CN and brain stem reflexes Flashcards
what most commonly causes an impairment in CN 1
mucosal swelling and inflammation during sinusitis or an upper respiratory infection
what can cause a permanent loss of smell
severe head trauma where the olfactory nerve branches are sheared or torn where they pass through the bony cribriform plate
or a tumor near the olfactory lobe at the skull base (i.e. meningioma)
how do you test CN III, IV, VI
pt tracking a target up and down and side to side
what eye movements is the superior oblique responsible for
depresses and abducts the eye and medial rotation
what eye movements is the inferior oblique responsible for
elevates and abducts they eye, and lateral rotation
what eye movements is the superior rectus responsible for
elevates and adducts the eye and medially rotates
what eye movements is the inferior rectus responsible for
depresses and adducts the eye and laterally rotates
if a patient cannot fully elevate the eye which muscles are you concerned are not functioning and how would you differentiated
superior rectus or inferior oblique
if the patient turns his eye inward (adducts) and has weakness then its mainly the inferior oblique
weakness of elevation when the eye is turned outward (abduction) is mainly the superior rectus
if a patient cannot fully depress the eye which muscles are you concerned are not functioning and how would you differentiated
superior oblique or inferior rectus
weakness when eye is turned outward = inferior rectus
weakness when the eye is turned inward = superior oblique
starting with the eye out/abducted which muscle are you testing by having the patient look up
superior rectus
starting with the eye out/abducted which muscle are you testing by having the patient look down
inferior rectus
starting with the eye in/adducted which muscle are you testing by having the patient look down
superior oblique
starting with the eye in/adducted which muscle are you testing by having the patient look up
inferior oblique
what are the signs of a CN III lesion
- complete ipsilateral ptosis (paralysis of leavator palpebrae superioris m)
- eye abducted
- pupil is large and unreactive to light directly and consensually
what are signs of a CN IV lesion
impairment of downward gaze - best seen when the involved eye is in the adducted position
where does CN IV exit the brainstem and what is unique about its pathway
exits the brainstem dorsally and decussates to innervate the contralateral superior oblique m
what does a CN VI lesion affect
the ipsilateral lateral rectus muscle impairing abduction of the affected eyeball
what causes binocular diplopia
the eyeballs are not perfectly aligned in primary position or when conjugately moving to other positions
how can binocular and monocular diplopia be differentiated
covering one eye will correct binocular diplopia
what CN lesions can cause binocular diplopia
CN III, IV, VI (or a lesion of their related muscles)
what is more common binocular or monocular diplopia
binocular - monocular is very rare
what is a nystagmus
repetitive, oscillatory, jerky eye movements
what causes a normal/physiological nystagums
suddenly stopping someone rotating in a chair
what causes an asymmetrical pathologic nystagmus
pathologic nystagmus could be due to a lesion of the vestibular system, brain stem, or cerebellum - all upset normal control or balance on conjugate eye movements (usually asymmetric and position dependent)
what causes a symmetrical pathologic nystagmus
drug toxicity - usually present with all eye movements
what is internuclear opthalmoplegia (INO)
paralysis of extraocular muscles (opthalmoplegia) due to a lesion between the nuclei (internuclear) involved with lateral gaze (oculomotor and abducens nuclei) which interrupts the ascending medial longitudinal fasciculus (MLF)
what syndrome is associated with an internuclear opthalmoplegia
MLF syndrome
describe the path of the MLF
it connects the PPRF (paramedian pontine reticular formation) and the contralateral oculomotor nucleus - it decussates early then rises from the pons to the midbrain
what would a lesion in the left MLF cause
paralysis of adduction of the left eye with nystagmus of the abducting right eye - since the left CN III nucleus never gets the MLF signal causing an impairment in right lateral gaze.
the left medial rectus still functions and both eyes will be able to converge via the near reflex
what are the 2 most common causes of a MLF lesion
young pts - MS
old pts - ischemic infarct
what is the pathway involved in the consensual pupillary response
retinal ganglion cells projecting bilaterally to the pretectal area (rostral to the superior colliculus) which then projects to the Edinger-Westphal nucleus of CN III
describe pupillary direct and consensual response with an optic nerve lesion
when light is shined into the affected eye there is no direct or consensual response
when light is shined in the other eye both pupils respond
describe pupillary direct and consensual response with a CN III lesion
when light is shined in the affected eye there is no direct response but the other eye has a consensual response
when light is shined in the other eye there is a direct response but no consensual response
what causes a relative afferent pupillary defect (RAPD)
a partial optic nerve or retinal lesion
what are the pupillary responses with a RAPD
both pupils may initially constrict to light but after moving the light source from the normal to affected eye there may be dilatation due to the relatively decreased afferent input
what 3 things occur during the near reflex
pupillary constriction, lens accommodation and convergence of the eyes
what is a dissociation of light and near reflexes (light-near dissociation)
when there is disruption of the pupillary light reflex pathway at the pretectal area but the near reflex is preserved
pupils constrict during the near reflex but not to a light stimulus
what are 2 causes of light-near dissociation
dorsal midbrain syndrome and Argyll Robertson pupils in neurosyphilis
what is the dorsal midbrain syndrome
aka Parinaud’s syndrome, classically refers to a pineal tumor compressing the dorsal midbrain but may also occur from an ischemic infarction there
what other deficit may be seen with dorsal midbrain syndrome in addition to light-near dissociation
impairment of upward gaze do to involvement of the midbrain’s centers for vertical gaze
what causes Horner’s syndrome
a lesion disrupting the oculosympathetic pathway
what are the symptoms of Horner’s syndrome
Miosis (constricted pupil), anhidrosis (lack of sweat), and mild ptosis (drooping of eyelid)
where is a lesion in Horner’s syndrome
- lateral medullary infarction aka Wallenberg syndrome (first order neuron)
- tumor of the apex of the lung (2nd order neurons)
- neck trauma (3rd order neuron)
where would you suspect a lesion affecting V1, CN III, CN IV, CN VI
superior orbital fissure or nearby cavernous sinus
what in Trigeminal neuralgia
painful syndrome of irritation or inflammation of one of the trigeminal nerve sensory branches causing it to “short circuit” or “misfire”
what are the symptoms of Trigeminal neuralgia
sharp episodic pain several times daily that may be provoked by talking, chewing or touching the face
no sensory or other CN deficits are found on exam
what causes Trigeminal neuralgia in younger patients
MS lesion at the trigeminal nerve entry regoin into the pons
what causes trigeminal neuralgia in older patients
a trigeminal nerve branch is often compressed by a tortuous or kinked blood vessel (often in the superior cerebellar artery)
this can be surgically repositioned or padded
what are treatments for trigeminal neuralgia
if due to compression - surgery
oral anticonvulsants i.e. carbamazepine, gabapentin or others
what are signs/symptoms of a LMN lesion of the trigeminal motor nerve
atrophy and weakness in the ipsilateral muscles of chewing (the masseter and temporalis) and jaw deviation towards the side of the lesion
what are the signs of an UML of the trigeminal nerve
there is bilateral innervation so no atrophy, weakness or deviation is seen
in a bilateral UMN lesion here there may be hyper-reflexia of the jaw jerk
what is the sign/symptoms of a CN VII lesion at or near the stylomastoid foramen (or a lesion in its nucleus)
severe paralysis of the entire ipsilateral half of the face
impaired taste over the anterior 2/3 of the tongue indicate a lesion where
involving the chorda tympani branch of the facial nerve.
hyperacusis is seen with a lesion involving what
the branch of CN VII that goes to the stapedius muscle
what would symptoms of lesion at the internal auditory meatus or cerebelloponine angle cause
facial weakness
hyperacusis
hearing impairment and tinnitus (involves CN VII and VIII, commonly caused by an acoustic neuroma)
A lesion of CN VII in the pons is likely to also involve what other nerve, causing what sign?
CN VI -causing a weakness of lateral gaze
where is the lesion in Bell’s palsy
its idopathic
what are the symptoms of Bell’s palsy
facial nerve paralysis - may occur suddenly
may have ipsilateral hyperacusis and impaired taste as well
how do yo treat Bell’s palsy
short course of oral corticosteroids and maybe antivirals since it is thought to possibly be due to inflammation of the facial nerve mediated by HSV-1 or other viruses
what is the distribution of weakness for an UMN CN VII lesion
facial paralysis of the lower part of the contralateral face (spares the forehead)
a lesion of what cranial nerves could cause difficulty speaking or swallowing and how could you differentiate clinically?
CN IX or X
gag-reflex or elevation of the palatal arch
how is a gag-reflex interpreted clinically
can try to differentiate between CN IX and X deficits with a gag reflex test- a decreased gag reflex when touching one side of the pharynx suggest a CN X lesion on that side (very difficult to differentiate)
how does a LMN CN X lesion present
impaired speech and swallowing
absent gag-reflex
ipsilateral drooping or sagging of the palatal arch (uvula points toward the normal side)
horse voice
a horse voice could be due to a lesion involving what nerve
X
what is seen with a LMN lesion of CN XI
decreased elevation or shrugging of the shoulder and weakness when turning the head to the opposite side
what does the CN XII innervate
tongue muscles most importantly the genioglossus muscle which protrudes each side of the tongue forward
what clinical sign of a LMN lesion of XII
the protruded tongue will point toward the side of the lesion.
over time there is atrophy and fasiculation and fibrillation of the tongue
what way would the tongue point in an UMN lesion of CNXII
in most patients toward the side of the lesion but in some patients the UMN is controlled by the opposite side
what is a crossed brain stem syndrome
cranial nerve involvement on one side and an adjacent fiber tract lesion creating a sensory or motor deficit on the opposite side of the body
what symptoms would be expected with a right pontine lesion
- LMN paralysis of the right face (CN VII)
* UMN paralysis of the left upper and lower limbs (rt CST)
where could a lesion be located causing deficits of pain and temperature over the left face and right limbs and body
Lesion of the left lateral medulla
Involves the Left descending spinal tract of CN V and the left STT
what is weber syndrome aka
the medial midbrain syndrome
what could cause the medial midbrain syndrome
ischemic infarction from an occluded branch of the posterior cerebral artery
What CNs and tracts are affected in a medial midbrain syndrome
CN III and the cerebral peduncle (CST and corticobulbar tracts)
what are the symptoms of a medial midbrain syndrome
ipsilateral oculomotor nerve lesion and upper motor neuron weakness of the contralateral face and limbs
what is the other name for the lateral medullary syndrome
wallenberg syndrome
what causes a lateral medullary syndrome
ischemic infarction from an occluded vertebral artery or its PICA branch
what are the symptoms of a lateral medullary syndrome
pain and temperature impairment in the ipsilateral face and contralateral limbs and body
others: hoarseness, vertigo, nausea and vomiting, clumsiness
there may be nystagmus, ipsilateral limb dysmetria, ipsilateral Horner’s syndrome and ipsilateral palatal and coal cord paralysis
what is preserved in a lateral medullary syndrome
position sense and strength
