Three major percutaneous procedures are currently used to treat trigeminal neuralgia (TN). Percutaneous balloon compression, glycerol rhizotomy, and radiofrequency thermocoagulation interrupt afferent pain fibers by injury to the trigeminal nerve root or ganglion. Each is capable of offering immediate and durable pain relief. Each is associated with relatively low, but variable rates of complications. Patient heterogeneity, technical variation, and nonstandard outcomes plague the existing outcomes literature and limit comparisons of treatments. Rendering treatment selection a function of individual physician preference and practice patterns. Randomized, prospective trials are needed; in the meantime, percutaneous rhizotomy remains an excellent treatment for selected patients.
Key points
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Percutaneous procedures are safe and effective options for the management of trigeminal neuralgia.
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The best outcomes are seen after careful patient selection and counseling.
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An individualized treatment plan for each patient is essential for maximizing pain relief.
Introduction
Three types of percutaneous rhizotomy are currently used to treat trigeminal neuralgia (TN). Percutaneous balloon compression (PBC), glycerol rhizotomy (GR), and radiofrequency thermocoagulation (RFT) are all designed to interrupt afferent pain fibers by causing injury to the trigeminal nerve root or ganglion. Conceived in the early 20th century, several decades of experience with these relatively simple techniques have demonstrated their efficacy in offering immediate and durable pain relief, as well as overall safety. Although microvascular decompression (MVD) has gained in popularity and the use of percutaneous rhizotomy has been on the decline, these percutaneous techniques offer several important advantages. Partial sensory rhizotomy, an open procedure that can be performed if no vascular nerve compression is found during MVD, is not discussed in this paper.
Introduction
Three types of percutaneous rhizotomy are currently used to treat trigeminal neuralgia (TN). Percutaneous balloon compression (PBC), glycerol rhizotomy (GR), and radiofrequency thermocoagulation (RFT) are all designed to interrupt afferent pain fibers by causing injury to the trigeminal nerve root or ganglion. Conceived in the early 20th century, several decades of experience with these relatively simple techniques have demonstrated their efficacy in offering immediate and durable pain relief, as well as overall safety. Although microvascular decompression (MVD) has gained in popularity and the use of percutaneous rhizotomy has been on the decline, these percutaneous techniques offer several important advantages. Partial sensory rhizotomy, an open procedure that can be performed if no vascular nerve compression is found during MVD, is not discussed in this paper.
History and conception
The first description of TN as a distinct disease entity dates back to 1688, by Fehr and Schmidt. More than a century later, the painful syndrome was localized to the trigeminal nerve, and eventually given the name that it bears today. At the time, despite an intimate knowledge of the anatomy of the trigeminal nerve and ganglion, the pathophysiology of the disease was poorly understood. The first attempted treatment of TN occurred in 1910, when Harris injected the trigeminal ganglion with alcohol. Shortly afterward, in 1914, Hartel described a method for accessing the foramen ovale for percutaneous injections still in use today. Only 2 years after Harris described his approach, Rethi attempted to treat TN by electrocoagulation of the trigeminal nerve and ganglion. Owing to limitations in electrode design, the procedure was associated with high complication rates as a result of unintended injury to the trigeminal nerve and surrounding structures. Decades passed before Sweet and Wepsic, in 1974, described RFT of the trigeminal rootlets. With the use of short-acting anesthetic agents to allow for electrical stimulation and temperature monitoring, their method allowed for precise lesion creation. Over the next few decades, Nugent further refined the technique with the use of a fine cordotomy-type electrode, and Tew and Taha introduced curved thermistor-tipped electrodes, achieving high rates of pain relief with lower complication rates.
The origins of GR date back to the late 19th century, when physicians injected various agents, including chloroform and osmic acid, next to nerve trunks with the goal of causing chemoneurolysis. Although reports indicate that this method was effective in producing pain relief, the effect was transient and often accompanied by significant weakness, sensory loss, and dysesthesias. GR as it is exists today was developed somewhat serendipitously in 1981, when Hakanson and colleagues were exploring the use of stereotactic radiotherapy as a treatment method for TN. Glycerol, as a trivalent alcohol naturally present in human tissue, was used as the vehicle to suspend tantalum dust, and injected into the trigeminal cistern. They found that injection of the carrier alone caused pain relief. Although it is thought that GR preferentially injures large myelinated fibers, the exact mechanism of action of glycerol is incompletely understood. Studies have suggested its hypertonicity, and more specifically, a rapid rate of change of intracellular osmolarity upon glycerol injection, results in axonal demyelination and fragmentation. Although the procedure has been modified and updated in many ways, the core elements of the technique remains true to Hakanson’s original method.
Balloon compression as a treatment for TN was discovered in the 1950s during investigations into scar tissue compressing the trigeminal nerve root or ganglion in the middle fossa as a cause of TN. In 1952, Taarnhøj described his method of decompression of the dorsal root of the trigeminal root, and Shelden and Pudenz reported a method for decompression of the second and third nerve divisions. In working to decompress the trigeminal ganglion, they and others concluded that the effectiveness of their techniques in producing pain relief derived from the resultant injury to the posterior trigeminal root posterior to the ganglion. However, Shelden and colleagues found that rubbing the posterior root was able to yield only transient pain relief. It was not until 1983, when Mullan and Lichtor described compression of the trigeminal ganglion with a percutaneously inserted Fogarty balloon catheter, that trigeminal compression became a viable treatment option. Later studies in rabbits revealed that compression seems to preferentially affect the medium and large myelinated pain fibers, sparing small fibers, which allows for recovery of motor and sensory function, and theoretically, preservation of the corneal reflex.
Patient selection and evaluation
The primary indication for percutaneous trigeminal rhizotomy remains Burchiel type 1 TN, or typical TN, an idiopathic condition in which patients experience episodic sharp or shooting electrical shocklike facial pain. TN is a progressive disease, and without treatment, can transform to Burchiel type 2 TN, or atypical TN. Burchiel type 2 TN is characterized by more constant pain and is associated with sensory impairment. A trial of medical therapy with anticonvulsants is typically the initial treatment for TN, but there are no standardized guidelines regarding the minimum duration of medical therapy necessary before moving to an interventional strategy. Although some reports have suggested that trials of at least 2 anticonvulsants should be performed before surgical intervention, little evidence exists to support this notion. Many patients experience initial pain relief with medication, but later develop breakthrough pain. Indeed, some studies have shown that more than 50% of patients with TN eventually undergo surgery.
Several factors should be taken into consideration when making the choice of which surgical procedure to undertake. Percutaneous procedures are thought to be well-suited for elderly patients or those with multiple medical comorbidities for whom MVD would present a greater risk, or younger patients who wish to minimize their risk of postoperative facial numbness. However, age alone is not an absolute contraindication for craniotomy, because MVD has been shown to be well tolerated in patients older than 75 years. RFT is not appropriate for patients who cannot tolerate an awake procedure or who are unable to cooperate with localization. There is a greater risk of the trigeminal depressor response and hypotension and bradycardia seen with PBC, making it less appropriate for some patients with cardiovascular disease. Each procedure allows for a varying degree division-specificity, but RFT can be used for more precise lesion creation than GR and PBC. Because of the supposed fiber-selective nature of PBC, many advocate the use of PBC for isolated first-division pain. The comparative efficacy of percutaneous therapies, MVD, and stereotactic radiosurgery (SRS) is discussed elsewhere in this paper.
There are several patient subgroups who exhibit divergent outcomes from patients with typical TN. Atypical facial pain can refer to the both the quality or frequency of pain, or the underlying etiology, which can be iatrogenic, owing to postherpetic neuralgia, or in association with multiple sclerosis (MS). Although it is a nonspecific term, atypical pain has been associated with poorer outcomes in terms of symptom recurrence across several treatment modalities. Management of patients with atypical facial pain will be discussed in detail (see Rahimpour S, Lad SP: Surgical Options for Atypical Facial Pain Syndromes , in this issue). Patients with MS also represent a unique subgroup, because they have a higher prevalence of TN compared with the general population. The pathophysiologic link between the 2 conditions is incompletely understood, but TN is thought to result from combination of inflammatory and mechanical demyelination.
Surgical technique
Percutaneous Balloon Rhizotomy
PBC is generally performed under general anesthesia. Entry into the foramen ovale can evoke the trigeminal depressor response, and the resultant hypotension and bradycardia can be significant. In preparation, a transcutaneous or transesophageal pacemaker is placed. Atropine is not given preoperatively to allow for monitoring of trigeminal compression intraoperatively, but should be prepared in the case of persistent bradycardia. The patient is positioned supine with a neck roll for 15° of extension. Hartel’s anatomic landmarks are plotted, with 1 point inferior to the medial aspect of the ipsilateral pupil and a second point 3 cm anterior to the external auditory meatus, serving as the target trajectory. A third point 2.5 cm lateral to the ipsilateral oral commissure is the skin insertion point. A 14-gauge needle cannula is inserted and advanced along the target trajectory to the foramen ovale. A free hand technique is then used to direct the needle with a gloved finger inside the oral cavity to prevent violation of the buccal mucosa and to ensure the needle remains medial to the mandible. The needle is directed in a trajectory that bisects a triangle between the insertion point, the midpupillary line, and the marking 3 cm anterior to the external auditory meatus. Intraoperative visualization of needle and balloon placement is performed with lateral view fluoroscopy. Once the cannula is at the skull base, a submental view is obtained, and used to guide the cannula to the foramen ovale. Entry into the trigeminal cistern results in egress of cerebrospinal fluid, although this is not always observed.
Engagement of the foramen ovale results in elicitation of the trigeminal depressor response, causing contraction of the masseter and pterygoid muscles. Under direct visualization of the foramen ovale, a straight guiding stylet is passed into the cannula. With an anteroposterior view, the stylet is directed toward the proximal entrance of the trigeminal fossa, the porus trigeminus, which is approximately 17 mm beyond the foramen ovale. Directing the stylet in the center of the porus is thought to treat second division or multidivision pain, whereas a lateral position treats third division pain, and medial, first division pain. Once the stylet has been advanced to the proper position, it is then removed, and a 4-F balloon catheter is introduced and advanced along the chosen trajectory to the target position. The balloon is inflated with 0.7 to 0.75 mL of iohexol to a target pressure of 1000 to 1200 mm Hg for 60 to 90 seconds. The balloon should take on a classic pear-shaped appearance, which reflects its position within the porus. During compression, the trigeminal depressor response is usually observed again and is a reflection of appropriate compression. The cannula and catheter can then be removed, and light manual pressure should be applied to the skin puncture site. An ice pack and sterile bandage is then applied to the site. The patient can be discharged home on the same day if stable, or observed overnight.
Radiofrequency Thermocoagulation
Because RFT requires patient cooperation during parts of the procedure, patients must be trained preoperatively to localize facial stimuli. Before the procedure, 0.4 mg of atropine is given intramuscularly to prevent bradycardia. As with PBC, the trigeminal depressor response can be evoked intraoperatively, but atropine can be preadministered because the response is not used for intraoperative monitoring. Induction is performed with a short-acting agent such as propofol, and patients are positioned as described for PBC. C-arm fluoroscopy is typically used to guide needle placement. A cannula with an obturator is then guided to the foramen ovale as noted previously, and its position confirmed with lateral view fluoroscopy. The obturator is then removed, and the electrode introduced. Caution should be taken to avoid placement of the electrode beyond 10 mm of the profile of the clivus, where the trochlear and abducens nerve lie. The patient can be awakened, and sensory and motor responses are tested. Locations to lesion are determined by detailed mapping to effect pain control and minimize sensory and motor side effects. Alternatively, the patient can be kept asleep throughout the surgery and the combination of fluoroscopy and nerve stimulation can be used to verify appropriate localization. The electrode is then removed, the thermocouple introduced to the previously chosen locations, and lesions are made at a maximum of 0.5 V at 5 and 75 cycles per second at 55 to 80°C for 30 seconds to 2 minutes. The electrode and cannula can then be withdrawn, pressure applied to the puncture site, and the site dressed. As with PBC, the patient can be discharged home on the same day if stable, or observed overnight.
Glycerol Rhizotomy
Induction is also performed with a short-acting agent such as propofol. The trigeminal depressor response can again be seen upon engagement of the foramen ovale and also upon injection of glycerol; atropine can be preadministered, as with RFT. C-arm fluoroscopy is used for guidance. A 20-gauge needle is used with Hartel’s landmarks to guide the needle to the foramen ovale. Contrast-enhanced cisternography can be used to assess the trigeminal cistern and determine the necessary amount of glycerol to be injected. However, injection of 1 cm 3 air can also be used to outline the cistern. The head of the bed is then elevated to 60°, and glycerol is injected. The volume of glycerol typically varies from 0.25 to 0.40 mL; different volumes can be used to target specific divisions. For multidivision pain, injection of the full volume will treat all divisions. After the injection, the needle is removed, and the patient is awakened to remain in a sitting position for 2 hours so that the glycerol does not spill out of Meckel’s cave. The patient can be discharged home on the same day if stable, or observed overnight.
Intraoperative Complications
Although the use of Hartel’s landmarks to access the foramen ovale has been in widespread use for decades, the proximity of the foramen ovale to critical neurovascular structures should not be forgotten. The internal carotid artery can be punctured at the C2, C3, or C4 segments, typically resulting in pulsatile blood flow through the cannula. Serious injuries can result from inadvertent cannulation of the inferior orbital fissure or jugular foramen. Inappropriate placement of the cannula lateral to the trigeminal fossa in the subdural space medial to the temporal lobe can also result in intracranial hemorrhage. Skirving and Dan noted 2 cases in which patients undergoing PBC experienced asystole upon engagement of the foramen ovale; in 1 case, the asystole resolved upon withdrawal of the needle, and the other patient required atropine. No mortality from the trigeminal depressor response during a percutaneous rhizotomy has been reported in the literature. Although all 3 of the percutaneous therapies are considered safe and associated with low mortality rates, there have been reports of intraoperative deaths during the procedures. For PBC, 2 deaths have been reported in the literature, in 1 case, from a punctured arteriovenous fistula, and in the second, from a brainstem hematoma. No intraoperative deaths during GR or RFT have been reported.
Patient outcomes
Percutaneous Balloon Compression
Rates of initial pain relief, which in most studies refers to complete pain relief without medications, are high in patients treated with PBC, ranging from 85% to 100% ( Table 1 ). One study of patients who required repeat procedures found a lower, but comparable, rate of pain relief at 83%. Rates of pain recurrence range from 20% to 48%, again with 1 report of recurrence rates at 64% in a cohort with almost 90% patients who had previously undergone surgery. Reporting of the time to recurrence also varies greatly across studies, with rates of recurrence at 5 years ranging from 19.2% to 29.5%. Postoperative facial numbness is present in the majority of patients, and typically resolves within 3 months. The most commonly reported complications are masseter weakness or masticatory muscle weakness, and dysesthesias ( Table 2 ). Some degree of motor weakness is expected postoperatively owing to the impact of the procedure on large myelinated nerve fibers, with the rates of masseter weakness reported ranging from 10% to greater than 50%. However, in the majority of cases, the weakness resolves within a few weeks to months. Rates of dysesthesia range from 1.5% to 11.4%, and decrease with decreasing compression times. As with masseter weakness, in the majority of cases dysesthesia is minor and transient. Early reports of PBC often highlight the low rates of corneal anesthesia associated with the procedure; indeed, in most contemporary reports of PBC, no patients experienced this complication.
| Study | n | No. of Procedures a | Follow-up Duration, (y) b | % Prior Procedure c | % MS | % Initial Relief d | % Recurrence e | Time to Recurrence f |
|---|---|---|---|---|---|---|---|---|
| Fraioli et al, 1989 | 159 | 162 | 3 | 8.2 | 1.9 | 89.9 | 9.8 | NR |
| Lichtor & Mullan, 1990 | 100 | 104 | (1–10) | 37 | 3 | 100 | 28 | 20% at 5 y |
| Lobato et al, 1990 | 144 | 155 | (0.5–4.5) | 43 | 2.1 | 100 | 9.7 | NR |
| Brown et al, 1993 | 50 | 50 | 3 (0.8–7.5) | 52 | 10 | 94 | 26 | 1.5 y |
| Correa & Teixeira, 1998 | 158 | 200 | 4 | 45.7 | 1.9 | 90 | 20 | 8.2% at 3 y |
| Skirving & Dan, 2001 | 496 | 531 | 10.7 | 4 | 2.2 | >99 | 31.9 | 19.2% in 5 y |
| Omeis et al, 2008 | 29 | 41 | 4.1 (0.1–8.4) | 100 | 7 | 83 | 45.5 | 0.6 y |
| Kouzounias et al, 2010 | 47 | 47 | 1.7 | 89.4 | 36.2 | 85 | 64 | 1.4 y |
| Chen et al, 2011 | 130 | 130 | 8.9 | 43.8 | 0 | 93.8 | 37.7 | 29.5% at 5 y |
| Bergenheim et al, 2013 | 100 | 100 | NR | 48 | 23 | 90 | 48 | 2.3 y |
| Abdennebi & Guenane, 2014 | 901 | 901 | 16.5 (0.5–27) | 0.4 | NR | 92.7 | 27.8 | NR |
a Many studies report performing >1 procedure per patient; that is, after initial treatment failure, the authors performed another surgery on the same patient and reported long-term outcomes based on results after the second, or third, operation.
b Given as mean value ± standard deviation or (range), unless otherwise indicated.
c Other surgical interventions for trigeminal neuralgia, including other percutaneous procedures, microvascular decompression, or stereotactic radiosurgery.
d Defined as complete relief without medications, unless otherwise indicated.
e Defined as the percentage of patients who experienced pain recurrence during the follow-up period.
f Given as median time to recurrence or percentage of patients who experienced recurrence by a certain time postoperatively, unless otherwise indicated.
| Study | n | % Dysesthesia | % Anesthesia Dolorosa | % Corneal Sensory Impairment a | % Diplopia | % Masticatory Weakness | % Meningitis |
|---|---|---|---|---|---|---|---|
| Fraioli et al, 1989 | 159 | 6.9 | 0.6 | 0 | 0 | 6.9 | NR |
| Lichtor & Mullan, 1990 | 100 | 4 | 0 | 0 | 1 | NR | 0 |
| Lobato et al, 1990 | 144 | 19 | 0 | NR | NR | 12 | NR |
| Brown et al, 1993 | 50 | NR | 0 | 0 | 2 | NR | 3 |
| Brown & Gouda, 1997 | 141 | 3.5 | 0 | 0 | NR | NA | NR |
| Correa & Teixeira, 1998 | 158 | NR | 0 | 0 | 3 | 33 | 0.6 |
| Skirving & Dan, 2001 | 496 | 3.8 | 0 | 0 | NR | NR | 0 |
| Chen et al, 2011 | 130 | 1.5 | 0 | 2.3 | 1.5 | 6.2 | 0 |
| Abdennebi & Guenane, 2014 | 901 | 2.8 | 0 | 0.9 | 1.2 | 10.8 | 2.2 |
Other complications that have been observed include hearing and olfactory disturbances, cranial nerve III, IV, and VI palsies, arteriovenous fistula development, meningitis, and herpes simplex labialis. Catheter or balloon misplacement can result in injury to other cranial nerves, most commonly, the abducens, resulting in transient diplopia. Meningitis is a rare complication; the highest rate reported was 5%, and in the majority of series, no patients experienced meningitis. Herpes reactivation is common after procedures involving manipulation of the trigeminal nerve, and is typically mild and prophylactic antiviral therapy is typically not administered. The development of more serious complications is extremely rare after PBC. There is only 1 case of anesthesia dolorosa reported in the literature, and 3 cases of corneal keratitis. One case of reversible blindness after PBC has been reported, owing to occlusion of orbital venous drainage to the cavernous sinus by the cannula, leading to increased intraocular pressure. With aggressive treatment with acetazolamide, visual acuity gradually returned.
In terms of prognostic factors, achieving a pear-shaped balloon during compression has been highlighted by several studies as a key predictor of durable pain relief. However, it remains a subjective criterion, and is ultimately a visual proxy for the position of the balloon catheter and the degree of compression. Objective variables that can be altered to change the degree of compression include the level of pressure and the duration of compression. Greater pressures, although associated with higher rates of pain relief, are also associated with added morbidity in the form of sensory alterations and motor weakness. Brown and Pilitsis attempted to define the ideal level of compression with continuous balloon pressure monitoring, ultimately concluding that the optimal pressure ranged from 750 to 1250 mm Hg for 1.15 minutes. In addition, numerous studies have demonstrated that longer compression times do not seem to appreciably improve outcomes, while increasing rates of complications. In the last few years, practice trends have shifted toward shorter compression times, with compression times of less than 60 seconds seeming to be adequate in achieving pain relief.
Radiofrequency Thermocoagulation
The goal of lesion production in RFT is to produce mild to moderate hypalgesia in the affected divisions, allowing for adequate pain control without causing significant sensory deficits. Although there is variability in the reported rates of initial pain relief, rates are generally relatively high, with most studies reporting greater than 95% complete pain resolution ( Table 3 ). Rates of pain control and the duration of pain relief consistently correlate with the degree of sensory loss. Taha and colleagues, in a prospective study of 154 patients, found that patients with anesthesia had the lowest rates of pain recurrence but the highest rates of dysesthesia. In contrast, patients with mild hypalgesia had the highest pain recurrence rates and the lowest rates of dysesthesia.
| Study | n | No. of Procedures | Follow-up Duration (y) | % Prior Procedure | % MS | % Initial Relief | % Recurrence | Time to Recurrence |
|---|---|---|---|---|---|---|---|---|
| Fraioli et al, 1989 | 533 | 582 | 6.5 | 4.7 | 3.4 | 97.4 | 10 | NR |
| Frank & Fabrizi, 1989 | 700 | 700 | 3 | NR | NR | NR | 25 | 25% in 3 y |
| Broggi et al, 1990 | 1000 | 1000 | 9.3 (5–14) | NR | NR | 94.8 | 18.1 | 12.8% in 3 y |
| Scrivani et al, 1999 | 215 | 215 | 2.7 (0.8–5.7) | NR | NR | 92 | 27 | NR |
| Tronnier et al, 2001 | 206 | 206 | 14.0 | NR | NR | NR | 20 | 50% in 2 y, 75% in 4.5 y a |
| Kanpolat et al, 2001 | 1600 | 2138 | 5.7 ± 5.5 (1–25) | 27.5 | NR | 97.6 | 25.1 | 7.7% in <0.5 y, 17.4% in >0.5 y |
| Tew et al, 2012 | 1200 | 1200 | 9 (1–21) | NR | NR | 99.4 | 20 | 15% at 5 y, 7% from 5-10 y, 3% from 10-15 y b |
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