What Is the Third Cranial Nerve?

The muscles dominated by the third cranial nerve (oculomotor nerve) show partial to complete weakness, causing the upper eyelids to sag, the pupils to enlarge, and the eyeballs to deflect outward when facing forward.

3rd cranial nerve palsy

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The muscles dominated by the third cranial nerve (oculomotor nerve) show partial to complete weakness, causing the upper eyelids to sag, the pupils to enlarge, and the eyeballs to deflect outward when facing forward.

When the patient tries to turn the eyeball inward, the eyeball moves slowly and only to the midline. The upward and downward gaze of the diseased side eyeball also hinders. When trying to gaze downward, the superior oblique muscle turns the eyeball to the inside.

There are many reasons that can cause paralysis of the third cranial nerve, including most of the main causes of central nervous system diseases, so the choice of auxiliary examination must be based on the specific clinical manifestations of oculomotor nerve paralysis. Intraorbital structural lesions and myopathies of the eye are distinguished from cranial nerve diseases. Exophthalmos or invaginations, a history of severe orbital trauma, or obvious manifestations of inflammation in the orbit all suggest that restrictive orbital diseases hinder the eyeballs. Activity. The diagnosis of myopathy is difficult, but partial third cranial nerve palsy suggests that myopathy is possible. In myopathy, the pupil is always unaffected.

The complete loss of parasympathetic nerve fibers (causing dilation and fixation of the pupil) is a strong indication of oculomotor nerve compression. The most common causes are aneurysms (especially posterior communication artery aneurysms), trauma, and intracranial space-occupying lesions. Occurrence of oculomotor nerve palsy in cases of progressively worsening consciousness suggests a cerebellar herniation, which is a major emergency. If the pupil is not affected at all, other muscles innervated by the oculomotor nerve are involved (such as diabetic eye movement (Nerve palsy) suggests that it may be an ischemic process of the oculomotor nerve or midbrain, and demyelinating lesions are less likely; however, the oculomotor nerve paralysis caused by the aneurysm of the communication artery does not affect the pupils about 5%.

If the oculomotor nerve is paralyzed with severe headaches or changes in consciousness, it indicates that there must be serious illness.

A comprehensive physical examination of the nervous system and CT or MRI should be performed. Lumbar puncture may be considered only in cases where no bleeding is seen on the CT scan but subarachnoid hemorrhage is still suspected. If the aneurysm is strongly suspected to cause subarachnoid hemorrhage, Or when the pupils are significantly affected without a history of head trauma severe enough to cause a skull base fracture, a cerebral angiogram must be performed.