Cranial Nerve Examination - Abnormal findings

What abnormalities might you find when carrying out the general inspection?

• Speech abnormalities

• Facial asymmetry

• Eyelid abnormalities

• Pupillary abnormalities

• Strabismus

• Limbs (not specific CN lesions, but may be suggestive of neurological syndromes):

  • Spasticity

  • Weakness

  • Atrophy

  • Tremor

  • Fasciculation

If there was a problem with CN I (olfactory), what might you find on examination?

Anosmia or other changes to the patient’s sense of smell.

Anosmia

Partial or complete loss of the sense of smell.

What can cause anosmia?

• Mucous blockage if the nose prevents odours from reaching CN I receptors.

• Head trauma can shear CN I nerve fibres.

• Genetics - congenital anosmia.

• Parkinson’s disease (early feature)

• COVID-19 - common feature (often transient)

What pupillary abnormalities might you see upon examination?

• Abnormal pupil size

• Dyscoria (abnormal pupil shape)

• Anisocoria

• Abnormal reflexes

What can cause abnormal pupil shapes (dyscoria)?

• Congenital conditions

• Posterior synechiae associated with uveitis

• Eye trauma (peaked pupils)

• Iritis

What is Posterior synechiae associated with uveitis?

Adhesion between the iris and lens / cornea due to inflammation in the uvea (rare). If the condition is very severe, then there can be associated glaucoma and permanent vision loss.

Peaked pupils

Irregularly stretched, teardrop shaped, or distorted pupils where a segment of the iris is pulled or stretched towards a point. In the context of trauma, it will likely be caused by a globe injury (eyeball injury).

Anisocoria

Asymmetry in pupil size. Causes include:

• Congenital anisocoria

• Migraines

• Surgery side effects

• Eye drops and other medicines

• Trauma to eye, head, or arteries that supply blood to them (e.g. brain aneurysm, stroke, brain tumours etc.)

• Oculomotor nerve palsy (causes large pupil)

• Horner’s syndrome (causes small reactive pupil)

Bilateral miosis

Abnormal constriction of both pupils (normal in infancy!!). Causes include:

• Senile miosis

• Medications (e.g. opioids, barbiturates, pilocarpine etc.)

• Brain trauma / haemorrhage / tumours / strokes

• Poisoning

• Untreated syphilis

Bilateral mydriasis

Abnormal dilation of both pupils. Causes include:

• Eye examinations - use of some eyedrops

• Medications

• Brain / eye trauma

• Microvascular cranial nerve palsy (blood flow to nerves is blocked)

• Migraine / ocular migraine

• Recreational drugs (cocaine, MDMA, LSD, methamphetamines, psychedelic mushrooms)

• Sexual arousal

• Adrenaline

If there was a CN II (optic) disorder, what might you find on examination?

• Decreased visual acuity (eg. optic neuritis)

• Abnormal pupillary light reflexes (shining a light on the affected eye will result in a reduced / absent direct and consensual response)

• Abnormal colour vision (eg. optic neuritis)

• Visual field defects

• Abnormal blind spots (enlarged)

• Abnormal fundoscopy

What are the different CN II disorders?

• Glaucoma (fluid pressure inside eyes rises, damaging CN II)

• Optic neuritis (inflammation of CN II)

• Optic nerve atrophy (causes: trauma, toxins, ischaemia, disease)

• Optic nerve head drusen (pockets of protein and calcium salts that build up in the optic nerve over time)

What types of visual field defects are there?

• Bitemporal hemianopia

• Homonymous field defects

• Scotoma

• Monocular vision loss

Bitemporal hemianopia

Loss of temporal visual field in both eyes resulting in central tunnel vision. It is typically caused by a tumour compressing the optic chiasm.

Homonymous field defects

Affect the same side of the visual field in each eye - can be hemianopias, or quadrantanopias. Typically caused by pathologies affecting visual pathways posterior to the optic chasm:

• Stroke

• Tumour

• Abscess

Scotoma

A visual field defects where there is an area of absent or reduced vision surrounded by areas of normal vision. Causes include:

• Optic neuritis

• Demyelinating disease (e.g. MS)

• Diabetic maculopathy

• Retinal injuries

• Cancer

• Stroke

• Age-related macular degeneration

• Medications

• Brain injuries

etc.

Monocular vision loss

Total loss of vision in one eye. Typical causes include:

• Optic nerve pathology (e.g. anterior ischaemic optic neuropathy)

• Ocular diseases (e.g. central retinal artery occlusion, total retinal detachment)

What causes an enlarged blind spot?

Papillitis - swollen optic nerve head (pictured). A dangerous subtype of this is Papilloedema - bilaterally swollen optic nerve head secondary to raised intracranial pressure (e.g. brain tumour, hypertensive crisis, intracranial haemorrhage).

What causes decreased visual acuity?

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 - will typically only be present in the affected eye

• Lesions higher in the visual pathways

What is an abnormal pupillary light reflex?

• No direct pupillary reflex present (no constriction in one pupil when light is shone on the ipsilateral pupil)

• No consensual pupillary reflex present (no constriction in one pupil when light is shone on the contralateral pupil).

• Relative afferent pupillary defect

Relative afferent pupillary defect

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.

Abnormal accommodation reflex

Bilateral constriction and convergence is not observed.

What can cause colour vision deficiencies?

• Congenital conditions (e.g. inherited red-green colour blindness)

• Acquired:

  • Optic neuritis (typically red colour vision is reduced)

  • Vitamin A deficiency

  • Chronic solvent exposure

What CN II pathologies are visible via ophthalmoscopy?

• Papilloedema (bilateral optic disc swelling)

• Papillitis (only visible when it affects the nerve head)

• Anterior ischaemic optic neuropathy (pale)

• Optic disc neuropathy (pallor)

• Pathological optic cupping

• Congenital and structural abnormalities

Visual neglect / inattention

A condition in which an individual develops a deficit in their awareness of one side (hemispace) of their visual field. It is not caused by optic nerve pathology, but typically caused by pathology affecting the cerebral hemisphere, such as a stroke damaging the parietal lobe.

If there was a CN III (oculomotor) pathology, what might you find on examination?

• Ptosis

• Strabismus - eye pulled inferolaterally (down and out appearance)

• Mydriasis (abnormal dilation of pupil)

• Limited range of movement: unable to move up, down, or inward towards the nose

Ptosis

Drooping of the upper eyelid. Typically caused by:

• Oculomotor nerve pathology

• Horner’s syndrome

• Neuromuscular pathology (e.g. Myasthenia Gravis)

What are some notable causes of CN III (oculomotor) palsy?

• Intracranial aneurysm

• Microvascular ischaemia

• High impact trauma (low impact trauma should not cause this)

• Recurrent painful ophthalmoplegic neuropathy

If there was a CN IV (trochlear) pathology, what might you find on examination?

• Vertical diplopia when looking inferiorly (may notice patient compensating for this by tilting their heads forward and tucking their chin in)

• Torsional diplopia (patient may compensate by tilting head go opposite side)

• Limited range of movement: impaired ability to move eye downward and inward

What are some notable causes of CN IV (trochlear) palsy?

• Congenital (most common)

• Idiopathic (tends to be congenital, but presenting in adult life)

• Moderate frontal head trauma (tends to be bilateral)

• Hypertension

• Diabetes

• post-neurosurgery

• Intracranial neoplasms

• Herpes zoster virus (shingles)

etc.

If there was a CN VI (abducens) pathology, what might you find on examination?

• Strabismus - convergent squint

• Horizontal diplopia which is worsened when they attempt to look towards the affected side

• Limited range of movement: impaired ability to abduct the eye (move outwards towards the side).

What are some notable causes of CN VI (abducens) palsy?

• Idiopathic

• Head injuries

• Infections (e.g. meningitis, herpes zoster etc.)

• Circulatory problems (stroke, microvascular ischaemia, brain haemorrhage etc.)

• Systemic, inflammatory, and metabolic conditions (MS, T2 DM, hypertension etc.)

• Blood disorders, cancers and tumours

• Other neurological conditions (migraines etc.)

• Medical procedures (LP, surgery etc.)

Strabismus

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. Certain tests can be used to assess this (corneal light reflex test, cover test).

If the patient has pathology affecting CN V (trigeminal), what might you observe upon examination?

• Loss of sensation in one or multiple of these areas:

  • Forehead (ophthalmic)

  • Cheeks (maxillary)

  • Lower jaw (mandibular)

• Atrophy of the temporalis and/or masseter muscles.

• 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.

• Absent / reduced jaw jerk reflex if there is damage to the nerve itself.

• Exaggerated / hyperactive jaw jerk reflex if there is UMN pathology.

• Absent corneal reflex

Interpretation of the jaw jerk reflex

• Normal jaw jerk reflex - slight closure of the mouth in response to tapping the chin with the tendon hammer.

• Absent / reduced jaw jerk reflex if there is damage to the nerve itself.

• Exaggerated / hyperactive jaw jerk reflex if there is UMN pathology.

Interpretation of the corneal reflex

• Normal - direct and consensual blinking in response to unilateral corneal stimulation.

• Abnormal - absence of direct and consensual blinking suggests a problem with either CN V or CN VII

• Afferent branches = CN V (absent direct and consensual blinking when affected eye is stimulated, but not in the unaffected eye)

• Efferent branches = CN VII (absent direct blinking when affected eye is stimulated, and absent consensual response when the non-affected eye is stimulated)

What notable pathologies affect CN V (trigeminal)?

• Head trauma

• Pressure from nearby blood vessels, tumours or swelling

• Inflammation from certain infections (e.g. herpes zoster virus)

• Circulatory problems (microvascular disease)

• Autoimmune conditions (e.g. scleroderma)

• Surgery complication

• Trigeminal neuralgia (extremely painful chronic pain disorder)

• Trigeminal neuropathy

• Cluster headache

• Lateral medullary syndrome (post-stroke or blood clot)

If the patient has pathology affecting CN VII (facial), what might you observe upon examination?

• Changes in sense of taste (responsible for anterior 2/3 of tongue conveyance of taste)

• Changes in hearing (paralysis of the stapedius muscle can result in hyperacusis)

• Asymmetry in the face at rest, particularly the forehead wrinkles, nasolabial folds and angles of the mouth.

• Impaired ability to raise eyebrow(s) close the eye(s), blow out cheeks against resistance, smile or purse lips.

What are the two presentations of CN VII lesions?

• UMN lesions

• LMN lesions

Facial nerve palsy - UMN lesion

• Presents with unilateral facial muscle weakness.

• Upper facial muscles are partially spared because of bilateral cortical representation (frontalis function is therefore somewhat maintained)

• Most common cause is a stroke

Facial nerve palsy - LMN lesion

• Presents with unilateral facial muscle weakness - ALL ipsilateral muscles.

• Most common cause is Bell’s palsy

What notable pathologies affect CN VII (facial)?

• UMN:

  • Cortical stroke (typically MCA)

• LMN:

  • Bell’s palsy

  • Pons pathology: stroke, demyelination (MS), tumour

  • Infections: meningitis, middle ear infections, tetanus etc.

  • Trauma

  • Tumours (meningioma, parotid gland, middle ear)

  • Surgery

  • Rare mononeuritis (diabetes, alcohol, HIV etc.)

If the patient has pathology affecting CN VII (facial), what might you observe upon examination?

• Impaired hearing during the whisper test

• Sensorineural hearing loss (Rinne’s + Weber’s tests)

• Impaired balance (turning test, vestibulo-ocular reflex)

Sensorineural vs conductive hearing loss

• Conductive hearing loss

  • Sound is unable to effectively transfer at any point between the outer ear, external auditory canal, tympanic membrane and middle ear (ossicles).

  • The patient will hear better when sound is conducted through bone rather than air.

  • Causes: excessive ear wax, otitis externa / media, perforated tympanic membrane and otosclerosis.

• Sensorineural hearing loss

  • Dysfunction of the cochlea and/or vestibulocochlear nerve.

  • The patient will not hear well when sound is conducted through bone or air.

  • Causes: ageing,, excessive noise exposure, genetic mutations, viral infections, and ototoxic agents (e.g. gentamicin).

What does the Hallpike test assess?

If the test is positive, it indicates that the patient has benign paroxysmal positional vertigo (BPPV). This is not a problem with CN VIII (it is due to loose calcium carbonate crystals).

What notable pathologies affect CN VIII (vestibulocochlear)?

• Idiopathic Sudden Sensorineural Hearing Loss (ISSHL - most common)

• Excessive noise

• Meniere’s syndrome

• Ototoxic drugs

• Labrynthitis

• Accoustic neuroma

• Small vessel disease

• Brainstem lesions

• Presbyacusis (age-related)

• Congenital infections

If the patient has pathology affecting CN IX (glossopharyngeal), what might you observe upon examination?

• Changes to taste (conveys taste from the posterior 1/3 of the tongue)

• Difficulty swallowing

• Difficulty with speech (also could be CN X pathology)

• Absent gag reflex (also could be CN X pathology)

If the patient has pathology affecting CN X (V), what might you observe upon examination?

• Difficulty with swallowing (also could be CN IX pathology)

• Difficulty with speech (also could be CN IX pathology)

• Weak, non-explosive sounding bovine cough caused by an inability to close the glottis.

• Absent gag reflex (also could be CN IX pathology)

• Deviation of uvula towards one side and asymmetrical elevation of palate.

What notable pathologies affect CN IX (glossopharyngeal)?

• Trauma (e.g. styloid fracture)

• Eagle syndrome (elongated styloid process)

• Glossopharyngeal neuralgia

• Iatrogenic

• Tonsillar carcinoma

• Stroke

What notable pathologies affect CN X (vagus)?