Cranial Nerve Examination

Question 1

What would speech abnormalities suggest?

Answer 1

Speech abnormalities: may indicate glossopharyngeal or vagus nerve pathology.

Question 2

What would facial asymmetry suggest?

Answer 2

Facial asymmetry: suggestive of facial nerve palsy.

Question 3

What is the following clinical sign and what would it suggest?

Answer 3

Ptosis- Ptosis (Drooping Eyelid) Ptosis is a condition where the upper eyelid droops. It is also called blepharoptosis, or upper eyelid ptosis.

Eyelid abnormalities: ptosis may indicate oculomotor nerve pathology.

Question 4

What is the following sign and what does it suggest?

Answer 4

Strabismus is a vision disorder in which the eyes do not properly align with each other when looking at an object.

Strabismus: may indicate oculomotor, trochlear or abducens nerve palsy.

Question 5

What is cranial nerve I and how is it tested?

Answer 5

The olfactory nerve (CN I) transmits sensory information about odours to the central nervous system where they are perceived as smell (olfaction). There is no motor component to the olfactory nerve.

Ask the patient if they have noticed any recent changes to their sense of smell.

Olfaction can be tested more formally using different odours (e.g. lemon, peppermint), or most formally using the University of Pennsylvania smell identification test. However, this is unlikely to be required in an OSCE.

Question 6

What are the causes of anosmia?

Answer 6

Causes of anosmia

There are many potential causes of anosmia including:

Mucous blockage of the nose: preventing odours from reaching the olfactory nerve receptors.

Head trauma: can result in shearing of the olfactory nerve fibres leading to anosmia.

Genetics: some individuals have congenital anosmia.

Parkinson’s disease: anosmia is an early feature of Parkinson’s disease.

COVID-19: transient anosmia is a common feature of COVID-19.

Question 7

What is cranial nerve II and what does it innervate?

Answer 7

Optic nerve (CN II)

The optic nerve (CN II) transmits sensory visual information from the retina to the brain. There is no motor component to the optic nerve.

Question 8

What is the following sign and what may it suggest in the context of trauma?

Answer 8

Peaked pupils in the context of trauma are suggestive of globe injury.

Question 9

What is the following clinical sign and what does it suggest?

Answer 9

asymmetry in pupil size between the pupils (anisocoria). This may be longstanding and non-pathological or relate to actual pathology. If the pupil is more pronounced in bright light this would suggest that the larger pupil is the abnormal pupil, if more pronounced in dark this would suggest the smaller pupil is abnormal.

Examples of asymmetry include a large pupil in oculomotor nerve palsy and a small and reactive pupil in Horner’s syndrome.

Question 10

List 5 causes of decreased visual acuity

Answer 10

Decreased visual acuity has many potential causes including:

Refractive errors

Amblyopia

Ocular media opacities such as cataract or corneal scarring

Retinal diseases such as age-related macular degeneration

Optic nerve (CN II) pathology such as optic neuritis

Lesions higher in the visual pathways

Optic nerve (CN II) pathology usually causes a decrease in acuity in the affected eye. In comparison, papilloedema (optic disc swelling from raised intracranial pressure), does not usually affect visual acuity until it is at a late stage.

Question 11

What is the following clincial sign and what does it indicate?

Answer 11

Relative afferent pupillary defect (Marcus-Gunn pupil): normally light shone into either eye should constrict both pupils equally (due to the dual efferent pathways described above). When the afferent limb in one of the optic nerves is damaged, partially or completely, both pupils will constrict less when light is shone into the affected eye compared to the healthy eye. The pupils, therefore, appear to relatively dilate when swinging the torch from the healthy to the affected eye. This is termed a relative…. afferent… pupillary defect. This can be due to significant retinal damage in the affected eye secondary to central retinal artery or vein occlusion and large retinal detachment; or due to significant optic neuropathy such as optic neuritis, unilateral advanced glaucoma and compression secondary to tumour or abscess.

Question 12

What is a unilateral efferent defect and what does it indicate?

Answer 12

Unilateral efferent defect: commonly caused by extrinsic compression of the oculomotor nerve, resulting in the loss of the efferent limb of the ipsilateral pupillary reflexes.

As a result, the ipsilateral pupil is dilated and non-responsive to light entering either eye (due to loss of ciliary sphincter function).

The consensual light reflex in the unaffected eye would still be present as the afferent pathway (i.e. optic nerve) of the affected eye and the efferent pathway (i.e. oculomotor nerve) of the unaffected eye remain intact.

Question 13

List three causes of acquired colour vision deficency

Answer 13

Colour vision deficiencies can be congenital or acquired. Some causes of acquired colour vision deficiency include:

Optic neuritis: results in a reduction of colour vision (typically red).

Vitamin A deficiency

Chronic solvent exposure

Question 14

What causes visual neglect?

Answer 14

Visual neglect (also known as visual inattention) is a condition in which an individual develops a deficit in their awareness of one side of their visual field. This typically occurs in the context of parietal lobe injury after stroke, which results in an inability to perceive or process stimuli on one side of the body. The side of the visual field that is affected is contralateral to the location of the parietal lesion. It should be noted that visual neglect is not caused by optic nerve pathology and therefore this test is often not included in a cranial nerve exam.

Question 15

What is bitemporal hemianopia?

Answer 15

Bitemporal hemianopia: loss of the temporal visual field in both eyes resulting in central tunnel vision. Bitemporal hemianopia typically occurs as a result of optic chiasm compression by a tumour (e.g. pituitary adenoma, craniopharyngioma).

Question 16

What are homonymous field defects?

Answer 16

Homonymous field defects: affect the same side of the visual field in each eye and are commonly attributed to stroke, tumour, abscess (i.e. pathology affecting visual pathways posterior to the optic chiasm). These are deemed hemianopias if half the vision is affected and quadrantanopias if a quarter of the vision is affected.

Question 17

What is scotoma?

Answer 17

Scotoma: an area of absent or reduced vision surrounded by areas of normal vision. There is a wide range of possible aetiologies including demyelinating disease (e.g. multiple sclerosis) and diabetic maculopathy.

Question 18

What is mononuclear vision loss?

Answer 18

Monocular vision loss: total loss of vision in one eye secondary to optic nerve pathology (e.g. anterior ischaemic optic neuropathy) or ocular diseases (e.g. central retinal artery occlusion, total retinal detachment).

Question 19

What are the causes for ptosis?

Answer 19

Inspect the eyelids for evidence of ptosis which can be associated with:

Oculomotor nerve pathology

Horner’s syndrome

Neuromuscular pathology (e.g. myasthenia gravis)

Question 20

What are the extraocular muscles and thier functions?

Answer 20

Actions of the extraocular muscles

Superior rectus: primary action is elevation, secondary actions include adduction and medial rotation of the eyeball.

Inferior rectus: primary action is depression, secondary actions include adduction and lateral rotation of the eyeball.

Medial rectus: adduction of the eyeball.

Lateral rectus: abduction of the eyeball.

Superior oblique: depresses, abducts and medially rotates the eyeball.

Inferior oblique: elevates, abducts and laterally rotates the eyeball.

Question 21

Explain the following condition?

Answer 21

Oculomotor nerve palsy (CN III)

The oculomotor nerve supplies all extraocular muscles except the superior oblique (CNIV) and the lateral rectus (CNVI). Oculomotor palsy (a.k.a. ‘third nerve palsy’), therefore, results in the unopposed action of both the lateral rectus and superior oblique muscles, which pull the eye inferolaterally. As a result, patients typically present with a ‘down and out’ appearance of the affected eye.

Oculomotor nerve palsy can also cause ptosis (due to a loss of innervation to levator palpebrae superioris) as well as mydriasis due to the loss of parasympathetic fibres responsible for innervating to the sphincter pupillae muscle.

Question 22

Explain the following condition?

Answer 22

Trochlear nerve palsy (CN IV)

The only muscle the trochlear nerve innervates is the superior oblique muscle. As a result, trochlear nerve palsy (‘fourth nerve palsy’) typically results in vertical diplopia when looking inferiorly, due to loss of the superior oblique’s action of pulling the eye downwards. Patients often try to compensate for this by tilting their head forwards and tucking their chin in, which minimises vertical diplopia. Trochlear nerve palsy also causes torsional diplopia (as the superior oblique muscle assists with intorsion of the eye as the head tilts). To compensate for this, patients with trochlear nerve palsy tilt their head to the opposite side, in order to fuse the two images together.

Question 23

Explain the following ?

Answer 23

Abducens nerve palsy (CN VI)

The abducens nerve (CN VI) innervates the lateral rectus muscle. Abducens nerve palsy (‘sixth nerve palsy’) results in unopposed adduction of the eye (by the medial rectus muscle), resulting in a convergent squint. Patients typically present with horizontal diplopia which is worsened when they attempt to look towards the affected side.

Question 24

What is strabismus?

Answer 24

Strabismus is a condition in which the eyes do not properly align with each other when looking at an object. Pathology affecting the oculomotor, trochlear or abducens nerves can cause strabismus

Question 25

What is the cover test used for?

How do you interpret it?

Answer 25

The cover test is used to determine if a heterotropia (i.e. manifest strabismus) is present.

Question 26

What is cranial nerve V and what does it innervate?

Answer 26

Trigeminal nerve (CN V)

The trigeminal nerve (CN V) transmits both sensory information about facial sensation and motor information to the muscles of mastication.

The trigeminal nerve has three sub-divisions, each of which has its own broad set of functions (not all are covered below):

Ophthalmic (V1): carries sensory information from the scalp and forehead, nose, upper eyelid as well as the conjunctiva and cornea of the eye.

Maxillary (V2): carries sensory information from the lower eyelid, cheek, nares, upper lip, upper teeth and gums.

Mandibular (V3): carries sensory information from the chin, jaw, lower lip, mouth, lower teeth and gums. Also carries motor information to the muscles of mastication (masseter, temporal muscle and the medial/lateral pterygoids) as well as the tensor tympani, tensor veli palatini, mylohyoid and digastric muscles.

Question 27

When inspecting the jaw how may a trigeminal nerve palsy present?

Answer 27

An inability to open the jaw against resistance or deviation of the jaw (typically to the side of the lesion) may occur in trigeminal nerve palsy.

Question 28

What is the jaw jerk reflex test?

Answer 28

The jaw jerk reflex is a stretch reflex that involves the slight jerking of the jaw upwards in response to a downward tap. This response is exaggerated in patients with an upper motor neuron lesion. Both afferent and efferent pathways of the jaw jerk reflex involve the trigeminal nerve.

Question 29

What is the corneal reflex test?

Answer 29

The corneal reflex involves involuntary blinking of both eyelids in response to unilateral corneal stimulation (direct and consensual blinking). The afferent branch of the corneal reflex involves V1 of the trigeminal nerve whereas the efferent branch is mediated by the temporal and zygomatic branches of the facial nerve.

Question 30

What is cranial nerve VII and what is its function?

Answer 30

The facial nerve (CN VII) transmits motor information to the muscles of facial expression and the stapedius muscle (involved in the regulation of hearing). The facial nerve also has a sensory component responsible for the conveyance of taste from the anterior two-thirds of the tongue.

Question 31

What is hyperacusis an indication of?

Answer 31

Ask the patient if they have noticed any changes to their hearing (paralysis of the stapedius muscle can result in hyperacusis).

Question 32

Explain the following condition?

Answer 32

Facial nerve palsy presents with unilateral weakness of the muscles of facial expression and can be caused by both upper and lower motor neuron lesions.

Facial nerve palsy caused by a lower motor neuron lesion presents with weakness of all ipsilateral muscles of facial expression, due to the loss of innervation to all muscles on the affected side. The most common cause of lower motor neuron facial palsy is Bell’s palsy.

Facial nerve palsy caused by an upper motor neuron lesion also presents with unilateral facial muscle weakness, however, the upper facial muscles are partially spared because of bilateral cortical representation (resulting in forehead/frontalis function being somewhat maintained). The most common cause of upper motor neuron facial palsy is stroke.

Question 33

What is cranial nerve VIII?

Answer 33

The vestibulocochlear nerve (CN VIII) transmits sensory information about sound and balance from the inner ear to the brain. The vestibulocochlear nerve has no motor component.

Question 34

What is rinnes test? What is rinnes positive?

Answer 34

Rinne’s test

1. Place a vibrating 512 Hz tuning fork firmly on the mastoid process (apply pressure to the opposite side of the head to make sure the contact is firm). This tests bone conduction.
2. Confirm the patient can hear the sound of the tuning fork and then ask them to tell you when they can no longer hear it.
3. When the patient can no longer hear the sound, move the tuning fork in front of the external auditory meatus to test air conduction.
4. Ask the patient if they can now hear the sound again. If they can hear the sound, it suggests air conduction is better than bone conduction, which is what would be expected in a healthy individual (this is often confusingly referred to as a “Rinne’s positive” result).

Summary of Rinne’s test results

These results should be assessed in context with the results of Weber’s test before any diagnostic assumptions are made:

Normal result: air conduction > bone conduction (Rinne’s positive)

Sensorineural deafness: air conduction > bone conduction (Rinne’s positive) – due to both air and bone conduction being reduced equally

Conductive deafness: bone conduction > air conduction (Rinne’s negative)

Question 35

What is Weber’s test?

What is a normal response?

Answer 35

Weber’s test

1. Tap a 512Hz tuning fork and place in the midline of the forehead. The tuning fork should be set in motion by striking it on your knee (not the patient’s knee or a table).
2. Ask the patient “Where do you hear the sound?”

These results should be assessed in context with the results of Rinne’s test before any diagnostic assumptions are made:

Normal: sound is heard equally in both ears.

Sensorineural deafness: sound is heard louder on the side of the intact ear.

Conductive deafness: sound is heard louder on the side of the affected ear.

A 512Hz tuning fork is used as it gives the best balance between time of decay and tactile vibration. Ideally, you want a tuning fork that has a long period of decay and cannot be detected by vibration sensation.

Question 36

Explain the difference between conductive vs sensorineural hearing loss

Answer 36

Conductive vs sensorineural hearing loss

Conductive hearing loss occurs when sound is unable to effectively transfer at any point between the outer ear, external auditory canal, tympanic membrane and middle ear (ossicles). Causes of conductive hearing loss include excessive ear wax, otitis externa, otitis media, perforated tympanic membrane and otosclerosis.

Sensorineural hearing loss occurs due to dysfunction of the cochlea and/or vestibulocochlear nerve. Causes of sensorineural hearing loss include increasing age (presbycusis), excessive noise exposure, genetic mutations, viral infections (e.g. cytomegalovirus) and ototoxic agents (e.g. gentamicin).

Question 37

What vestibular tests exist?

Answer 37

Vestibular testing – “Unterberger” or “Turning test”

Ask the patient to march on the spot with their arms outstretched and their eyes closed:

Normal result: the patient remains in the same position.

Vestibular lesion: the patient will turn towards the side of the lesion

Vestibular testing – “Head thrust test” or “Vestibular-ocular reflex”

Before performing this test you need to check if the patient has any neck problems and if so you should not proceed.

1. Explain to the patient that the test will involve briskly turning their head and then gain consent to proceed.
2. Sit facing the patient and ask them to fixate on your nose at all times during the test.
3. Hold their head in your hands (one hand covering each ear) and rotate it rapidly to the left, at a medium amplitude.
4. Repeat this process, but this time turn the head to the right.

The normal response is that ocular fixation is maintained. In a patient with loss of vestibular function on one side, the eyes will first move in the direction of the head (losing fixation), before a corrective refixation saccade occurs towards your nose.

Question 38

What is cranial nerve IX and X?

What do they innervate?

Answer 38

The glossopharyngeal nerve transmits motor information to the stylopharyngeus muscle which elevates the pharynx during swallowing and speech. The glossopharyngeal nerve also transmits sensory information that conveys taste from the posterior third of the tongue. Visceral sensory fibres of CN IX also mediate the afferent limb of the gag reflex.

The vagus nerve transmits motor information to several muscles of the mouth which are involved in the production of speech and the efferent limb of the gag reflex.

The glossopharyngeal and vagus nerves are assessed together because of their closely related functions.

Question 39

How would a vagus nerve lesion affect the mouth?

Answer 39

vagus nerve lesions result in deviation of the uvula towards the unaffected side.

A vagus nerve lesion will cause asymmetrical elevation of the palate and uvula deviation away from the lesion.

Vagus nerve lesions can result in the presence of a weak, non-explosive sounding bovine cough caused by an inability to close the glotti

Question 40

What does an inneffective swallow indicate?

Answer 40

Ask the patient to take a small sip of water (approximately 3 teaspoons) and observe the patient swallow. The presence of a cough or a change to the quality of their voice suggests an ineffective swallow which can be caused by both glossopharyngeal (afferent) and vagus (efferent) nerve pathology.

Question 41

What does a gag reflex test?

Answer 41

The gag reflex involves both the glossopharyngeal nerve (afferent) and the vagus nerve (efferent). This test is highly unpleasant for patients and therefore the swallow test mentioned previously is preferred as an alternative. You should not perform this test in an OSCE, although you may be expected to have an understanding of what cranial nerves are involved in the reflex.

Question 42

What is cranial nerve XI and what does it innervate?

How does accessory nerve palsy present?

Answer 42

Accessory nerve (CN XI)

The accessory nerve (CN XI) transmits motor information to the sternocleidomastoid and trapezius muscles. It does not have a sensory component.

Sternocleidomastoid or trapezius muscle wasting.

Ask the patient to raise their shoulders and resist you pushing them downwards: this assesses the trapezius muscle (accessory nerve palsy will result in weakness).

Ask the patient to turn their head left whilst you resist the movement and then repeat with the patient turning their head to the right: this assesses the sternocleidomastoid muscle (accessory nerve palsy will result in weakness).

Question 43

What is the hypoglossal nerve and what does it innervate?

Answer 43

The hypoglossal nerve (CN XII) transmits motor information to the extrinsic muscles of the tongue (except for palatoglossus which is innervated by the vagus nerve). It does not have a sensory component.

Question 44

What kind of pasly is present below?

Answer 44

Hypoglossal nerve palsy causes atrophy of the ipsilateral tongue and deviation of the tongue when protruded towards the side of the lesion. This occurs due to the overaction of the functioning genioglossus muscle on the unaffected side of the tongue.

Left hypoglossal nerve palsy

Question 45

What further investigations would you request after completing a cranial nerve exam?

Answer 45

Full neurological examination including the upper and lower limbs.

Neuroimaging (e.g. MRI head): if there are concerns about space-occupying lesions or demyelination.

Formal hearing assessment (including pure tone audiometry): if there are concerns about vestibulocochlear nerve function.

Question 46

What is the following clinical sign and what would it suggest?

Answer 46

Mydriasis- Dilated pupils (mydriasis) are when the black center of your eyes are larger than normal.

Pupillary abnormalities: mydriasis occurs in oculomotor nerve palsy.