Trigeminal neuralgia, also known as tic douloureux, is defined as a sharp, unilateral, electric shock-like pain in the distribution of one or more of the braches of the trigeminal nerve that occurs in paroxysms and only lasts a few seconds at a time. The patient may experience spontaneous remission with pain-free intervals without any treatment. The most common cause is compression of the trigeminal nerve at the root entry zone by the superior cerebellar artery (SCA), and less commonly by a large vein. Other arteries that may be involved are a persistent primitive trigeminal artery or dolichoectatic basilar artery. Alternate etiologies include posterior fossa tumor, such as vestibular schwannoma, and multiple sclerosis plaque within the brainstem.

The annual incidence of trigeminal neuralgia is 4/100,000. Average age is 63, with most cases occurring over the age of 50. There is a slight female predominance, with female: male ratio being 1.8:1. The right trigeminal nerve is more commonly involved, implicated in 60% of cases, whereas the left trigeminal nerve is affected in 39% of cases. Only 1% of patients have bilateral involvement. The maxillary (V2) and mandibular (V3) branches together are most commonly affected (42%), followed by V2 only (20%), then the ophthalmic branch (V1) and V2 (14%). Medical therapy of Trigeminal neuralgia includes treatment with carbamazepine (Tegretol), an anticonvulsant. Second-line therapy is with baclofen (Lioresal), a muscle relaxant that is not as affective as carbamazepine but has fewer side effects. Gabapentin (Neurontin), another anticonvulsant, may be combined with carbamazepine or baclofen.

Cases refractory to medical management may be treated with surgery. Surgical strategy varies by the territory involved and origin of neuralgia. Peripheral nerve ablation and neurectomy are options for distal branch involvement or for patients unable to undergo general anesthesia. However, sensory loss occurs in the targeted nerve distribution and neuralgia may recur as the nerve regenerates. Repeat neurectomy is common. Percutaneous trigeminal rhizotomy (PTR) is another minimally invasive option for patients who are not candidates for major surgery or have a limited life expectancy (< 5 years). This may be used to treat failed peripheral nerve ablation. Techniques include radiofrequency rhizotomy that uses radiofrequency energy to thermocoagulate pain fibers of the trigeminal nerve, glycerol injection into Meckel’s cave, balloon compression of pain fibers inducing mechanotrauma, and injection of sterile boiling water. Common complications include recurrence and dysesthesia. (However, a certain extent of sensory loss, or “numbness”, is expected in successful PTR.) Other adverse effects include alterations in salivation and tear production and meningitis.

Microvascular decompression (MVD) (see figure) is nowadays the best treatment with more long lasting effect compared to other alternatives. It is best used for patients with an expected survival > 5 years who are able to undergo a small retrosigmoid craniectomy. The offending artery or vein is dissected off of the root entry zone (Obersteiner-Redlich zone) of the trigeminal nerve a few millimeters distal to its exit off of the brain stem and a Teflon or Dura pledget is put in between so that the pulsations of the vessel should be avoided. Due to movement of the brain with every heart beat and risk of dislocation of this pledget, we usually make the pledget in a horse-shoe fashion to fit around both sides of the nerve and use special glue (Tisseel) to make it firmly attached there.


Figure : Post-operative microvascular decompression CT-Scan. A. Axial B. Sagittal C. Coronal

In younger patients, the thicker layer over the brain, dura is primarily closed. In older patients with thinner dura, we use a piece of patients pericranial or temporalis muscle fascia to patch the dural opening and close it tightly as CSF-leak is a normal complication for this approach. If non-autologous grafts are used there is some low risk of septic meningitis and for this reason and in order to avoid that, we do not use artificial material.  Relief is typically long-lasting, exceeding 10 years in 70% of patients. Dysesthesias are less common than with PTR. Complications include aseptic meningitis in up to 20% of cases and major neurologic morbidity in 1-10% of patients - including vestibulocochlear nerve and facial nerve dysfunction causing hearing loss, deafness, balance problems, and facial paralysis - with a failure rate of 20-25%. Patients with trigeminal neuralgia secondary to multiple sclerosis plaque will not improve with MVD and should undergo PTR instead. One uncommon complication is development of pledget grasnuloma 1. (See figure and video)


Figure : Operative images. A. Accessory Trochlear Nerve B. Microvascular Decompression showing transected tentorium for access to Meckel’s cave. See the deformed Trigeminal nerve.
See Video :  https://www.dropbox.com/s/0o8stetgyshk3ob/Last%20-%20Teflon%20Granuloma.wmv?dl=0

References

  1. N Adeeb, SA Fard, MA Liker, MM Mortazavi. Trigeminal Teflon Granuloma: A Case Report with Operative Nuances. Journal of Neurological Surgery Part B: Skull Base 77 (S 01), P112 ,2016. DOI: 10.1055/s-0036-1580058

Stereotactic radiosurgery is another minimally invasive option. 80-96% of patients experience significant pain reduction but only 65% will become pain free. It can take up to 3 months for pain relief to occur. Hypesthesia (diminished sensation) is the most common complication and occurs in 20% of cases after first SRS and 32% of those undergoing repeat SRS. The major risk of this treatment is conversion of the trigeminal neuralgia to Anesthesia Dolorosa, a severely painful trigeminal neuralgia involving all 3 branches of the trigeminal nerve and losing all the sensory function in these branches including the sensation of the cornea.