Cranial Nerves I, II, V, VII

CN I: The Olfactory Nerve

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•First cranial nerve

•Unique - Constituting the only examples of neuronal regeneration in humans

- The olfactory cells = Receptor cells = Bipolar neurons

- Olfactory impulses reach the cerebral cortex without relay through the thalamus

The primary olfactory cortex=medial and cortical nuclei of the amygdaloid complex and the prepiriform area

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Connected with the neighboring entorhinal cortex and medial dorsal nucleus of the talamus

•To be perceived as an odor, an inhaled sustance must be volatile

Disturbances of olfaction

1. Quantitative abnormalities: anosmia, hyposmia, hyperosmia

2. Qualitative abnormalities: distortions or illusions of smell – dysosmia or parosmia

3. Olfactory halucinations

4. Olfactory agnosia

Anosmia

•If unilateral – usually not recognized by the patient

•Categories –

Nasal: odorants do not reach the olfactory receptors - hypertrophy and hyperemia of the nasal mucosa (heavy smoking, chronic rhinitis and sinusitis)

- Neuroepithelial: destruction of receptors or their axon filaments – influenza, herpes simplex, hepatitis virus infections; local radiation therapy; esthesioneuroblastoma; Kallman syndrome; toxic agents (benzen); head injury

- Central: olfactory pathway lesions, head injury, tumors, aneurysms

The Foster Kennedy syndrome

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•A meningioma of the olfactory groove may implicate the olfactory bulb and tract and may extend posteriorly to involve the optic nerve

•Clinical - ipsilateral: anosmia and optic atrophy

- Opposite site: papilledema

Anosmia or hyposmia in Parkinson disease and Multiple sclerosis – for reasons that are quite unclear

Hyperosmia

•Migraine attacks, aura in epilepsy, neurotic individuals

Dysosmia or Parosmia

•Pervertion of the sense of smell - in local nasopharingeal conditions such as empyema of the nasal sinuses – ex: cacosmia and cacogeuzia in ozena

- In middle-aged and elderly persons with depression

Olfactory halucinations

•Are always of central origin

•Episodic – in temporal lobe seizures or as aura in epilepsy

•In combinations with delusions – in psychiatric illnesses (endogenous in depression and exogenous in schizophrenia) or in dementia

•In alcohol withdrawal syndrome

Olfactory agnosia

•The primary perceptual aspects of olfaction are intact, but the capacity to distinguish between odors and the recognition is impared or lost

•Is most likely due to lesions in the medial dorsal nucleus of the thalamus

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•Characterize patients the alcoholic form of Korsakoff psychosis

CN II: The Optic Nerve

•The second cranial nerve

•The photoreceptors are the rod cells and the cones cells

•The bipolar cells = the first neuron

•The ganglionic cells = the second neuron

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The axons traverse the optic disc→the optic nerve; the nasal fibers cross in the optic chiasm→optic tract → lateral geniculate body (the third neuron) → visual radiations → visual striate cortex

•Pupillary fibers → optic nerve → optic tract → terminate in the pretectum and both Edinger-Westphal nuclei which subserve puppilary constriction

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Abnormalities of vision

1. Reduced or loss of vision

2. Visual field defects

3. Positive sensory visual experiences

4. Abnormalities of colour vision

5. Visual agnosia

6. Visual halucinations

The diagnosis is based on:

- the historical data (age of the patient at the time of onset, mode of onset, evolution)

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- the topography of the lesion

Optic nerve examination involves:

•Test of visual acuity

•Examination of the visual field

•FO exam

A. Transient monocular blindness

-Amaurosis fugax (TIA)

-Migraine

B. Irreversible monocular blindness – acute onset

-Ocular pathology

-Vascular occlusion

-Ischemic optic neuropathy

-Leber neuropathy

C. Progressive (evolves over hours-several days) impairment of visual acuity

-Typical/atipical optical neuropathies: granulomatous, parainfectious, imune

D. Progressive (evolves over days-months) impairment of visual acuity

-Compressive and infiltrative neuropathies

-Chronic inflamatory diseases

-Heredo-familial neuropathies

Abnormalities of the optic nerve

•Can be inspected only in the optic nerve head → may reflect:

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-The presence of raised intracranial pressure - papilledema

-Optic neuritis – papillitis

-Infarction of the optic nerve head – disc edema

-Congenital defects of the optic nerve – colobomas

-hypoplasia and atrophy of the optic nerve

-glaucoma

Papilledema

•Has a great neurologycal significance → increased intracranial pressure

•Steps of evolution:

1. Blurring and slight elevation of the disc especially of the superior and inferior margins ≠ hypermetropia

2. Disappearance pulsations of the retinal veins

3. Mushrooming of the entire disc and surrounding retina with edema and obscuration of vessels at the disc margins and peripapillary hemorrhages

4. When advanced, papilledema is almost always bilateral

5. as it becomes chronic, elevation of the disc margin becomes less prominent and pallor of the optic nerve head more evident→optic atropy

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•Acute papilledema does not affect visual acuity except during waves of greatly increased pressure

Differential diagnosis:

-papillitis (severly reduced vision)

-infarction of the nerve head (severe loss of vision; extension of the swelling beyond the nerve head)

•Papilledema without raised intracranial pressure may occure in children with cyanotic congenital heart diseases and polycythemya

Main causes of unilateral and bilateral optic neuropathy

I. Demyelinative (optic neuritis)

-Multiple sclerosis, Devic

-Postinfectious and viral neuroretinitis

II. Ischemic

-Arterioslerotic

-Granulomatous (giant cell) arteritis

-Syphilitic arteritis

III. Parainfectious

-Cavernous sinus thrombosis

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-Paranasal sinus infection

IV. Toxins and drugs

-Methanol, ethambutol, chloroquine, streptomicin, ergot

V. Deficiency states

-B 12

-Thiamine (tobacco-alcohol amblyopia)

VI. Heredofamilial and developmental

-Leber optic atrophy

VII. Compressive and infiltrative

-Meningioma of sphenoid wing or olfactory roove

-Metastasis to optic nerve or chiasm

-Glioma of optic nerve (neurofibromatosis type I)

-Optic atrophy following long standing papilledema

-Thyroid ophtalmopathy

-Sarcoid

-Wegener granulomatosis

-Lymphoma and leukemia

Papillitis and the Syndrome of Retrobulbar Neuropathy (Optic Neuritics)

•Clinical – acute impairment in vision in one or both eyes (the eyes may be affected either simultaneously of succesively)

- scotoma

- Impairment of color vision

- Pain on movement and tenderness on presure of the globe

- The pupil on the affected side- mute response to direct light

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FO exam – swelling of the optic disc; the disc margins are elevated, blurred and rarely surrounder by hemorrhages

PEV – modified

•CSF may be normal or may contain 10-100 Lf, ↑ protein, ↑ γ-globulin, oligoclonal bands

•Recovery in 2-6 weeks; vision returns to normal in more than 2/3 of cases

•Demyelinative disease is the most common cause of unilateral retrobulbar neuritis→check-up for MS

Ischemic Optic Neuropathy

•In persons over 50 years of age is the most common cause of persistent monocular loss of vision

Clinical

- abrupt onset

- Painless

- Visual field defect is often altitudinal and involves the area of central fixation, accounting for the severe loss of acuity

- 1/3 cases bilateral affection (HTA, DZ)

FO exam – swelling of the optic disc and beyond the disc margin small, flamed-shaped hemorrhages

Pathogenesis – ischemia in the posterior ciliary artery circulation; in cranial or giant-cell arteritis; may complicate intraocular surgery of severe blood loss or other type of ischemia and hypotension

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Toxic and nutrition optic neuropathies

Clinical - impairment of vision in the two eyes evolves over several days or a week or two

- centrocecal scotomas

•Ex: tobbaco-alcohol amblyopia or B 12 deficiency

Heredofamilial neuropathies

•Hereditary Optic Atrophy of Leber = mitochondrial disease

Age of onset – 20-30 years

Clinical - acute onset amblyopia

- After weeks and months the second eye is affected

- Central vision is affected before peripheral vision

- Painless

- The vision loss is irreversible

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Lesions of the Chiasm, Optic tract and Geniculocalcarine Pathway

•Generates hemianopia (hemianopsia) = blindness in half of the visual field

a. Lesions in the chiasm→bitemporal hemianopia: extrasellar extension of a tumor of the pituitary gland, craniopharyngioma, sacular aneurysm of the circle of Willis

→binasal hemianopia: arachnoiditis

b. Lesions in the optic tract→incongruous homonymous hemianopia + RFM absent

c. Lesions in the visual radiations→homonymous quadran anopia

d. Lesions in the visual cortex→congruous homonimous hemianopia

e. Lesions of both occipital lobes→cortical ambliopia →below or above the calcarine sulcus→homonimous altitudinal hemianopia

Visual Agnosia

•Disturbance of central origin; pacients cannot understand the meaning of what they see

Positive sensory visual experiences

•Phosphenes (flashes of light and colored spots in the absence of luminous stimuli)

-occur in migraine, epilepsy

•Visual halllucinations

-simple and unformed in epilepsy

-complex or formed (people, animals) – in the withdrawal state following chronic intoxication with alcohol, in Alzheimer disease, diseases of occipito-parietal or occipito-temporal lesions

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CN V: The Trigeminal Nerve

•The fifth cranial nerve; is a mixt, sensory and motor nerve

•It conducts sensory impulses from the greater part of the face and head; from the mucous membranes of the nose, mouth and paranasal sinuses; from the cornea and conjunctiva; it also inervates the dura of the anterior and middle cranial fossae

•The motor portion of the fifth nerve supplies the masseter and pterygoid muscles

•To exam the fifth nerve you must check-up:

-the sensibility in the oftalmic, maxilar and mandibular teritory

-movements of the mandibula against opposition (the motor fibers are seldom affected; a motor deficit is observed in pseudobulbar palsy)

-brainstem reflexes: corneal reflex, jaw jerk

•Because of their wide anatomic distribution, complete interruption of both the motor and sensory fibers is rarely observed

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Trigeminal neuralgia

A. Idiopatic – mean age of onset is 52-58 years

=Tic Douloureux=paroxysms of intense, stabbing pain

- in the distribution of the mandibular and maxilary divisions

- the pain seldom lasts more than a few seconds and recur frequently

- is so intense that the patient involuntarly winces

- initiated by stimulation of certain areas of the face, lips or gums as in shaving or brushing the teeth or by chewing, talking or yawning=trigger zones

- the clinical exam is normal

- the mechanism of paroxismal pain is in the nature of allodynia

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- Differential diagnosis:

A) Other forms of facial and cefalic neuralgia and pain arising from diseases of the jaw, teeth or sinuses

B) Symptomatic forms

- Is important to have a MRI-may reveal a possible cause-in the elderly vascular compression of the trigeminal ganglion

- Prognosis – most patients can be treated effectively medicaly

Treatment:

1. Medications used: anticonvulsant drugs-carbamazepine 600-1200 mg/day, phenytoin, clonazepam, sodium valproate, gabapentin, lamotrigine

2. Surgical options: radiofrequency thermocoagulation, microvascular decompression, stereotactic radiosurgery

B. Symptomatic - mean age of onset is 30-35 years, caused by trauma, vascular, neoplastic and demyelinative diseases

•the branches of the trigeminal nerve can be affected in: -inflamatory and infectious diseases: HSV infection, HZV infection, middle ear infections, osteomyelitis of the apex of the petrous bone, LES, Sjögren syndrome

-demyelinative diseases: Multiple sclerosis, especially in young patients

-trauma

-vascular diseases: aneurysmal dilatation of the basilar artery or an arteriovenous malformation

-neoplasia: the trieminal root can be compressed or invaded by intracranial meningiomas, acoustic neuromas, trigeminal neuromas; in elderly-infiltrative glioma of the brainstem; can be the first sign of metastatic diseases especially from carcinoma of the brest and prostate and multiple myeloma

In rare cases trigeminal neuralgia is preceded or accompanied by hemifacial spasm, a combination that Cushing called tic convulsif

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CN VII: The Facial Nerve

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The facial nerve (cranial nerve VII) carries motor, secretory, and afferent fibers from the anterior two thirds of the tongue.

•It originates in the facial nucleus, which is located at the caudal pontine area.

•Corticobulbar fibers from the precentral gyrus (frontal lobe) project to the facial nucleus, with most crossing to the contralateral side. As a result, crossed and uncrossed fibers are found in the nucleus.

•Moreover, the facial nucleus can be divided into two parts:

(1) The upper part, which receives corticobulbar projections bilaterally and later courses to the upper parts of the face, including the forehead, and

(2) The lower part, the predominantly crossed projections of which supply innervation to lower facial muscles (stylohyoid; posterior belly of digastric, buccinator, and platysma).

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The nervus intermedius

Conveys:

(1) Afferent taste fibers from the chorda tympani nerve, which come from the anterior two thirds of the tongue;

(2) taste fibers from the soft palate via the palatine and greater petrosal nerves;

(3) Preganglionic parasympathetic innervation to the submandibular, sublingual, and lacrimal glands.

•The fibers for taste originate in the nucleus of the tractus solitarius (NTS), and the fibers to the lacrimal, nasal, palatal mucus, and submandibular glands originate in the superior salivatory nucleus. Fibers to the lacrimal gland are carried with the greater superficial petrosal nerve until it exits the skull, at which point the fibers branch off as the Vidian nerve.

(4) The nervus intermedius also has a small cutaneous sensory component from afferent fibers originating from the skin of the auricle and postauricular area

•Is the seventh cranial nerve; is a mixt, mainly motor nerve→supplies all the muscles corcerned with facial expression on one side

→sensory component is small (the anterior wall of the external auditory canal)

→convase taste sensation of the 2/3 anterior of the tongue

→secretomotor fibers innervate the lacrimal gland, sublingual and submaxilary glands

•The exam of the facial nerve:

-exam of facial movements

-exam of the sensibility

-exam of the taste and the lacrimal gland, sublingual and submaxilary glands

-brainstem reflexes (corneal reflex)

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Facial Palsy

A. Supranuclear type

- It manifests only in the lower part of the face, since the upper facial muscles receive upper motor neuron innervation from the motor cortex of the both hemispheres

B. Peripheral type

- The skin folds are effased

- The forehead is unfurrowed

- The palpebral fissure is widened

- The eyelids will not close – when attempted both eyes roll upward

- The tears spill over the cheek

- The salyva may dribble from the corner of the mouth

Ethiology:

Idiopatic=Bell‘s Palsy

-the most common disease of the facial nerve

-occurs in all ages

-the onset is acute, ½ attain maximum paralysis in 48 hours

-pain behind the ear may precede the paralysis by a day or 2 +/- impairment of taste and hyperacusis or distortion of sound in the ipsilateral ear (paralysis of the stapedius muscle)

MRI: gadolinium enhanced of the facial nerve

CSF: ↑ Lf, mononuclear cells; important for diffential diagnosis of GB syndrome and Lyme disease

Prognostic: 80% recover in a few weeks, recovery of taste preccedes recovery of motor function; early recovery of the motor function in the first 5-7 days is the favorable prognostic sign - ! EMG

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Treatment: prednisone 40-60 mg/day during the first week to 10 days + vitamins + massage of the weakened muscles + protection of the eye during sleep +/- surgical lid closure +/- acyclovir

Secondary:

-inflamatory and infectious diseases: Lyme disease, HIV infection, TBC, HZV infection (Ramsey Hunt syndrome), otitis media

-neoplasia: tumors that invade the temporal bone tumors of the ponto-cerebelar angle: acustic neuromas, neurofibromas

-trauma: fracture of the temporal bone, middle ear surgery

-aneurysmal dilatation of the vertebral or basilar artery

*intranevraxial lesions may be (( vascular \ demyelinative \ neoplastic )) Millard-Gubler Syndrome \ Foville Syndrome

! Bilateral Bell‘s palsy is most often manifestation of the GB syndrome, Lyme disease, HIV, sarcoidosis

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