ConditionBrain & nerves
Cranial Nerve Injury
A cranial nerve injury is damage to one or more of the 12 pairs of nerves that leave the brain directly and control smell, vision, eye movements, facial feeling and expression, hearing, balance, swallowing, speech and some neck and tongue muscles. Causes include head injury, surgery, stroke, tumors, infections, inflammation and reduced blood supply from diabetes. Symptoms depend on which nerve is affected, such as double vision, a drooping face or loss of smell. Many injuries recover partly or fully over months.
Also called: Cranial neuropathy, cranial nerve palsy, cranial nerve damage, cranial nerve dysfunction
At a glance
- What it is
- Damage to one or more of the 12 cranial nerves that leave the brain and brainstem.
- Common causes
- Head trauma, surgery, stroke, tumors, diabetes and high blood pressure, infections, inflammation.
- Symptoms
- Depend on the nerve: loss of smell, vision problems, double vision, facial weakness or numbness, hearing loss, swallowing or voice problems.
- Diagnosis
- Neurological examination, MRI or CT, and targeted tests of hearing, vision or nerve function.
- Treatment
- Treat the cause, protect the eye if it cannot close, therapy for swallowing and speech, surgery in selected cases.
When to get help
Call 911 or go to the ER
- Sudden double vision, facial droop, slurred speech, trouble swallowing or weakness of an arm or leg: call 911 or your local emergency number
- A drooping eyelid with a dilated pupil or severe headache
- Cranial nerve symptoms after a head injury, especially with drowsiness, vomiting or clear fluid from the nose or ear
- Several cranial nerves affected at once with fever, stiff neck or rapidly spreading weakness
See a doctor within a day or two
- New facial weakness on one side (possible Bell's palsy or other cause), ideally assessed within 72 hours
- Sudden hearing loss in one ear
- New double vision in someone with diabetes, even if the pupil is normal
- Hoarseness or swallowing difficulty after neck or chest surgery
Book a routine appointment
- Gradual loss of smell, hearing or facial sensation
- Facial pain attacks like electric shocks
- Slowly progressive weakness of the tongue, face or eye muscles
The 12 cranial nerves and what injury causes
| Nerve | Function | Signs of injury |
|---|---|---|
| I Olfactory | Smell | Loss of smell (anosmia) and reduced taste of flavors |
| II Optic | Vision | Vision loss, field defects, color washout |
| III Oculomotor | Most eye movements, eyelid lift, pupil | Drooping eyelid, eye turned down and out, large pupil, double vision |
| IV Trochlear | Eye moves down and in | Vertical double vision, worse reading or going downstairs; head tilt |
| V Trigeminal | Face sensation, chewing | Facial numbness, jaw weakness, facial pain |
| VI Abducens | Eye moves outward | Horizontal double vision, worse looking to the affected side |
| VII Facial | Facial expression, taste, tears | Facial droop, cannot close eye, drooling, altered taste |
| VIII Vestibulocochlear | Hearing and balance | Hearing loss, tinnitus, vertigo |
| IX Glossopharyngeal | Throat sensation, swallowing | Swallowing difficulty, reduced gag |
| X Vagus | Voice, swallowing, heart rate | Hoarseness, swallowing problems, nasal speech |
| XI Accessory | Shoulder shrug, head turning | Shoulder drop and weakness |
| XII Hypoglossal | Tongue movement | Tongue deviates to the weak side, slurred speech |
Causes of cranial nerve injury
Trauma
Head injuries are a leading cause. Smell is commonly lost after blows to the back of the head. Fractures of the skull base and temporal bone can damage the facial and hearing nerves. The fourth and sixth nerves are vulnerable because of their long paths.
Surgery
Operations on the brain, skull base, ear, neck, thyroid and chest can injure nerves. Damage to the recurrent laryngeal branch of the vagus nerve causes vocal cord paralysis and hoarseness.
Reduced blood supply
Diabetes and high blood pressure can cause a "microvascular" palsy, most often of the third, fourth or sixth nerve, causing sudden double vision. The pupil is usually spared, and most recover within 3 months.
Stroke
Brainstem strokes affect cranial nerve nuclei, often with weakness or numbness of the body on the opposite side. See stroke.
Tumors and aneurysms
Acoustic neuromas, meningiomas, pituitary tumors, skull base cancers and brain aneurysms can compress nerves. A third nerve palsy with a dilated pupil can be caused by an expanding aneurysm and is an emergency.
Infections and inflammation
- Bell's palsy: sudden, usually temporary facial nerve weakness, thought to be viral.
- Shingles (Ramsay Hunt syndrome affects the facial and hearing nerves).
- Lyme disease, which can cause facial palsy, sometimes on both sides.
- Meningitis, HIV and tuberculosis.
- Sarcoidosis, multiple sclerosis, Guillain-Barré syndrome and other inflammatory conditions.
Other causes
Raised pressure in the skull (affecting the sixth nerve), giant cell arteritis, and conditions such as myasthenia gravis can mimic cranial nerve injury by affecting the nerve-muscle junction.
Diagnosis
- History: speed of onset, injuries, surgery, diabetes, infections and other symptoms.
- Neurological examination of each cranial nerve, plus strength, sensation and coordination.
- Imaging: MRI of the brain and cranial nerves is the main test; CT for trauma and fractures; CT or MR angiography for suspected aneurysm.
- Other tests: hearing tests, eye examinations and visual fields, swallowing studies, laryngoscopy for voice problems, nerve conduction studies, blood tests for diabetes, inflammation, Lyme disease and other causes; sometimes a lumbar puncture.
Treatment
Treatment targets the cause and protects function while the nerve recovers:
- Bell's palsy: steroids within 72 hours improve recovery; antivirals are sometimes added.
- Eye protection: lubricating drops, ointment and taping the eyelid at night when the eye cannot close, to prevent corneal damage.
- Double vision: an eye patch or prism glasses; botulinum toxin or eye muscle surgery if it persists beyond 6 to 12 months.
- Microvascular palsies: control blood sugar and blood pressure and wait for recovery.
- Tumors and aneurysms: surgery, radiosurgery or endovascular treatment.
- Swallowing and speech problems: speech and language therapy and diet changes; vocal cord injection or surgery for hoarseness.
- Smell loss: smell training with a set of strong scents twice daily may help recovery.
- Facial nerve injury: physical therapy, and nerve repair, grafting or reanimation surgery in selected cases.
- Nerve pain: medicines such as carbamazepine for trigeminal neuralgia.
Recovery and outlook
Recovery depends on the cause and how badly the nerve was damaged. Nerves that are bruised or stretched often recover over weeks to months. Most microvascular palsies resolve within 3 months, and most people with Bell's palsy recover fully within 6 months. Nerves that are cut or crushed recover more slowly and less completely, at roughly 1 mm a day if they regrow. Smell loss after head injury improves in a proportion of people over the first year or two.
Frequently asked questions
What are the symptoms of cranial nerve damage?
Symptoms depend on which nerve is affected. Common signs are loss of smell, vision loss, double vision, a drooping eyelid, facial numbness or weakness, hearing loss, dizziness, hoarseness, swallowing difficulty and tongue weakness. Sudden symptoms need urgent medical assessment.
Can damaged cranial nerves heal?
Often, yes. Many cranial nerve injuries improve over weeks to months, particularly microvascular palsies and Bell's palsy. Recovery is slower and less complete after severe trauma or when the nerve has been cut, but therapy and surgery can improve function.
What causes a sixth nerve palsy?
The sixth (abducens) nerve can be affected by diabetes and high blood pressure, head injury, raised pressure inside the skull, tumors, infections and inflammation. It causes horizontal double vision that is worse when looking toward the affected side. In children it can follow viral infections.
Is Bell's palsy a cranial nerve injury?
Yes. Bell's palsy is sudden weakness of the seventh (facial) cranial nerve, usually on one side, thought to be caused by viral inflammation. Most people recover fully within weeks to months, and early steroid treatment improves the chance of complete recovery.
Sources
This guide was written from current patient and clinical guidance, including:
- National Institute of Neurological Disorders and Stroke: Bell's palsy; Trigeminal neuralgia
- American Academy of Ophthalmology: Fourth, sixth and third nerve palsies
- MedlinePlus: Cranial mononeuropathy
- Merck Manual Professional: Overview of cranial nerves
- American Academy of Otolaryngology-Head and Neck Surgery: Facial nerve disorders