Cranial mononeuropathy III is a problem with the function of the third cranial nerve, which is located on the bottom surface of the brain.

Cranial mononeuropathy III - compression type is a mononeuropathy, which means that only one nerve is affected. In this case, the third cranial (oculomotor) nerve, one of the cranial nerves that controls eye movement, is damaged by compression of the nerve caused by localized lesions or by swelling in the area of the nerve.

Specific causes may include tumors or other lesions (especially tumors located at the base of the brain and pituitary gland), trauma, infections, infarction (tissue damage from loss of blood flow), some cerebral aneurysms, other vascular malformations, sinus thrombosis, and disorders such as mononeuritis multiplex.

On rare occasions, people with migraine headaches may demonstrate a temporary type of oculomotor nerve involvement, probably because of a spasm of the blood vessels. In some cases, no cause can be found.

• Double vision
• Drooping of one eyelid
• Headache or eye pain

Other symptoms may occur if the disorder is caused by tumors or trauma. Decreasing consciousness is a particularly ominous sign, and implies impending severe brain damage or death.

Examination of the eyes may indicate cranial mononeuropathy III. The pupil of the affected eye may be dilated (enlarged). Eye movement abnormalities will vary depending on whether the nerve is damaged completely or incompletely. The gaze may be dysconjugate (the eyes do not align). Investigation must include a complete medical and neurological examination to ascertain whether any other systems of the body are affected.

Blood tests and imaging studies such as a CT scan or MRI are usually necessary. An angiogram of the brain or spinal tap may be important if an aneurysm is suspected.

Some cases may resolve without treatment if the cause is benign. Treatment of the cause (if it can be identified) may relieve the symptoms in many cases. In some cases, corticosteroids may reduce swelling and relieve pressure on the nerve. Surgery may be appropriate to treat eye lid drooping or dysconjugate gaze.

The outcome varies. Some cranial nerve dysfunctions will respond to treatment, but a few cases result in some degree of permanent loss of function. If the dysfunction is caused by brain swelling due to a tumor or stroke, those conditions may cause death.

• Permanent vision changes
• Disfigurement, permanent eyelid drooping

Call the local emergency number such as 911 or go to the emergency room if double vision develops, if there are signs of altered consciousness, unusual headache, or inability to feel or control parts of the body.

Prompt treatment of disorders that could compress the nerve may reduce the risk of developing cranial mononeuropathy III.