Neuro Lect 6
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Pathway in which light impulse travels up the optic nerve, divides at the chasm, and arrives at the pretectal nucleus. Efferent signals sent via CN III causes direct and consensual constriction.
What does the sudden onset of blindness imply?
What does the slow evolution of visual complaints imply?
inflammatory or neoplastic disease
What do transient or recurrent visual symptoms imply?
- myasthenia gravis
What is the term for the inability to maintain a conjugate gaze?
Transient monocular blindness, optic neuritis, and giant cell arteritis are monocular vision disorders affect which cranial nerve?
Monocular vision disorder caused by amaurosis fugax which refers to decreased blood flow to the retinal artery. Causes unilateral loss of vision that resolves within about 20 mins, and presents "like a curtain coming down over one eye".
- transient monocular blindness
- Note: pt must have complete eval for TIA/stroke
Inflammation of the optic nerve most commonly due to MS that causes unilateral vision loss that may improve. Scotomata is noted on the visual field testing. Ophthalmoscopic exam reveals a swollen, blurred optic disc. Pupils are slow to react.
- optic neuritis
- Note: requires immunotherapy (includes steroids)
Inflammation of the external carotid artery at the superficial temporal artery that may extend to the ophthalmic artery and lead to blindness. Presents as tenderness over the temporal artery.
- giant cell arteritis
- Note: dx tests include ESR, artery biopsy; tx with prednisone burst
An afferent pupillary defect caused by a defective sensory system associated with disease of the retina or optic nerve. Causes pupil to dilate when penlight shines on it with a consensual reflex being present in the opposite eye.
marcus gunn pupil ("swinging flashlight test")
Binocular vision disorders due to papilledema, pituitary tumors or occipital cortex lesions affect what cranial nerve?
Binocular vision disorder that is a sign of increased intracranial pressure that requires urgent search for the cause. Presents with additional symptoms of HA, N/V, other neurologic dysfunction, and possible enlargement of a physiologic blind spot as well as CN VI palsy.
Binocular vision disorder caused by a neoplasm that presses on the optic chiasm that gradually causes bitemporal hemianopia. Other presenting symptoms include HA, galactorrhea, amenorrhea, or acromegaly. Best evaluated with MRI.
- pituitary tumor (prolactinoma most common)
- also check prolactin levels
How are pituitary tumors treated?
- surgical excision
- bromocriptine (drug)
What are the effects of a prolactinoma in women?
- menstrual irregularities
- vaginal dryness
- decreased bone density
What are the effects of a prolactinoma in men?
- decreased libido
Binocular vision disorder that can be caused by trauma, tumor, infarction of the posterior cerebral artery and can present with homonymous hemianopia that may be subtle.
occipital cortex lesions
Characterized by diplopia, ptosis, fixed position of eye downward and outward, and dilation of pupil. New onset of this condition with pupillary involvement requires eval to r/o cerebral artery aneurysm (MRI), trauma, meningeal inflammation, tumors or ophthalmoplegic migraine.
CN III palsy ("down and out")
What are the major ddx in an adult with an isolated CN III palsy?
- vasculopathic infarction
- compressive lesion (aneurysm)
- meningeal inflammation
- ophthalmoplegic migraine
Sometimes benign (congenital) asymmetric pupils. However it can be caused by trauma, infection, or any other reason that would make this a new finding in a person.
What is the main distinguishing factor between physiologic aniscoria and pathologic causes?
in physiologic aniscoria the amount of disparity between pupils is the same in the light and dark
Interruption of the cervical sympathetic nerves to the eye that leads to ptosis, meiosis (affected abnormal pupil does not dilate in the dark) and anhydrosis on the involved side of the face.
How is the diagnosis of Horner's syndrome confirmed?
- instill 2 drops of 10% cocaine which blocks the reuptake of norepi at the sympathetic nerve synapse, causing pupillary dilation in eyes with intact sympathetic innervation
- one hour after instillation a normal pupil dilates more than the Horner's pupil which increases aniscoria
- aniscoria >/= 1mm is considered positive
How is preganglionic Horner's syndrome evaluated for?
- imaging (CT/MRI) of neck and chest if brainstem signs are absent
- neuroimaging of the head and brainstem signs are present
How is postganglionic Horner's syndrome evaluated for?
- head and neck MRI
- hagiography if carotid artery dissection is a diagnostic possibility
If there is ptosis of the eyelid on the side of the SMALL pupil, the patient has _________ on that side.
If there is ptosis of the eyelid on the side of the LARGE pupil, the patient has a ________ on that side.
- Horner's syndrome
- partial third nerve lesion
Pupil that accommodates to near vision but does not react to light either directly or consensually. Is associated with CNS syphilis (common outside military) and other conditions such as MS (common everywhere else).
argyll-robertson pupil AKA "the prostitute's pupil" (accommodates but doesn't react)
A tonic pupil with parasympathetic denervation due to damage in the parasympathetic ciliary ganglion, that constricts poorly to light but reacts better to accommodation.
- Adie's pupil
- Note: tonic pupil also demonstrates denervation supersensitivity to low-low pilocarpine by constricting better than the left pupil
Pts present with vertical diplopia (common), is most commonly caused by head trauma. Eye deviates upward and slightly medially. Signature motility dysfunction is a hyper deviation and increases on opposite gaze and ipsilateral head tilt.
- CN VI palsy (superior oblique palsy)
- Note: head may be turned down with the chin depressed, eyes up, and face turned to the side opposite the paresis to diminish diplopia
What are the most common causes for CN VI palsy? What should be assumed as the cause with bilateral CN VI palsy?
- trauma, microvascular disease, basal intracranial neoplasms
- increased intracranial pressure until proven otherwise
6th CN palsy + Horner's syndrome + 3rd CN palsy + 4th CN palsy.
cavernous sinus syndrome
6th CN palsy + facial weakness +/- ipsilateral Horner's syndrome, ipsilateral face hypoalgesia, ipsilateral deafness +/- ipsilateral gaze palsy to the side of the lesion.
pons (ventro-lateral) lesion (Foville syndrome)
6th CN palsy + 7th cranial nerve palsy +/- contralateral loss of touch and proprioception + internuclear ophthalmoplegia with gaze palsy to the side of the 6th nerve palsy due to interruption of connecting fibers to the opposite 3rd nerve nucleus.
pons (paramedian) lesion
6th CN palsy + 7th nerve cranial palsy + contra lateral hemiplegia.
pons (basal) lesion (Millard-Gubler syndrome)
6th CN palsy + 5th CN palsy + 8th CN palsy.
apex of petrous bone pathology (Gradenigo's syndrome)
Microvascular compression of the sensory fibers of the trigeminal root by a blood vessel (usually the superior cerebellar artery). Causes lancinating pain in the distribution of one or more branches of the nerve (lower 2/3 of face), and is triggered by touch, eating or drafts.
CN V (trigeminal neuralgia, AKA tic douloureux)
What are the findings on exam, CT, MRI and/or arteriography for trigeminal neuralgia?
How is trigeminal neuralgia (tic douloureux) treated?
- usually has spontaneous recovery
- options include carbemazepine, phenytoin, baclofen
Thought to be possibly due to reactivation of HSV infection causing unilateral facial paresis. Accompanying symptoms include aural pain, numbness in affected region, auditory hyperacusis and impaired taste on anterior 2/3 of tongue that develop over 1-3 days.
CN VII (idiopathic facial nerve palsy, AKA Bell's palsy)
What is found during physical exam in a patient with Bell's palsy?
- weakness in territory of CN VII
- Note: when forehead muscles are spared, think of a central lesion instead since the forehead gets input from each cerebral hemisphere
How is Bell's palsy treated?
- spontaneous recovery in ~80%
- prednisone burst and taper w/ eye lubrication (may speed recovery)
- acyclovir 400mg po 5x daily for 7 days
- referral to ENT for refractory cases
HSV (re)eruption along CN VII producing facial weakness similar to Bell's palsy. Pts have significant prodrome of pain and vesicular rash (otoscopic shows vesicles in ear). Pts also have decreased hearing on the affected side which can cause nausea and a loss of balance.
What does an MRI and NCV show in a patient with Ramsy-Hunt syndrome? How is it treated?
- MRI: may show inflamed CN VII
- NCV: may show damaged CN VII
- treat with antivirals (acyclovir) and steroids
How is the diagnosis of Ramsay-Hunt syndrome generally determined?
observation of evident facial weakness and vesicular rash
What are the results for the Weber and Rinne tests in a patient with conductive hearing loss (affects external auditory canal/middle ear)?
CN VIII (cochlear portion)
- Weber: lateralizes to side of lesion
- Rinne: BC>AC on side of lesion
What are the results for the Weber and Rinne tests in a patient with sensorineural hearing loss (affects inner ear or CN VIII)?
CN VIII (cochlear portion)
- Weber: lateralizes away from the lesion
- Rinne: AC>BC on side of lesion
A lesion on what cranial nerve causes diminished gag reflex, and disturbed swallowing?
A lesion on what cranial nerve causes the asymmetric rise of the uvula?
A lesion on what cranial nerve causes flaccid paralysis of the tongue with atrophy and speech difficulties?
A lesion on what cranial nerve causes paralysis of the SCM and trapezius muscles?
Injury to this cranial nerve can cause drooping shoulder, muscle atrophy, weakened or limited elevation of the arm/shoulder, shoulder pain and scapula winging.
CN XI (spinal accessory)
What cranial nerve is responsible for somatosensory sensations of taste (hot peppers)?
What cranial nerves are mainly responsible for taste?
CN VII, IX, X
What affect does Bell's palsy have on taste?
loss of taste on anterior 2/3 of tongue
What affect does a lesion on CN IX have on taste?
loss of taste on posterior 1/3 of tongue
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