• Clinical science

Cranial nerve palsies

Summary

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 Function
I Olfactory nerve
  • Sensory
II Optic nerve
  • Sensory
III Oculomotor nerve
  • Motor (somatic)
IV Trochlear nerve
  • Motor
V Trigeminal nerve
  • Sensory
VI Abducens nerve
  • Motor
VII Facial nerve
  • Sensory
  • Motor (somatic)
VIII Vestibulocochlear nerve
  • Sensory
  • Balance and equilibrium: vestibular nerve
  • Hearing: cochlear nerve
IX Glossopharyngeal nerve
  • Sensory
  • Motor (somatic)
X Vagus nerve
  • Sensory (somatic)
  • Sensory (visceral)
  • Motor (somatic)
XI Accessory spinal nerve
  • Motor
XII Hypoglossal nerve
  • Motor

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.

References:[1][2][3]

Origin and pathways of the cranial nerves

Cranial Nerve Nerve Origin Pathway of the cranial nerve
I
II
III
IV
V
VI
VII
VIII
IX
  • Medulla
X
XI
  • Medulla
XII
  • 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)

Neuroanatomy

Structure Anatomy Typical lesions Localizing clinical features
Oculomotor nuclei
  • A pair of oculomotor nuclei are located at the level of the midbrain
  • Fascicles (efferent fibers) from each oculomotor nucleus pass through the red nuclei and the emerge anteriorly as the oculomotor nerve
Basilar segment
  • Tentorial herniation
Intracavernous segment
  • Associated palsies of the trochlear (IV), trigeminal (V1, V2 nerve), and/or abducens (VI) nerve
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

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

Trochlear nerve palsy (IV)

Trigeminal nerve lesion (V)

References:[6]

Abducens nerve palsy (VI)

References:[7][8] [9]

Facial nerve lesion (VII)

Vestibulocochlear nerve lesion (VIII)

References:[10]

Glossopharyngeal nerve lesion (IX)

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)

Accessory nerve lesion (XI)

Hypoglossal nerve lesion (XII)

  • Etiology
    • Tumors
    • Trauma
  • Clinical features

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

Multiple sclerosis

CN II

Connection between III, IV, and VI

References:[11][12][13][14]