Trusted medical expertise in seconds.

Access 1,000+ clinical and preclinical articles. Find answers fast with the high-powered search feature and clinical tools.

Evidence-based content, created and peer-reviewed by physicians. Read the disclaimer.

Cranial nerve palsies

Last updated: July 13, 2021

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]
Cranial nerve		Nerve type	Function
I	Olfactory nerve	Sensory	Smell
II	Optic nerve	Sensory	Vision Afferent limb of the pupillary light reflex
III	Oculomotor nerve	Motor (somatic)	Eyelid opening (indirect): levator palpebrae superioris muscle Eye movement Superior rectus muscle: elevation, intorsion, and adduction Inferior rectus muscle: depression and extorsion Medial rectus muscle: adduction Inferior oblique muscle: extorsion, elevation, and abduction
III	Oculomotor nerve	Motor (parasympathetic)	Pupillary constriction Pupillary sphincter (Edinger-Westphal nucleus and muscarinic receptors) Efferent limb of the pupillary light reflex Accommodation: ciliary muscle
IV	Trochlear nerve	Motor	Eye movement: superior oblique muscle (intorsion, depression, and abduction) ^[2]
V	Trigeminal nerve	Sensory	Facial sensation: ophthalmic (CN V1), maxillary (CN V2), mandibular nerve (CN V3) Innervation of: Mucous membranes of the oral and nasal cavity and the soft and hard palate Teeth Temporomandibular joint Meninges Anterior wall of the external auditory canal Somatosensation of anterior ⅔ of the tongue Afferent limb of the corneal and lacrimation reflexes (nasociliary branch) Afferent limb of the jaw jerk reflex (muscle spindle from masseter)
V	Trigeminal nerve	Motor (only mandibular nerve)	Muscles of mastication Masseter, temporalis, medial pterygoid muscles close the jaw Lateral pterygoid muscles open the jaw Efferent limb of the jaw jerk reflex (masseter) Innervation of: Tensor tympani muscle (contraction dampens loud sounds) Tensor veli palatini muscle Anterior belly of the digastric muscle Mylohyoid muscle
VI	Abducens nerve	Motor	Eye movement: lateral rectus muscle: abduction
VII	Facial nerve	Sensory	Taste: anterior ⅔ of the tongue (chorda tympani) Innervation of: Tympanic membrane (chorda tympani) Skin behind the ear (posterior auricular branch)
		Motor (somatic)	Facial expression Eyelid closing: orbicularis oculi muscle Efferent limb of the corneal reflex (temporal branch, bilaterally) Jaw opening: posterior belly of the digastric muscle Hyoid elevation: stylohyoid muscle Efferent limb of the acoustic reflex (stapedius muscle) → auditory volume modulation
		Motor (parasympathetic)	Salivation: submandibular and sublingual glands Lacrimation: lacrimal gland Efferent limb of the lacrimation reflex
VIII	Vestibulocochlear nerve	Sensory	Balance and equilibrium: vestibular nerve Hearing: cochlear nerve
IX	Glossopharyngeal nerve	Sensory	Taste perception: posterior ⅓ of the tongue (lingual branch) Somatosensation: posterior ⅓ of the tongue, middle ear, and Eustachian tube (tympanic nerve) Afferent limb of the gag reflex Visceral sensation: carotid sinus (baroreceptors for blood pressure) Chemoreception: carotid body (chemoreceptors for PaO₂, PaCO₂, and pH)
		Motor (somatic)	Swallowing: pharyngeal muscles (CN IX and CN X) Innervation of stylopharyngeus muscle (elevation of pharynx/larynx)
		Motor (parasympathetic)	Salivation: parotid gland
X	Vagus nerve	Sensory (somatic)	Posterior wall of the external auditory canal Supraglottic region, larynx, trachea (cough reflex)
		Sensory (visceral)	Taste perception: supraglottic region Visceral sensation: aortic body (baroreceptors for blood pressure), lung, stomach, liver, kidneys, intestines up to left colonic flexure Chemoreception: aortic body (chemoreceptors for PaO₂ and PaCO₂)
		Motor (somatic)	Swallowing: pharyngeal muscles (glossopharyngeal and vagus nerves) Middle and inferior pharyngeal constrictor muscles: passage of bolus Palatoglossus muscle: elevates posterior tongue upon swallowing Efferent limb of the gag reflex Speech: laryngeal muscles (recurrent laryngeal branch)
		Motor (parasympathetic)	SA and AV node: ↓ heart rate Blood vessels: vasodilation Visceral function: promotes the motility of the esophagus, stomach, intestines (up to the splenic flexure)
XI	Accessory spinal nerve	Motor	Head turn: sternocleidomastoid muscle Shoulder elevation: trapezius muscle
XII	Hypoglossal nerve	Motor	Tongue protrusion: intrinsic and extrinsic muscles of the tongue

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.

Cranial nerve functions overview

Origin and pathways of the cranial nerves

Origin and pathways of the cranial nerves
Cranial nerve	Nerve origin	Foramina/Structures	Cranial nerve nuclei	Destination	Pathway
CN I	Olfactory epithelium of the nasal mucosa	Cribriform plate	-	Lateral stria → telencephalon Medial stria → amygdala	Olfactory receptor cells (first order neurons) → fila olfactoria → penetrate cribriform plate of the ethmoid bone → olfactory bulb → olfactory tract (second order neurons) → (split into two) lateral portion connects directly with telencephalon (prepyriform area), medial portion connects with amygdala ^[3] Only cranial nerve with no thalamic relay to cortex
CN II	Retinal ganglion cells	Optic canal	Lateral geniculate nucleus	Visual cortex on the occipital lobe	Ganglion cells of the retina → optic nerve → optic canal (sphenoid bone) → optic chiasm (middle cranial fossa) Fibers from nasal retina: cross at the optic chiasm Fibers from temporal retina: continue ipsilaterally at the optic chiasm Optic chiasm → optic tract → projects to pretectal area, superior colliculi , suprachiasmatic nuclei, and lateral geniculate nucleus Lateral geniculate nucleus → optic radiation Upper optic radiation: fibers from superior retinal quadrants → parietal lobe → visual cortex Lower optic radiation: fibers from inferior retinal quadrants → temporal lobe (Meyer loop) → visual cortex Visual cortex on the occipital lobe: comprises the calcarine sulcus between lingual and cuneus gyrus ^[4]
CN III	Midbrain	Lateral cavernous sinus Superior orbital fissure	Somatic: oculomotor nucleus Visceral: Edinger-Westphal nucleus	Ocular and orbital muscles	Somatic: efferent fibers from oculomotor nucleus → red nuclei → medial aspect of the cerebral peduncle Visceral: Edinger-Westphal nucleus → preganglionic parasympathetic fibers join CN III in the basilar segment Interpeduncular fossa → between posterior cerebral artery and superior cerebellar artery → dura mater → lateral wall of cavernous sinus → (together with sympathetic fibers from internal carotid plexus) superior orbital fissure → division into superior and inferior branch ^[5] Superior branch Superior rectus and levator palpebrae superioris Sympathetic fibers → superior tarsal muscle Inferior branch Inferior rectus, medial rectus, and inferior oblique muscle Preganglionic parasympathetic fibers → ciliary ganglion → sphincter pupillae and ciliary muscles
CN IV	Posterior midbrain	Lateral cavernous sinus Superior orbital fissure	Trochlear nucleus	Contralateral superior oblique muscle	Trochlear nucleus in the posterior midbrain → fibers cross within midbrain → subarachnoid space → through dura mater → lateral wall of cavernous sinus → superior orbital fissure → contralateral superior oblique muscle ^[6]
CN V	Pons	CN V1: superior orbital fissure CN V2: foramen rotundum CN V3: foramen ovale (skull)	Three sensory nuclei: mesencephalic, principal sensory, and spinal nuclei One motor nucleus	CN V1: frontonasal skin and mucous membranes CN V2: maxillary skin and mucous membranes CN V3: mandibulary skin and mucous membranes, muscles of mastication	One motor nucleus: motor root passes inferiorly to the sensory root Three sensory nuclei: sensory root on the anterior pons at the middle cerebellar peduncle → trigeminal ganglion → divides into 3 nerves: Ophthalmic nerve (CN V1): lateral wall of cavernous sinus → recurrent tentorial branch (supplies tentorium cerebelli) → superior orbital fissure → division into three branches that provide sensory innervation to the skin and mucous membranes of frontonasal structure ^[7] Upper eyelid and conjunctiva, cornea, ciliary bodies, iris Scalp, forehead Frontal, ethmoid, and sphenoid sinuses Superior anterior nasal cavity, bridge of nose Parasympathetic and sensory fibers to lacrimal gland Sympathetic fibers to dilator pupillae muscle Maxillary nerve (CN V2): lateral wall of cavernous sinus→ foramen rotundum → division into branches that provide sensory innervation to the skin and mucous membranes of maxillary structures ^[8] Lower eyelid and conjunctiva Inferior posterior portion of the nasal cavity, lateral nose Upper lip, cheeks, maxillary sinus, upper teeth, and gingiva, superior palate Postganglionic parasympathetic fibers from the pterygopalatine ganglion (from CN VII): lacrimal gland, nasal mucous glands Mandibular nerve (CN V3) Sensory root → foramen ovale (skull) → infratemporal fossa → 4 branches that provide sensory innervation to the skin and mucous membranes of mandibular structures Sensory innervation of: Lower third of the face, including chin and lower lip Buccal membranes, mandibular teeth, and gingiva Anterior ⅔ of the tongue Anterior auricle, external meatus, and tympanic membrane Autonomic fibers via submandibular ganglion to submandibular and sublingual glands Parasympathetic fibers from the chorda tympani (from CN VII): taste in the anterior ⅔ of the tongue Parasympathetic fibers from CN IX to parotid gland Motor root runs along trigeminal cave → joins sensory root → foramen ovale (skull) ^[9] Muscles of mastication: masseter, medial pterygoid, temporalis , and lateral pterygoid muscles Tensor tympani muscle Tensor veli palatini muscle Anterior belly of digastric muscle Mylohyoid muscle
CN VI		Dorello canal Medial cavernous sinus	Abducens nucleus	Lateral rectus muscle	Abducens nucleus (caudal pons) → through the dura mater → Dorello canal → medial wall of cavernous sinus → superior orbital fissure → lateral rectus muscle ^[10]
CN VII		Stylomastoid foramen	Facial motor nuclei Solitary nucleus (gustatory sensation) Salivatory nuclei (parasympathetic)	Muscles of facial expression	Intracranial: large motor and small sensory root exit the brain in the cerebellopontine angle → internal acoustic meatus → roots fuse in the facial canal → geniculate ganglion → branches: Greater petrosal nerve: parasympathetic fibers to mucous glands of the oral cavity, nose, and pharynx as well as the lacrimal gland Nerve to stapedius: motor fibers to stapedius muscle of the middle ear Chorda tympani: sensory fibers to the anterior ⅔ of the tongue, parasympathetic fibers to the submandibular and sublingual glands Exits facial canal via stylomastoid foramen Extracranial: travels anterior to the outer ear Posterior auricular nerve: Motor fibers to intrinsic and extrinsic muscles of the outer ear Sensory fibers to a small area around the concha of the auricle Motor branches to posterior belly of the digastric muscle and stylohyoid muscle Travels through parotid gland → within parotid gland, CN VII splits into five branches that innervate the muscles of facial expression (e.g., orbicularis oculi, platysma) ^[11]
CN VIII		Internal auditory meatus	Vestibular nuclei complex Ventral and dorsal cochlear nuclei	Cochlear pathway: auditory cortex Vestibular pathway: vestibular cortex	Vestibular nuclei complex and ventral and dorsal cochlear nuclei form the vestibulocochlear nerve → internal auditory meatus at the cerebellopontine angle → splits in vestibular nerve and the cochlear nerve ^[12] Cochlear pathway: outer and inner hair cells (from the organ of Corti) → bipolar neurons of the spiral (cochlear) ganglion → cochlear nerve → ventral and dorsal nuclei → superior olivary nucleus → lateral lemniscus → inferior colliculus → medial geniculate body → auditory radiations → primary auditory cortex (transverse temporal gyri of Heschl) and amygdala → auditory association cortex Vestibular pathway: hair cells of the otolith organs and the three semicircular canals → bipolar neurons of the vestibular ganglion → vestibular nerve → vestibular nuclei complex → cerebellum (flocculonodular lobe), nuclei of CN III, CN IV, and CN VI , reticular formation , spinal cord, and thalamus → vestibular cortex
CN IX	Medulla	Jugular foramen	Inferior salivatory nucleus Solitary nucleus Spinal nucleus of the trigeminal nerve Nucleus ambiguus	Pharyngeal mucosa	Postolivary sulcus → jugular foramen (along with CN X and CN XI) → superior and inferior (petrous) ganglia Tympanic nerve: sensory and parasympathetic fibers Sensory fibers to middle ear, internal surface of the tympanic membrane, and Eustachian tube Parasympathetic fibers to parotid gland Descends anterolateral to the internal carotid artery Motor innervation of stylopharyngeus muscle Carotid sinus nerve: sensory fibers to carotid sinus and body Enters pharynx between superior and middle pharyngeal constrictors ^[13] Divides into several sensory branches Unites with vagus fibers → pharyngeal plexus: sensory innervation of oropharyngeal mucosa Taste and sensation to posterior ⅓ of the tongue Tonsillar plexus: sensory innervation of palatine tonsils
CN X		Jugular foramen Esophageal hiatus	Nucleus ambiguus: responsible for motor output and parasympathetic output to the heart and motor innervation of the upper part of gastrointestinal tract (including pharynx, larynx, upper esophagus) Nucleus solitarius: responsible for visceral sensory input (e.g., due to bowel distention, signaling from baroreceptors due to pressure increase) and taste sensation Dorsal nucleus of vagus nerve: responsible for parasympathic output to viscera (heart, lungs, and upper GI) Spinal trigeminal nucleus	Multiple viscera, including the larynx, pharynx, esophagus, heart, lungs, and greater part of the intestine	Cranium: postolivary sulcus → jugular foramen (together with CN IX and CN XI) → sensory innervation of external auditory canal and external ear Neck: carotid sheath → inferior of the internal jugular vein and common carotid artery Right vagus nerve: anterior of the subclavian artery → thorax Left vagus nerve: between left common carotid and left subclavian arteries → thorax Branches Pharyngeal branches: motor innervation of pharyngeal and soft palate muscles Afferent fibers to root of tongue and epiglottis: minor role in taste sensation Superior laryngeal nerve: splits into 2 branches Internal laryngeal nerve: passes underneath the mucosa of the piriform recess, sensory innervation of laryngopharynx and larynx above the vocal cords External laryngeal nerve: motor innervation of cricothyroid muscle Right recurrent laryngeal nerve: under right subclavian artery Left recurrent laryngeal nerve: under aortic arch Both recurrent laryngeal nerves ascend to larynx Motor innervation of majority of intrinsic laryngeal muscles Sensory innervation of larynx below the vocal fold Thorax Right vagus nerve forms posterior vagal trunk → runs along the dorsal esophagus Left vagus nerve forms anterior vagal trunk → runs along the ventral esophagus Both trunks form oesophageal plexus: motor innervation of esophageal smooth muscles Cardiac plexus Parasympathetic fibers → regulation of heart rate (SA node and AV node) Sensory fibers: visceral sensation of heart Pulmonary plexus: visceral sensation of lungs Abdomen: via esophageal hiatus → anterior and posterior vagal trunk → parasympathetic and sensory innervation of lower esophagus, stomach, small intestine, and large intestine up to the splenic flexure
CN XI		Enters: foramen magnum Exits: jugular foramen	Spinal accessory nucleus (C1–C5) Nucleus ambiguus	Sternocleidomastoid and trapezius muscles	Spinal portion: ventral horn of C1–C5/C6 spinal nerve roots → form spinal part of the accessory nerve → enters cranial cavity via foramen magnum → posterior cranial fossa → meets the cranial portion of the accessory nerve → exits via jugular foramen → descends along internal carotid artery → motor fibers to sternocleidomastoid muscle → through posterior triangle of the neck → motor fibers to trapezius muscle Cranial portion: lateral aspect of the medulla oblongata → meets spinal part of the accessory nerve → jugular foramen → combines with CN X at its inferior ganglion ^[14]
CN XII		Hypoglossal canal	Hypoglossal nucleus	Muscles of the tongue	Hypoglossal nucleus → preolivary sulcus → hypoglossal canal → inferior of angle of the mandible → crosses internal and external carotid arteries →intrinsic and extrinsic muscles of the tongue ^[15]

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 4^th 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).

Brainstem and origin of cranial nerves II-XII Brainstem and cerebellar peduncles Cranial nerve nuclei Origin of the cranial nerves Blood supply and cranial nerves of brain Cranial nerve nuclei of the medulla oblongata Mesencephalon (midbrain) Canals and foramina of base of skull Neurovasculature of the inner ear Course and branches of the facial nerve (VII) Trigeminal nerve branches and areas of sensory innervation

Olfactory nerve palsy

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)
- Congenital
  - Primary: congenital anosmia
  - Secondary in diseases such as Kallmann syndrome and primary ciliary dyskinesia
Clinical features: anosmia ^[16]
Testing: identification of certain smells (e.g., peppermint, coffee) ^[3]

Olfactory groove meningioma

Optic nerve palsy

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
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 ^[4]
Testing:
- Visual field test
- Visual acuity test
- Fundoscopy (e.g., papillitis)

Optic glioma Optic atrophy Overview of visual field defects Fundus in optic neuritis

Oculomotor nerve palsy (III)

Clinical features
- Lesions of the motor portion typically produce paralytic squint:
  - Adduction weakness
  - Down-and-out gaze: affected eye looks outwards (exotropia) and downwards (hypotropia)
  - Ptosis
  - Horizontal diplopia: worsens when head is turned away from the side of the lesion
- Lesions of the autonomic (parasympathetic) portion lead to the absence of the pupillary reaction
- 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
Structure	Etiology	Clinical features
Oculomotor nuclei	Ischemic stroke (posterior cerebral artery) Multiple sclerosis	The corticospinal tract is usually also affected, causing syndromes characterized by ipsilateral oculomotor palsy and contralateral hemiparesis: Benedikt syndrome Weber syndrome Unilateral lesion of the oculomotor nucleus can cause bilateral superior rectus muscle palsy. ^[17]
Basilar segment	Aneurysm of the posterior communicating artery Skull base fracture Basal meningitis	Headache Paralytic squint Pupillary involvement: nonreactive, dilated pupil (blown pupil)
Basilar segment	Transtentorial herniation (uncal herniation)	Abducens nerve palsy Features of elevated intracranial pressure (e.g., coma, blown pupil) Hutchinson pupil
Intracavernous segment	Cavernous sinus thrombosis Tolosa-Hunt syndrome Internal carotid artery aneurysms Large parasellar tumors (e.g., meningioma)	CN IV, CN V (CN V1, CN V2), and/or CN VI palsy
Intraorbital segment	Tumors within the orbital cavity Trauma Orbital cellulitis	Loss of vision Pain Proptosis Palsies associated with CN IV and/or CN VI Nonreactive pupil
Isolated oculomotor nerve palsy	Ischemic microangiopathy (e.g., diabetic cranial mononeuropathy, hypertension) Others: multiple sclerosis, myasthenia gravis, giant cell arteritis	Paralytic squint Pupillary involvement: typically sparing the pupil

Testing
- Pupillary response
  - 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
  - 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
- Ocular and extraocular movements
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.

Right-sided Oculomotor Nerve Palsy Pupillary light reflex Clinical testing of the extraocular muscles

Trochlear nerve palsy (IV)

Etiology
- Acquired
  - Microvascular damage (diabetes, hypertension, arteriosclerosis)
  - Cavernous sinus thrombosis
  - Trauma
- Congenital: fourth nerve palsy
Clinical features
- Extorsion of the eye: inability to depress and adduct the eyeball simultaneously
- Diplopia
  - Vertical or oblique diplopia
    - Exacerbated on downgaze (e.g., reading, walking downstairs) away from side of affected muscle ^[18]
    - Worsens when patient turns the head towards the paralyzed muscle → compensatory head tilt to the opposite side of the lesion
- Mild hypertropia and excyclotorsion

With damage to the CN IV, you cannot look at the floor.

Right-sided trochlear nerve palsy Hypertropia

Trigeminal nerve palsy (V)

Etiology
- Tumor
- Vascular compression
- Oral surgery
- Inflammation of the nerve
- Cavernous sinus thrombosis
Clinical features
- Peripheral trigeminal nerve lesions
  - 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.”
- 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
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)

Innervation of the tongue Trigeminal neuralgia Cutaneous innervation of the trigeminal nerve

Abducens nerve palsy (VI)

Etiology ^[10]
- 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) ^[19]
Clinical features
- Horizontal diplopia that worsens when looking at distant objects
- Esotropia: medial deviation of the affected eye at primary gaze
- Inability to abduct the eye (affected individuals will rotate the head to look to the side)

Right-sided Abducens Nerve Palsy

Vestibulocochlear nerve palsy (VIII)

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
- Sensorineural hearing loss
- Vertigo
- Horizontal nystagmus
- Motion sickness ^[20]
Testing ^[21]
- 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)

Glossopharyngeal nerve palsy (IX)

Etiology
- Idiopathic
- Compression of nerve by a blood vessel
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
- Diminished or absent gag response
- Loss of taste in posterior third of the tongue

Lesions that affect the glossopharyngeal nerve typically also affect the vagus nerve because the glossopharyngeal nerve exits the medulla above the vagus nerve.

Innervation of the tongue

Vagus nerve palsy (X)

Etiology
- Trauma
- Diabetes
- Inflammation
- Aortic aneurysms
- Tumors
- Surgery (e.g, recurrent nerve injury during thyroidectomy)
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)
- 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
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 ^[22]
- Barium or water-swallow tests: signs of coughing, choking, or dysphonia, exclusion of differential diagnosis (e.g., achalasia, foreign body aspiration) ^[23]
- Increased resting heart rate (> 100 beats per minute) ^[22]
- Endoscopy or gastric emptying scan: gastroparesis ^[24]

Thyroid gland and relations to surrounding structures Vocal cord paralyses

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)
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
Testing ^[14]
- 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)

Etiology
- Tumors
- Trauma
- Dissection of the internal carotid artery
Clinical features: atrophy and fasciculation of the tongue on the side of the lesion
Testing ^[15]
- 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

Hypoglossal nerve lesion Innervation of the tongue

Multiple cranial neuropathies

Overview of multiple cranial neuropathies ^[25]^[26]^[27]
Condition	Affected cranial nerve	Etiology	Clinical features
Chronic meningitis	Any	Infection (Lyme disease, tuberculosis, cryptococcosis) Inflammation (e.g., sarcoidosis, SLE, neoplasm)	Insidious or subacute headache, fever, and neck stiffness Additional symptoms depend on which CN is involved
Jugular foramen syndrome	CN IX, CN X, and CN XI	Glomus tumor Schwannoma Meningioma Metastatic tumor Cholesteatoma	Loss of taste in the posterior third of the tongue (CN IX) Impaired speech and swallowing: paralysis of vocal cords, palate, and pharyngeal muscles (CN X) Impaired head turning and shoulder elevation: weakness of the trapezius and sternocleidomastoid muscles (CN XI)
Cavernous sinus syndrome	CN III, CN IV, CN V1, CN V2, and CN VI	Neoplasm or inflammation (e.g., Tolosa-Hunt syndrome) Intracavernous aneurysms Cavernous sinus thrombosis	Impaired movement of the eye: paralysis of extraocular muscles (CN III, CN IV, CN VI) Horner syndrome Decreased sensation of the upper face (CN V1, CN V2) See “Skull base syndromes.”
Cerebellopontine angle syndrome	CN V, CN VI, CN VII, CN VIII, CN IX, CN X	Neoplasms of the cerebellopontine angle Vestibular schwannoma Meningioma Metastases Cholesteatoma	Impairment of facial sensation (CN V) Tinnitus Progressive sensorineural hearing loss Gait disequilibrium Vertigo is uncommon. See “Skull base syndromes.”
Guillain-Barré syndrome	Any (most commonly CN III, CN VII, CN IX, CN X)	Autoimmune inflammation of peripheral cranial nerves	Facial droop (CN VII) Dysphonia, dysarthria, and dysphagia (CN IX and CN X) Ophthalmoplegia and diplopia (CN III)
Multiple sclerosis	Any cranial nerve can be affected CN II impairment (retrobulbar neuritis) is a common feature	Autoimmune inflammation of the cranial nerves Ischemic stroke	Vision loss (CN II) Internuclear ophthalmoplegia (INO)

References

Trochlear Nerve Palsy (Fourth Nerve Palsy). https://emedicine.medscape.com/article/1200187. Updated: November 21, 2018. Accessed: April 2, 2019.
The abducens nerve (CN VI). https://teachmeanatomy.info/head/cranial-nerves/abducens-nerve/. Updated: March 13, 2019. Accessed: April 2, 2019.
Duane syndrome. https://rarediseases.org/rare-diseases/duane-syndrome/. . Accessed: April 6, 2017.
The vagus nerve (CN X). https://teachmeanatomy.info/head/cranial-nerves/vagus-nerve-cn-x/. Updated: January 28, 2019. Accessed: April 4, 2019.
Bedside Water-Swallow Testing for Dysphagia. https://www.jwatch.org/na41936/2016/07/28/bedside-water-swallow-testing-dysphagia. Updated: July 28, 2016. Accessed: April 9, 2019.
Gastroparesis Diagnosis. https://www.ucsfhealth.org/conditions/gastroparesis/diagnosis.html. . Accessed: April 9, 2019.
The accessory nerve (CN XI). https://teachmeanatomy.info/head/cranial-nerves/accessory/. Updated: January 2, 2018. Accessed: April 4, 2019.
The hypoglossal nerve (CN XII). https://teachmeanatomy.info/head/cranial-nerves/hypoglossal/. Updated: January 20, 2019. Accessed: April 4, 2019.
Blumenfeld H. Neuroanatomy Through Clinical Cases. Wiley-Blackwell ; 2010
Carroll CG, Campbell WW. Multiple Cranial Neuropathies. Seminars in Neurology. 2009; 29 (1): p.53-65.
Willison HJ, Jacobs BC, van Doorn PA. Guillain-Barré syndrome. Lancet. 2016; 388 : p.717-727. doi: 10.1016/ S0140-6736(16)00339-1 . | Open in Read by QxMD
Multiple Sclerosis (MS). https://www.merckmanuals.com/professional/neurologic-disorders/demyelinating-disorders/multiple-sclerosis-ms. Updated: August 1, 2016. Accessed: April 6, 2017.
Peripheral Vestibular Nystagmus. https://www.aao.org/bcscsnippetdetail.aspx?id=d20f8ad8-845e-46fc-b7ed-7d00216c2726. . Accessed: April 6, 2017.
DIAGNOSIS: How are vestibular disorders diagnosed?. https://vestibular.org/understanding-vestibular-disorder/diagnosis. . Accessed: April 4, 2019.
The olfactory nerve (CN I) and olfactory pathway. https://teachmeanatomy.info/head/cranial-nerves/olfactory-cni/. Updated: December 24, 2018. Accessed: April 2, 2019.
The optic nerve (CN II) and visual pathway. https://teachmeanatomy.info/head/cranial-nerves/optic-cnii/. Updated: October 19, 2018. Accessed: April 2, 2019.
The oculomotor nerve (CN III). https://teachmeanatomy.info/head/cranial-nerves/oculomotor/. Updated: March 13, 2019. Accessed: April 2, 2019.
The trochlear nerve (CN IV). https://teachmeanatomy.info/head/cranial-nerves/trochlear-nerve/. Updated: March 13, 2019. Accessed: April 2, 2019.
The opthalmic division of the trigeminal nerve (CNV1). https://teachmeanatomy.info/head/nerves/ophthalmic-nerve/. Updated: December 22, 2017. Accessed: April 3, 2019.
The opthalmic division of the trigeminal nerve (CNV2). https://teachmeanatomy.info/head/nerves/maxillary-nerve/. Updated: December 24, 2018. Accessed: April 3, 2019.
The opthalmic division of the trigeminal nerve (CNV3). https://teachmeanatomy.info/head/nerves/mandibular-nerve/. Updated: April 2, 2018. Accessed: April 3, 2019.
The facial nerve (CN VII). https://teachmeanatomy.info/head/cranial-nerves/facial-nerve/. Updated: December 31, 2017. Accessed: April 4, 2019.
The vestibulocochlear nerve (CN VIII). https://teachmeanatomy.info/head/cranial-nerves/vestibulocochlear/. Updated: August 7, 2018. Accessed: April 4, 2019.
The glossopharyngeal nerve (CN IX). https://teachmeanatomy.info/head/cranial-nerves/glossopharyngeal-nerve/. Updated: January 2, 2018. Accessed: April 4, 2019.
Bähr M, Frotscher M. Duus' Topical Diagnosis in Neurology. Thieme Medical Pub ; 2012
Ahmed HU. A case of mistaken muscles. BMJ. 2002; 324 (7343): p.962-962. doi: 10.1136/bmj.324.7343.962 . | Open in Read by QxMD
Wrobel BB, Leopold DA. Smell and taste disorders.. Facial Plast Surg Clin North Am. 2004; 12 (4): p.459-68, vii. doi: 10.1016/j.fsc.2004.04.006 . | Open in Read by QxMD