Cranial Nerves, Brain Stem Reflexes, and Brain Stem Disorders

Question 1

CN1 (Olfactory)-what causes impaired smell?

Answer 1

-mucosal swelling and inflammation during sinusitis or an URI

Question 2

what can cause permanent loss of smell

Answer 2

• severe head trauma

- tumor near the olfactory lobe

Question 3

How do you test CN3, 4, and 6?

Answer 3

capital H

Question 4

Clinically, what does the deficit from a complete CN3 lesion look like?

Answer 4

paralysis of the levator palpebrae superioris muscle may cause complete ptosis…pupil of involved eye is large and unreactive to light

Question 5

What is so special about CN4 (trochlear)

Answer 5

only CN that exits the brain stem dorsally and decussates to innervate the contra superior oblique muscle

Question 6

binocular diplopia

Answer 6

• more common type of diplopia and resolves if the pt covers either eye
• can be caused by lesions of CN3,4,6, or their related extraocular muscles.

Question 7

monocular diplopia

Answer 7

• rare, occurs when looking with one eye alone

- 2/2 dislocated lens or detached retina, or psych

Question 8

INO (internuclear ophthalmoplegia)

Answer 8

-paralysis of extraocular muscles (“ophthalmoplegia”) from a lesion between the muclei (“internuclear”) involved with lateral gaze (oculomotor and abducens nuclei)

Question 9

INO interrupts the ascending medial longitudinal fasciculus (MLF)

Answer 9

-most common causes of MLF lesions are multiple sclerosis in younger pts and ischemic infarction in older patients

Question 10

pupillary light reflex

Answer 10

-elicited by shining light into one eye, causing its pupil to constrict (direct response) and also the other eye (consensual response)

Question 11

anatomy of pupillary light reflex

Answer 11

-involves retinal ganglion cells projecting b/l to pretectal area (rostral to superior colliculus) which then projects to EW nucleus of CN3

Question 12

relative afferent pupillary defect (RAPD)

Answer 12

• may occur form partial optic nerve or retinal lesion
• after swinging flashlight test pupillary dilatation occurs b/c of relatively reduced afferent input at the affected eye

Question 13

near reflex

Answer 13

• occurs when viewing a nearby object
• consists of:
• -pupillary constriction
• -lens accommodation (“thickening”)
• -convergence of the eyes

Question 14

light-near dissociation

Answer 14

• selective disruption of pupillary light reflex but connections for near reflex preserved
• -aka dissociation of light and near reflexes
• -pupils only constrict d/r near reflex but not to a light stimulus

Question 15

causes of light-near dissociation

Answer 15

• dorsal midbrain (Parinaud’s) syndrome
  
  • classically 2/2 pineal tumor compressing midbrain
• Argyll Robertson pupils in neurosyphilis

Question 16

Horner’s syndrome

Answer 16

-occurs from a lesion disrupting oculosympathetic pathway (three neurons in series)
-Horny PAM
Ptosis=paralysis of superior tarsal muscle
Anhidrosis=dec sweat on ipsi face b/c sweat glands have sympathetic innervation
Miosis=smaller constricted pupil, dilates poorly in darkness

Question 17

what can sensory deficits not confined to the trigeminal nerve territory be due to?

Answer 17

• lesions in the contra thalamus or parietal lobe

- psych disorders

Question 18

trigeminal neuralgia and MS

Answer 18

-ms lesion at the trigeminal nerve entry region into the pons is often the cause of trigem neuralgia in younger pts

Question 19

trigem neuralgia and older pts

Answer 19

-trigem nerve branch is often compressed by a tortuous or kinked blood vessel (often the superior cerebellar artery)

Question 20

trigem motor

Answer 20

-muscles of chewing or mastication–masseter and temporalis muscles

Question 21

LMN facial paralysis

Answer 21

• involves CN7 and causes a paralysis of the entire ipsi half of the face
• impaired taste over ant 2/3 of tongue indicates that chorda tympani branch of facial nerve is involved
• plus hyperacusis from stapedius muscle denervation

Question 22

lesions at the internal auditory meatus or cerebellopontine angle

Answer 22

• stuff from CN7 and tinnitus

- 2/2 acoustic neuroma (involvement of adjacent CN8)

Question 23

what about a lesion at or near the facial nucleus in the pons?

Answer 23

create ipsi weakness of lateral gaze from involvement of adjacent PPRF and CN6

Question 24

Bell’s palsy

Answer 24

• idiopathic facial nerve paralysis
• may be due to Herpes simplex or other viruses
• hasten recovery with corticosteroids

Question 25

UMN facial paralysis

Answer 25

milder paralysis of only LOWER PART of contra face, SPARING forehead

Question 26

palatal arch test which cranial nerve

Answer 26

pt say “ah”=test vagal nerve function

Question 27

LMN lesion of vagal nerve

Answer 27

• ipsi drooping or sagging of palatal arch with uvula pointing to nml side
• hoarseness from ipsi paralysis of vocal cord muscles

Question 28

LMN lesions of CN12

Answer 28

protruded tongue deviates toward the affected/weak side

-over time affected half of tongue will atrophy and will see fasciculations and fibrillations

Question 29

crossed brain stem syndromes

Answer 29

-consist of CN involvement on one side and an adjacent fiber tract lesions=clinical sensory or motor deficit on the opposite side of the body

Question 30

R. pontine lesion

Answer 30

-involves R. facial nucleus and R. corticospinal tract=LMN paralysis of entire R. half of face AND UMN paralysis of the left upper and lower limbs (left hemiparesis)

Question 31

L. lateral medulla lesion

Answer 31

-involves L. descending spinal tract of CN5 and L. STT=deficits of pain and temp over let face and right limbs and body

Question 32

Weber (medial midbrain) syndrome caused by?

Answer 32

• may be d/t an ischemic infarction from an occluded branch of the posterior cerebral artery
• CN3 and nearby cerebral peduncle (corticospinal and corticobulbar tracts) are involved

Question 33

Wallenberg (lateral medullary) syndrome caused by?

Answer 33

ischemic infarction from occluded vertebral artery or its PICA branch

Question 34

Weber (medial midbrain) syndrome presentation

Answer 34

• –ipsi oculomotor nerve lesion

- –UMN weakness of the contra face and limbs

Question 35

Wallenberg (lateral medullary) syndrome features that make it a crossed brainstem syndrome?

Answer 35

—pain (pinprick) and temp impairment on ipsi face and contra limbs and body
—plus: hoarseness, vertigo, n/v, clumsiness
plus: nystagmus (vestibular nuclei)
:ipsi limb dysmetria (inferior cerebellar peduncle)
:ipsi Horner’s (descending sympathetic tract)
:ipsi palatal and vocal cord paralysis (nucleus ambiguus)