Localisation of lesions and life threatening emergencies

Question 1

what is a false localising sign

Answer 1

where there are clinical features of a certain palsie present e.g. 6th nerve palsie - which makes you believe there is a problem at the level of the 6th nerve - however there is something more globally going on in the body

Question 2

what structures are involved on eye movement control and visual processing

Answer 2

all of our visual information is processed at the occipital cortex In the occipital lobe and there are multiple sites which. relay information to the occipital cortex and to other parts of the brain - this includes the frontal eye fields and the supplementary eye fields which relay information down the pyramidal tracts and down to the gaze centres within the brain stem

Question 3

what is the pprf involved with in the brainstem , and what is the rRimlf involved with

Answer 3

(paramedian pontine reticular formation) is involved with horizontal gaze the Rimlf is involved with longnitudinal gaze and so is the INC

Question 4

what is the function of the medial longitudinal fasiculus

Answer 4

situated next to the pons and involved with the third and 6th nuclei relaying information about horizontal gaze

Question 5

what is the function of the brainstem

Answer 5

• comprised of 4 structures medulla oblongata , pons , pituitary gland and thalamus

contains ocular motor nuclei and gaze centres

has a critical role in regulating cardiac and respiratory functions

Question 6

define localisation of function

Answer 6

a concept that certain areas of the brain are responsible for particular functions

motor cortex = movement and somatosensory- (feel and touch) inputs ,visual cortex = processing visual information

brocas and wernickes area = speech production and speech comprehension

Question 7

define hemispheric laterlisation

Answer 7

each hemisphere is specalised to perform certain functions

corpus callous connects the pathways between the 2 hemispheres

Question 8

what is the reason for left sided visual inattention

Answer 8

due to hemispheric lateralisation- the right part of the brain is more heavily involved with visual perception - the left side of the brain is involved more with speech

Question 9

how is eye movement coordinated

Answer 9

visual information is coming from the visual cortex - everything is being passed down the brain down to the level of the brainstem at the level of the midbrain and the pons level information is fed from superior colliculus and pontine nuclei and down to the vestibular nuclei it is then fed to the nuclei and then the eoms

Question 10

what is the pathway for the coordination of eye movements

Answer 10

supranuclear centres

brain stem

infra nuclear pathways

eoms

Question 11

what are the different eye movement systems

Answer 11

smooth pursuit- i.e. the ability to smoothly track items , from side to side or up and down

saccades - rapid and fast eye movements

vestibular ocular reflex- if you move your head to one side your eyes tend to remain in a central position

optokinetic

vergence

control of pupils and eyelids

Question 12

what is a fasicle

Answer 12

part of the nerve that is travelling within the brainstem itself - when it leaves the brainstem that is when it is called a nerve fibre

Question 13

how are ocular motility defects localised

Answer 13

e.g. 6th nerve

6th nerve nuclei located in the pons but has a long intracranial course from the brainstem to the orbit so there could be a lesion anywhere from the nucleus along to the orbit

Question 14

what is a nuclear lesion of. 6th nerve palsie likely to cause

Answer 14

likely to cause a horizontal gaze palsie and because of the proximity to the structures within the brainstem the patient may also present with a facial nerve (7th nerve) palsie

Question 15

what is the syndrome called where there is a nuclear lesion at the 6th nerve

Answer 15

FAVILLE syndrome

both facial nerve palsie (7th nerve) and 6th nerve is affected

Question 16

what is the 6th nerve particularly vulnerable to

Answer 16

the 6th nerve is particularly vulnerable to the false localising sign e..g. patient presents with an abuction defect however due to the long intrcranial course It is very susceptible to damage due to raised intracranial pressure i.e so if in the brain you have raised ice you have compression of structures and because the 6th nerve runs along the petrous bone and passes over the petrous apex it can be very vunreable to being squished

Question 17

in what context does a false localising sign of a 6th nerve usually occur

Answer 17

raised iCP- needs to be released through a lumbar puncture or shunt or patient will present with larger range of symtpins e.g. nausea

or could be space occupying lesion

idiopathic intracrhail hypertension

cerebral venous sinus thrombosis

Question 18

what are some of the mechanisms of the false localising sign (6th nerve)

Answer 18

mechanisms could be stretching of long intracranial course

compression against the ridge of the petrous temporal bone

effects of backward brain stem displacement

Question 19

what is a infranuclear lesion

Answer 19

when the nerve has left the brainstem itself

Question 20

what conditions can supranucler lesions cause

Answer 20

horizontal gaze palsy - lesion of the PPRF OR CN6 NUCLEUS

VERTICAL GAZE OLASY - LESION OF THE rIMLF or intestinal nucleus of cajal

horizontal and vertical gaze centres are disrupted which is above the level of the nucleus

global paralysis - loss of all movement e.g. (saccades , pursuits)

lesion in upper midbrain i.e. if patient had a stroke or some kind of tumour

convergence retraction nystagmus - dorsal midbrain syndrome - pineal tumour (tumour of the pineal gland) - sits at the top of the brainstem

diplopia is not often a problem

Question 21

what are some of the ways you can differentiate between different supra nuclear lesions

Answer 21

VOR - intact shows horizontal gaze centres in brainstems (pons) intact

Impaired saccades (lesion in the frontal lobe_ , few , sc

failure of saccades to contralateral side e.g. r lesion = failure saccades to left

impaired smooth pursuit - cog wheel pursuit

catch up saccades
lesion in partial occipital lobe

failure of smooth pursuit to ipsilateral side
hemispaitial neglect

Question 22

what is the pprf

Answer 22

pprf is the horizontal gaze centre which relays information into the 6th nerve nuclei - from there if you want to look left or right the 6th nerve relays information to the third nerve nuclei - specifically the medial rectus sub nucleus of the this nerve because you want the lateral or medial rectus to look to the left or to the right you want this in the opposite eye do you have the medial longntiudinal fasiculus which is a pathway which decussates across the midline the contralateral third nerve nucleus from there you are able to initiate a movement to the right or to the left

Question 23

what happens if you have a lesion at the level of the 6th nerve nucleus

Answer 23

when you try and adduct the eye there is no Information going to the left lateral rectus and there is no movement going to the medial rectus so you have a complete gaze palsy on the left hand side

Question 24

what is abducting nystagmus

Answer 24

a form of abucting nystagmus you get when the patient looks in abduction and is a characteristic of intranuclear opthalmoplegia

Question 25

if someone has a gaze palsy to the left and half a gaze palsy to the right what is it called

Answer 25

it is called a one and a half syndrome - is a characteristic feature of a lesion at the level of the horizontal gaze centre and the 6th nerve nucleus

Question 26

what does the mlf carry

Answer 26

the mlf cares multidirectional fibres from cn3 , cn4 and cn6

Question 27

what will a patient with intranuclear optahlmoplegia present with

Answer 27

skew deviation - hypertrophic deviation of just one eye -that needs to be differentiated from a fourth nerve palsy

Question 28

what is trochlear syndrome

Answer 28

impairment with the level of the fourth cranial nerve

Question 29

what does an ino + skew deviation tell you

Answer 29

result of sorption to the otolithic projection carried in the mld ipsilateral ino and ipsilateral hypertropia

Question 30

what does an ino and trochlear syndrome tell you

Answer 30

tells you that there is a lesion at the caudal midbrain at the level oof the superior colliculus adjacent to the cranial nerve 3 nucleus ipsilateral ino and contralateral hypertropia

Question 31

how do you differentiate between different brainstem lesions

Answer 31

parks 3 step test and upright supine test parks 3 step pct test in pp, horizontal gaze, and in head tilt and upright supine test (get pt do do pct in pp and when they are lying down) if convergence is intact then this indicates a lower lesion of the mlf as the mr sub nucleus is unaffected

Question 32

what could a 6th + 7th nerve palsy indicate

Answer 32

fovilles syndrome or miller gables syndrome

Question 33

what could contralateral hemiparesis be due to

Answer 33

cerebral penducele, red nucleus or pyramidal tracts Benedikts syndrome webers syndrome §

Question 34

how would you rule out a infra nuclear lesion

Answer 34

progressive vs recovering (tumour vs vascular) pupil involvemen (compressive lesion) cn3 palsy affecting superior/inferior division only (splits before orbital fissure) abberent regeneration suggestive of traumatic lesion

Question 35

what are multiple cranial nerve palsies suggestive of

Answer 35

multiple cn palsies (infra nuclear) are suggestive of lesions around the globe - cavernous sinus - superior orbital fissure - orbital apex large midbrain stroke associated clinical signs and symptoms will aid localisation

Question 36

what are clinical signs indicative of orbital involvement

Answer 36

eye pain enopthalmos proptosis multiple cranial nerve involvement opthalmoplegia loss of vision

Question 37

what clinical signs are indicative of life threatening disease

Answer 37

known neurological or systemic disease multiple cn palsies signs of generalised ons disease recurrent or deteoriating nerve palsies fails to recover

Question 38

what are life threatening emergencies

Answer 38

ortthotpic emergencies anyerusm subdural hameotoma (following head injury - blow out fracture) raised ice - enecphalitties , hydrocephalus- headache - 6th np , paipillodema arteriovenous malformations (headaches , migraines , seizures , can affect control of eye. movements) myasthenic crisis whiles disease (reduced very saccades , gaze plays) tumours , some types if untreated diabetes , wernickes encephopthalny, whiles disease

Question 39

what type of anyeurm is most common of an isolated cranial nerve 3 palsy

Answer 39

posterior communicating artery is the most common caused of isolated cranial nerve 3 palsy in 34 - 56% of cases treatment of a symptomatic , non ruptured anyerum provides the best chance for a favourable neurological outcome high risk of morbidity and mortality if ruptured

Question 40

what factors should be considred in terms of orthoptic emergencies

Answer 40

age - are they younger than 59 microvascular risk factors clinical presentation isolated low or high. threshold for neuroimaging in different cranial nerve palsies

Question 41

when to scan for a patient with a third Neve palsy

Answer 41

literature suggests that all patients with a third nerve palsy should have a MRI and a supplementary study to rule out an aneurysm in a study of 47 isolated third nerve palsies - 28/47 60% had causative pathology on neuroimaging 19/47 were on anyeurms

Question 42

is immediate neuroimaging in fourth and sixth nerve palsies controversial

Answer 42

majority of cases are caused by ischamic or deymyleinating process? excellent prognosis for spontaneous recovery over 3 months low yield of pathology cost savings delay in neuroimaging does not lead to adverse outcomes

Question 43

what are the types of scans

Answer 43

computed tomography (ct) magnetic resonance imaging (mri) angiography (ct/mra)