Causes

The exact cause of trigeminal neuralgia isn't known, but it's often thought to be caused by compression of the trigeminal nerve or an underlying condition that affects this nerve.

The trigeminal nerve also called the fifth cranial nerveprovides sensation to the face. You have one on each side.

Pressure on the trigeminal nerve

Evidence suggests that in up to 95% of cases, trigeminal neuralgia is caused bypressure on the trigeminal nerve close to where it enters the brain stem, the lowest part of the brain that merges with the spinal cord.

In most cases the pressure is caused by an artery or vein squashing (compressing) the trigeminal nerve. These are normal blood vessels that happen to come into contact with the nerve at a particularly sensitive point.

It's not clear why this pressure can cause painful attacks in some people but not others, 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 (myelin sheath), which may cause uncontrollable pain signals to travel along the nerve.

However, this doesn't fully explain why periods without symptoms (remission) 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 cyst a fluid-filled sac
• arteriovenous malformation an abnormal tangle of arteries and veins
• multiple sclerosis (MS) a long-term condition that affects the nervous system