What does raised intra-cranial pressure mean?
Increase in pressure within the cranial cavity
What can cause an increase in intra-cranial pressure?
Brain tumours
Head injury
Hydrocephalus
Meningitis
Stroke
A raised ICP causes damage to what CNS structures?
Brain
Spinal cord
What is the Monro-Kellie hypothesis?
The volumes of the brain, blood and CSF exist in equilibrium
An increase in one volume causes a DECREASE in the volumes of the others to compensate
So a brain tumour decreases the volume of the blood and CSF and also causes an increase in intracranial pressure (pressure increases as volume decreases)
What symptoms do people with a raised ICP tend to have?
Headache
Visual disturbance
blurry vision, double vision, loss of vision, papilloedema, pupillary changes
What is diplopia?
Double vision
The optic nerve arises from which structure of the brain?
Diencephalon
(thalamus + hypothalamus)
Which space is the optic nerve found in?
Subarachnoid space
Name the layers of the CNS from outer to inner.
Dura mater (outer)
Arachnoid mater
Pia mater (inner)
Between which layers of the CNS is the subarachnoid space found?
Arachnoid mater
Pia mater
What fills the subarachnoid space?
Cerebrospinal fluid (CSF)
What does CSF do?
Nourishes the brain and removes toxins
Once the CSF has circulated in the subarachnoid space, where does it drain?
Dural venous sinuses
What structures in the arachnoid mater allow CSF to drain into the dural venous sinuses?
Arachnoid granulations
spaces which allow CSF to drain into venous circulation
Which important artery, supplying the brain, is found in the subarachnoid space?
Circle of Willis
At which level does the spinal cord end?
At which level does the subarachnoid space end?
L2
S2
What can be taken from the subarachnoid space to diagnose CNS diseases?
What is this procedure called?
CSF
Lumbar puncture
At which levels can a lumbar puncture be performed?
Why are these areas safe?
L3/4
L4/5
Subarachnoid space but no spinal cord (cauda equina instead, which is much harder to damage)
How much CSF circulates in the subarachnoid space at any one time?
500 ml
Where is CSF produced?
Choroid plexus of the lateral, third and fourth ventricles
CSF drains from the subarachnoid space via the ___ venous sinus, through ___ ___.
dural venous sinus
via arachnoid granulations
What secretes CSF?
Where is it found?
Choroid plexus
Lateral, third and fourth ventricles
The lateral ventricles are found on the right and left sides of the brain.
Where is the third ventricle found?
Midline
Which structure connects the third and fourth ventricles?
Cerebral aqueduct
The cerebral aqueduct connects which structures of the brain?
Third ventricle
Fourth ventricle
Most CSF passes from the fourth ventricle to the ___ ___.
subarachnoid space
Most CSF passes from the fourth ventricle to the subarachnoid space?
Where does the rest of it go?
Central canal
Where does CSF circulate once it has passed through the fourth ventricle?
Where is it then reabsorbed?
Subarachnoid space
Central canal
Dural venous sinuses
Where does the central canal go?
Spinal cord
Cauda equina
This is why you can get CSF from a lumbar puncture
The dura, arachnoid and pia maters are known as ___.
meninges
i.e the lining of the CNS
Because it’s an extension of the CNS, the optic nerve has its own meninges and ___ ___.
subarachnoid space
The subarachnoid space of the optic nerve is filled with CSF.
What else is found in the optic nerve sheathe?
Central artery of the retina
Central vein of the retina
Common tendinous ring forms the outside of the sheathe
What does increased ICP cause in the optic sheathe?
Compression of optic nerve, central artery and vein of retina
⇒ papilloedema
Which cranial nerve controls most of the extraocular muscles?
Oculomotor nerve (CN III)
Looking at the brain from below, where does CN III arise?
Midbrain
anterior to CN IV and V
How does the oculomotor nerve leave the cranial cavity?
Superior orbital fissure
What are the
a) somatic motor
b) parasympathetic
functions of the oculomotor nerve?
a) Medial rectus, Superior rectus, Inferior rectus, Inferior oblique and Levator palpebrae superioris
b) Constriction of pupils by Sphincter pupillae muscles
Which reflex is slowed or lost if the oculomotor nerve is compressed by raised ICP?
Pupillary light reflex
because it relies on parasympathetic constriction of pupils by sphincter pupillae muscles, which CN III is responsible for
What will the
a) eyelid
b) pupil
c) eye itself
look like in a person with a compressed oculomotor nerve?
a) Droopy (ptosis)
b) Dilated (mydriasis)
c) DOWN AND OUT (palsy of all extraocular muscles except lateral rectus and superior oblique)
What direction will the eye point in if a patient has a compressed oculomotor nerve?
Inferolaterally
Where does the trochlear nerve exit the cranial cavity?
Superior orbital fissure
What extraocular muscle does the trochlear nerve (CN IV) supply?
What movement does it produce when the eye is adducted?
Superior oblique
Depression
Which muscle is paralysed if the trochlear nerve is compressed by raised ICP?
Superior oblique
What eye position is produced by compression of the trochlear nerve?
UP AND IN
What visual symptom is produced by unilateral compression of the trochlear nerve?
Diplopia
(double vision)
What may a patient complain of if they have a compressed trochlear nerve?
Why?
Diplopia (especially when going downstairs) - one eye can’t look down properly; leading to blurry vision, trips and falls
Need to tilt head to see correctly - affected eye is slightly extorted
Where does the abducent nerve (CN VI) arise?
Pons-medullary junction
posterior to CN III and IV
Where does the abducent nerve exit the cranial cavity?
Superior orbital fissure
Which muscle is paralysed by compression of the abducent nerve in raised ICP?
Lateral rectus
What eye problem is produced by paralysis of the lateral rectus in abducent nerve compression?
Inability to abduct eye
so a medial squint
Where do the oculomotor, trochlear and abducent nerves exit the cranial cavity?
Superior orbital fissure
