Cranial Nerve Damage From Head Trauma

The cranial nerves are vulnerable to damage during head trauma. Many of them run over the surface of the skull, protected only by the muscles and tissues of the face. Head trauma occurs when there is an injury to the scalp, skull, or brain, like if you have a scalp wound or skull fracture.

Even mild head trauma like a concussion can cause cranial nerve damage. The symptoms may appear immediately following the trauma, or they may not appear until days or weeks after the incident. The effects of cranial nerve injury may be temporary or permanent, depending on the nature of the injury.

This article covers the functions of the 12 cranial nerves and the symptoms you may see if one or more of these nerves are damaged. It also explains how cranial nerve damage is diagnosed and treated, and what to expect if you or someone you know has cranial nerve damage.

Cranial Nerve Functions

There are a total of 12 cranial nerves. These nerves exit from the base of the brain and run through different parts of the face and head. The cranial nerves perform essential functions from providing sensation and controlling facial movements to initiating protective reflexes.

Since the cranial nerves control observable activities such as moving the eyes, chewing, and smiling, damage can be seen and felt when the nerve’s associated function is altered. Here is what the 12 cranial nerves do:

• CN I—Olfactory: provides the sense of smell
• CN II—Optic: communicates visual information from the eye to the brain
• CN III—Oculomotor: controls numerous movements of the eyes and the eyelids; also controls the size of the pupils in response to light
• CN IV—Trochlear: controls the movement of the eyes downward and inward toward the nose
• CN V—Trigeminal: communicates the sensation of touch to the face; also controls the chewing muscles
• CN VI—Abducens: controls the horizontal movement of the eyeball
• CN VII—Facial: moves the muscles that create facial expressions; provides the sense of taste to the front two-thirds of the tongue
• CN VIII—Vestibulocochlear: provides the sense of hearing, communicates information about the body’s position in space to the brain
• CN IX—Glossopharyngeal: controls throat muscles and salivary glands; provides taste information from the back third of the tongue; senses changes in blood pressure and communicates that to the brain so it can respond
• CN X—Vagus: controls the heart, lungs, and abdominal organs
• CN XI—Spinal Accessory: controls throat and neck muscles
• CN XII—Hypoglossal: moves the tongue and enables speech

These nerves control essential functions of the head, face, neck, and more. While sometimes the damage is noticeable right away, it can also take hours to days for a disability to manifest. For example, if there is a growing blood clot pressing on a cranial nerve and the nerve begins to die, this can take some time to show up. 

Symptoms of Cranial Nerve Damage

Different types of cranial nerve damage will cause different symptoms depending on which nerves are damaged. General symptoms of nerve damage include:

• Pain
• Tingling sensation
• Numbness
• Abnormal smell or taste
• Skin that feels sensitive to touch
• Ringing in the ears (tinnitus)
• Weak or paralyzed muscles, which may result in drooling, choking, or slurred speech
• Vision changes and double vision

Damage to specific cranial nerves can produce specific types of symptoms:

• Nose—CN I: One of the most common causes of damage to the olfactory nerve is a traumatic brain injury. Damage to this nerve not only affects the sense of smell but also the ability to taste food since smell is an important component of taste.
• Vision—CN II: Damage to the optic nerve can cause several visual impairments, depending on the location of the injury. Vision loss can affect one or both eyes.
• Eye movements—CN III, IV, and VI: These three cranial nerves control the eyes. Damage to the oculomotor nerve (CN III) can cause a droopy eyelid, changes in the pupil's response to light, and abnormalities in eye movements (up and down, and side to side). Trochlear nerve (CN IV) injury can result in double vision and involuntary (uncontrolled) eye movement (nystagmus).
• Forehead, cheeks, jaw—CN V: Trigeminal nerve damage can affect motor and sensory function in your forehead, cheeks, and jaw. It can also affect teeth clenching and blinking.
  
• Facial motor and sensory dysfunction—CN VII: If the facial nerve is damaged, one side of the face will not be able to make expressions, and lips may not move normally. A droop in the eyebrows, mouth, or both may be seen. Taste may be altered as well. Damage to this nerve is distressing because it impairs one of our most relied upon forms of expression, and also affects one’s self-image.
• Hearing and balance—CN VIII: Damage to the vestibulocochlear, or acoustic, nerve can affect your sense of hearing, as well as your balance, causing dizziness or difficulty walking, sitting, or standing. This can increase your risk of falls.
• Swallowing—CN IX and X: Your ability to swallow and your gag reflex may be affected if your glossopharyngeal and vagus nerves are injured. Hoarseness is another symptom of damage to these nerves.
• Shoulders and head—CN XI: If your spinal accessory nerve is damaged, you may have difficulty shrugging your shoulders and turning your head to the side.
• Tongue—CN XII: Damage to the hypoglossal nerve may cause problems with your ability to control tongue movements.

How Is Cranial Nerve Damage Diagnosed?

Depending on the extent of the injury, healthcare providers may test the cranial nerves as part of a neurological exam, or they may perform specific tests to check the function of individual cranial nerves that may be injured.

To test for sensory and motor function of the cranial nerves, your healthcare provider may ask you to follow a finger with your eyes, say "ah," and stick your tongue out. The provider may also touch certain parts of your face, use a tuning fork, assess your pupillary response to light, and perform other tests.

If necessary, an MRI may be ordered because it can visualize the fine details of the nerves. A CT may be necessary if damage to the structure around the nerves is suspected.

Treatment for Cranial Nerve Damage

If a cranial nerve is completely cut in two, it cannot be repaired. However, if it is stretched or bruised but remains intact, the nerve can recover. This takes time and can cause a variety of unpleasant symptoms including tingling and pain. These symptoms are a good sign that the nerve is healing.

Steroids may be used to decrease inflammation around a cranial nerve. Surgery is sometimes needed if a collection of blood, called a hematoma, is squeezing the nerve and leading to paralysis or dysfunction.

Neurologists and neurosurgeons have specialized assessments and interventions that address this type of nerve damage and should be consulted.

Outlook for Cranial Nerve Damage

Cranial nerve damage may cause partial or complete dysfunction, and the symptoms may be temporary or permanent.

One study looking at cranial nerve damage in patients with traumatic brain injury found that recovery tended to be seen more often among the participants in the younger age group and in people with delayed symptoms.

Nerve damage can be disabling and may require rehabilitation. The nerves that control eye movement and facial expressions may have a greater chance of regaining function than the olfactory, optic, and vestibulocochlear nerves.

Summary

The cranial nerves can be damaged from mild head injuries like concussions or more major injuries like fractures. Symptoms of cranial nerve damage can include pain, abnormal sensations, changes in vision, and weak or paralyzed muscles. They may show up immediately after the incident or may not appear until days or weeks later.

Talk to a healthcare provider immediately if you notice signs or symptoms of cranial nerve damage following head trauma. Treatment is available and, in some cases, the damage can be completely reversed, allowing you to make a full recovery.