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|THE EDITORIAL DEBATE
|Year : 2015 | Volume
| Issue : 6 | Page : 834-836
Trigeminal neuralgia: Centuries of pain and the era of minimally invasive pain relief
Bhagavatula Indira Devi, Chirag Solanki, Dhananjay Bhat
Department of Neurosurgery, National Institute of Mental Health and Neurosciences, Bengaluru, Karnataka, India
|Date of Web Publication||20-Nov-2015|
Bhagavatula Indira Devi
Department of Neurosurgery, National Institute of Mental Health and Neurosciences, Bengaluru, Karnataka
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Devi BI, Solanki C, Bhat D. Trigeminal neuralgia: Centuries of pain and the era of minimally invasive pain relief. Neurol India 2015;63:834-6
From the beginning of civilization, pain has been the oldest and the most distressing ailment. Painful conditions constitute a major public health burden, which have plagued mankind. It is generally agreed that the exceptional pain in trigeminal neuralgia (TN) is the worst among all the painful conditions afflicting humans.
The syndrome of idiopathic typical TN has been clearly defined by five cardinal features: Paroxysmal, provocable, unilateral pain, confined to the trigeminal territory, without loss of light touch or pinprick by the usual sensory testing. Idiopathic atypical TN has less clearly defined features and is characterized by long periods of unprovoked milder pain along with superimposed major paroxysms. In addition, there is an ill-defined category of facial pain commonly labeled atypical facial pain (neuralgia). Here, the clinical manifestations bear little or no resemblance to the syndrome of idiopathic TN. The unusual symptoms of this painful condition were described by Sir Charles Symonds in 1949. Patients in this category present with pain not limited to the areas supplied by a single nerve or to one side of the face or head. The pain is often bilateral, constant, non-paroxysmal, although severe exacerbations may be superimposed, and not provoked by external stimuli. The specific categorization of pain into typical or atypical TN, or atypical facial pain is important to predict the success of a surgical procedure. Patients with signs of deafferentation should not be subjected to glycerol rhizotomy, which would cause additional damage to the nerve. However, many patients with TN previously treated by other methods display signs of neural lesions, such as hypoesthesia, allodynia, hyperalgesia, and some degree of continuous deafferentation pain. Patients with atypical facial pain or deafferentation pain from a previous procedure may also be considered for glycerol rhizotomy only if the paroxysmal pain component is dominant and there are no sensory deficits. In addition, these patients should undergo glycerol rhizolysis, using only a small amount of glycerol. The similar principle is applied for atypical facial pain syndromes.
Understanding of the anatomy of the Gasserian ganglion More Details and retro-Gasserian region is also of utmost importance for rhizotomy. The sensory rootlets emerging from the Gasserian ganglion form a plexus with anastomotic connections lying in the Meckel's cave in the middle cranial fossa, called pars triangularis. The rootlets merge to pass through a meningeal opening at the petrous ridge (porus trigemini) and proceed through the posterior fossa within the pontine cistern to become a compact bundle (pars compacta radicis trigemini). The compact bundle of roots enters the midpons continuing as tracts to synapse with their respective brainstem nuclei. These retro-Gasserian sensory roots, which also form the root entry zone (REZ), are the main targets of all therapeutic procedures.
The choice between open microvascular decompression and percutaneous procedures for the treatment of trigeminal neuralgia is a contentious issue. Therapeutic minimally invasive methods with a low surgical risk, little impact on facial sensibility and the possibility of being performed under local anesthesia with only slight sedation, are the driving forces for the use of these techniques. The discovery of the beneficial effects of glycerol in patients with TN was accidental. The beneficial effects were found when glycerol was used as a vehicle for the radiopaque tantalum powder while trying to treat trigeminal neuralgia by Gamma knife in the 1970s, and was originally described by Sten Hakanson.
The glycerol rhizotomy requires an exact anatomical localization of the postganglionic fibers. For that, many recommend the use of contrast medium injection in all cases, called trigeminal cisternography. In that case, intolerance to iodine and previous adverse reactions to contrast medium should be investigated. Most patients tolerate the procedure well under local anesthesia, with adequate premedication and mild sedation. However, very anxious patients may require general anesthesia with endotracheal intubation. In some cases, it is helpful to give 0.5 mg of atropine intravenously immediately before the procedure to protect against bradycardia due to the risk of precipitating the trigemino-cardiac reflex during needle insertion. An intravenous line with a slow infusion of Ringer's solution is maintained during and for some hours after the session. If correct localization is done, the smallest possible volume of pure, sterile glycerol will be effective in each case. In most cases, fluoroscopy with lateral projection is adequate to localize the foramen ovale. However, if required, further guidance is obtained by switching to the anteroposterior projection. Rarely, in difficult situations, in patients in whom entering the proper part of the oval foramen is a problem, the patient's head may be extended and rotated 15°–20° away from the affected side, and the fluoroscopy arm tilted to give an axial–oblique projection of the skull base including the foramen ovale. As a rule, the cannula should not reach beyond the clival contour as seen on the orthogonal lateral projection. When the tip of the cannula is located inside the arachnoid of the trigeminal cistern, there should be a spontaneous egress of cerebrospinal fluid (CSF). However, spontaneous CSF drainage is not an absolute requisite for accepting the location as intracisternal. A brisk CSF flow may be misleading because placement of the cannula a few millimeters laterally will introduce the tip in the subtemporal subarachnoid space. Slow CSF drip from the cannula is a more specific indicator for intracisternal needle tip position and correlates with a successful outcome. If the needle is misplaced, inserting another needle using the first needle as a guide is a better choice than removing the needle and reinserting it. Glycerol injection should always be performed with the patient in the sitting position to minimize an extracisternal spillover. The anhydrous (99.5%) glycerol should be injected slowly using a 1-ml syringe. The usual dose is approximately 0.2–0.3 ml except when involvement of all three divisions with multiple trigger points is present. When the neuralgia encompasses all three branches with multiple trigger points, a somewhat larger volume has to be used. Forfirst-branch neuralgia, the head should be maximally flexed (i.e., approximately 40°) and should be kept in approximately that position for 1 hour after the injection. For second-branch treatment, flexion should be approximately 25° and for the third branch, the head should be slightly tilted laterally toward the affected side, but kept upright in the anteroposterior plane.
The percentage of patients enjoying immediate (within 2 weeks) relief from paroxysmal facial pain varies among different series (between 67% and 97%). Incomplete pain relief after the initial injection seems in most cases to be the result of technical problems during the procedure. Reinjections should not be performed within 3–4 weeks after the initial trial, as some patients are late responders. The average risk of recurrence within 2 years in well-controlled series appears to be approximately 20%, and the rate of late reappearance of symptoms (within 5–10 years) may approach 50%. Two major series of patients with TN treated by glycerol rhizolysis, presented by Spaziante et al., and Lunsford and Duma  in a Congress, comprised 191 and 480 patients, respectively. Immediate pain relief was observed in 93% of patients after treatment in the series of Spaziante et al; a 10-year follow-up showed that 77% and 75% of patients were pain free in the two series, respectively., Mild hypoesthesia was found in 46% and 20% of patients, respectively. A 1997 report of the Pittsburgh series by Jho and Lunsford  showed that of their large group of 523 patients, 90% were immediately pain free, and 55% stayed pain free at follow-up. Trigeminal glycerol rhizolysis should be offered to healthy patients in their eighth decade or older with classic TN, as well as to somatically fragile patients and those with multiple sclerosis.
The authors in this study have shown good results. They included a fairly large number of patients and were able to reproduce results that corresponded to those of other international studies. Even more important is that the follow-up of the patients was fairly long, and they also reported all adverse effects in detail. This outpatient procedure is one of the essential procedures that a neurosurgeon or a pain specialist should know because it can relieve a patient from an extremely agonizing pain within minutes, especially when the pain is not responding to drugs or the patient is not compliant with the minimal side effects produced by other techniques. However, a matter of slight concern is that the volume of anhydrous glycerol used by the authors is almost double that of the usual quantity required. Is it due to either the quality of the anhydrous glycerol or the positioning of the tip of the cannula? This higher dose could perhaps explain the relatively higher incidence of persistent dysesthesia.
Another technically similar procedure is radiofrequency ablation. The advantage of this procedure over glycerol injection is that uncomfortable patient positioning (an essential component of glycerol rhizotomy) following the radiofrequency thermocoagulation is not required and there is a significantly low risk of chemical meningitis. In addition, a repeat procedure is easier and more productive than can be performed using glycerol rhizotomy. However, it has a higher risk of motor weakness involving the trigeminal nerve than glycerol. The setup and instrumentation required are costlier than that required for glycerol injection, and this forms an important consideration in various setups.
In conclusion, the basic factors determining the success of glycerol rhizotomy are establishing the correct diagnosis, a proper patient selection, having sound anatomical knowledge, and utilizing a proper technique. Flaws in either of these factors can lead to a failed procedure or suboptimal results.
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Spaziante R, Cappabianca P, Graziussi G, Cacace G, Peca C, de Divitiis E. Percutaneous retrogasserian glycerol rhizolysis for treatment of trigeminal neuralgia. Results in 191 patients (abstract). Acta Neurochir (Wien) 1992;117:97.
Lunsford LD, Duma CH. Percutaneous retrogasserian glycerol rhizotomy: A ten-year-experience. Acta Neurochir (Wien) 1992;117:97.
Jho HD, Lunsford LD. Percutaneous retrogasserian glycerol rhizotomy. Current technique and results. Neurosurg Clin N
Kodeeswaran M, Ramesh VG, Saravanan N, Udesh R. Percutaneous retrogasserian glycerol rhizotomy for trigeminal neuralgia: A simple, safe, cost-effective procedure. Neurol India 2015:63:890-5.