Summary
Cranial nerve palsy is characterized by a decreased or complete loss of function of one or more cranial nerves. Cranial nerve palsies can be congenital or acquired. Multiple cranial neuropathies are commonly seen in lesions caused by tumors, trauma, ischemia, and infections. While a diagnosis can usually be made based on clinical features, further investigation is often warranted to determine the specific etiology, which should determine the course of treatment.
For more information on facial nerve damage, see “Facial nerve palsy.”
Cranial nerve types and functions
Overview of cranial nerves and their function [1] | |||
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Cranial nerve | Nerve type | Function | |
I | Olfactory nerve |
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II | Optic nerve |
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III | Oculomotor nerve |
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IV | Trochlear nerve |
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V | Trigeminal nerve |
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VI | Abducens nerve |
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VII | Facial nerve |
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VIII | Vestibulocochlear nerve |
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IX | Glossopharyngeal nerve |
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X | Vagus nerve |
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XI | Accessory spinal nerve |
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XII | Hypoglossal nerve |
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A useful mnemonic to remember the function of all the 12 cranial nerves is “Some Say Marry Money, But My Brother Says Big Brain Matters More”: CN I is sensory, CN II is sensory, CN III is motor, CN IV is motor, CN V is both (mixed), CN VI is motor, CN VII is both (mixed), CN VIII is sensory, CN IX is both (mixed), CN X is both (mixed), CN XI is motor, and CN XII is motor.
Remember that CN VII (Seven) controls Salivation by innervating Submandibular and Sublingual glands.
Origin and pathways of the cranial nerves
Origin and pathways of the cranial nerves | |||||
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Nerve origin | Foramina/Structures | Nuclei | Destination | Pathway | |
CN I |
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CN II |
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CN III |
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CN IV |
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CN V |
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CN VI |
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CN VII |
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CN VIII |
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CN IX |
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CN X |
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CN XI |
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CN XII |
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To remember the location of the cranial nerves, organize them into three groups of four: I–IV in the midbrain, V–VIII in the pons, IX–XII in the medulla.
The nuclei located in the medial brainstem are factors of 12, except 1 and 2 (i.e., CN III, CN IV, CN VI, and CN XII).
“Standing Room Only”: CN V1 exits through Superior orbital fissure, CN V2 exits through foramen Rotundum, and CN V3 exits through foramen Ovale.
The sulcus limitans in the 4th ventricle separates the CN Motor nuclei in the Medial part of the brain stem (basal plate) from the sensory nuclei in the Lateral part (aLar plate).
Olfactory nerve palsy
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Etiology
- Acquired
- Most commonly due to trauma to the lateral and occipital regions (e.g., ethmoid bone fracture)
- Intracranial space-occupying lesion (e.g., meningioma)
- Infection (e.g., meningitis)
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Congenital
- Primary: congenital anosmia
- Secondary in diseases such as Kallmann syndrome and primary ciliary dyskinesia
- Acquired
- Clinical features: anosmia [15]
- Testing: identification of certain smells (e.g., peppermint, coffee) [2]
Optic nerve palsy
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Etiology
- Acquired
- Ischemic optic neuropathy (i.e., caused by microvascular disease)
- Inflammation: multiple sclerosis, sarcoidosis, viral infections (e.g., measles, mumps)
- Trauma
- Tumors (e.g., optic nerve glioma, pituitary adenoma)
- Elevated intracranial pressure (e.g., hydrocephalus)
- Malnutrition: vitamin B12 deficiency
- Drugs: sildenafil, amiodarone, ethambutol
- Congenital
- Primary: optic nerve hypoplasia
- Secondary: infantile nystagmus, sensory strabismus
- Acquired
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Clinical features
- Impaired vision
- Complete transection → ipsilateral blindness and loss of direct pupillary light reflex
- Papilledema (in ↑ ICP)
- Compression (e.g., tumor) → optic atrophy
- Pituitary adenoma → compression to the optic chiasm → bitemporal hemianopia [3]
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Testing:
- Visual field test
- Visual acuity test
- Fundoscopy (e.g., papillitis)
Oculomotor nerve palsy (III)
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Clinical features
- Lesions of the motor portion typically produce paralytic squint:
- Lesions of the autonomic (parasympathetic) portion lead to the absence of the pupillary reaction
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Parasympathetic fibers are located more superficially than motor fibers, causing the following features:
- Prominent motor dysfunction and sparing of the pupil in ischemic lesions due to vascular disease (e.g., vasculitis, diabetes): parasympathetic fibers are less affected by decreased diffusion of nutrients from the vasa nervorum
- Severely impaired pupillary reaction with relatively spared motor function in compressive lesions (e.g., uncal herniation, aneurysm of the posterior communicating artery): parasympathetic fibers are affected by compression first
- Additional features may be present, depending on the etiology and the level of the oculomotor nerve lesion.
Etiology of CN III palsy | ||
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Structure | Etiology | Clinical features |
Oculomotor nuclei |
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Basilar segment |
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Intracavernous segment |
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Intraorbital segment |
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Isolated oculomotor nerve palsy |
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Testing
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Pupillary response
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Dilated pupil is often due to compressive lesion (e.g., posterior communicating artery aneurysm)
- Best initial test: urgent MRI with MR angiography
- If MRI is normal: perform a lumbar puncture
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Pupillary sparing is often due to ischemic microangiopathy
- Assess risk factors for atherosclerosis or arteritis (e.g., blood pressure, glucose, ESR, lipid profile)
- If no recovery in 3 months, perform an MRI
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Dilated pupil is often due to compressive lesion (e.g., posterior communicating artery aneurysm)
- Ocular and extraocular movements
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Pupillary response
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Treatment
- Compressive lesions: surgery, e.g., posterior communicating artery aneurysm → urgent neurosurgical clipping or endovascular coiling
- Ischemic microangiopathy or demyelinating lesions: medical management with adequate control of the underlying disease
For more details about oculomotor nerve lesions and drugs affecting pupillary size, see “Physiology and abnormalities of the pupil.”
Oculomotor nerve palsy leaves you down and out.
Motor fibers are in the Middle of CN III, while Parasympathetic fibers are on the Periphery of the nerve.
Compression of the oculomotor nerve can cause isolated pupillary dilation due to injury of the parasympathetic fibers. Microangiopathy (e.g., due to diabetes mellitus) typically affects the deeper somatic fibers first, causing ophthalmoplegia without pupillary dilation.
Trochlear nerve palsy (IV)
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Etiology
- Acquired
- Microvascular damage (diabetes, hypertension, arteriosclerosis)
- Cavernous sinus thrombosis
- Trauma
- Congenital: fourth nerve palsy
- Acquired
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Clinical features
- Extorsion of the eye: inability to depress and adduct the eyeball simultaneously
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Diplopia
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Vertical or oblique diplopia
- Exacerbated on downgaze (e.g., reading, walking downstairs) away from side of affected muscle [17]
- Worsens when patient turns the head towards the paralyzed muscle → compensatory head tilt to the opposite side of the lesion
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Vertical or oblique diplopia
- Mild hypertropia and excyclotorsion
With damage to the CN IV, you cannot look at the floor.
Trigeminal nerve palsy (V)
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Etiology
- Tumor
- Vascular compression
- Oral surgery
- Inflammation of the nerve
- Cavernous sinus thrombosis
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Clinical features
- Peripheral trigeminal nerve lesions
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Ophthalmic nerve (CN V1)
- Absent corneal reflex (afferent limb)
- Loss of sensation in the ipsilateral forehead
- Maxillary nerve (CN V2): loss of sensation in the ipsilateral midface
- Mandibular nerve (CN V3): anesthesia of the ipsilateral lower ⅓ of the face and anterior ⅔ of the tongue, paresis of contralateral muscles of mastication → jaw deviates towards the side of the lesion due to unopposed action from the opposite pterygoid muscle
- Trigeminal neuralgia (any of the 3 nerves can be affected): See “Trigeminal neuralgia.”
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Ophthalmic nerve (CN V1)
- Lesion of the tensor tympani branch → hearing impairment (particularly affecting low-pitched sounds)
- Lesions of the trigeminal nerve nuclei (depending on the nuclei affected): ipsilateral weakness of muscles of mastication and/or ipsilateral loss of sensation
- Peripheral trigeminal nerve lesions
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Testing
- Facial sensation: decreased sensation to light touch, pain (can also be increased), and/or temperature
- Diminished/absent corneal reflex or lacrimation reflex (CN V1)
- Muscles of mastication (temporalis, masseter): signs of atrophy, decreased strength (e.g., open mouth against resistance), diminished/absent jaw jerk reflex (CN V3)
Abducens nerve palsy (VI)
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Etiology [9]
- Most common ocular cranial nerve palsy
- Acquired
- Trauma (e.g., at the superior orbital fissure)
- Pseudotumor cerebri
- Cavernous sinus thrombosis
- Space-occupying lesion causing downward pressure (e.g., tumor)
- Diabetic neuropathy
- Congenital: Duane syndrome (a rare type of strabismus characterized by an impaired abduction and ptosis on adduction) [18]
- Clinical features
Vestibulocochlear nerve palsy (VIII)
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Etiology
- Bacterial meningitis (most common cranial nerve palsy)
- Lyme disease
- Tumor (e.g., acoustic neuroma, neurofibromatosis type 2)
- Trauma: basilar skull fracture (damage to the CN VIII within the internal acoustic meatus → symptoms of vestibular and cochlear nerve damage)
- Clinical features
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Testing [20]
- Audiometry
- Hearing test
- Rinne test, Weber test
- Otoacoustic emissions (OAE)
- Electrocochleography (ECoG)
- Auditory brainstem response test (ABR)
- Vestibular function
- Electronystagmography (ENG) or videonystagmography (VNG)
- Rotation test
- Video head impulse testing (vHIT)
- Vestibular evoked myogenic potential (VEMP) testing
- Computerized dynamic posturography (CDP)
- Imaging (e.g., MRI, CT)
- Audiometry
Glossopharyngeal nerve palsy (IX)
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Etiology
- Idiopathic
- Compression of nerve by a blood vessel
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Clinical features
- Loss of the gag reflex (afferent limb)
- Loss of the carotid sinus reflex
- Sensory loss over the soft palate, upper pharynx, and posterior third of the tongue (including loss of taste sensation)
- Mild dysphagia
- Glossopharyngeal neuralgia: throat and ear pain
- Testing
Lesions that affect the glossopharyngeal nerve typically also affect the vagus nerve because the glossopharyngeal nerve exits the medulla above the vagus nerve.
Vagus nerve palsy (X)
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Etiology
- Trauma
- Diabetes
- Inflammation
- Aortic aneurysms
- Tumors
- Surgery (e.g, recurrent nerve injury during thyroidectomy)
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Clinical features
- Flaccid paralysis and ipsilateral lowering of soft palate → nasal speech and deviation of the uvula away from the lesion
- Dysfunction of the pharyngeal muscles → dysphagia, aspiration
- Loss of gag reflex (efferent limb) and/or cough reflex (afferent limb; impulses travel via the internal laryngeal nerve)
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Recurrent laryngeal nerve injury
- Lesion of one nerve: unilateral vocal cord paralysis → dysphonia (hoarseness)
- Lesion to both nerves: bilateral vocal cord paralysis → aphonia and inspiratory stridor
- Features of gastroparesis, e.g., poor gastric emptying
- Cardiovascular dysfunction, e.g., tachycardia
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Testing
- Diminished or absent gag and/or cough response
- Articulating "ahh" will cause the uvula to deviate away from the affected side
- Indirect laryngoscopy: vocal cord possibly in paramedian or intermediate position
- Fiber-optic nasopharyngoscopy: dysphagia, possible aspiration [21]
- Barium or water-swallow tests: signs of coughing, choking, or dysphonia, exclusion of differential diagnosis (e.g., achalasia, foreign body aspiration) [22]
- Increased resting heart rate (> 100 beats per minute) [21]
- Endoscopy or gastric emptying scan: gastroparesis [23]
Accessory nerve palsy (XI)
- Etiology: iatrogenic, most commonly from surgery of lateral cervical region; , especially posterior border of sternocleidomastoid muscle (e.g., resection of cervical lymph nodes)
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Clinical features
- Paresis, atrophy, and/or asymmetry of the sternocleidomastoid
- Paresis, atrophy, and/or asymmetry of the trapezius muscle → ipsilateral shoulder drooping and lateral winging of the scapula
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Testing [13]
- Possibly asymmetrical neckline
- Shrug shoulders → weakness during elevation of the ipsilateral shoulder
- Turn head from side to side → weakness turning the head towards the contralateral side (each sternocleidomastoid muscle turns the head toward the contralateral side)
Hypoglossal nerve palsy (XII)
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Etiology
- Tumors
- Trauma
- Dissection of the internal carotid artery
- Clinical features: atrophy and fasciculation of the tongue on the side of the lesion
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Testing [14]
- Signs of unilateral lower motor neuron damage: tongue atrophy, fasciculations, or asymmetry
- The tongue will deviate to the side of the lesion when protruded due to weakness of the ipsilateral tongue muscles
- Press tongue against each cheek → pressure to the cheek of the affected side might be increased