Introduction

Do you know which region of our body has a high number of nerves? It is the head and neck region. 

Among the twelve pairs of cranial nerves, four pairs supply the jaw and lower face (maxillofacial region). They are the: 

• Facial nerve 
• Glossopharyngeal nerve 
• Hypoglossal nerve 
• Trigeminal nerve

These nerves and their branches are so close to the surface of the skin and mucosa that they are more susceptible to injury and damage.

Let us uncover the rabbit hole of trigeminal nerve and trigeminal neuralgia that we will dive into now.

What is trigeminal neuralgia?

Trigeminal neuralgia is a most debilitating form of neuralgia characterised by sudden sharp, severe, stabbing pain in the lower part of the jaw and face.¹ It affects the fifth cranial nerve, the trigeminal nerve, which sends signals to the face and head regions. 

Trigeminal neuralgia most frequently affects only one side of the face (unilateral) and can involve any branch of the trigeminal nerve. Bilateral neuralgia is very rare. It is also known as Tic douloureux or Fothergill’s disease.

Cranial nerves

Our body consists of 12 pairs of cranial nerves.² Cranial nerves originate directly from the brain and not the spinal cord. To reach their specific areas the nerves should exit or enter from the cranium (the base of the skull), hence the name cranial nerves.

The twelve pairs of cranial nerves are called:

1. Olfactory nerve
2. Optic nerve
3. Oculomotor nerve
4. Trochlear nerve
5. Trigeminal nerve
6. Abducent nerve
7. Facial nerve
8. Vestibulocochlear nerve
9. Glossopharyngeal nerve
10. Vagus nerve
11. Accessory nerve
12. Hypoglossal nerve

Trigeminal nerve (CN V)

• It is the fifth cranial nerve, which supplies the head and face region
• It is the largest among the twelve cranial nerves, with the smallest being the trochlear nerve
• The trigeminal nerve is derived from the first pharyngeal arch³
• The trigeminal nerve is a mixed nerve, meaning that it has both sensory and motor fibres
• Its main function is sending sensory information to the skin and mucous membrane, and motor information like movements of the jaw
• The trigeminal nerve arises from four nuclei, where three are sensory and one is motor
  • Nuclei are the collection of neuron cell bodies within the central nervous system
  • The three sensory neurons are called mesencephalic, principal sensory and spinal nuclei
• These nuclei combine and give rise to the three branches of the trigeminal nerve:⁴
  • V1- ophthalmic 
  • V2- maxillary 
  • V3- mandibular
• V1 and V2 have purely sensory components whereas V3 has mixed components (both sensory and motor)

Divisions of the trigeminal nerve

The peripheral aspect of the trigeminal ganglion (ganglion is the collection of neuron cell bodies outside the central nervous system), gives rise to three divisions, they are:

1. V1- ophthalmic nerve. This nerve gives rise to three branches, lacrimal, frontal and nasociliary
2. V2 - maxillary nerve. It gives rise to 14 terminal branches
3. V3 - mandibular nerve. It gives rise to four terminal branches

The sensory part of the nerve supplies the face and the motor nerve supplies the muscles of mastication (chewing).

The trigeminal nerve has a role in sensations in your maxillofacial region like: 

• Touch 
• Smell 
• Motor (moving the jaw to chew)

Aetiology of the trigeminal nerve

The cause of trigeminal neuralgia is still a mystery today, hence the cause of this pain is not completely understood.⁵

There are three types of trigeminal neuralgia. 

Classical trigeminal neuralgia

• In this type, the cause is purely due to damage or pressure on the trigeminal nerve
• The pressure on the arteries or veins puts pressure on the trigeminal nerve causing pain
  • This happens because blood vessels are near the trigeminal nerve
• Sometimes, it's the demyelination of the nerve, which means the pressure on the nerve wears away the protective layer surrounding it (myelin sheath)
  • This leads to pain transmission directly through the nerve

Secondary trigeminal neuralgia

• This type of neuralgia is caused due to other associated problems or medical conditions
• Dental-related problems - sometimes the dental pain is connected, causing trigeminal neuralgia pain due to its proximity to the facial region
• Long-standing multiple sclerosis has its effect on the trigeminal nerve
• Tumours or cysts can also cause pain due to their enlarged mass
• Any head and neck surgery can cause numbness in the facial region

Idiopathic trigeminal neuralgia

• In this type, the cause is unknown

Symptoms of trigeminal neuralgia

Trigeminal neuralgia usually affects the population between 50-70 years of age group.It is most common in women (assigned female at birth). Trigeminal neuralgia comes with several symptoms to be aware of 

• Pain is usually unilateral, affecting one side of the face
• Pain is characterised by severe, sharp, stabbing, recurrent pain where the trigeminal nerve travels
• The sudden or recurrence of pain attacks (paroxysmal) lasts between a few seconds to less than two minutes
• During the attacks of pain, one may experience facial grimacing, watering of the eyes or stress around the face region
•  The pain is so severe that it affects and interrupts the daily routine of individuals

Diagnostic criteria of trigeminal neuralgia

There are five major diagnostic criteria for trigeminal neuralgia:

1. Paroxysmal, unilateral facial pain lasting for a few seconds to less than two minutes
2. The pain is distributed along the course of the trigeminal nerve
3. The pain is characterised by sudden, sharp, stabbing , severe in nature
4. There is no sign of neurological deficit
5. Positive trigger zones⁷

Trigger points or trigger zones are the sensitive areas of the body that cause pain in a specific region when stimulated.

The trigger points that cause pain in the head and face region for trigeminal neuralgia are: 

• Angle of the mouth 
• Bridge of the nose 
• Cheeks 
• Stimulation or irritation from the light breeze
• While brushing teeth 
• Washing face 
• Shaving face

Summary 

• Trigeminal neuralgia is a condition characterised by sudden, sharp, severe stabbing paroxysmal attacks of pain in the facial region
• The trigeminal nerve is the fifth longest cranial nerve. It supplies the sensation like touch, smell, and movement of muscles in the head and face region. Its branches are completely supplied in the face region
• Trigeminal neuralgia is caused due to nerve demyelination, damage to the blood vessels near the trigeminal nerve, tumours, multiple sclerosis and dental problems
• The main symptom of trigeminal neuralgia is pain, which is distributed along the course of the trigeminal nerve in the face region
• The characteristics of pain are a severe, stabbing type, lasting for a few seconds to less than two minutes and usually only affects one side of the face (unilateral)