- Clinical science
Cranial nerve palsy is characterized by a decreased or complete loss of function of one or more . 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||Nerve type||Function|
|I||Olfactory nerve|| |
|II||Optic nerve|| || |
|III||Oculomotor nerve|| |
|IV||Trochlear nerve|| |
|V||Trigeminal nerve|| || |
| || |
|VI||Abducens nerve|| |
|VII||Facial nerve|| |
|VIII||Vestibulocochlear nerve|| || |
|IX||Glossopharyngeal nerve|| || |
| || |
|X||Vagus nerve|| |
|XI||Accessory spinal nerve|| |
|XII||Hypoglossal nerve|| |
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||Nerve Origin||Pathway of the cranial nerve|
|IX|| || |
- Clinical features: impaired vision
|Structure||Anatomy||Typical lesions||Localizing clinical features|
|Oculomotor nuclei|| |
|Basilar segment|| |
|Intracavernous segment|| |
|Intraorbital segment|| |
|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
- Horizontal diplopia that is worse when the head is turned away from the side of the nerve palsy
- Compressive lesions: a non-reactive, dilated pupil
- Ischemic microangiopathy: typically sparing of the pupil
- A dilated pupil → often a compressive lesion (e.g., posterior communicating artery aneurysm)
- Pupillary sparing → often due to ischemic microangiopathy
For more details about oculomotor nerve lesions and , see the article .
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.
- Extorsion of the eye: inability to depress and adduct the eyeball simultaneously
Vertical or oblique diplopia
- Exacerbated on downgaze (e.g., reading) away from side of affected muscle 
- Worsens when patient turns the head towards the paralyzed muscle → head tilt to the opposite side of the lesion
- Vertical or oblique diplopia
- Mild esotropia 
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 .
- 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.
- Peripheral trigeminal nerve lesions
- Most common ocular cranial nerve palsy
- Congenital: Duane syndrome (A rare type of strabismus characterized by an impaired abduction and ptosis on adduction.)
- Clinical features
- See .
- Etiology: often unknown; may be associated with compression by a blood vessel
- 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
- Loss of the gag reflex (efferent limb)
- Flaccid paralysis of the soft palate → nasal speech and deviation of the uvula away from the lesion
- Epiglottic paralysis → aspiration
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)
- Etiology: surgeries of the lateral cervical region, especially the posterior border of the sternocleidomastoid (e.g., resection of cervical lymph nodes)
- Clinical features
|Chronic||Any cranial nerve|| |
|Jugular foramen syndrome||CN IX, X, and XI|
|CN III, IV, V1,V2, VI|
|CN V, VI, VII, VIII, IX, X|| |
Any cranial nerve; most commonly III, VII, IX, X
Connection between III, IV, and VI