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Introduction
  • What is Trigeminal Neuralgia (TN) ? TN is a form of nerve pain affecting the facial region (forehead, nose, sinuses, cheek, lips, teeth, jaw etc). TN is often perceived as the most severe kind of neuralgia, probably because the facial area has a high density of sensory nerve endings per square centimetre. TN is particularly nasty because it affects activities of daily living like eating, swallowing, brushing your teeth, washing / touching your face etc. It more commonly occurs in women, and is usually one sided. There may be an association with the later development of Multiple Sclerosis (MS). The pain is often described by sufferers as paroxysmal, lightening, electric shock/like, lancinating. often followed by a severe dull ache once the lightening pains have subsided. TN is also known as tic douloureux because of uncontrollable facial twitching associated with the pain.
  • The Trigeminal Nerve The trigeminal nerve is the 5th cranial nerve (roman V), and is the major sensory nerve to the face and associated structures. It also supplies the muscles involved in chewing (mastication). The nerve arises from the brain stem, and passes forwards into the temporal bone forming the Gasserian Ganglion (nerve junction box), which sits in a bony hole called Meckles Cave. Three main nerves leave the Gasserian Ganglion to supply the face and are called:-
    • Ophthalmic (V1) Anatomy Diagram - Ophthalmic Nerve (V1)
    • Maxillary (V2) Anatomy Diagram - Maxillary Nerve (V2)
    • Mandibular (V3) Anatomy Diagram - Mandibular Nerve (V3)
  • What is the cause of the pain ? The cause of TN is not completely understood. TN can occur when the trigeminal nerve becomes irritated or compressed anywhere along its length, thereby producing referred pain to the face. The most common cause of nerve compression is by the superior cerebellar artery just as the nerve leaves the brain stem. Other causes include nerve compression by tumours and vascular malformations inside the skull and sinus cavities. Once the nerve becomes irritated, central sensitization occurs in the dorsal horn producing hypersensitivity to a range of sensory modalities. These modalities include light touch, vibration, hot and cold, and position receptors (proprioceptors) in the muscles of mastication.
  • What triggers TN ? A trigger is something that seems to start off an episode of TN, but which is not the direct cause. Various triggers have been identified, dental work being the most common. It may also herald the onset of MS. Hardening of the arteries (arteriosclerosis) may explain why TN becomes more common in the later decades. This combined with high blood pressure may increase the nerve irritation by the overlying superior cerebellar artery i.e. stiff (high blood pressure) hardened (arteriosclerotic) artery.
  • Which parts of the face are most commonly affected ?

Trigeminal Branches

% Affected

V1 only

2.8

V2 only

17.7

V3 only

14.6

V1 + V2

17.2

V2 + V3

35.4

V1 + V3

0

V1 +V2 +V3

12.3
  • What are the clinical findings in TN ? There is frequently mild sensory loss to pinprick and light touch in the same distribution as the neuralgia. There is also loss of the corneal reflex (blink reflex produced by touching the surface of the eye with cotton wool) if the neuralgia is in V1. Gently stroking the affected area or applying hot or cold may reproduce the usual neuralgic symptoms. The pain is usually so severe that many patients are reluctant to be examined in this way.
  • Which investigations should be performed ? Magnetic Resonance Imaging (MRI) can be used to exclude tumours within the head. Demyelination associated with MS can also be excluded at the same time. Magnetic Resonance Angiography (MRA) can be used to investigate whether there is vascular compression of the trigeminal nerve root close to the brain stem.
Treatment

  • Drug Treatments

    • Low dose amitriptyline (10 / 50 mg per day) combined with either carbamazepine (600 / 800 mg per day) or gabapentin (1800 / 2400 mg per day) is most commonly used.
    • Oxcarbamazepine is still being evaluated.
    • All the other common anti-convulsants have been used in TN.
  • Surgery
    • Microvascular Decompression (MVD) of the irritated trigeminal nerve is the treatment of choice for younger fitter patients who have failed a trial of maximal oral medication. The trigeminal nerve is exposed by performing a Craniotomy Diagram - Craniotomy Position for MVD (small hole in the skull behind the ear). The vascular loop of the Superior Cerebellar Artery Anatomy Diagram - Superior Cerebellar Artery is teased out from underneath the trigeminal nerve. A piece of surgicel gelfoam or similar substance is placed between the artery and the nerve to prevent future compression.
    • Complications include bleeding, infection, and nerve damage to the trigeminal, facial or vestibular nerves. Trigeminal nerve injury can produce permanent numbness in the face (and associated structures) with loss of chewing ability on that side. Facial nerve injury can cause paralysis of the facial muscles of expression. Vestibular nerve injury can cause loss of hearing and balance on that side. Like any surgical procedure, the risks and benefits must be weighed.
  • Injections
    • For patients where surgery and anaesthesia is too risky, Injection Techniques Injection Technique - Gausserian Ganglion may offer relief. The Gasserian Ganglion can be partially ablated as it sits in Meckles Cave either by using Glycerol or with a radiofrequency lesion. A small thin needle is inserted into the middle of the cheek under local anaesthesia, and gently guided with x-ray assistance through the foramen ovale into Meckles Cave where the Gasserian Ganglion sits. It is important to treat the correct branch of the trigeminal nerve involved in the pain, to avoid excessive numbness post-procedure.
    • Complications include failure of pain relief and permanent facial numbness. Anaesthesia dolorosa can occur where there is a permanent painful facial numbness.
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