Neuralgia, trigeminal - Causes of trigeminal neuralgia

Although the exact cause is not known, trigeminal neuralgia is often thought to be caused by compression of the trigeminal nerve or an underlying condition affecting this nerve.

The trigeminal nerve

The trigeminal nerve (also called the fifth cranial nerve) is the largest nerve inside the skull. You have two trigeminal nerves, one in each side of your face. Small branches from different parts of the face join into three major nerve branches. These are:

• the upper branch (ophthalmic) – which carries sensory information from the skin above the eye, forehead and front of the head
• the middle branch (maxillary) – which carries sensory information from the skin through the cheek, side of the nose, upper jaw, teeth and gums
• the lower branch (mandibular) – which carries sensory information from the skin through the lower jaw, teeth and gums

These branches enter the skull through three different routes and then join together in what is called the Gasserian ganglion, before connecting to the brainstem in the part of the skull called the posterior fossa. 

Trigeminal neuralgia can involve one or more branches of the trigeminal nerve. The maxillary and mandibular branches are affected most often, and the ophthalmic branch is the least commonly affected.

Pressure on the trigeminal nerve

Evidence suggests that in up to 95% of cases, the cause of trigeminal neuralgia is pressure on the trigeminal nerve close to where it enters the brain stem (the lowest part of the brain that merges with the spinal cord), past the Gasserian ganglion.

In most cases, this pressure seems to be caused by an artery or vein compressing the trigeminal nerve, although it's not known why this happens.

It's also not clear exactly why this pressure can cause painful attacks, as not everyone with a compressed trigeminal nerve will experience pain. It may be that, in some people, the pressure on the nerve wears away its protective outer layer called the myelin sheath, which may cause uncontrollable pain signals to travel along the nerve. 

However, this does not fully explain why periods of remission (periods without symptoms) can occur and why pain relief is immediate after a successful operation to move the blood vessels away from the nerve.

Other underlying causes

Other reasons why the trigeminal nerve can become compressed or damaged include:

• a tumour (a growth or lump)
• a cyst (fluid-filled sac)
• arteriovenous malformation (an abnormal tangle of arteries and veins)
• multiple sclerosis (MS) – a long-term condition that affects the central nervous system (the brain and spinal cord)