• Clinical science

Cranial nerve palsies


Cranial nerve palsy is characterized by a decreased or complete loss of function of one or more cranial nerves. The etiology may be congenital or acquired. Multiple cranial neuropathies are common, particularly in lesions arising from tumors, trauma, impaired blood flow, 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.

Cranial nerve types and functions

Cranial nerve Nerve Type Nerve Function
I Olfactory nerve
  • Sensory
II Optic nerve
  • Sensory
  • Vision
  • Afferent arm of the pupillary light reflex
III Oculomotor nerve
  • Motor (somatic)
IV Trochlear nerve
  • Motor
V Trigeminal nerve
  • Sensory
  • Facial sensation: ophthalmic (V1), maxillary (V2), mandibular nerve (V3)
  • Mucous membranes of the oral and nasal cavity; soft and hard palate
  • Teeth; temporomandibular joint
  • Meninges
  • Anterior wall of the external auditory canal
  • Somatosensation of anterior ⅔ of the tongue
  • Afferent arm of the corneal reflex
  • Motor
  • Muscles of mastication: masseter, temporalis, medial pterygoid, lateral pterygoid muscles
  • Tensor tympani muscle
  • Tensor veli palatini muscle
  • Anterior belly of the digastric muscle
  • Mylohyoid muscle
VI Abducens nerve
  • Motor
VII Facial nerve
  • Sensory
  • Taste perception: anterior ⅔ of the tongue (chorda tympani)
  • Skin behind the ear (posterior auricular branch)
  • Tympanic membrane (chorda tympani)
  • Motor (somatic)
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 arm of the gag reflex
  • Visceral sensation: carotid sinus (baroreceptors detect blood pressure)
  • Chemoreception: carotid body (chemoreceptors detect partial pressure of O2 and CO2, and pH)
  • Motor (somatic)
  • Swallowing: pharyngeal muscles
  • Stylopharyngeus
X Vagus nerve
  • Sensory (somatic)
  • Posterior wall of the external auditory canal
  • Supraglottic region; larynx; trachea
  • Sensory (visceral)
  • Heart rate
  • Blood vessel vasodilation
  • Visceral function: promotes the motility of the esophagus, stomach, intestines (up to the splenic flexure), and other abdominal organs
  • Motor (somatic)
  • Swallowing
    • Middle and inferior pharyngeal constrictor muscles (passage of bolus)
    • Palatoglossus muscle (elevates posterior tongue upon swallowing)
  • Speech: laryngeal muscles
XI Accessory spinal nerve
  • Motor
XII Hypoglossal nerve
  • Motor
  • Tongue protrusion: intrinsic and extrinsic muscles of the tongue


Origin and pathways of the cranial nerves

Cranial Nerve Nerve Origin Pathway of the cranial nerve
  • Medulla
  • Postolivary sulcus (along with CN X and XI) → superior ganglionjugular foramen (formed by temporal and occipital bones)
    • Innervates part of the external ear: passes through the external auditory meatus
    • Innervates the carotid body: via the inferior petrosal ganglion
    • Innervates taste buds: via the inferior petrosal ganglion
    • Stylopharyngeus muscle: from the nucleus ambiguus (in the lateral medulla)
    • Parotid glands: inferior salivary nucleusotic ganglionauriculotemporal nerveparotid glands
  • Postolivary sulcus → jugular foramen (formed by temporal and occipital bones)
  • Synapses
    • Superior (jugular) ganglion
    • Inferior (nodose) ganglion
    • Intramural ganglia of visceral organs (e.g., esophagus, stomach)
  • Medulla
  • Medulla

Cranial mononeuropathies

A cranial nerve mononeuropathy is a condition in which only a single cranial nerve or nerve group is damaged. The clinical presentation of cranial nerve mononeuropathies depends on the underlying cause as well as the region that is affected along its pathway.

Olfactory nerve palsy

Optic nerve palsy

Oculomotor nerve lesion (III)


Structure Anatomy Typical lesions Localizing clinical features
Oculomotor nuclei
  • A pair of oculomotor nuclei are located at the level of the midbrain, ventral to the aqueduct of Sylvius
  • Fascicles (efferent fibers) from each oculomotor nucleus pass through the red nuclei and the emerge anteriorly through the medial aspect of the cerebral peduncle as the oculomotor nerve
Basilar segment
  • Tentorial (uncal) herniation
Intracavernous segment
  • Associated palsies of the trochlear (IV), trigeminal (V1, V2 nerve), and/or abducens (VI) nerve
Intraorbital segment
  • Tumors within the orbital cavity
  • Trauma
  • Orbital cellulitis
  • Loss of vision
  • Pain
  • Proptosis
  • Associated palsies of the trochlear (IV) and/or abducens nerve (VI)
  • Non-reactive pupil
Ischemic microangiopathy can affect any part of the oculomotor nerve from the basilar segment and typically results in an oculomotor nerve palsy with pupillary sparing.

Isolated oculomotor nerve palsy

  • Etiology
  • Clinical features
    • Paralytic squint
      • Adduction weakness
      • The affected eye looks outwards (exotropia) and downwards (hypotropia)
    • Ptosis
    • Horizontal diplopia that is worse when the head is turned away from the side of the nerve palsy
    • Pupillary involvement
      • Compressive lesions: a non-reactive, dilated pupil
      • Ischemic microangiopathy; or demyelinating cranial neuropathies: typically sparing of the pupil
  • Diagnostics
    • A dilated pupil → often a 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 → often due to ischemic microangiopathy
  • Treatment
    • Compressive lesions: surgery
      • Posterior communicating artery aneurysm: urgent neurosurgical clipping or endovascular coiling
    • Ischemic microangiopathy or demyelinating lesions: medical management with adequate control of the underlying disease
  • Prognosis
    • Compressive lesions: Partial recovery may occur within 6–7 months.
    • Ischemic microangiopathy or demyelinating lesion: usually resolves spontaneously within 3–4 months.

For more details about oculomotor nerve lesions and drugs affecting pupillary size, see the learning card pupillary abnormalities.

With an isolated ocuLOVEmotor nerve palsy, nobody loves you when you are down and out (the pupil points outwards and downwards)!

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.

The rule of pupillary involvement is not infallible since approx. 20% of patients with ischemic microangiopathy may have pupillary involvement.

Trochlear nerve lesion (IV)

In acquired lesions of fourth nerve, patients report vertical, torsional, or oblique diplopia. Diplopia is usually worse on downgaze and gaze away from side of affected muscle.

  • Etiology
  • Clinical features
    • Extorsion of the eye: inability to depress and adduct the eyeball simultaneously (the pupil shoots upward during attempted adduction of the eyeball)
    • Diplopia (double vision)
      • Vertical or oblique diplopia , which is exacerbated on downgaze (e.g., reading)
      • Diplopia worsens when the patient turns their head towards the paralyzed muscle; The patient compensates by turning his head to the opposite side of the lesion.
    • Mild esotropia

Trigeminal nerve lesion (V)

  • Etiology
  • Clinical features
    • Peripheral trigeminal nerve lesions
      • Ophthalmic nerve (V1) is affected → absent corneal reflex (afferent limb), anesthesia of the forehead
      • Maxillary nerve (V2) is affected; anesthesia of the midface
      • Mandibular nerve (V3) is affected anesthesia of the chin, lower lip, and anterior two-thirds of the tongue; muscles of mastication are paralyzed
        • The jaw deviates towards the side of the lesion because of unopposed action from the opposite pterygoid muscle.
      • Involvement of any of the three branches can cause trigeminal neuralgia.
    • Lesion of the tensor tympani branch → hearing impairment (particularly difficulty hearing low-pitched sounds)
    • Lesions of the trigeminal nerve nuclei: Depending on which nuclei are affected; , the patient may present with ipsilateral weakness of muscles of mastication and/or ipsilateral loss of sensation.
    • Complete trigeminal nerve lesions are rare.


Abducens nerve lesion (VI)


Facial nerve lesion (VII)

Vestibulocochlear nerve lesion (VIII)


Glossopharyngeal nerve lesion (IX)

  • Etiology: often unknown; may be associated with compression by a blood vessel
  • Clinical features
    • Loss of the gag reflex (afferent limb)
    • Loss of the carotid sinus reflex
    • Flaccid paralysis of the soft palate deviation of the uvula away from the lesion (similar to vagus nerve lesions)
    • 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

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 lesion (X)

  • Etiology
  • Clinical features
    • Loss of the gag reflex (efferent limb)
    • Flaccid paralysis of the soft palatenasal speech and deviation of the uvula away from the lesion
    • Epiglottic paralysisaspiration
    • Dysphagia
    • Features of vocal cord paralysis
      • Dysphonia (hoarseness)
      • The vocal cord assumes a paramedian position.
    • Dysfunction of vagal nerve in the stomach → features of gastroparesis (poor gastric emptying)

Accessory nerve lesion (XI)

Hypoglossal nerve lesion (XII)

  • Etiology
    • Tumors
    • Trauma
  • Clinical features
    • Atrophy and fasciculation of the tongue on the side of the lesion
    • The tongue deviates to the side of the lesion when protruded.

Multiple cranial neuropathies

Lesion Etiology Clinical features
Chronic meningitis Any cranial nerve
Jugular foramen syndrome CN IX, X, and XI
Cavernous sinus syndrome CN III, IV, V1,V2, VI
Cerebellopontine angle syndrome CN V, VI, VII, VIII, IX, X
Guillain-Barré syndrome

Any cranial nerve; most commonly III, VII, IX, X

  • Facial droop (CN VII)
  • Dysarthria and dysphagia (CN IX and X)
  • Ophthalmoplegia and diplopia (CN III)
Multiple sclerosis


Connection between III, IV, and VI