Introduction

Trigeminal neuralgia is a painful, sudden, high intensity condition that lasts a few seconds in the distribution of the trigeminal nerve (1). It is one of the most frequent causes of orofacial pain in the world, being more prevalent in the female sex and in the elderly (2).

The causes are multiple, being the most common a vascular compression of the nerve (2). The diagnosis is eminently clinical, supported with cabinet studies, such as nuclear magnetic resonance imaging, to rule out malignant causes (2).

Pharmacological medical treatment is based on carbamazepine and oxcarbazepine, as well as adjuvant drugs such as opioids and gabapentinoids (3).

Invasive treatment includes surgery, radiosurgery and conventional percutaneous radiofrequency ablation as well as cryoanalgesia of peripheral branches (4).

Percutaneous radiofrequency ablation is considered a safe method, with low mortality and a high safety profile; however, one of the disadvantages of this method, despite low morbidity, is the high recurrence that occurs in the next 2-3 years, with a percentage of up to 41 % (5).

Usually the preferred method of radiofrequency ablation is monopolar, i.e., entering the cavum of meckel with a 5 to 10 mm radiofrequency cannula and placing it in the affected branch or branches, and performing several cycles, mostly staggered, of 1 minute duration at temperatures that can range from 60 to 70 °C.

The IASP defines trigeminal neuralgia as sudden, unilateral, high intensity, lancinating pain of brief duration that occurs in the distribution of one or more branches of the trigeminal nerve (1).

Trigeminal neuralgia is the most common form of orofacial pain in elderly patients. Its incidence is 4-5 per 100,000. With approximately 15,000 new cases annually in the United States. It is 1.5 times more common in females (2).

Three types of trigeminal neuralgia have been described: idiopathic, secondary and classic, where the most common cause is intracranial vascular compression, most commonly by the superior cerebellar artery. Most patients will have compression of the trigeminal ganglion, which is evident on MRI studies (2).

Imaging studies should always be performed to rule out secondary causes, such as malignant processes (2).

The pain usually affects the V2 and V3 branches of the trigeminal nerve, and is predominantly unilateral, and is not usually accompanied by autonomic symptoms such as lacrimation, conjunctival injection, rhinorrhea (3).

The intensity of the pain varies with time, most patients have recurrent episodes lasting from weeks to months, as well as there may be pain-free periods, in some cases only exhibiting decreased pain for periods. The number of daily attacks varies from one to hundreds per day (3).

The presence of trigger events and trigger zones are typical in trigeminal neuralgia and are key in the diagnosis. Trigger zones are in the distribution of the affected branch, usually near the mouth or nose. Even a gentle touch to these areas can evoke pain. Trigger events include brushing teeth, chewing, talking, smiling (3).

On physical examination there is no neurological deficit and this is key in the diagnosis, especially if patients are in an episode of pain. The goal of the examination is to exclude alternative diagnoses and neurological processes (3).

Always watch for red flags in the diagnosis, such as rapid onset, throbbing pain, neck pain, fever or neurological abnormalities, as well as age over 50 or under 30 (3).

Medical treatment is varied and limited. First choice is carbamazepine which is beneficial in 70 % of patients. It has more pronounced adverse effects in the elderly or with rapid dose increases. Among the most important adverse effects are hyponatremia, osteoporosis, hematological alterations, among others. A derivative, oxcarbazepine, has fewer interactions and adverse effects, as well as a similar beneficial profile. Other options such as gabapentinoids as well as opioids depending on the case are also useful (1).

Among the interventional therapeutic options, thermal and pulsed radiofrequency ablation of Gasser’s ganglion is available, with multiple studies indicating the superiority of thermal RF, with symptom relief of up to 70 % for at least 6 months, and a decrease in oral drugs. There are also other percutaneous options such as balloon decompression, as well as surgical options with varying degrees of effectiveness and morbidity (4).

In a 2005 study comparing the recurrence rate of trigeminal neuralgia after different treatments (surgery, radiosurgery, radiofrequency), percutaneous radiofrequency ablation was the treatment with the highest recurrence rate, with up to 41 %, but with lower morbidity (5). The method associated with the highest success rate of up to 75 % is monopolar, trans-oval, thermal radiofrequency ablation of Gasser’s ganglion (6). Generally, the best results are obtained in primary trigeminal neuralgia, when the condition is limited to the V3 branch (7).

The disadvantage of trans-oval ablation is that it may require multiple repositioning of the needle to isolate the branch to be treated, which can be associated with treatment failure, as well as complications such as collateral injury to adjacent branches, subarachnoid injury, intracranial hemorrhage and infection (8).

Similarly, although the standard of care is a monopolar lesion, it has been associated with recurrent pain, mainly in patients with a foramen ovale larger than 6 mm. The cause of this is not fully elucidated but it is theorized to be related to inadequate thermocoagulation of branch V3 due to incomplete coverage of the foramen ovale by the monopolar lesion (9).

Bipolar radiofrequency ablation where two radiofrequency cannulae are placed close to each other and the two electrodes complete a circuit. Initially each electrode generates an isolated lesion, which eventually merges to generate an ablation of a larger volume (10). Therefore, we can assume that by performing bipolar radiofrequency in a foramen ovale larger than 6 mm, we have the possibility of initially covering a larger lesion area, with potentially less recurrent pain.

Presentation of the cases and description of the technique

Case 1

Male, 57 years old, with no significant chronic degenerative history, denies smoking or alcoholism. He starts with facial pain in 2014, of lacinating character, intensity 10/10 according to the NRS (numerical rate scale), sudden onset, in left V3 territory of trigeminal nerve. He was diagnosed with trigeminal neuralgia and underwent medical treatment with carbamazepine, with adequate control for 2 years. In 2016 the pain increased despite medical treatment, so he underwent percutaneous monopolar radiofrequency ablation of the trigeminal ganglion. He reported immediate improvement with a pain-free period for one year. In 2017 he underwent a new percutaneous ablation of the trigeminal ganglion, without improvement of more than 50 %, so in 2018 he underwent surgical microvascular decompression, without improvement. He was managed with multiple pharmacological therapy, presenting variable control with multiple pain peaks. In 2022 we evaluated this case for the first time in the pain medical center, and after the analysis of the history, with a percutaneous approach and a failed surgical one, a percutaneous trans-oval bipolar radiofrequency ablation technique was decided.

Description of the bipolar technique and ablation protocol.

After signing the informed consent for percutaneous interventional procedure, consent for taking photographs and consent for publication purposes, a previous dose of cephalothin 1 gram is administered before admission to the room, under noninvasive ASA monitoring, in the hemodynamics room, in a decubitus supine position, under superficial sedation with midazolam, 2 mg, sufentanil 10 mcg, nasal prongs at 2 liters/min and local anesthesia. The patient’s head is fixed and under aseptic technique the C-arm is positioned in a submental oblique position (30° caudal, 15° left oblique) to identify the foramen ovale as shown in figure 1. The medial and lateral commissure of the foramen ovale is identified and it is decided to enter with double cannula, 22 G caliber, curved tip, 10 mm active tip 10 cm long, EVA© brand, one in each edge (medial and lateral of the foramen ovale), it is advanced in tunnel vision until contacting the bony surface of each edge (see figure 2). At this point the true lateral view is obtained and the sedation is deepened, the curved tips are turned towards the foramen and the cavum of meckel is entered; the lateral cannula is left just in the inferior position of the cavum, and the medial cannula is advanced up to the superior half of the cavum see figure 3. Sensitive test is performed at 50 Hz evoking the response at 0.2 V, motor stimulation 2 Hz, up to 2 V observing masseter contraction.

It was decided to deepen the sedation with propofol 40 mcc IV and sufentanil 10 mcc additional, achieving a plane of deep sedation, bipolar ablation was performed at 70 °C, 16 V, with 2 minutes duration with Boston Scientific G4 radiofrequency generator. After ablation, the patient was admitted to postanesthesia recovery for monitoring and discharge.

The patient was evaluated 2 hours in recovery, reporting NRS 0/10, without motor deficit, and preserving ipsilateral corneal reflex, leaving the center 3 hours later with telephone follow-up as follows: At 48 hours after the procedure, she reported NRS 2/10, limited to the insertion site of the cannulas, with adequate control by paracetamol 500 mg only for necessary reason; at one month follow-up, she reported NRS 0/10, without neurological deficit, preserved corneal reflex, and minimal weakness of the masseter, adjuvant medication: carbamazepine 200 mg per day. The evaluation at 3 months with persistence of the analgesic effect NRS 0/10 and minimal medication, at one year of follow-up refers sporadic NRS 1/10 and minimal medication, at two years of control refers adequate pain control NRS 1/10 with carbamazepine 200 mg per day.

Case 2

82-year-old female, diagnosed with right trigeminal neuralgia V2, V3. history of hypertension and type 2 diabetes mellitus under pharmacological control, comes to evaluation with right facial pain, with lacinating character, with intensity NRS 10/10, without neurological deficit. She has a history of trigeminal neuralgia for 6 years, monopolar ablation was performed 6 years ago with significant improvement of pain and minimal analgesia requirements, therapeutic effect of 1 year, and restarted with pain 5/10 according to the NRS, medication was adjusted without improvement so it was decided to undergo a new percutaneous intervention by monopolar RF in V2, V3, showing improvement for 8 months, time in which the pain increased to 8/10 despite the pharmacological adjustment. Due to the recurrence and the short duration of the effect of previous ablations, it was decided to schedule a percutaneous trigeminal ganglion ablation with bipolar technique. This technique was performed with the same approach and ablation protocol previously described, at 70°C, 2 minutes, under sedation and informed consent was obtained for the procedure, sedation and taking photographs for publication purposes. In recovery room with NRS 0/10, without loss of corneal reflex and without motor deficit.

The patient was followed up at 48 hrs via telephone, reporting pain at the puncture site 4/10, of nocieptive character without neuropathic characteristics, and was managed with paracetamol 500 mg as necessary. At 1 month follow-up she reported pain NRS1/10, carbamazepine 200 mg per day. At 3 months of follow-up with persistence of improvement NRS 1/10, residual symptoms; slight hyperesthesia in the V2, V3 region of the face, and improvement of mood and satisfaction. Annual evaluation with persistence of analgesic effect and minimal medication, at 2 years refers a NRS 2/10 once a week, lasting less than 2 seconds.

Case 3

66-year-old female, diagnosed with right trigeminal neuralgia V2, V3 right of 30 years of evolution, with no history of chronic degenerative diseases. A percutaneous RF ablation of Gasser’s ganglion was performed 5 years ago by a properly trained interventional Algologist, with improvement of 2 years, time in which the pain increased, adjustments were made in the pharmacological management without improvement, it was decided to perform a second ablation with improvement of 1 year and recurrence of pain, it is evaluated by our center, pain of lacinating character NRS 10/10, The evaluation by MRI party modality does not refer vascular alterations, so due to the recurrence is scheduled for a new percutaneous ablation of Gasser’s ganglion with bipolar technique according to the ablation protocol 70 °C, 2 minutes under deep sedation during ablation, following the same technique described previously.

On discharge from the ward she reported NRS 0/10, with residual effect of sedation, leaving the center 3 hours later with minimal pain at the puncture site. Follow-up at 48 hours with pain 2/10 at the puncture site. At one month of evaluation she reported NRS 1/10, with minimal analgesia requirements, improved mood and quality of life. At 3 months of follow-up with persistent improvement of pain, which has been maintained for 18 months, the current evaluation, 18 months after the approach with NRS 1/10, without motor or sensory deficit, and carmazepine 200 mg / day.

Discussion

Trigeminal neuralgia is usually a complex disease, research has been done on the pathophysiology, and demyelination has been postulated as the axis in its development. Multiple percutaneous treatments have been developed, such as blockade of peripheral branches, and cryoablation of terminal branches has recently been performed with promising results, although of short duration (11). Percutaneous ablation of the trigeminal ganglion by monopolar radiofrequency has been considered as a standard when referring to percutaneous ablative techniques, with excellent results; however, a decrease in the time of effectiveness has been noted with a second or third ablation. Balloon decompression is a technique that consists of inflating a balloon in the cavum of meckel and achieving analgesia; it is an excellent option, however less available in some places (11). Regenerative medicine applications have recently been described in the ganglion of Gasser, but the evidence is not conclusive (12).

The trigeminal nerve is the V cranial nerve, it consists of 3 divisions from the trigeminal ganglion, V1 also known as ophthalmic division, V2 maxillary and V3 mandibular, it is a pure sensory nerve that innervates the face, usually the V2 and V3 divisions are more affected, with predominance of the right side over the left. Bilateral trigeminal neuralgia is rare and when it occurs, the diagnosis should be focused on a neurological condition. Carbamazepine and oxcabazepine are usually the first line drugs, however many patients have adverse effects, and sometimes control is not achieved despite the ceiling doses. Diagnostic tests, particularly neuroimaging tests, are often useful to identify the cause or to identify patients with neurological diseases in which small branches of the basilar artery compress the preganglionic portion (13).

It is well known that radiofrequency nerve ablation is usually performed in sensitive or sympathetic nerves without risk of pain by deafferentation, that is why in the management of trigeminal neuralgia is usually resorted to thermoablation of the sensitive ganglion containing only A delta and C fibers with putative purely nociceptive functions. Even if the trigeminal ganglion is very different from a dorsal root ganglion, the same differences help in the understanding of this disorder. Since the trigeminal ganglion and the DRG (dorsal root ganglion) have different neuronal expression, as well as altered responses to injury such as the expression of the sympathetic system in the DRG in response to injury that does not occur in the TG (14).

It is known that after thermoablation of a nerve, there is a Wallerian degeneration in anterograde direction to the site of the lesion, however there is also a nerve regeneration at a rate of 1 to 2 mm per day, unlike cryoablation in which the endoneurium is preserved, in RF thermal ablation it is not, so regeneration may not be in the same site where the target was previously located, which may explain why subsequent ablations in our cases had a shorter duration or no response (15).

There is increasing evidence of bipolar techniques in sensory branch ablation for pain control, even for neuropathic pain secondary to resistant radiculopathy in the DRG with excellent results. In refractory cases, the proposal of a bipolar ablation technique significantly improves the success rates in refractory or recurrent neuralgia. Note that the three cases are long-standing neuralgias with previous ablative treatment, which means that reinnervation may not be anatomically concordant and require a larger lesion that includes the aberrant fibers (16). In addition, the arrangement of the cannulas has a somatotopic relationship with the trigeminal nerve; that is, the most medial and superior ophthalmic division and the most lateral and caudal V3 mandibular division (17). The technique performed in our series of cases has three particularities:

1. Two cannulas are used as opposed to one in monopolar RF.

One cannula is more cephalic and medial than the second, which is more lateral and inferior.

2. A single cycle of bipolar RF at 70 °C for 2 minutes is performed.

3. The latter is based on the concept that temperatures above 70 °C are associated with high recurrence rates.

The application of bipolar electromagnetic energy in the trigeminal ganglion is not new. V. Silva previously reported two cases in which bipolar radiofrequency was used, however it was not ablative, and the patients reported were subjected to a percutaneous technique in the trigeminal ganglion for the first time. It should also be noted that the placement of the cannulas was not somatotopic, although the results were good after 2 years (18). Huang et al. He performed a series of cases in which continuous bipolar RF was performed guided by tomography obtaining a 100 % response in the bipolar group, which was maintained at 15 months, some differences in this study were the active tip they used of 5 mm compared to ours of 10 mm, also the tomographic guide that was used while that of this series of cases was with fluoroscopy, in addition the branches in Huang’s article are V3, thus leaving the cannulas just at the entrance of the foramen, referring to this technique as extracranial (19). One of the side effects was masticatory atony, perhaps due to the anatomical relationship with the motor nerve that is not part of the trigeminal nerve but that exits through the eighth pair. In our series of cases, masticatory atony was not reported. This may be explained by the arrangement of the intracranial cannulas, unlike Huang’s, which was extracranial. However, this atony is not only shown in the bipolar technique, but also in the monopolar one (12).

Bipolar radiofrequency ablation in the treatment of trigeminal neuralgia could be a valuable tool in the interventionist’s arsenal, especially in refractory or recurrent cases.

The reason for the bipolar technique is to increase the size of the lesion, achieving coverage of the entire area of interest in thermocoagulation, not only in a patient without previous ablation, but especially in patients who have previous procedures, in which the anatomy is not maintained, this is where a larger lesion is required to improve the probability of covering the nerve area of interest. The nerve ablation generated by radiofrequency depends on multiple factors, such as the size of the active tip, its length, temperature and time of injury (10). Therefore, it is essential for a successful technique, both a correct location of the needles, as well as an adequate selection of our work tools and an adequate programming of the RF generator.

This publication has important limitations, being a series of cases, results cannot be generalized, however, it opens the door to more research in this field, especially in the somatotopic projection of the trigeminal ganglion, based on the results we intend in the near future to carry out prospective studies that compare with the standard that is monopolar radiofrequency.

Conclusion

Bipolar radiofrequency ablation of the Gasserian ganglion in recurrent or treatment-resistant trigeminal neuralgia is an effective technique for pain control in this complex pathology. There is only one published article on bipolar tonic ablation by tomography; this report was carried out with fluoroscopy, which implies a reduction in costs as well as less radiation. It is usually a simple and effective technique in resident or recurrent neuralgia; more research is required in this regard.

Conflict of interest

None.

Funding

None.

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