Localisation of lesions and life threatening emergencies Flashcards
what is a false localising sign
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
what structures are involved on eye movement control and visual processing
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
what is the pprf involved with in the brainstem , and what is the rRimlf involved with
(paramedian pontine reticular formation) is involved with horizontal gaze the Rimlf is involved with longnitudinal gaze and so is the INC
what is the function of the medial longitudinal fasiculus
situated next to the pons and involved with the third and 6th nuclei relaying information about horizontal gaze
what is the function of the brainstem
- 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
define localisation of function
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
define hemispheric laterlisation
each hemisphere is specalised to perform certain functions
corpus callous connects the pathways between the 2 hemispheres
what is the reason for left sided visual inattention
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
how is eye movement coordinated
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
what is the pathway for the coordination of eye movements
supranuclear centres
brain stem
infra nuclear pathways
eoms
what are the different eye movement systems
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
what is a fasicle
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
how are ocular motility defects localised
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
what is a nuclear lesion of. 6th nerve palsie likely to cause
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
what is the syndrome called where there is a nuclear lesion at the 6th nerve
FAVILLE syndrome
both facial nerve palsie (7th nerve) and 6th nerve is affected
what is the 6th nerve particularly vulnerable to
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
in what context does a false localising sign of a 6th nerve usually occur
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
what are some of the mechanisms of the false localising sign (6th nerve)
mechanisms could be stretching of long intracranial course
compression against the ridge of the petrous temporal bone
effects of backward brain stem displacement
what is a infranuclear lesion
when the nerve has left the brainstem itself
what conditions can supranucler lesions cause
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
what are some of the ways you can differentiate between different supra nuclear lesions
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
what is the pprf
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
what happens if you have a lesion at the level of the 6th nerve nucleus
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
what is abducting nystagmus
a form of abucting nystagmus you get when the patient looks in abduction and is a characteristic of intranuclear opthalmoplegia
if someone has a gaze palsy to the left and half a gaze palsy to the right what is it called
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
what does the mlf carry
the mlf cares multidirectional fibres from cn3 , cn4 and cn6
what will a patient with intranuclear optahlmoplegia present with
skew deviation - hypertrophic deviation of just one eye -that needs to be differentiated from a fourth nerve palsy
what is trochlear syndrome
impairment with the level of the fourth cranial nerve
what does an ino + skew deviation tell you
result of sorption to the otolithic projection carried in the mld
ipsilateral ino and ipsilateral hypertropia
what does an ino and trochlear syndrome tell you
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
how do you differentiate between different brainstem lesions
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
what could a 6th + 7th nerve palsy indicate
fovilles syndrome
or miller gables syndrome
what could
contralateral hemiparesis be due to
cerebral penducele, red nucleus or pyramidal tracts
Benedikts syndrome
webers syndrome §
how would you rule out a infra nuclear lesion
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
what are multiple cranial nerve palsies suggestive of
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
what are clinical signs indicative of orbital involvement
eye pain
enopthalmos
proptosis
multiple cranial nerve involvement
opthalmoplegia
loss of vision
what clinical signs are indicative of life threatening disease
known neurological or systemic disease
multiple cn palsies
signs of generalised ons disease
recurrent or deteoriating nerve palsies
fails to recover
what are life threatening emergencies
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
what type of anyeurm is most common of an isolated cranial nerve 3 palsy
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
what factors should be considred in terms of orthoptic emergencies
age - are they younger than 59
microvascular risk factors
clinical presentation
isolated
low or high. threshold for neuroimaging in different cranial nerve palsies
when to scan for a patient with a third Neve palsy
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
is immediate neuroimaging in fourth and sixth nerve palsies controversial
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
what are the types of scans
computed tomography (ct)
magnetic resonance imaging (mri)
angiography (ct/mra)
