Cranial Nerves: Tutor Information - PowerPoint Presentation

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Cranial Nerves: Tutor Information

PULSE: Preparation for FinalsTutor name

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Resource summary

Common OSCE questions/topicsCase-based additional information (Cases 1 – 3)

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Common questions

Things you might pick up and questions you will get asked…

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What are the names and functions of the cranial nerves?

12 pairs of nerves running directly from the brain

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What are the patterns of visual field loss and where is the lesion?

Monocular visual loss: pre-chiasm

e.g. MS, optic nerve tumour, GCABitemporal hemianopia: at chiasm e.g. pituitary tumour, internal carotid artery aneurysm

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Contralateral

homonomous hemianopia: behind the chiasm

E.g. stroke, tumour, abscessBecomes more congruent as lesion more posteriorUpper quadrantanopia = temporal lobeLower

quadrantanopia

= parietal lobe

Macula sparing

seen in occipital lobe lesions

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What are the muscles and nerves controlling eye movements?

CN3 - SR, IO, MR, IR

CN4 – SOCN6 – LR

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Clinical signs

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What are the causes and patterns of

opthalmoplegia?

CN3 palsy – down and outPartial vs completeCN4 palsy - eye bobs up, may hold head squint (torticollis)

CN6 palsy -

esotropia

E.g. false localising sign

Maximum

separation of the image is in the direction of the affected eye muscle; lateral image is the false one

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Why is the pupil spared in diabetic palsies?

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What is a false localising sign?

A misleading physical sign

e.g. dilated pupil in raised ICP

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What is the differential diagnosis for ptosis?

Unilateral:

CN3 palsy – dilated pupilHorners – contstricted pupilCongenital

Bilateral:

Myaesthenia

Gravis –

fatiguable

Myotonic

Dystrophy

Congenital

Remember ptosis is not a feature of CN7 palsy (

obicularis

oculi problem means can’t close eye)

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What is

intranuclear

ophthalmoplegia and what causes it?A problem with the medial longitudinal fasciculus, which co-ordinates the abduction of CN6 with the adduction of CN3 (i.e. conjugate lateral gaze)

Failure of adduction on eye of affected side

So if right eye affected:

DDx

-

MS

, stroke, Lyme disease, TCAs

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What are the causes of a facial nerve palsy?

LMN: Bells, malignant parotid tumour, Ramsay Hunt, sarcoid, acoustic neuroma, brainstem infarct, DM

UMN: Stroke, tumour

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Why is the forehead spared in UMN lesion?

Due

to bilateral cortical representation, where the upper part of the facial nerve nucleus (not the face itself) has bilateral supply, whereas the lower part has only unilateral supply

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What are

Rinne and Weber tests?

Unlikely you would have to perform this in finals but could certainly get asked about it!Rinne - air v bone conduction at ear

Weber - put tuning fork on forehead

SNACRIP

- in sensorineural loss or normal, air conduction > bone conduction,

Rinne

is positive.

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What is the difference between bulbar and

pseudobulbar palsy?

Both are impaired CN9-12, resulting in unilateral facial paralysis and problems with speechBulbar = LMN. Tongue fasciculates.

Pseudo = UMN. Tongue spastic. Associated with emotional lability.

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What is the differential diagnosis of a cranial nerve palsy?

Common differentials

Vascular – CVA/stroke (ischaemic/haemorrhagic), vasculitis

Inflammatory

– demyelination (MS)

SOL

– tumour, abscess, vascular, oedema, hydrocephalus

Infectious

– viruses (HIV, CMV), bacteria (TB, Lyme, leprosy, syphilis),

protozoal

(toxoplasma)

Mononeuritis multiplex

Metabolic – DM, amyloidosis

Vasculitis – Wegener’s, PAN, SLE, RA

Granulomatous – sarcoid,

lyme

, leprosy

Malignancy – primary or secondary, SOL or paraneoplastic

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Or…

Lesions along the path of the nerve:

Central – within brain/brainstemIntra-cranial – as the nerve passes out from the brain along the vault of the skullThrough the cranium – whichever foramen it pops out ofExtra-cranial – within the soft tissues of the orbit/face/neck/etc

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Causes of cerebellopontine angle lesions?

Neoplastic

Acoustic neuroma (vestibular schwannoma)Meningioma, cholesteatoma, haemangioblastomaPontine gliomaNasopharyngeal carcinomaInfective

Local mengingeal involvement, e.g. TB

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What is Horner’s syndrome?

Horner’s Syndrome

= collection of signs: unilateral pupillary constriction (miosis),

ptosis and

anhydrosis

(i.e. loss of sympathetic pathway on that side).

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What are the causes of Horner’s syndrome?

Hemisphere and brainstem

Massive cerebral infarctionPontine gliomaVascular disease (esp. lateral medullary syndrome – infarction of lateral medulla, due to occlusion of vertebral artery, posterior inferior cerebellar artery, superior, middle or inferior medullary arteries)

‘Coning’ of the temporal lobe

Cervical cord

Syringomyelia

Cord tumours

T1 root

Apical bronchial neoplasm (usually SCC)

Apical TB

Cervical rib

Brachial plexus trauma or tumour

Sympathetic chain in neck

Post thyroid/laryngeal surgery

Malignancy, e.g. thyroid; neoplastic infiltration

Cervical

sympathectomy

Carotid artery

Occlusion/dissection

Pericarotid

tumours (Raeder’s syndrome)

Cluster headache

Miscellaneous

Congenital

Migrainous

neuralgia (usually transient)

Isolated and unknown cause

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What are the causes of ptosis?

Unilateral ptosis

IIIrd nerve palsy – complete ptosis, pupil dilated, eye deviated down and outHorner’s syndrome – partial ptosis, pupil constricted, intact light reaction, eye midline, ?anhydrosis

Congenital/idiopathic

Bilateral ptosis

Myasthenia gravis

Myopathy (e.g. dystrophia myotonica, mitochondrial dystrophy)

Congenital

Syringomyelia (



bilateral Horner’s)

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Case 1: visual field defect

Case 2: facial nerve palsyCase 3: Horners Syndrome