clinical examinationof the cranial nerves

Dr. Craig G. Adams

Dept of Surgery at RMH

The University of Melbourne

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review neuroanatomy

• position of cranial nerve nuclei in the brainstem

• central pathways of CN’s– brainstem; cerebral

peduncles; diencephalon; internal capsule; corona radiata; cerebral cortex

• intracranial & extracerebral course

• exit foramina• extracranial (peripheral)

course

consider:

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introduction to patient • smile, make eye contact and shake

hands

• explain what you are about to do in simple terms

• patient should be seated comfortably in a chair or resting on pillows in bed

• while this is happening take a few seconds to look around the bed and make mental note of any relevant clues or hints … (eg mobility aids, drugs, IV drips, catheter bags, drainage bags, cards/flowers from relatives etc)

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introduction

• methodically & systematically examine each cranial nerve

• from olfactory nerve ---> hypoglossal nerve

• consider fibre types in each cranial nerve:– somatic motor; visceral

motor; special motor; general sensory; special sensory; visceral sensory

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olfactory nerve (CN I)

• olfactory nerve arises in nasal cavity from central processes of bipolar cells in mucosal epithelium

• enters cranial cavity as filaments through cribriform plate of ethmoid bone ---> olfactory bulb on the ventral portion of frontal lobe

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olfactory nerve

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olfactory nerve

• sense of smell is tested in both nostrils separately

• make sure nostrils are clear & not blocked

• use familiar smells (eg coffee, tobacco, peppermint, cloves)

patient in pub brawl - presented with epistaxis ? # nose

special sensory

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olfactory nerve

don’t use pungent or irritating substances like smelling salts or ammonia as they stimulate the sensitive trigeminal nerve endings in the nasal mucosa!

# nasal bones

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loss of smell

causes of anosmia

• colds, allergies, sinusitis, deviated nasal septum

• head injury (with or without # of bone) causing damage to olfactory filaments as they pass through cribriform plate

• tumours such as meningiomas, gliomas, others

• meningitis (acute or chronic)

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anterior cranial fossa #’s

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anterior cranial fossa tumours

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nasal tumours

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severe lacerations/fractures

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warning ...

the next slide contains a most horrible image … deformities of the very worst kind … turn away now if you are squeamish !

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optic nerve (II)

special sensory

• visual acuity (Snellen’s)• visual fields & blind spot

(red hat-pin)• visual attention• optic fundi

(ophthalmoscope)• colour vision (Ishihara)

QuickTime™ and aCinepak decompressor

are needed to see this picture.

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optic nerve

• contains nerve fibres arising from the inner layer of the retina

• proceeding posteriorly to enter the cranial cavity via the optic foramen

• some fibres crossing to the opposite side via the optic chiasm

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oculomotor nerve (III)

• leaves brain on medial side of cerebral peduncle between the posterior cerebral artery & the superior cerebellar artery

• passes anteriorly, lateral to internal carotid artery, through cavernous sinus

• leaves skull through superior orbital fissure

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oculomotor nerve

• orbit– assess for any unusual

prominence of the eye (exophthalmos/proptosis)

• eyelids– the oculomotor nerve

supplies skeletal muscle component of levator palpebrae superioris

(? partial or complete ptosis)

04/11/23 35retro-orbital tumour - most commonly rhabdomyosarcoma

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oculomotor nerve

pupils• parasympathetic fibres

course in the 3rd CN to synapse in the ciliary ganglion --> postganglionic fibres emerge as ciliary nerves and innervate sphincter pupillae

• therefore check pupillary size, shape & symmetry

QuickTime™ and a decompressor

are needed to see this picture.

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oculomotor nervepupillary reflexes• direct/consensual response

– the normal pupil contracts briskly in the eye to which light is directed (direct response)

– and also in the opposite eye (consensual response)

• afferent limb is the optic nerve• efferent limb is the Edinger-

Westphal nucleus & 3rd CN

• accommodation response• normal pupils constrict as the

eyes converge (near response)

QuickTime™ and a decompressor

are needed to see this picture.

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oculomotor nervemotor to 4 EOM’s

(except LR & SO)

• look at position of patient’s eyes at rest and during movement– ? squint/strabismus– ? nystagmus

• test movement in all directions– ? diplopia

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analysis of eye movements

right eye deviated medially--> pull of SO directly down

right eye deviated laterally--> pull of SR directly up!

note: when eyes looking straight ahead (0 deg.) superior & inferior recti contribute mostly to vertical eyeball movement and the obliques to rotation (intortion & extortion) of the eye

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oculomotor nerve lesions• ptosis (partial or complete)

• paralysis (varying degrees) of the extra-ocular muscles it supplies (MR, IR, SR, IO)

• pupil widely dilated (unopposed action of sympathetics on dilator pupillae)

• unreactive to light (disrupted parasympathetics)

patient is being asked to lookstraight ahead

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trochlear nerve (IV)

• motor to superior oblique

• exits brainstem on dorsal surface

• curves around cerebral peduncles

• passes anteriorly through lateral wall of cavernous sinus

• enters orbit via superior orbital fissure

• assess for:– squint/strabismus; diplopia;

nystagmus

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trochlear nerve lesions

• paralysis of superior oblique muscle --> weakness of downward gaze

• resulting in:– vertical diplopia– torsional diplopia– diplopia worse when the

patient is asked to look down & in (as in reading)

patient has been asked to lookdown and to his left

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abducens nerve (VI)

• motor to lateral rectus• emerges from ventral

brainstem in groove b/n pyramid of medulla & caudal pons

• passes through cavernous sinus to exit cranial cavity via superior orbital fissure

• assess for:– squint/strabismus; diplopia;

nystagmus

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abducens nerve lesions

paralysis of abduction (lateral deviation)– because of its long

intracranial course the sixth nerve is often involved secondarily to raised intracranial pressure (the nerve being stretched as it passes over the tip of the petrous temporal bone

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left 6th CN lesion

at risk with deep lacerations/#’s lateral aspect of orbit

this is the result of a MBA (Harley) with no face plate on his helmet

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left 6th CN nerve lesion

patient is looking straight ahead

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left 6th CN nerve lesion

patient is now asked to look to his left ...

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‘blow-out’ fracture of orbit

weakest link is inferiorly

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‘blow-out’ fracture of orbit

patient is trying to look up

soft tissue trapped in maxillary antrum

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Horner’s syndrome

“disruption to the sympathetic supply to the head and neck”

• associated classically with a ‘Pancoast’ tumour of apex lung

• also many other causes …. so be able to trace the course of the sympathetic fibres!

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clinical features - Horner’s

on side of lesion:• partial drooping upper

eyelid• constricted pupil• ‘blood-shot’ eye• warm, red skin• dry face

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trigeminal nerve (V)

• contains large sensory root & smaller motor root

• sensory (semilunar) ganglion near apex of petrous bone in middle cranial fossa– ophthalmic division enters

skull through superior orbital fissure

– maxillary division through foramen rotundum

– mandibular division (joined by motor portion) through foramen ovale

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trigeminal nerve

? motor deficits• motor to muscles of

mastication

? sensory deficits• sensory distribution to entire

face

? alteration in reflexes• corneal reflex (afferent limb)

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muscles of masticationask the patient to bite down hard - look and feel temporalis & masseter contracting!

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sensory distribution

• test response to:– soft touch (cotton wool)

and– pain (‘orange’ stick or new safety pin)

– DO NOT use hypodermic needle!!

• map out any sensory deficit and compare with known territories of the 5th CN

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trigeminal HZV neuralgia

maxillary division ophthalmic division

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corneal reflex

“reflex bilateral tight closure of eyes if object touches cornea”

• afferent limb mediated by ophthalmic division of trigeminal nerve (5th CN)

• efferent limb mediated by facial nerve (7th CN)

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corneal reflex

• test by gently touching centre of cornea with wisp of cotton wool

• look for reflex closing of BOTH eyes and ask patient if it felt uncomfortable!!

make sure you do not accidentally startle patient---> (startle or blink reflex)

try to ‘park’ the cotton wool on the cornea ...if you can ---> this is most abnormal !

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facial nerve (VII)

• emerges from brainstem at the cerebellopontine angle

• leaves cranium through internal acoustic foramen

• exits skull through stylomastoid foramen

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facial nervemotor - muscles facial

expression

– look for facial asymmetry (drooping of angle of mouth, loss of the nasolabial fold, loss of forehead wrinkles)

– test strength of frontalis, orbicularis oculi & orbicularis oris muscles

– ? sparing of upper part of face in UMN lesions

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facial nerve (cont.)

• motor– stapedius, stylohyoid,

posterior belly of digastric– ? hyperacusis

(intensification of loud sounds)

• sensory to posterior aspect EAM (contentious)

• corneal reflex (efferent limb)---> strong bilateral closureof orbicularis oculi

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facial nerve (cont.)

also consider nervus intermedius …

• taste (anterior 2/3rds)

• secreto-motor (parasympathetic)– lacrimal glands– submandibular glands– sublingual glands

“secreto-motor to every gland in the head except for the parotid gland”

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vestibulocochlear nerve (VIII)

acoustic component

• ? tinnitus• simple bedside tests for

hearing • special tests

– Rinne’s– Weber’s

• formal audiometric testing

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Rinne’s test

• activate a tuning fork (with a vibrating frequency of 256 Hz or 512 Hz)

• place it on the mastoid process

• ask patient if they hear the tone

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Rinne’s test

• then hold the tuning fork directly in front of the external auditory meatus

• ask the patient: “does it sound louder in front or behind ?”

• determine if air conduction > bone conduction!

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Weber’s test

• place tuning fork at the vertex of the skull

• ask patient to determine which side sounds louder

• if there is a problem with the middle ear complex, which side will be louder?

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vestibulocochlear nerve

vestibular component

• concerned with posture & equilibrium

• caloric testing ‘COWS’• positional tests

– Hallpike test

• stepping test– Unterberger test

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glossopharyngeal nerve (IX)

sensory fibres

• general sensory– oropharynx– post. 1/3rd tongue– soft palate– tonsils– middle ear

• special sensory– taste posterior 1/3rd

tongue

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glossopharyngeal nerve

sensory fibres

• visceral sensation– blood pressure via

carotid sinus baro- (stretch) receptors

– pO2/pCO2 via carotid body chemoreceptors

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glossopharyngeal nerve

motor fibres

• branchial motor to stylopharyngeus muscle

• visceral motor to parotid gland– parasympathetic secreto-

motor

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glossopharyngeal nerve

reflexes• swallowing reflex

(afferent limb)

• pharyngeal ‘gag’ reflex (afferent limb)

• visceral reflexes– salivary (parotid)

– baroreceptor (carotid sinus)

– chemoreceptor (carotid body)

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pharyngeal ‘gag’ reflex arc

• afferents– glossopharyngeal nerve

(receptors in oropharynx)

• CNS– brainstem (medulla)

• efferents– glossopharyngeal nerve– vagus nerve– accessory nerve (cranial

part)

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pharyngeal ‘gag’ reflexthis reflex is subsumed in the swallowing reflex, being elicited by momentary & artificial

stimulation of the oropharynx (in contrast with food or drink which produce sustained, familiar stimulation)

• gently touch posterior oropharynx with sterile swab

• look for abnormal deviation away from side of lesion

the two key features are:

• inhibition of respiration

• raising of soft palate

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vagus nerve (X)

sensory branches• meningeal branch

– dura

• auricular branch– to EAC

• pharyngeal branch– to soft palate

• superior laryngeal nerve– internal & external brs

• recurrent laryngeal nerve

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vagus nerve

sensory branches (cont.)

• visceral branches– aortic arch baroreceptors – heart– lungs– abdominal organs

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cranial accessory nerve (XI)

motor• functionally the motor part of the

vagus nerve– to muscles of pharynx & larynx

• same named branches as for the vagus

• test by:– assessing speech (laryngeal

muscles) & swallowing (efferent limb pharyngeal mm)

– looking at position of uvula at rest and with elevation on saying “Ahh”

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spinal accessory nerve

motor

• trapezius muscle

• sternocleidomastoid muscle (SCM)

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hypoglossal nerve (XII)

motor

• look for fasciculations & wasting (with tongue at rest)

• look for deviation on protrusion

• test strength on both sides, assess for paresis/paralysis

forward pull of genioglossus deviatestongue towards the side of a unilateralhypoglossal lesion

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this patient has a unilateral CN XII lesion and is attempting to poke his tongue straight out … which side is the lesion ?

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this patient is also attempting to poke her tongue straight out … the camera has‘freeze framed’ fasciculations on the effected right side

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ventral surface of tongue

veinlingual frenulum

papilla

submandibularduct

‘tongue deviates to side of lesion’ … verify by visualizing (in 3D) the attachments & action of both genioglossus muscles

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references

• Introductory Neuroscience• Professor J.G. McLeod• Professor J.W. Lance

• Essential Neurosurgery• Professor Andrew H. Kaye• Professor Stephen Davis

• clinical anatomy/surgery lecture notes• Dr Craig G. Adams

http://www.surgeryrmh.unimelb.edu.au