ICL 6.5: Localization of Brainstem Lesions Flashcards
which nerves exit the brainstem at the junction of the pons and medulla?
- abducens nerve
- facial nerve
- vestibulocochlear nerve
CN 6, 7, and 8
which nerves exit from the medulla?
CN 9-12
what are the two parts of the medulla that you can see from the anterior view?
pyramids and the olive!
the pyramids are more centrally located
what is the function of the superior vs. inferior colliculus?
superior colliculus = gaze looking up and down
inferior colliculus is involved with hearing
they’re located on the dorsal side of the midbrain
what is the only nerve to come out of the dorsal side of the brainstem?
CN 4 = trochlear nerve
where are the nucleus cuneatus and gracilus located?
on the dorsal brainstem under the rhomboid fossa in the medulla
the nucleus gracilus is more medially located than the nucleus cuneatus and they convey information through the DCML tract from the lower and upper body, respectively
what is the function of the lateral and medial geniculate bodies and where are they located?
they are structures of the midbrain and they are located lateral to the superior colliculus –> they’re actually part of the thalamus
lateral geniculate body = light
medial geniculate body = music
what are the 4 ascending and descending tracts of the spinal cord?
- corticospinal = descending motor tract
- DCML = ascending sensory tract
- medial longitudinal fasciiculus
- descending sympathetic pathway from the hypothalamus to the spinal cord
what is the function of the medial longitudinal fasciculus pathway?
it’s the pathway that connects the 6th nucleus with the contralateral 3rd CN nucleus
so it’s what allows you to have conjugate gaze so that your eyes move the same degree when looking from left to right
which two pathways originate from the red nucleus?
the red nucleus is in the midbrain and it gives off the:
- rubrospinal tract which provides contralateral motor function
- central tegmental tract which goes to the contralateral inferior olivary nucleus
what is the pathway of the corticospinal tract?
it arises from the motor cortex in the frontal lobe and then passes through the anterior limb of the internal capsule
then it passes through the peduncle of the midbrain, through the brainstem, until it gets to the pyramids of the medulla where it will decussate
so if you have a lesion of this tract in the pons the weakness in the body will be on the contralateral side while a lesion in the spinal cord will cause ipsilateral weakness
what is the corticobulbar tract?
it’s a part of the corticospinal tract that goes to the CN nuclei in the brainstem!
where does proprioception information go too?
proprioception is conveyed via muscle spindles, golgi organs, joint bodies etc. and this information enters he spinal cord through the DCML tract in the dorsal horn of the spinal cord then ascends ipsilaterally in the anterior and posterior cerebellar tract to the cerebellum on the SAME side
where does vibration, two point touch information go to?
this information enters the spinal cord and ascends ipsilateral through the DCML tract to the nucleus cuneatus and gracilus in the medulla where they decussate
then this info goes to the thalamus and somatosensory cortex in the parietal lobe
what are the important structures of the brainstem at the level of the midbrain?
slide 13
- corticospinal tract
- medial longitudinal fasiculus
- DCML
- spinothalamic tract
what are the important structures of the brainstem at the level of the pons?
slide 14 and 15
- corticospinal tract
- medial longitudinal fasiculus
- DCML
- spinothalamic tract
what are the important structures of the brainstem at the level of the medulla?
slide 16
- corticospinal tract
- medial longitudinal fasiculus
- DCML
- spinothalamic tract
what is the hypothalamo-spinal sympathetic pathway?
aka Horner’s tract
the fibers originate in the hypothalamus then cross over in the brainstem WITHOUT synapsing and then go to the contralateral spinal cord
in the lateral horn of the spinal cord, the 2nd order neurons leave the spinal cord and form sympathetic chains on either side of the spinal column –> then the 3rd order neurons leaving from the sympathetic chains go to the end targets
what structures does the hypothalamo-spinal sympathetic pathway supply?
the 3rd order neurons exiting from the superior cervical ganglion wrap around the internal carotid artery and they supply:
- tarsal muscle of the eye
- dilator pupilae
- sweat glands
so if there’s a lesion anywhere in this pathway you’ll get Horner’s syndrome!!
what is Horner’s syndrome? what side of the body will you see symptoms?
- anhydrosis = sweat gland dysfunction
- ptosis = tarsal muscle dysfunction
- miosis = dilator pupilae dysfunction
all of these structures are supplied by the hypothalamo-spinal sympathetic pathway and if there’s a lesion in this pathway, you’ll develop Horner’s syndrome due to loss of the sympathetic system
symptoms will be on the SAME side as the lesion since the pathway crosses over as soon as it leaves the hypothalamus before it gets to the spinal cord – if the lesion were somehow in the hypothalamus, then the symptoms will be on the contralateral side but this is EXTREMELY rare
so if there is a lesion in the right brainstem, right sympathetic chain, right internal carotid artery or right spinal cord that means you’ll see symptoms of the right side of the body
what are the four rules of 4?
- 4 structures in ‘midline’ and begin with ‘M’
- 4 motor nuclei in midline and are those that are divisors of 12 (3,4,6,12)
- 4 structures to the ‘side’ (lateral) and begin with ‘S’
- 4 CN in medulla, 4 in pons and 4 above pons
what is the first rule of 4?
4 structures in ‘midline’ and they begin with ‘M’
- motor pathway = corticospinal tract
- DCML
- medial longitudinal fasciulus
- motor nucleus and nerve
what is the second rule of 4?
4 motor nuclei in midline and are those that are divisors of 12
CN 3, 4, 6 and 12 are near midline
CN 5, 7, 9 and 11 are laterally located
what is the third rule of 4?
4 structures to the ‘side’ (lateral) and begin with ‘S’
- spinocerebellar pathway (carries proprioception to ipsilateral cerebellum)
- spinothalamic pathway
- sensory nucleus of CN5
- sympathetic pathway (Horner’s tract)
what is the fourth rule of 4?
4 CN in medulla, 4 in pons and 4 above pons
midbrain = CN 3 and 4 (CN 1 and 2 arise from the brain)
pons = CN 5, 6, 7, 8
medulla = 9, 10, 11 and 12
what would happen to the 4 medial structures of the brainstem if there was a brainstem lesion?
- corticospinal tract –> contralateral weakness
- DCML –> contralateral proprioception/vibration loss
- medial longitudinal fasciuculus –> ipsilateral internuclear ophthalmoplegia
- motor nucleus and nerve –> ipsilateral CN function loss
what is internuclear ophthalmoplegia?
a disorder of conjugate lateral gaze in which the affected eye shows impairment of adduction
so if the right eye wants to look right, the right CN 6 will activate the LR to do so and at the same time it will send information via the medial longitudinal fasciculus to the contralateral CN 3 to activate the left medial lectus (the MLF is on the same side as CN 3)
if there’s a problem with the MLF, then the left eye will not follow and you’ll have double vision!! the right eye will look right but the left eye will get stuck in the middle and look straight = discordant gaze due to a lesion in the MLF
how can you differentiate between a medial longitudinal fasciculus problem and a CN 3 palsy?
patients with MLF problems can perform convergence, so the medial rectus will activate when doing convergence!
but if they have a CN 3 palsy then they won’t be able to do convergence since the medial rectus is knocked out
so INO patients have preserved convergence
iNO = internuclear ophthalmoplegia
what would happen to the 4 lateral structures of the brainstem if there was a brainstem lesion?
- spinocerebellar –> ipsilateral ataxia because spinocerebellar tract goes to the ipsilateral cerebellum
- spinothalamic –> contralateral pain and temperature sensory loss
- sensory nucleus of CN V –> ipsilateral pain and temperature loss in the face
- sympathetic pathway –> ipsilateral horner’s syndrome
what would happen to the 4 CNs in the medulla if there was a brainstem lesion?
- CN 9 glossopharyngeal –> ipsilateral pharyngeal sensory loss
- CN 10 vagus –> ipsilateral palatal weakness (CN 10 pulls the uvula to the same side so if there’s R sided weakness the uvula will deviate left away from the lesion)
- CN 11 spinal accessory –> ipsilateral shoulder weakness
- CN 12 hypoglossal –> ipsilateral weakness of the tongue (CN 12 pushes the tongue to the opposite side)
what would happen to the 4 CNs in the pons if there was a brainstem lesion?
- CN 5 trigeminal –> ipsilateral facial sensory loss
- CN 6 abducens –> ipsilateral abduction weakness due to lateral rectus weakness
- CN 7 facial –> ipsilateral facial weakness; incomplete eye closure, pulling of the face towards the normal side, loss of naso-labial fold on weak side
- CN 8 vestibulocochlear nerve –> ipsilateral deafness
what is the course of the auditory pathway?
ACS-LIMiT
auditory nerve–> cochlear nucleus –> contralateral superior olivary nucleus –> lateral leminiscus tract –> inferior colliculus –> medial geniculate body –> temporal cortex
M(IC) like microphone because the inferior colliculus is what does sound!
what would happen to the 4 CNs in the midbrain if there was a brainstem lesion?
CN 1 and CN 2 are not in the brainstem
- CN 3 oculomotor –> ipsilateral eye would be turned out and down with ptosis because no levator palpebrae and the superior oblique supplied by CN 4 and lateral rectus supplied by CN 6 would be unopposed; there would also be an absent pupillary reflex
- CN 4 trochlear –> eye unable to look down when looking towards nose because superior oblique isn’t working = no intorsion
how do patients compensate for 4th nerve palsy?
if CN 4 is knocked out, then you can’t do intorsion = look down and in
their eye will be up and out so to compensate the patient will tilt their head opposite to the side of weakness
what are the 3 questions you ask when trying to localize a brainstem lesion?
- does the patient have crossed clinical signals = head/neck signs opposite the trunk and limb –> most likely a brainstem problem if there’s opposite signs
- what is the location on the y axis based on which cranial nerves are involves = medulla, pons or midbrain?
- what is the location on the x axis –> is it on the left or right side of the brainstem; is it a medial or lateral lesion based on which spinal tracts are involved
a 70 year old male with a hypertension suddenly develops:
- left sided ipsilateral ophthalmoplegia
- loss of pupillary light reflex in the left eye
- paralysis of the right arm and leg
what’s wrong?
left medial midbrain lesion = Weber syndrome
- patient has crossed clinical signs = brainstem lesion
- CN 3 is effected with loss of pupillary reflex = midbrain
- left body corticospinal tract is effected = medial
what is Weber syndrome?
a stroke that effects the medial midbrain in the area of the cerebral peduncle/cruz cerebri
this would involve the corticospinal and corticobulbar tracts so you’d have ipsilateral loss of pupillary light reflex and ophthalmoplegia along with contralateral body paralysis
so it’s a stroke characterized by the presence of an ipsilateral oculomotor nerve palsy and contralateral hemiparesis or hemiplegia
patients will also experience UMN cranial nerve motor weakness, exaggerated gag reflex, tongue spasticity (no wasting), and spastic dysarthria from effects on the corticobulbar tract
slide 122
a 70 year old male with hypertension suddenly develops:
- left sided ipsilateral ophthalmoplegia
- right sided proprioception loss
- right sided involuntary movements
what’s wrong?
left medial midbrain lesion = Benedikt’s syndrome
- patient has crossed symptoms = brainstem lesion
- CN 3 is effected with the left ipsilateral ophthalmology = midbrain
- left DCML tract is effect with loss of right proprioception = left, medial located
there is involuntary movements due to the involvement of the red nucleus which is responsible for coordination –> without the red nucleus, you’ll have ataxia and involuntary movements on the contralateral side
what is Benedikt’s syndrome?
stroke of the medial midbrain in the central part that effects the medial lemniscus and red nucleus
it leads to:
- ipsilateral ophthalmoplegia
- contralateral proprioception loss in the body
- involuntary movements
slide 122
what is the difference between Weber’s and Benedikt’s syndrome?
WEBER’S
- CN 3
- corticospinal tract
- corticobulbar tract
- medial midbrain
BENEDIKT’S
- CN 3
- medial lemniscus
- red nucleus
- medial midbrain
even though both are medial midbrain lesions, weber’s has contralateral weakness while benedikts has contralateral sensation loss
what is Parinaud Syndrome?
usually due to a pineal gland tumor in the midbrain or some other dorsal midbrain lesion that effects the superior colliculus and pretectal area
clinical presentation includes:
- patients will be unable to look upwards***
this signifies that the superior colliculus is involved since it controls vertical gaze
- nystagmus when asked to perform convergence and loss of pupillary reflex
- pineal tumor can also cause cerebral aqueduct obstruction which can lead to non-communicating hydrocephalus!
70 year old man presents with:
- left sided weakness
- right eye medial deviation
- right sided facial weakness
right medial pons lesion = Foville syndrome
- patient has crossed signs = brainstem problem
- CN 6 damage: medial deviation indicates they can’t abduct so LR is weak
CN 7: facial weakness
both indicate right pon damage
- medial lesion because CN 6 nucleus is medially located. also there is body weakness which is the corticospinal tract which is medially located too
what is Foville syndrome?
inferior medial pontine stroke that involves the corticospinal tract and potentially also the nuclei of CN 6 and 7
clinical presentation includes:
- contralateral weakness
- ipsilateral medial eye deviation because of CN 6 palsy
- ipsilateral facial weakness
35 year old man presents with:
- double vision with left gaze with normal left eye abduction
- exam shows limited adduction of the right eye with left gaze
- exams shows normal convergence
what’s the problem?
internuclear ophthalmoplegia = medial, right MLF involvement in the pons/midbrain
- no crossed signs, all the signs are in the head and neck
- left eye can abduct but the right eye doesn’t follow = right medial longitudinal fasciculus problem
it’s not a CN 3 problem because there is preserved convergence which means nothing is wrong with the MR of the right eve
60 year old woman presents with:
- left sided ptosis, mitosis, anhidrosis
- left sided ataxia
- uvula deviated to the right
what’s wrong?
left, lateral medullary syndrome = Wallenberg syndrome due to PICA stroke
- left CN 10 problems because the uvula is decimated to the right which indicates left sided CN 10 weakness
- CN 10 = medulla
- left sided ataxia = left lateral lesion because the spinocerebellar tract is involved
- left sided Horner’s syndrome = sympathetic tract = lateral lesion
what is Wallenberg syndrome?
stroke in the lateral medulla usually from a PICA stroke
this would effect the spinocerebellar, spinothalamic, spinal nucleus of V and sympathetic tracts = ataxia and Horner’s syndrome
also CN 9 would be effected so so you’d have horseless and dysphagia
50 year old woman present with:
- left hemiparesis
- left sided loss of proprioception
- right sided tongue deviation
what’s wrong?
right medial medullary syndrome due to stroke in the anterior spinal artery
- crossed signs
- CN 12 is involved with tongue deviation = medulla
- tongue deviates to the right which indicates the right CN 12 is weakened
- left hemiparesis and proprioception loss = right DCML and corticospinal tract problems = medial
what is a Chiari malformation?
sometimes the tonsils of the cerebellum and the medulla can herniate into the spinal cord through the foramen magnum
this results in a blockage of CSF from the 4th ventricle which leads to internal hydrocephalus
this is associated with craniovertebral anomalies or various forms of spina bifida
symptoms are related to pressure on the cerebellum and the medulla which would involve the last 4 cranial nerves:
- dysphagia
- dysarthria
- dizziness
31 Year old man involved in a MVA is found to have dilated and unreactive pupil on left side, along with right arm and leg weakness and irregular breathing. His heart rate is 45/min and blood pressure is 200/90 mmHg. what could be the cause of his symptoms?
left, medial midbrain lesion that is causing Cushing’s triad! this is when increased intracranial pressure causes hypertension, bradycardia and irregular breathing
this is because there is a hemorrhage on the left side of the brain that is causing a transtentorial herniation = the brain is herniating over the tentorium cerebelli and compressing on the brainstem which causes midbrain problems and Cushing’s triad!
- unreactive left pupil = left CN 3 problem = midbrain
- right body weakness = medial lesion involving corticospinal tract
70 year old man presents with:
- left arm resting tremors
- left arm bradykinesia
- rigidity on examination
Parkinson’s
parkinson’s usually effects the midbrain because it’s the substantia nigra in the midbrain that normally secretes dopamine but with Parkinson’s the substantia nigra is destroyed so this isn’t happening and the patient presents with jerky movements and tremors because they can’t initiate fluid movement
treatment is dopamine replacement to counteract lost substantia nigra
what is the side of deviation for the structures associated with CN 5, 7, 10 and 12?
CN 5 pushes jaw to the opposite side –> weakness would cause the jaw to deviate to the weak side
CN 7 pulls the face to the same side –> weakness would cause the face to be pulled to the normal side
CN 10 pulls the uvula to the same side –> weakness would cause the uvula to be pulled to the normal side
CN 12 pushes the tongue to the opposite side –> weakness would cause the tongue to be pushed to the weak side
