Aims_and_Objectives

Aim:           To be familiar with the general principles of a cranial nerve assessment.

 Objectives:  

  • To understand the applied anatomy of a cranial nerve examination
  • To be able to perform a basic cranial nerve assessment.

Theory_and_background

Cranial nerve assessment is a sequence of neurological examinations with some tests being simple to perform and others not so. The tests themselves yield a lot of information ranging from vestibulocochlear function to eye sight and whether the patient can swallow.

It may seem daunting, but with practise and knowledge of the underlying anatomy & physiology the tests and their interpretation can be learned.

The nerves arise in pairs and are numbered anteriorly too posteriorly. 10 out of the 12 directly arise from the brain stem. The 1st two pairs arise from the cerebrum

For numbering purposes the convention is to use the Roman numeral system when designating the nerves.

I         Olfactory

II        Optic

III       Oculomotor

IV      Trochlear

V       Trigeminal

VI      Abducens

VII     Facial

VIII    Acoustic (auditory & vestibular)

IX      Glossopharyngeal

X       Vagus

XI      Accessory

XII     Hypoglossal

Mnemonic for the cranial nerves

  • On
  • Our
  • Outing
  • To
  • The
  • Airport
  • Fatty
  • Arbuckle
  • Gave
  • Vicky
  • A
  • Hamburger

Patient safety

Examination

1st (Olfactory) nerve

This nerve is responsible for the sense of smell. A sense of smell may be lost as a result of

  • trauma
  • infection
  • ageing

Smell is an important component of the appreciation of taste (which may be the principal complaint of a patient). A crude bedside test may be to identify the odour of coffee or fresh orange.

1st (Olfactory) nerve – formal test

Test one nostril at a time – occlude the other and use a couple of test smells.

Ask the patient to sniff and signal detection

  • Prompt response needed, or smell may spread to the other nostril
  • Few can identify the classic test smells
    • Exclude misinterpretation / malingering

Remember ammonia is detected through nasal pain fibres, patients should still taste sugar, salt, vinegar, quinine.

The 2nd (Optic) nerve

Various tests are possible which depend to some extent (though not exclusively) on the integrity of the optic nerve(s)

These include

  • ophthalmoscopy (see separate study guide)
  • pupillary reflexes
  • visual acuity
  • visual fields
  • blind spots

The pupils – inspection

  1. Size and shape
  2. Regularity in outline and equality of both sides
  3. Defects in the iris
  4. Foreign bodies in anterior chamber
  5. Obvious cataract

Pupillary light reflexes (2)

Shield the non-examined eye. Move the light beam abruptly in from the side, or switch on from the front

A direct reflex – ipsilateral pupil constricts

A consensual reflex – contralateral pupil constricts

Accommodation

To test for accommodation, the patient fixes on a distant object. The patient is then asked to look at a close object ideally placed 10cm in front of their nose.

The patient’s eyes should converge and pupils constrict

Documenting P.E.R.L.A.

The acronym P.E.R.L.A. is used to both help remind us what tests we should do and for documentation purposes.

  • Pupils
  • Equal and
  • Reactive to
  • Light and
  • Accommodation

When documenting, it is permissible to write PERLA this signifies that it was checked and is ok.

If there was a problem then you should document in full what the problem was.

Visual acuity measurement – Snellen Chart

There are a series of different sized letters on the chart.

Viewed at 6 metres (half sized charts are viewed at 3 metres)

Above or below each line is a number that represents in metres the distance from which that size letter would be visible in someone with normal eyesight.

  • Ask the patient to cover each eye in turn and determine the smallest print size that can be read
  • Record separately for each eye e.g. R = 6/6 L = 6/5.
  • For short-sighted patients their glasses should be worn, but if not available reading through a pin-hole will help to compensate.
  • For patient unable to read the 60 print size, move them nearer to the chart (e.g. 3 metres) and record acuity as 3/xx.
  • For patients unable to read the chart as close as 1 metre record acuity as:

CF = Count fingers   (Hold hand 0.5 of a metre from the patient)

HM = Hand movement

PL = Perceives light

NPL = No perception of light

  • For children and illiterate patients there are charts showing shapes rather than letters.

Visual field testing

The “bedside” test: face the patient at a distance of about 1 metre. Keep patient’s visual background uncluttered, with light behind patient.

To test the right eye

Close or cover your right eye. Say “cover your left eye and look at my left eye”. This matches the visual fields

Visual field testing

Ensure patient doesn’t look away from your eye

Keeping in a plane midway between you and the patient, bring a white pin head from the extreme of vision (arm’s length) in towards the midline. Test each quadrant using diagonal track bisecting the quadrant. Establish rough boundary then define with slower target movements (see Fig. 1-4)

Visual field testing

  • Ask the patient to indicate when they first appreciate the white ball entering their visual field.
  • Compare this to your own detection.
  • Produce a more detailed “map” of a defect by increasing the number of spokes used.
  • The field is limited superiorly by the supra-orbital ridge and medially by the nose.
  • Any defect should be assessed formally.

Blind spot & scotoma

  • Sit opposite the patient at the same eye level.
  • Compare your right eye with the patient’s left eye and vice versa closing one eye at a time
  • Using a 1cm red pin if available, move the pin slowly from the midline outwards
  • Ask the patient to report any distortion or disappearance of the pin.
  • The pin may disappear and reappear due to the blind spot

Sit approx 1 metre apart

Eye movements (3rd, 4th & 6th)

The arrows indicate the direction of movement of the eyes and not necessarily the position of the muscles.

Muscle nerve links

A way to remember which muscle is controlled by which nerve is LR6 SO4 & EE3.

  • LR6 Lateral rectus muscle is controlled by the 6th nerve. Abducens.
  • SO4 Superior oblique muscle is controlled by the 4th nerve. Trochlear.
  • EE6 Everything else is controlled by the 3rd nerve. Oculomotor

Rectus muscle

Improveeyesighthq ©

Testing eye movements

Hold a pen or similar object 50 cm from the patient in the midline and on a level with the patient’s eyes

Ask patient to follow object (“with their eyes”), keeping their head still, and to report any double vision (diplopia)

Move the object slowly

Side to side, up and down centrally, then at extremes of lateral gaze

Eye movements

Observe

  • range of movement
  • smoothness and speed
  • whether conjugate (moving together)
  • nystagmus (see 8th nerve for details)

Are there any obvious dysconjugate eye movements

  • Is there double vision?
  • If present, establish which muscle(s) affected
  • If not, test for latent squint (to be covered in 2nd year)

Diplopia

If the patient reports diplopia, remember:

  • False image is from the affected eye
  • Outer image is the false one
  • Double vision is maximal in the direction of gaze of the affected muscle

Diplopia – which eye and muscle

For each direction of gaze with diplopia

  • Establish position where images are widest apart
  • Cover each eye in turn and confirm binocular diplopia (present only with both eyes looking).
  • Cover one eye and if outer image disappears that eye and the muscle turning it that way are the abnormal ones.
  • Cross-check by covering the other eye. Inner image should disappear.

  • Test light touch with cotton wool
  • For pain use sharp end of a neuro tip
  • Use the blunt end to act as a discriminator if the patient is unable to readily sense pain
  • Compare sides

Corneal reflex

  • Sensation – trigeminal nerve
  • Motor – facial nerve
  • Twist a wisp of cotton wool to a point.
  • Ask the patient to look up and in
  • Touch the lateral cornea
  • Both eyes should blink
  • Be careful to touch the peripheral cornea and not the conjunctiva
  • Avoid the central cornea.
  • Don’t drag the cotton across the cornea

Unlikely to work on people who wear contact lenses

Testing 5th nerve motor function

Place your fingers on masseter muscles first. Ask patient to clench teeth and you feel masseter and temporalis contracting.

Ask patient to open mouth to left, and stop you trying to push the open jaw back to midline. Repeat for right side. Testing power of lateral and medial pterygoids.

Jaw jerk

  • ask the patient to open their mouth slightly
  • place a finger on the chin
  • percuss the finger
  • observe and feel jaw movement

 

 

 

 

 

 

 

Testing the jaw reflex

The 7th (Facial ) nerve

The facial nerve supplies;

  • Muscles of facial expression
  • Stapedius muscle
  • Sensation including taste to the anterior 2/3rds of the tongue
  • Parasympathetic fibres to the lacrimal gland
  • The right facial nerve supplies motor function to the left facial muscles (contralateral / opposite) as well as the right (ipsilateral / same side forehead muscles)
  • Therefore the fore head is innervated with both left and right facial nerves

Tests of facial nerve function

Ask person to:

  • Show their teeth
  • Purse their lips
  • Blow out their cheeks
  • Close their eyes tight shut
  • Open their eyes as wide as they can

Tests of facial nerve power

  • With eyes tight shut
    • Attempt to gently pull the eyelids apart
  • With eye brows raised
    • Attempt to pull the eyebrows downwards
  • With their lips pursed
    • Attempt to pull their lips apart
  • With cheeks blown out
    • Press against their cheeks to assess strength

The 8th (Acoustic) nerve

The 8th nerve has 2 functions

Auditory – hearing

Vestibular – balance

Tests of auditory function

  • Test each ear, one at a time
  • Block the opposite ear
  • Use a watch or rubbing fingers together (in a quiet environment), judge how far away the sound can be detected
  • If impaired in either ear perform Rinne’s and Weber’s test

 

Rinne’s test – method 1

  • Use a 512 Hz tuning fork, set it vibrating by gently tapping on your knee
  • Place on mastoid process (bone conduction)
  • Ask the person to tell you when they can no longer “hear” the sound
  • Then place fork in front of ear directly over the auditory meatus (air conduction)
  • Ask the patient again if they can hear the sound (normally louder as air conduction is better than bone conduction)

Interpretation of Rinne’s (Method 1)

In normal hearing the sound will be heard better when the tuning fork is placed in front of the ear

In conductive deafness (the sounds cannot conduct from the external to the inner ear) the sound will not be heard when the tuning fork is placed in front of the ear

In partial sensorineural deafness (due to damage to the cochlea, auditory nerve or auditory centres of the brain) the sound may be heard when the tuning fork is placed in front of the ear (but at a higher pitch normal hearing).

In complete sensorineural deafness no sound will be heard when the tuning for is placed in either position. (Although there are exceptions to this)

Rinne’s method 2

Alternatively

  • Place base of tuning fork on mastoid process
  • Confirm it can be heard
  • Then immediately place prongs in front of external auditory meatus
  • Ask patient which is louder – “behind the ear or in front?

Interpretation of Rinne’s (method 2)

  • Hold the base of the 512 Hz tuning fork on the vertex of the patient’s head.
  • Ask which ear seems to hear it louder.

Weber’s test

  • In normal hearing the sound is equal in both ears
  • In conductive deafness then the sound will be loudest in the affected ear (as all external sound is removed and effected ear picks up the vibrating sound more acutely)
  • In sensorineural deafness all sounds are diminished or absent.

Interpretation of Weber’s

  • In normal hearing the sound is loudest when the tuning fork is placed in front of the ear
  • In conductive deafness the sound is loudest on the mastoid process
  • In partial sensorineural deafness the sound is loudest when the tuning fork is placed in front of the ear (but at a higher pitch than in normal hearing).
  • In complete sensorineural deafness no sound will be heard at the mastoid process or in front of the ear.

Interpreting hearing tests (an overview)

  • Loss of hearing may be conductive (transmission of sound to the nerves involved with hearing fails.
  • Sensorineural deafness reflects disorders of the nerve tissues.

Vestibular function of the 8th nerve

Gait

  • Ask the patient to walk heel to toe.
  • Gait veers to the affected side and is unsteady. (Ipsilateral)
  • Usually worse with eyes closed.

Nystagmus

  • Involuntary rhythmic eye movements.
  • Peripheral, central vestibular or arising from the cerebellum.
    • Tested during eye movement assessment.
      • Look in the central position
      • Look during up, down & lateral movement
      • Hold the target steady at the limit of binocular vision in each direction.

Care: Normal people may have a few jerky eye movements at extreme lateral gaze, especially if the target is outside the field of binocular vision – ensure it is visible to both eyes.

Nystagmus types

The eyes may move in the following ways:

  • May be rotary or linear
  • Jerk – slow drift of eye position in one direction with a fast correction in the opposite direction.
    • Nystagmus direction is that of fast phase
  • Pendular – oscillations roughly equal in both directions.
  • May be caused by: (this list is not exhaustive)
    • Stroke
    • Certain medications
    • Excessive alcohol consumption
    • Head injury or trauma
    • Disease of the eye or inner ear

Points to note if nystagmus is present

  • Position of the eye and gaze direction when nystagmus occurs
  • Direction of the fast movement and plane – horizontal, vertical & rotary.
  • Is the abducting eye affected more than the adducting eye?
  • Does it occur in both directions of gaze?
  • Typical description – “linear nystagmus, fast phase to the left and in both eyes on a left lateral gaze”.

9th (Glossopharyngeal) nerve

Sensory

  • Posterior 1/3rd of the tongue, the pharynx & middle ear.

Motor

  • Stylopharyngeus

Autonomic

  • Parotid salivary gland
  • Afferents from carotid barorecepters

Testing the 9th nerve (sensory)

Gag reflex (not routinely done) Test both sides

Afferent – glossopharyngeal:

Efferent – vagus

  • Touch the posterior pharyngeal wall behind the pillars of fauces with a sterile tongue depressor.
  • Ask the patient can they can feel the tongue depressor & observe for any gagging.
  • No sensation or gagging may mean ipsilateral 9th nerve dysfunction.
  • Deviation (efferent response) of the uvula one way indicates weakness on the opposite side UMN / LMN lesion of the vagus, 10th cranial nerve and not the 9th .
  • Uvula moves on saying “Ahh” but not on a gag reflex
    • Isolated 9th nerve palsy is rare.

The 10th (Vagus) nerve

Sensory

  • Tympanic membrane, external auditory canal & external ear.

Motor

  • Muscles of the palate, pharynx & larynx

Autonomic

  • Parasympathetic supply to and from the thorax and abdomen.

Testing the 10th nerve

  • Look at the uvula (use a sterile tongue depressor if necessary)
  • Ask the patient to say “Ahh”
  • Deviation to one side indicates weakness of the opposite side (contralateral) In other words the unaffected muscle pulls the uvula towards it.
    • Upper or lower motor neurone lesion
  • Does not move on saying “Ahh” or gag.
    • Bilateral palatal muscle paresis.

11th (Accessory) nerve

  • Purely motor
  • Each cerebral hemisphere supplies
    • The ipsilateral sternomastoid muscle
    • The contra lateral trapezius muscle
  • Therefore, a lesion on one side can give rise to signs on both sides.

Testing the 11th nerve

Sternocleidomastoid

Ask patient to turn their head to one side. Stabilise patient with shoulder counter pressure. Then put your hand against patient’s chin and cheek and ask patient to resist your rotating their head back to midline. Watch the opposite sternomastoid contract, and test its power.

Trapezius

Ask the patient to shrug shoulders, push down against movement. Do one side at a time.

 

 

12th (Hypoglossal) nerve

This nerves controls the movements of the tongue and is solely a motor nerve. It arises out of the hypoglossal nucleus in the brainstem.

Motor function – intrinsic & extrinsic muscles of the tongue (palatoglosus is controlled by the vagus)

Testing the 12th nerve

Open mouth. Examine tongue at rest inside the mouth.

  • Observe for fasciculation and / or wasting (atrophy)
    • LMN lesion (Bulbar palsy). It is the nerve itself that is compromised.

Put out tongue

  • The tongue will deviate to the affected side.
  • Fasciculation during active movement is normal

Waggle tongue (demonstrate to the patient.)

  • Normal smooth bulk is what you want to see
  • Poor movement / control and usually bilateral indicates an Upper Motor Neurone lesion (pseudobulbar palsy)

Glossary

Atrophy – Muscle wasting

Diplopia – Double Vision

Conjugate – Moving together

Contralateral – Occurring on the opposite side of the body

Disconjugate – Not moving together

Fasiculation – spontaneous, involuntary, contraction of a number of muscle fibres, often causing a flickering under skin.

Ipsilateral – Occurring on the same side of the body

Nystagmus – Rapid, repetitive, involuntary eye movement