Cranial Nerve Disorders

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Cranial nerves are a set of 12 nerves behind your brain. They are connected to your brain and other parts of your face, neck and torso and play an essential role in your ability to feel and move.

A cranial nerve disorder, also known as cranial neuropathy, refers to an impairment in one or more of these nerves, affecting our ability to move, feel, taste, smell and/or hear. This damage may be caused by injury or an underlying condition, such as diabetes.

A tumour pressing against the olfactory nerve

Sensory Nerves

responsible for your senses, such as smell, hearing and touch.

Motor Nerves

responsible for movement and function of your muscles or glands.

Special Senses

the olfactory nerve, the optic nerve, the facial nerve, the vestibulocochlear nerve, the glossopharyngeal nerve, and the vagus nerve are responsible for conveying sensations to the brain.

What are the functions of different cranial nerves?

I. Olfactory nerve

transmits sensory information to the brain regarding smells and sense of taste.

II. Optic nerve

the sensory nerve that involves eyesight.

III, IV, VI nerves

these 3 cranial nerves are responsible for the synchronised movement of the eyeballs. Any dysfunction or defect in one of these nerves can cause distortion of the eyeball and cause double vision.

V. Trigeminal nerve

the largest cranial nerve that has both sensory and motor functions. Sends information to different parts of the face, from the forehead to the jaw. It also supplies sensations of the face, nose and mouth.

VII. Facial nerve

this nerve has sensory and motor functions in charge of facial expressions, salivary glands, tear-producing glands, and sensations in the ears.

VIII. Vestibulocochlear nerve

this nerve is responsible for our sense of hearing and balance.

IX. Glossopharyngeal nerve

nerve involved in motor and sensory functions for swallowing and sensations of the throat and taste.

X. Vagus nerve

the longest and most complex nerve responsible for various sensory and motor functions, and is part of the circuit responsible for the digestive tract, urogenital tract, respiration and heart rate functioning. It also controls changes in our voice.

XI. Accessory nerve

responsible for controlling certain muscles of the shoulder.

XII. Hypoglossal nerve

responsible for controlling muscles of the tongue.

What are the types of Cranial Nerve Disorders?

There are various types of cranial nerve disorders and are usually classified based on which nerve is affected. Some of these are:

Bell’s palsy

This refers to a condition involving damage in the 7th cranial nerve, the facial nerve. This often results in facial muscle weakness or paralysis. You may experience pain or discomfort on one side or your entire face or head.

Microvascular cranial nerve palsy

This refers to damage to the nerves in the eye. This more commonly occurs in the elderly, or in patients with diabetes or high blood pressure.

Third nerve palsy

Fourth nerve palsy

Also known as fourth nerve palsy, this refers to damage in the 4th nerve, affecting the superior oblique muscle. This may have subtle symptoms, only noticed when the patient walks down a flight of stairs with a tilted head.

Abducens palsy

Also known as sixth nerve palsy, this refers to damage in the 6th nerve, responsible for controlling the horizontal movement of the eyes.

Hemifacial pain and spasm

This refers to a condition where the muscles on one or both sides of the face twitch involuntarily. It may be caused by an injury to the nerves or a tumour.

Trigeminal nerve compression

This condition refers to facial pain or sensations of electric shock as a result of a blood vessel pressing against the trigeminal nerve.

A tumour pressing against the olfactory nerve

Acoustic tumours

How are Cranial Nerve Disorders caused?

Depending on the disorder, some cranial nerve disorders can be caused by an underlying disease, a tumour, injury from trauma, infection, inflammation or stroke. Certain disorders may also be an abnormality or birth defect.

This is why during your consultation, it is important to provide detailed information about any accompanying symptoms, your lifestyle, and your personal and family medical history to get a clearer understanding of your condition.

What are the Symptoms of Cranial Nerve Disorders?

The symptoms you experience may vary greatly and largely depend on the affected nerve involved. Some of these symptoms are, but are not limited to:

● Facial weakness
● Facial dropping
● Dropping of the eyelid
● Headaches
● Loss of taste perception

● Severe excruciating pain associated with trigeminal neuralgia
● Unilateral hearing loss
● Tinnitus
● Loss of smell
● Double vision or blurred vision

● Numbness of the face and mouth
● Throataches or irritation
● Hoarseness of voice
● Absence of gag reflex
● Dizziness

When should I see a doctor?

Cranial nerve disorders should be treated as early as diagnosed. Consult your neurosurgeon for an appointment if you experience any of the symptoms mentioned above.

What can I expect during my first consultation?

For a detailed consultation, the doctor would begin by asking certain questions to better understand your condition: Some of these may be:

● A comprehensive history of your personal and family medical history
● Onset of symptoms
● Symptoms you experience
● Your lifestyle

We would generally conduct a physical exam and run certain tests for an accurate diagnosis.

How are Cranial Nerve Disorders Diagnosed?

Some diagnostic tests typically run are:

Magnetic Resonance Imaging (MRI) scan

MRI is a technique in which high-energy magnetic waves and radio waves produce detailed images. For example, a higher resolution MRI with contrast and other special sequences (CIS) are routinely used for clarification of lower cranial nerves and their relationship with vascular structures to rule out the cause of neuropathy and associated tumours.

Nerve Conduction Velocity (NCV) test and Electromyography (EMG)

It is a procedure in which a needle is used which is inserted into the muscle to assess electrical activity in the area. NCV and EMG tests are important modalities for the functional assessment of nerve fibres and their innervation.

Audiometry

Audiometry is a painless procedure where your hearing capabilities are tested by exposing you to different frequencies in a controlled environment. This helps diagnose acoustic tumours.

Diagnostic tests run largely depend on the initial consultation and the symptoms the patient experiences.

Can Cranial Nerve Disorders be cured?

This is dependent on the type of cranial nerve disorder that the patient suffers from. Some cranial neuropathies can heal on their own, others may need medication, while more severe types require surgery.

Other underlying conditions may need to be treated and managed first such as diabetes, high blood pressure or certain infections. Management may require lifestyle changes as well.

How are Cranial Nerve Disorders treated?

Treatment of the nerve disorder is largely based on the type, severity and location of the disease.

Medical treatments

Certain conditions can be effectively managed with medication:

• Trigeminal neuralgia is treated with medication of carbamazepine or phenytoin.
• Bells palsy is treated with steroid medication.
• Third nerve palsy or Oculomotor nerve palsy caused by diabetes can be treated medically.

Surgical treatments

• Microvascular decompression

This is a minimally invasive (keyhole) approach that addresses trigeminal neuralgia symptoms by creating a cushion between the cranial nerve and vessel to alleviate pressure. A small keyhole incision is made behind the ear. Using sophisticated imaging and an endoscope or microscope, minute pads of Teflon are inserted between the nerve and the vessel to relieve irritation of the nerves.

Alternatively, gamma knife surgery (radiosurgery) can provide targeted doses of radiation to the root entry of the nerve to alleviate the pain.

• Excision of cranial nerve sheath tumours

In some cases, the cranial nerve sheath tumour is excised via a minimally invasive microscopic or endoscopic approach. This takes great skill from the neurosurgeon because of the proximity of the neurovascular structures.

Small tumours (less than 2.5cm) can also be treated via gamma knife radiosurgery.

Summary

Cranial nerve disorders can cause serious illnesses like dysphagia, severe pain, and other symptoms. Early diagnosis leads to early treatment and, therefore, if you do suffer from symptoms of a cranial nerve disorder, please do not hesitate to visit your neurosurgeon. They will work with you in managing these symptoms effectively or providing surgical treatment.

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