Trigeminal neuralgia

Conflitti Neuro-vascolari

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Definition and Etiology

Neurovascular conflicts include a set of syndromes caused by the compression of the cranial nerves and generally corresponding to their entry point into the brainstem (root entry zone or REZ).

The REZ corresponds to the point in which the sheath (myelin) of central origin (oligodendrocytes) is modified into peripheral myelin (Schwann cells).

Trigeminal neuralgia or tic doloreux is one of the most frequent causes of facial pains and affects the areas that are innervated by the trigeminal nerve. The latter is the fifth pair of cranial nerves, which is in charge of the sensory perception of the face and exerts some motor functions (such as chewing).

The incidence of neuralgia is equal to 4-5 new cases per year for every 100,000 inhabitants and is higher in the female gender.

Being a prevalently sensitive nerve, the surface of the face is considered as its origin. From there the fibres converge through the three branches (hence the name trigeminal) ophthalmic (V1), maxillary (V2), and mandibular (V3) into the Gasserian ganglion to then end in their own nucleus within the brainstem.

The ophthalmic branch supplies sensations to the frontal region of the face and to the maxillary region of the nose and jaw, while the mandibular branch supplies sensations to the mouth and mandibular arch.

Trigeminal neuralgia in its typical form is characterised by four elements:

piercing or electrical pain generally in one or more of the three territories or divisions of the trigeminal nerve
presence of points on the face which, if stimulated, evoke the pain (trigger points) (middle of the eyebrow, nose wing, hemilip)
specific stimuli inducing the pain (triggers)
sudden beginning of the symptoms

Trigeminal neuralgia generally appears in subjects who are older than 50, and can induce extremely negative effects on the patient’s emotional structure, since he/she will experience periods of intense pain alternated by moments of fear for the possible return of the symptoms.

In the past, when there was no possible cure, some patients would even face suicide to end this atrocious pain.

In most patients, typical trigeminal neuralgia is caused by the close contact of the nerve with a cerebellar artery (neurovascular conflict), in a smaller number of cases the conflict can be with a vein.

The repeated contact with an artery (and its respective pulsatility) causes the trigeminal to lose the myelin sheath covering the sensory fibres, which tend to develop anomalous spontaneous impulses that reveal themselves with the well-known painful sensations.

Atypical trigeminal neuralgia is characterised by an absence of defined trigger points, intermittent or persistent pain, numbness of the face. In these cases, even a reduction of taste, in particular of salty foods, can be perceived.

The causes of atypical trigeminal neuralgia should be investigated in other concomitant pathologies, such as multiple sclerosis, Herpes infections, skull base tumor, with consequent direct compression of the nerve.

Multiple sclerosis is the cause of about 2% of trigeminal neuralgias. 18% of all patients with bilateral trigeminal neuralgia suffers from multiple sclerosis.

Symptoms

The pain is extremely strong, and can last from a few seconds to some minutes. It is described by patients as “piercing” or similar to “electrical shock” or a “stab”.

Trigeminal neuralgia usually affects only one side of the face and is often triggered by simple actions in daily life, such as chewing, brushing your teeth, talking, blowing your nose.

In the period between one seizure and the next, the patient does not feel any pain.

Spontaneous remissions can last weeks, months, or years. Frequently, as time goes by, the intervals become shorter and shorter, and the relapses more serious and of a longer duration.

Diagnosis

To diagnose trigeminal neuralgia, first of all, an accurate and complete medical history is required, in order to distinguish the typical from the atypical form.

A diagnostic suspicion shall then need to be confirmed with a brain MRI aimed at the ponto-cerebellar region. This will make it possible to visualise the trigeminal nerve and the artery that determines the compression or to rule out the presence of tumor lesions interfering with the course of the trigeminal nerve.

A differential diagnosis shall be carried out in cases of postherpetic neuralgia (characterised by continuous pain, blisters, and distribution in territory V1), dental pathologies, orbital pathologies, or giant-cell arteritis.

Treatment

Pharmacological treatment

Pharmacological treatment of trigeminal neuralgia is constituted by anti-epileptic drugs, such as Carbamazepine, either associated to Gabapentin or not.

Carbamazepine can lead to side effects such as drowsiness, leukopenia (reduction of white blood cells), gastric intolerance.

Both drugs may lose their effectiveness in controlling the neuralgia over time and induce so-called drug resistance.

Surgical treatment

Microsurgical neurovascular decompression

The curative treatment of trigeminal neuralgia is surgical treatment, which consists in microsurgical compression of the trigeminal nerve by separating it from the artery that determines the conflict.

The artery conflicting with the nerve is thus identified, separated and distanced from the nerve by interposing synthetic material or a foam swab.

In expert hands, this procedure can be considered very safe. It lasts a couple of hours and implies about 4 days of hospitalisation.

The surgical procedure is always indicated as a first option in patients younger than 70 years of age, or, in the absence of important diseases, in older refractory patients or patients who are intolerant to the pharmacological treatment.

Success percentages in terms of the cure of neuralgia are higher than 90% of all cases.

Percutaneous microcompression of the Gasserian ganglion

Percutaneous microcompression is a technique generally performed on a sedated patient and not in general anaesthesia, which consists in mechanically compressing the Gasserian ganglion by means of a Fogarty balloon catheter. X-ray imaging makes it possible to visualise the ideal filling of the balloon in order to exert a microcompression on the ganglion during 1-2 minutes.

The immediate success rate of the technique ranges from 80% to 90%, but relapses in time are possible. The technique can however be repeated since it is not very invasive.

It is indicated in elderly patients suffering from serious basic diseases and has the unquestionable advantage of being a mini-invasive technique and of not implying any significant complications or side effects (usually a reduction of sensitivity or tingling sensation in the affected branch remains).

The biggest limitation is that the initial high success rate is significantly reduced over time.

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