Anatomy of Raised Intracranial Pressure

Question 1

what is the Monro-Kellie hypothesis

Answer 1

describes how the brain, blood and CSF exist at equilibrium with each other in the cranial cavity

Question 2

what makes up the intracranial volume and how does it vary

Answer 2

blood, brain and the CSF

intracranial volume is constant

Question 3

the cranial cavity is an enclosed space, so what can raised intracranial pressure cause

Answer 3

damage to tissues, shifts in tissues, herniation, constriction in blood tissues, visual problems(65-75% cases)

Question 4

what are the optic nerves/tracts(CN II) covered by and what runs within them

Answer 4

covered by meninges; dura, arachnoid and pia

central retinal vein and artery run within

Question 5

describe why raised intracranial pressure affects the optic nerve/tract(CN II)

Answer 5

raised ICP is transmitted along subarachnoid space in the optic nerve sheath as it is filled with CSF

Question 6

describe what happens in the optic nerve/tract due to raised ICP

Answer 6

raised ICP compresses the optic nerve(CN II) as well as the central retinal artery and vein

Question 7

what is the subarachnoid space and what is it filled with

Answer 7

subarachnoid space = space between arachnoid and pia

filled with CSF

Question 8

what does raised ICP affecting the optic nerve(CN II) lead to

Answer 8

bulging or swollen optic disc = papilloedema

Question 9

what does the term decompensated state mean in terms of raised ICP

Answer 9

when the brain, blood and CSF can co longer accommodate increased pressure

Question 10

what are the different folds of the dura mater that divide the cranial cavity

Answer 10

falx cerebri, tentorium cerebelli, falx cerebelli and diaphragm sellae

Question 11

describe how raised ICP can affect the oculomotor nerve(CN III)

Answer 11

rasied ICP can compress/stretch oculomotor nerve if medial temporal lobe herniates through the tentorial notch

Question 12

what are the problems caused by raised ICP affecting oculomotor nerve(CN II)

Answer 12

paralysis of somatic nerve innervation, paralysis of parasympathetic innervation sphincter of pupil, loss/slowness of pupillary light reflex, dilated pupil, ptosis, eye turned inferolaterally

Question 13

describe the eye changes seen with raised ICP affecting oculomotor nerve(CN III)

Answer 13

downward and outward gaze, dilated pupil, have to manually lift eyelid due to ptosis

Question 14

what is ptosis

Answer 14

drooping of upper eyelid

Question 15

what is affected in the paralysis of somatic nerve innervation due to raised ICP affecting CN III

Answer 15

4 extraocular muscles and upper eyelid

Question 16

what 2 CN have the longest intracranial course and what does that make them susceptible to

Answer 16

CN IV Trochlear nerve and CN VI Abducent nerve

susceptible to compression and stretching due to raised ICP

Question 17

describe the effects raised ICP has if it acts on CN IV trochlear nerve

Answer 17

paralysis of superior oblique muscle, inferior oblique is then unopposed so eye cannot move inferomedially and there is diplopia(esp when looking down)

Question 18

describe the effects raised ICP has if it acts on CN VI abducent nerve

Answer 18

paralysis of lateral rectus muscle, eye cannot move laterally on horizontal plane, therefore medial deviation of eye