9: Anatomy - raised intra-cranial pressure

Question 1

What does raised intra-cranial pressure mean?

Answer 1

Increase in pressure within the cranial cavity

Question 2

What can cause an increase in intra-cranial pressure?

Answer 2

Brain tumours

Head injury

Hydrocephalus

Meningitis

Stroke

Question 3

A raised ICP causes damage to what CNS structures?

Answer 3

Brain

Spinal cord

Question 4

What is the Monro-Kellie hypothesis?

Answer 4

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)

Question 5

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

Answer 5

Headache

Visual disturbance

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

Question 6

What is diplopia?

Answer 6

Double vision

Question 7

The optic nerve arises from which structure of the brain?

Answer 7

Diencephalon

(thalamus + hypothalamus)

Question 8

Which space is the optic nerve found in?

Answer 8

Subarachnoid space

Question 9

Name the layers of the CNS from outer to inner.

Answer 9

Dura mater (outer)

Arachnoid mater

Pia mater (inner)

Question 10

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

Answer 10

Arachnoid mater

Pia mater

Question 11

What fills the subarachnoid space?

Answer 11

Cerebrospinal fluid (CSF)

Question 12

What does CSF do?

Answer 12

Nourishes the brain and removes toxins

Question 13

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

Answer 13

Dural venous sinuses

Question 14

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

Answer 14

Arachnoid granulations

spaces which allow CSF to drain into venous circulation

Question 15

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

Answer 15

Circle of Willis

Question 16

At which level does the spinal cord end?

At which level does the subarachnoid space end?

Answer 16

L2

S2

Question 17

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

What is this procedure called?

Answer 17

CSF

Lumbar puncture

Question 18

At which levels can a lumbar puncture be performed?

Why are these areas safe?

Answer 18

L3/4

L4/5

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

Question 19

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

Answer 19

500 ml

Question 20

Where is CSF produced?

Answer 20

Choroid plexus of the lateral, third and fourth ventricles

Question 21

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

Answer 21

dural venous sinus

via arachnoid granulations

Question 22

What secretes CSF?

Where is it found?

Answer 22

Choroid plexus

Lateral, third and fourth ventricles

Question 23

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

Where is the third ventricle found?

Answer 23

Midline

Question 24

Which structure connects the third and fourth ventricles?

Answer 24

Cerebral aqueduct

Question 25

The **cerebral aqueduct** connects which structures of the brain?

Answer 25

**Third ventricle** **Fourth ventricle**

Question 26

Most CSF passes from the **fourth ventricle** to the ___ \_\_\_.

Answer 26

**subarachnoid space**

Question 27

Most CSF passes from the fourth ventricle to the **subarachnoid space**? Where does the rest of it go?

Answer 27

**Central canal**

Question 28

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

Answer 28

**Subarachnoid space** **Central canal** Dural venous sinuses

Question 29

Where does the **central canal** go?

Answer 29

**Spinal cord** **Cauda equina** This is why you can get CSF from a lumbar puncture

Question 30

The dura, arachnoid and pia maters are known as \_\_\_.

Answer 30

**meninges** i.e the lining of the CNS

Question 31

Because it's an extension of the CNS, the **optic nerve** has its own meninges and ___ \_\_\_.

Answer 31

**subarachnoid space**

Question 32

The subarachnoid space of the optic nerve is filled with CSF. What else is found in the optic nerve sheathe?

Answer 32

**Central artery of the retina** **Central vein of the retina** Common tendinous ring forms the outside of the sheathe

Question 33

What does **increased ICP** cause in the optic sheathe?

Answer 33

**Compression of optic nerve, central artery and vein of retina** ⇒ papilloedema

Question 34

Which **cranial nerve** controls most of the extraocular muscles?

Answer 34

**Oculomotor nerve** (CN III)

Question 35

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

Answer 35

**Midbrain** anterior to CN IV and V

Question 36

How does the **oculomotor nerve** leave the cranial cavity?

Answer 36

**Superior orbital fissure**

Question 37

What are the a) somatic motor b) parasympathetic functions of the **oculomotor nerve**?

Answer 37

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

Question 38

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

Answer 38

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

Question 39

What will the a) eyelid b) pupil c) eye itself look like in a person with a compressed oculomotor nerve?

Answer 39

**a) Droopy** (ptosis) **b) Dilated** (mydriasis) **c) DOWN AND OUT** (palsy of all extraocular muscles except lateral rectus and superior oblique)

Question 40

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

Answer 40

**Inferolaterally**

Question 41

Where does the trochlear nerve exit the cranial cavity?

Answer 41

**Superior orbital fissure**

Question 42

What extraocular muscle does the **trochlear nerve** (CN IV) supply? What movement does it produce when the eye is **adducted**?

Answer 42

**Superior oblique** **Depression**

Question 43

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

Answer 43

**Superior oblique**

Question 44

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

Answer 44

**UP AND IN**

Question 45

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

Answer 45

**Diplopia** | (double vision)

Question 46

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

Answer 46

**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

Question 47

Where does the **abducent nerve** (CN VI) arise?

Answer 47

**Pons-medullary junction** posterior to CN III and IV

Question 48

Where does the **abducent nerve** exit the cranial cavity?

Answer 48

**Superior orbital fissure**

Question 49

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

Answer 49

**Lateral rectus**

Question 50

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

Answer 50

**Inability to abduct eye** so a medial squint

Question 51

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

Answer 51

**Superior orbital fissure**