Trigeminal neuralgia is defined as "sudden usually unilateral severe brief stabbing recurrent pains in the distribution of one or more branches of the fifth cranial nerve". It has an incidence rate of 12.6 per 100,000 person years and more commonly affects older age groups. The fifth cranial nerve is one of the largest in the head. The nerve is called trigeminal because it splits into three main branches. It provides sensation to the face. When neuralgia (nerve pain) occurs in the trigeminal nerve it causes severe and sudden face pain.
The causes of trigeminal neuralgia are unclear. Treatment of all people with classical trigeminal neuralgia begins with drug therapy, most frequently using one of several drugs also used to treat epilepsy, among which the gold standard remains carbamazepine. If drug therapy fails then surgical interventions may be used. Surgical treatments divide into two main categories: ablative (destroying the nerve) or non-ablative (preserving nerve function and relieving the pressure on the nerve). These procedures result in pain relief for variable lengths of time.
For this review, we searched for all of the surgical procedures for trigeminal neuralgia. We found 11 studies, which included 496 patients, but only three had sufficient outcome data to report. These three studies, which involved a total of 181 participants, fulfilled the inclusion criteria and form the basis of this review. The primary aim of all three studies was to determine if one technique was better than the other. All three included studies evaluated destructive techniques. None of the three studies evaluated the non-destructive procedure of microvascular decompression and this is a major drawback in the literature.
One study compared two different techniques of radiofrequency thermocoagulation, in 40 participants six months after the procedure. This technique involves heating the nerve by passing an electrical current through the tip of a special needle which has been introduced through the skin into a hole in the base of the skull and into the ganglion from which the three divisions of the trigeminal nerve branch out (Gasserian ganglion). If the radiofrequency was given as pulsed treatment (which causes the tip of the needle to heat up intermittently and not continuously) the original pain in all participants returned by three months. The continuous radiofrequency treatment then had to be applied, and these participants then achieved pain control comparable to those who had received continuous radiofrequency throughout. Changes in sensation ranging from mild to severe numbness were common in the conventional (continuous) radiofrequency treatment group.
A second trial, in 87 participants, looked at using one or two isocentres (specific points in the nerve) to deliver radiation to the trigeminal nerve just as it leaves the brainstem inside the skull. Use of medication afterwards was considered a surrogate measure for pain. Use of two isocentres increased the occurrence of sensory loss as a complication. Increased age and prior surgery were predictors for poorer pain relief. There were insufficient data given to judge the effectiveness of one procedure better than the other.
A third study compared two techniques for performing radiofrequency thermocoagulation of the Gasserian ganglion in 54 participants. The study compared two ways of introducing the needle and guiding it, using either X-rays or a special neuronavigation system. Pain relief was measured by a questionnaire at three months. Both techniques provided pain relief (which did not differ significantly between the two arms) but it was more sustained if a neuronavigation system was used and this system also decreased side effects.
All the reviewed procedures resulted in pain relief and some participants were then able to stop taking medications. However, many procedures tended to result in sensory side effects. All the studies in this review had flaws in their methods and all but two showed considerable risk of bias. There is little evidence from these trials to guide the person with trigeminal neuralgia as to the most effective surgical procedure. There is now an urgent need to evaluate the surgical interventions used in trigeminal neuralgia and to design robust studies; either randomised controlled trials or long-term prospective independently assessed cohort studies.