Cranial Nerves
Nerve | Function | Possible Abnormal Findings | Possible Causes*,† |
|---|---|---|---|
Olfactory (1st) | Provides sensory input for smell | Anosmia | Head trauma Nasal disorders (eg, allergic rhinitis) Neurodegenerative disorders (eg, Alzheimer disease, Parkinson disease) Paranasal sinusitis Tumors of the cranial fossa, nasal cavity, and paranasal sinuses Viral infections (eg, COVID-19 due to severe acute respiratory syndrome coronavirus 2 [SARS-CoV2]) |
Optic (2nd) | Provides sensory input for vision | Amaurosis fugax (transient monocular blindness), unilateral loss of superior or inferior visual field | Embolism of the ophthalmic artery Ipsilateral internal carotid disease Embolism of retinal arteries |
Anterior ischemic optic neuropathy | Crowded optic disk morphology (with a small-cup-to-disk ratio, called disk at risk) Complications after cataract extraction Connective tissue disease that causes arteritis (eg, giant cell [temporal] arteritis, antiphospholipid antibody syndrome) Hypotension or hypovolemia if severe Ipsilateral internal carotid artery obstruction | ||
Optic neuritis (papillitis and retrobulbar) | Acute demyelinating disease (eg, multiple sclerosis, neuromyelitis optica) Bacterial infections (eg, TB, syphilis, Lyme disease) Postinfectious or disseminated encephalomyelitis Uveitis Viral infections (eg, HIV, herpes simplex, hepatitis B, cytomegalovirus) | ||
Toxic-nutritional optic neuropathy (toxic amblyopia) | Methanol ingestion Nutritional deprivation if severe Organic mercury Vitamin B12 deficiency | ||
Hereditary optic neuropathies | |||
Bitemporal hemianopia | Craniopharyngioma Meningioma of tuberculum sellae Saccular aneurysm in the cavernous sinus Suprasellar extension of pituitary adenoma | ||
Oculomotor (3rd) | Raises eyelids Moves eyes up, down, and medially Adjusts amount of light entering eyes Focuses lenses | Palsies | Aneurysm of posterior communicating artery Ischemia of the 3rd cranial nerve (often due to small-vessel disease as occurs in diabetes or hypertension) or its fascicle in the midbrain Transtentorial herniation due to intracranial mass (eg, subdural hematoma, tumor, abscess) Trauma |
Trochlear (4th) | Moves eye in and down via the superior oblique muscle | Palsies | Often idiopathic Infarction often due to small-vessel disease (eg, in diabetes) Tentorial meningioma Pinealoma |
Para | Myokymia of the superior oblique muscle (typically with brief episodic ocular movements that cause subjective visual shimmering, ocular trembling, and/or tilted vision) | Entrapment of the trochlear nerve by a vascular loop (similar to the pathophysiology of trigeminal neuralgia) | |
Trigeminal (5th) | |||
| Provides sensory input from the eye surface, tear glands, scalp, forehead, and upper eyelids | Neuralgia | Vascular loop compressing the nerve root Multiple sclerosis (occasionally) Lesions of cavernous sinus or superior orbital fissure |
| Provides sensory input from the teeth, gums, lip, lining of palate, and skin of the face | Neuralgia | Lesions of cavernous sinus or superior orbital fissure Multiple sclerosis (occasionally) Vascular loop compressing the nerve root |
Moves masticatory muscles (chewing, grinding the teeth) | Neuropathy | Carcinomatous or lymphomatous meningitis Connective tissue disorders Meningiomas, schwannomas, or metastatic tumors at the skull base | |
Abducens (6th) | Moves the eye outward (abduction) via the lateral rectus muscle | Often idiopathic Increased intracranial pressure Infarction (may be mononeuritis multiplex) Infections or tumors affecting the meninges Nasopharyngeal carcinoma Pontine or cerebellar tumors Pontine infarction | |
Facial (7th) | Moves muscles of facial expression Proximal branches: Innervate tear glands and salivary glands and provide sensory input for taste on the anterior two thirds of the tongue | Palsies | Vestibular schwannoma Basilar skull fracture Infarcts and tumors of the pons Melkersson-Rosenthal syndrome Mobius syndrome Ramsay Hunt syndrome (herpes zoster oticus) Tumors that invade the temporal bone Uveoparotid fever (Heerfordt syndrome) |
Artery loop compressing the nerve root | |||
Vestibulocochlear (8th) | Provides sensory input for equilibrium and hearing | Tinnitus, vertigo, sense of fullness in the ear, and hearing loss | |
Otolithic aggregation in the posterior or horizontal semicircular canal, related to aging and/or trauma Infection (occasionally) | |||
Viral infection | |||
Hearing loss or disturbance | Aging Barotrauma Cerebellopontine angle tumors Exposure to loud noises Hereditary disorders Meningitis Viral infection (possibly) Ototoxic drugs (eg, aminoglycosides) | ||
Glossopharyngeal (9th) | Provides sensory input from the pharynx, tonsils, posterior tongue, and carotid arteries | Ectatic artery or tumor (less common) compressing the nerve | |
Moves muscles of swallowing and controls parotid gland secretion Helps regulate BP | Glossopharyngeal neuropathy | Tumor or aneurysm in the posterior fossa or jugular foramen (jugular foramen syndrome) | |
Vagus (10th) | Moves vocal cords and muscles for swallowing Transmits impulses to the heart (slows the heart rate) and smooth muscles of visceral organs (regulates peristalsis) | Hoarseness, dysphonia, and dysphagia Vasovagal syncope | Entrapment of recurrent laryngeal nerve by mediastinal tumor Infectious or carcinomatous meningitis Medullary tumors or ischemia (eg, lateral medullary syndrome) Tumor or aneurysm in the posterior fossa or jugular foramen (jugular foramen syndrome) |
Accessory (11th) | Turns the head Shrugs the shoulders | Partial or complete paralysis of the sternocleidomastoid and upper trapezius muscles | Iatrogenic (eg, due to lymph node biopsy in posterior triangle of the neck) Idiopathic Trauma Tumor or aneurysm in the posterior fossa or jugular foramen (jugular foramen syndrome) |
Hypoglossal (12th) | Moves the tongue | Atrophy and fasciculation of tongue | Intramedullary lesions (eg, tumors) Lesions of the basal meninges or occipital bones (eg, platybasia, Paget disease of skull base) Surgical trauma (eg, due to endarterectomy) Motor neuron disease (eg, amyotrophic lateral sclerosis) |
* Disorders that cause diffuse motor paralysis (eg, myasthenia gravis, botulism, variant Guillain-Barré syndrome, poliomyelitis with bulbar involvement) often affect the motor part of the cranial nerves. | |||
† Hypertension (microvascular disease), diabetes, and infections can cause individual cranial nerve palsies. | |||