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Ophthalmology Week 1 2017/18 > 9: Anatomy - raised intra-cranial pressure > Flashcards

9: Anatomy - raised intra-cranial pressure Flashcards

1
Q

What does raised intra-cranial pressure mean?

A

Increase in pressure within the cranial cavity

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2
Q

What can cause an increase in intra-cranial pressure?

A

Brain tumours

Head injury

Hydrocephalus

Meningitis

Stroke

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3
Q

A raised ICP causes damage to what CNS structures?

A

Brain

Spinal cord

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4
Q

What is the Monro-Kellie hypothesis?

A

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)

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5
Q

What symptoms do people with a raised ICP tend to have?

A

Headache

Visual disturbance

blurry vision, double vision, loss of vision, papilloedema, pupillary changes

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6
Q

What is diplopia?

A

Double vision

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7
Q

The optic nerve arises from which structure of the brain?

A

Diencephalon

(thalamus + hypothalamus)

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8
Q

Which space is the optic nerve found in?

A

Subarachnoid space

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9
Q

Name the layers of the CNS from outer to inner.

A

Dura mater (outer)

Arachnoid mater

Pia mater (inner)

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10
Q

Between which layers of the CNS is the subarachnoid space found?

A

Arachnoid mater

Pia mater

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11
Q

What fills the subarachnoid space?

A

Cerebrospinal fluid (CSF)

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12
Q

What does CSF do?

A

Nourishes the brain and removes toxins

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13
Q

Once the CSF has circulated in the subarachnoid space, where does it drain?

A

Dural venous sinuses

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14
Q

What structures in the arachnoid mater allow CSF to drain into the dural venous sinuses?

A

Arachnoid granulations

spaces which allow CSF to drain into venous circulation

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15
Q

Which important artery, supplying the brain, is found in the subarachnoid space?

A

Circle of Willis

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16
Q

At which level does the spinal cord end?

At which level does the subarachnoid space end?

A

L2

S2

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17
Q

What can be taken from the subarachnoid space to diagnose CNS diseases?

What is this procedure called?

A

CSF

Lumbar puncture

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18
Q

At which levels can a lumbar puncture be performed?

Why are these areas safe?

A

L3/4

L4/5

Subarachnoid space but no spinal cord (cauda equina instead, which is much harder to damage)

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19
Q

How much CSF circulates in the subarachnoid space at any one time?

A

500 ml

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20
Q

Where is CSF produced?

A

Choroid plexus of the lateral, third and fourth ventricles

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21
Q

CSF drains from the subarachnoid space via the ___ venous sinus, through ___ ___.

A

dural venous sinus

via arachnoid granulations

22
Q

What secretes CSF?

Where is it found?

A

Choroid plexus

Lateral, third and fourth ventricles

23
Q

The lateral ventricles are found on the right and left sides of the brain.

Where is the third ventricle found?

A

Midline

24
Q

Which structure connects the third and fourth ventricles?

A

Cerebral aqueduct

25
Q

The cerebral aqueduct connects which structures of the brain?

A

Third ventricle

Fourth ventricle

26
Q

Most CSF passes from the fourth ventricle to the ___ ___.

A

subarachnoid space

27
Q

Most CSF passes from the fourth ventricle to the subarachnoid space?

Where does the rest of it go?

A

Central canal

28
Q

Where does CSF circulate once it has passed through the fourth ventricle?

Where is it then reabsorbed?

A

Subarachnoid space

Central canal

Dural venous sinuses

29
Q

Where does the central canal go?

A

Spinal cord

Cauda equina

This is why you can get CSF from a lumbar puncture

30
Q

The dura, arachnoid and pia maters are known as ___.

A

meninges

i.e the lining of the CNS

31
Q

Because it’s an extension of the CNS, the optic nerve has its own meninges and ___ ___.

A

subarachnoid space

32
Q

The subarachnoid space of the optic nerve is filled with CSF.

What else is found in the optic nerve sheathe?

A

Central artery of the retina

Central vein of the retina

Common tendinous ring forms the outside of the sheathe

33
Q

What does increased ICP cause in the optic sheathe?

A

Compression of optic nerve, central artery and vein of retina

⇒ papilloedema

34
Q

Which cranial nerve controls most of the extraocular muscles?

A

Oculomotor nerve (CN III)

35
Q

Looking at the brain from below, where does CN III arise?

A

Midbrain

anterior to CN IV and V

36
Q

How does the oculomotor nerve leave the cranial cavity?

A

Superior orbital fissure

37
Q

What are the

a) somatic motor
b) parasympathetic

functions of the oculomotor nerve?

A

a) Medial rectus, Superior rectus, Inferior rectus, Inferior oblique and Levator palpebrae superioris
b) Constriction of pupils by Sphincter pupillae muscles

38
Q

Which reflex is slowed or lost if the oculomotor nerve is compressed by raised ICP?

A

Pupillary light reflex

because it relies on parasympathetic constriction of pupils by sphincter pupillae muscles, which CN III is responsible for

39
Q

What will the

a) eyelid
b) pupil
c) eye itself

look like in a person with a compressed oculomotor nerve?

A

a) Droopy (ptosis)

b) Dilated (mydriasis)

c) DOWN AND OUT (palsy of all extraocular muscles except lateral rectus and superior oblique)

40
Q

What direction will the eye point in if a patient has a compressed oculomotor nerve?

A

Inferolaterally

41
Q

Where does the trochlear nerve exit the cranial cavity?

A

Superior orbital fissure

42
Q

What extraocular muscle does the trochlear nerve (CN IV) supply?

What movement does it produce when the eye is adducted?

A

Superior oblique

Depression

43
Q

Which muscle is paralysed if the trochlear nerve is compressed by raised ICP?

A

Superior oblique

44
Q

What eye position is produced by compression of the trochlear nerve?

A

UP AND IN

45
Q

What visual symptom is produced by unilateral compression of the trochlear nerve?

A

Diplopia

(double vision)

46
Q

What may a patient complain of if they have a compressed trochlear nerve?

Why?

A

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

47
Q

Where does the abducent nerve (CN VI) arise?

A

Pons-medullary junction

posterior to CN III and IV

48
Q

Where does the abducent nerve exit the cranial cavity?

A

Superior orbital fissure

49
Q

Which muscle is paralysed by compression of the abducent nerve in raised ICP?

A

Lateral rectus

50
Q

What eye problem is produced by paralysis of the lateral rectus in abducent nerve compression?

A

Inability to abduct eye

so a medial squint

51
Q

Where do the oculomotor, trochlear and abducent nerves exit the cranial cavity?

A

Superior orbital fissure

Ophthalmology Week 1 2017/18 (10 decks)

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