Cranial Nerve Palsy

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Introduction

Cranial nerve palsy is a neurological disorder. The cranial nerves consist of twelve pairs of nerves that emerge directly from the brain, as opposed to emerging from the spinal cord. The function of the cranial nerves may be sensory, motor or both. Cranial nerve palsy occurs when a cranial nerve responsible for motor control is damaged, as a result of a congenital defect, vascular disease or traumatic injury. The causes of cranial nerve palsies vary, and may include bleeding in or around the brain, brain tumors, viruses, abscesses or migraines, according to the American Association for Pediatric Ophthalmology and Strabismus. In some cases the cause cannot be determined. Appropriate treatment options for cranial nerve palsies are based on the underlying cause.

Cranial Nerves

Of the twelve cranial nerve pairs, the oculomotor, trochlear, abducens, accessory, and hypoglossal nerves serve primarily motor functions, according to the Merck Manual Home Edition. These are the 3rd, 4th, 6th, 11th and 12th cranial nerves, respectively. The trigeminal, facial, glossopharyngeal, and vagus nerves also demonstrate motor, as well as sensory, functions.

Oculomotor Nerve Palsy

Oculomotor nerve palsy is a palsy of the 3rd cranial nerve pair. This cranial nerve controls the movement of the majority of the muscles of the eye. A patient with oculomotor nerve palsy may experience double vision, because the palsy causes the eye to look down and outward, according to Merck Manual Home Edition. The 3rd cranial nerve is also responsible for constriction of the iris. A patient with 3rd cranial nerve palsy experiences a dilated pupil and the inability to focus on close-up objects.

Fourth Cranial Nerve Palsy

Fourth cranial nerve palsy, or trochlear nerve palsy, results in paralysis or weakness of the extraocular muscle, called the super oblique muscle. Trochlear nerve palsy prevents the vertical alignment of the eye. The eyes can be realigned with strabismus surgery, according to the American Association for Pediatric Ophthalmology and Strabismus,.

Sixth Cranial Nerve Palsy

Individuals with sixth cranial nerve palsy may experience double vision and an inability to look outward. The eye may turn inward. Other symptoms may include headache, fluid build-up in the conjunctiva, facial numbness, and loss of vision. Sixth cranial nerve palsy results from disorders that restrict blood flow to the nerve, increased skull pressure or increase nerve pressure from swelling in the area. Treatment of sixth cranial nerve palsy depends on the underlying cause but in some instances may require removal of tumors or treatment of blood vessel abnormalities.

Twelfth Cranial Nerve Palsy

The hypoglossal nerve, also known as the twelfth cranial nerve, innervates the tongue. Hypoglossal nerve palsy impairs the motor function of the tongue on one side, causing the tongue to deviate to one side and resulting in weakness and atrophy of the muscle, according to the Merck Manual. Individuals affected by this disorder have difficulty eating and speaking. Hypoglossal nerve palsy is rare. Healthcare providers may use CT and MRI to locate lesions on the nerve, reports Elizabeth Thompson, author of “Hypoglossal Nerve Palsy: A Segmental Approach.”

References

American Association for Pediatric Ophthalmology and Strabismus, https://www.aapos.org/terms_faqs/faq_list/cranial_nerve_palsy_general_information

The Merck Manual Online Medical Library, https://www.merckmanuals.com/home/sec06/ch096/ch096a.html

Thompson, Elizabeth O. “Hypoglossal Nerve Palsy: A Segmental Approach”, https://radiographics.rsna.org/content/14/5/939.full.pdf