Anatomy 3

Question 1

Define what raised ICP is

Answer 1

This is an increase in pressure within the cranial cavity

Question 2

What can raised ICP be caused by ?

Answer 2

Caused by an increased pressure in fluid surrounding the brain or an increase in pressure within the brain itself:

• Brain tumour
• Head injury
• Hydrocephalus (increased fluid around the brain)
• Meningitis
• Stroke

Question 3

Why does the cranial cavity not cope well with an increase in pressure (raised ICP)?

Answer 3

Because the cranial cavity is an enclosed space. It is not flexible or elastic so can’t cope well with an increase in pressure

Question 4

What can raised ICP result in ?

Answer 4

Damage to tissues, shifts in tissues, herniation and constriction of blood vessels

Question 5

What do most patients with raised ICP report ?

Answer 5

Visual problems:

• Transient blurred vision
• Double vision
• Loss of vision
• Papilloedema (swelling of optic disc due to increased ICP)
• Pupillary changes

Question 6

Why is the optic nerve affected by raised ICP?

Answer 6

• Because the optic ‘nerves’ are actually CNS tracts covered by the meninges
• The sub-arachnoid space is filled with CSF & ==> Raised ICP will be transmitted along the subarachnoid space in the optic nerve sheath

Question 7

Raised ICP will compress optic nerve, what will it also compress and what can this lead to ?

Answer 7

It will also compress central artery and vein of the retina. This Can lead to bulging or swollen optic discs (Papilloedema)

Visual symptoms can then occur:

• Transient visual obscurations (graying-out of vision),
• Transient flickering
• Blurring of vision
• Constriction of the visual field
• Decreased colour perception

Question 8

How can raised ICP affect CN III (oculomotor nerve)?

Answer 8

• Paralysis of somatic motor innervation - this affects the 4 extra-ocular muscles and eyelid (Levator palpebrae superioris)
• Paralysis of parasympathetic innervation of sphincter pupillae

Presents as lose/slowness of pupillary light reflex, dilated pupil, ptosis, eye turned inferolaterally ‘Down and Out’ (because only SO & LR functioning)

Question 9

What are some additional causes of CN III palsy?

Answer 9

• MS
• Congenital
• Aneurysm

Question 10

If someone presents with a painful CN III palsy what should you think of as the cause ?

Answer 10

An aneurysm being the cause

Question 11

How can raised ICP affect CN IV (trochlear nerve)?

Answer 11

• Paralysis of superior oblique muscle. Inferior oblique action is then unopposed. Resulting in eye not being able to move inferomedially
• Diplopia when looking down

Question 12

What are the causes of a CN IV palsy?

Answer 12

• Congenital decompensated
• Microvascular
• Tumour
• Bilateral – closed head trauma

Question 13

How can raised ICP affect CN VI (abducent nerve)?

Answer 13

• Results in paralysis of lateral rectus muscle. The eye cannot therefore move laterally in horizontal plane
• Presents as medial deviation of the eye (affected eye cannot abduct)

Question 14

What are the causes of a CN VI palsy ?

Answer 14

• Microvascular
• Raised ICP
• Tumour
• Congenital