe
Temporal lobe
Basal ganglia [may be more than one part]
Thalamus
Internal capsule [both anterior and posterior limbs seen in
horizontal plane]
Optic chiasma
Midbrain
Pons
Medulla
Cerebellum
3) Identify the different tissue components of the scalp
 The layers of the scalp:
 Skin
 Connective tissue
 Aponeurosis
 Loose areolar tissue
 Periosteum
 It is important to avoid infection of lacerations to the scalp as it can spread infection into the cranial cavity via
emissary vessels which go through the skull – thus bypassing the blood-brain barrier
 See below for picture
4) Demonstrate the relationship between the brain and the different cranial fossae
 See above:
 Generally the named part of the brain lies in the named fossa, e.g. frontal lobe in the anterior cranial fossa, occipital
lobe in the posterior cranial fissure and temporal lobe in the middle cranial fossa
5) Describe the structure and function of the meninges
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Meninges for sacs around the brain
Outer layer = dura mater
Middle layer = arachnoid
Inner layer, inseparable from the brain = pia mater
Between the arachnoid and pia = sub arachnoid space – continuous and containing CSF
The contours of the dura reflect the folds of the brain
No cranial equivalent of the extradural space as the durae mater is adherent to the periosteum of the skull except at
certain sites where they part company to form venous sinuses for venous drainage
 Haemorrhages can be subdural (generally venous), subarachnoid (generally arterial) or cerebral (generally arterial)
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Dura sensitive to pain and stretching via fibres from several nerves given off as they leave or enter the skull through
foramina
 From the larger venous sinuses a double layer of dura projects into the cranial cavity forming:
 The falx cerebri in the midline – partially separates the cranial cavity into right and left – attached to ethmoid
bone at front and the vault of the skull above and below
 The tentorium cerebelli – a more or less horizontally arranged sheet extending back from the ridge of the
petrous temporal bone to the internal occipital protuberance. It forms a complete diaphragm over the posterior
cranial fossa except for the tentorial notch through which the brain stem and surrounding nerves and vessels
pass
 When there is raised pressure above the tentorium due to pressure either from a mass or bleed the medial temporal
lobe can herniate round the rigid free edge of the tentorium and put pressure on the brainstem (tentorial herniation)
6) Draw a simple diagram to explain the flow of CSF in and around the brain
 CSF is produced by the choroids plexus – a vascular plexus formed where the vesself of the pia mater come into
contact with the Ependymal lining of the central canal
 Lateral ventricles → through the foramina of Monro → third ventricle → through cerebral aqueduct → fourth ventricle
→ some enters the central canal of the spinal cord, most enters the subarachnoid space through foramina in the roof
of the fourth ventricle → flows to the flows around the brain and is absorbed back into the venous circulation through
arachnoid villi/granulations in the venous sinuses
 Hydrocephalous is over production of CSF or reduced absorption
7) Identify on a skull the main exit/entry routes for the cranial nerves and the major blood vessels
Cribiform Plate
Optic Canal
Olfactory (I) Nerve Fibres
Optic Nerve (II) including (central artery of
retina)
Opthlamic Artery
Oculomotor Nerve (III)
Trochlear Nerve (IV)
Superior Orbital
Opthalmic division of Trigeminal (V)
Fissure
Abducens Nerve (VI)
Superior Opthalmic Vein
Foramen Rotundum
Foramen Ovale
Maxillary Division of Trigeminal Nerve (V)
Mandibular Division of Trigeminal Nerve (V)
Foramen Spinosum
Foramen Lacerum
Middle Meningeal Artery and Vein
Carotid Canal
Internal Carotid Artery
Facial Nerve (VII) (including intermediate nerve
Internal Acoustic
Vestibulocochlear Nerve (VIII)
Meatus
Labyrinthine Artery
Glossopharyngeal Nerve (IX)
Hypoglossal Canal
Hypoglossal Nerve (XII)
Jugular
Foramen
Vagus Nerve (X)
Accessory Nerve (XI)
Sigmoid Sinus → Internal Jugular Vein
Vertebral Arteries, Medulla of Brain
Foramen Magnum
8) Draw a simple diagram of the circle of willis
Spinal roots of Accessory (XI) Nerve
9) Demonstrate the main venous sinuses
 The Superior Saggital Sinus:
 In the midline at the attachment to the falx cerebri to the skull vault
 Blood in it drains posteriorly and at the internal occipital protuberance turns right, forming the right transverse
sinus
 Transverse sinus turns into the sigmoid sinus as it passes the petrous temporal bone
 Sigmoid sinus passes through the jugular foramen and becomes the right internal jugular vein
 The Inferior Saggital Sinus:
 In the midline in the inferior free margin of the flax cerebri
 Blood in it drains posteriorly and is joined at the tentorium/falx junction by blood from the great cerebral vein
emerging at the back of the brain stem
 They unit to form the straight sinus which passes back in the attachment of the falx and turns left at the
internal occipital protuberance becoming the left transverse sinus
 The pattern mirror this on the right forming the left internal jugular vein
 Sometimes the pattern is reversed with the superior saggital sinus turning left and the straight saggital sinus turning
right
 At the internal occipital protuberance the venous channels may communicate – the confluence of sinuses
 Right sided drainage normally bigger than left, indeed the left jugular vein can be absent all together
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The Cavernous Sinus:
Formed in the embryo from the coalescence of several venous channels
Forms a system of interconnecting caverns around the internal carotid
The right and left cavernous sinuses lie either side of the pituitary fossa and communicate with the transverse
sinuses and internal jugulars via petrosal sinuses
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Arachnoid Granulations:
The dural walls of the sinuses, particular in the superior saggital sinus posses small defects
These defects allow underlying arachnoid to billow out into the sinus
Only the arachnoid, and endothelium of the sinus separate CSF from venous blood
The site of CSF reabsorption
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See picture below:
10) Outline how venous anatomy presents opportunities for intracranial infection
 As the venous channels leaving the head are valveless, compression of the thorax can force venous blood from
these areas into the dural sinus system – bypassing the BBB and possibly leading to infection or metasteses
11) Identify the pterion and explain the clinical importance of its relationship to the middle meningeal artery
 An area on the lateral side of the skull where the frontal, parietal, temporal and sphenoid bones meet
 Its surface marking is about 4cm above a point 1/3 of the way from ear to eye
 The middle meningeal artery is a branch of the maxillary artery and enters the middle cranial fossa through thr
foramen spinosum
 The anterior division runs deep to the pterion – the thinnest and weakest part of the cranium
 Injury at this site can easily tear the artery causing an extradural bleed.
 The MCA also runs deeper to this point and if damaged can cause a subarachnoid haemorrhage