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Percutaneous retrogasserian glycerol rhizotomy for trigeminal neuralgia: A simple, safe, cost-effective procedure
Correspondence Address: Source of Support: None, Conflict of Interest: None DOI: 10.4103/0028-3886.170103
Objective: Trigeminal neuralgia (TN) is a condition that has been studied over decades and whose pathogenesis has still not been well defined. Various open and minimally invasive procedures are in vogue for the treatment of intractable TN. All these procedures have their complications and recurrence rates. Percutaneous retrogasserian glycerol rhizotomy (PRGR) is one of the minimally invasive procedures that have been popular for quite a long time. Keywords: Percutaneous retrogasserian glycerol rhizotomy; procedures for pain relief; treatment of trigeminal neuralgia; trigeminal neuralgia
Trigeminal neuralgia (TN) is a clinical syndrome characterized by brief paroxysms of unilateral lancinating facial pain triggered by cutaneous stimuli such as breeze on the face, chewing, talking, brushing teeth, or shaving. It is classified as typical or type 1 TN characterized by intermittent episodic pain with pain-free intervals, and atypical or type 2 TN characterized by continuous pain with no triggers or pain-free periods. The exact pathogenesis of idiopathic TN has not been identified and is still speculative. Although the initial treatment is medical, the efficacy tends to wear-off in course of time. Various percutaneous and surgical options are available if the condition becomes refractory to medication or when the patient experiences intolerable side effects from the initial treatment. Percutaneous retrogasserian glycerol rhizotomy (PRGR) is one of the percutaneous procedures that has with stood the test of time. This paper analyzes a series of patients with TN treated with PRGR. The short- and long-term outcomes, safety, and cost-effectiveness of the procedure have been studied and analyzed.
A prospective observational study was conducted between July 2009 and January 2012 on patients admitted with the clinical diagnosis of typical or type 1 TN based on the International Headache Society criteria.[1] The patients in the study were classified as "intractable typical TN" not responding to medical management and "TN intolerant to medications". All study patients were evaluated with a detailed history with an emphasis on pain assessment by the Numerical Rating Scale [(NRS) - 0 (no pain) to 10 (worst pain ever experienced by the patients)] and by a thorough neurological examination. All patients were evaluated with contrast computed tomographic (CT) scanning or magnetic resonance imaging (MRI) to rule out secondary TN due to various causes. The Institutional Ethics Committee clearance was obtained prior to recruiting patients for the study. The study patients were explained in detail about the condition, the benefits, and possible adverse effects of the procedure, as well as other treatment options available for their disorder. A written consent was obtained from all those patients involved in the study. Preparation of anhydrous glycerol The efficacy of glycerol in chemical ablation of nerves depends on its anhydrous nature. Small quantities of glycerol were taken in glass vials, closed air-tight with a rubber stopper with a needle inserted through. The vials were then heated so that water evaporated through the needle making the glycerol anhydrous. This anhydrous glycerol was then preserved air- and water-tight and used for injection into the retrogasserian region through a wide bore needle. Procedure All patients were worked up with routine hematological tests including their coagulation profile and electrocardiogram prior to the procedure. The procedure was done with the patient lying in supine position and the head in a neutral position. Some patients required mild sedation and all patients were monitored for their vital parameters during the procedure. Under strict aseptic conditions, the classic Hakanson method [2] was followed to reach the trigeminal cistern or the retrogasserian region through the foramen ovale. The entry point was marked 2.5 cm lateral to the corner of the mouth with the needle directed towards a point on the line joining the ipsilateral pupil and a point 2.5 cm anterior to the external auditory meatus on the symptomatic side. 1% lidocaine was injected subcutaneously for local anesthesia. A 20-guage lumbar puncture (LP) needle was inserted through the marked entry point until the foramen ovale was penetrated which was evidenced by cerebrospinal fluid (CSF) flow on slow removal of the stylet. In repeat procedures, entry into the foramen ovale was not always marked by the CSF flow. The position of the needle was confirmed by a submentovertical check X-ray showing the needle passing through the foramen ovale and a lateral view showing the needle within 5–10 mm to the point of intersection of the floor of the sella with the clivus. After confirming the position of the needle, sterile anhydrous glycerol (0.6–1 ml) was injected through the needle to ensure its accummulation in the retrogasserian region. Then the needle was withdrawn and the patient was made to sit with the neck flexed for 2 h to prevent escape of glycerol into the posterior fossa and to allow efficient contact of glycerol with the structures in the retrogasserian region. The patients were monitored overnight in the hospital and discharged the next day. The patients were followed up to assess for the onset and extent of pain relief and for the development of any complications. Medications for TN were tapered and stopped over a week. The outcome was assessed based on the Barrow Neurological Institute (BNI) pain intensity score as shown in [Table 1].{Table 1} Patients with BNI - 3b were considered to have a good outcome. Safety of the procedure was assessed based on any complications that developed. These were graded as "mild and self-limiting" or "severe and disabling". The patients were followed up on an out-patient basis to assess for recurrence of pain. The details of the individual patients were entered in a proforma and the results tabulated and statistically analyzed using SPSS version 17 software (SPSS Inc., Chicago).
A total of 93 patients with typical TN who were successfully injected with glycerol between July 2009 and January 2012 were included in the study. Majority of the patients in the study were in the 51–60 years age group constituting about 38.7% of the total group. There were 54 males and 39 female patients, with their age ranging from 38 to 85 years. Males constituted 58.1% and females constituted 41.9% of the study patients. The dermatomal pattern of pain distribution in our study was as follows: 6 patients in V1, V2 region; 34 patients in V2 region; 51 patients in V2, V3 region; 2 patients in V1, V2, V3 region [Figure 1]. Most patients had their pain along the distribution of the maxillary nerve - 91.3% (inclusive of V3). 67.8% of patients had pain on the right side and 32.2% on the left side [Figure 2].{Figure 1}{Figure 2} The severity of pain was assessed preoperatively using the NRS from 0 to 10. Pain was graded as mild (NRS 0–3): 14 patients (15.1%); moderate (NRS 4–6): 36 patients (38.7%); and, severe (NRS 7–10): 43 patients (46.2%). All patients had prior medical management and were on preoperative medications. Three patients developed intractable side effects like vomiting, drowsiness and rash so that their medication had to be discontinued [Table 2].{Table 2} The indications for the procedure are shown in [Figure 3]. Preoperatively 79 patients had contrast CT to rule out any intracranial mass lesions or pathology causing secondary TN; 39 patients had MRI among whom 26 cases had a normal MRI and 12 cases showed a vascular loop in the vicinity of the dorsal root entry zone of trigeminal nerve. These patients refused microvascular decompression (MVD) or were not medically fit for MVD and one of them had a failed MVD.{Figure 3} 55.9% of patients had pain relief within 1–2 h after the procedure of which 25.8% had pain relief within an hour, and 10.8%, within half an hour of the procedure [Figure 4]. 4.3% of patients had a lingering pain lasting for more than 2 h that settled within a day; 3.2% (3 patients) had pain lasting for more than a day. One among them was relieved of his pain over the subsequent 2 months; the other 2 patients, however, had persistent pain.{Figure 4} The mean follow-up duration was 18.8 months. Of the 93 patients, 16 patients (18.3%) were lost to follow-up and 1 patient died due to an unrelated medical cause. During the follow-up, drugs were tapered off slowly for all study patients and stopped completely. Five patients (5.4%) had recurrent pain and were started on carbamazepine. Seventy-six patients (93.4%) are completely off drugs. The efficacy of the procedure was analyzed in terms of immediate pain relief and long-term pain relief based on the NRS comparison and grouped based on the BNI pain intensity score. Ninety patients (95.7%) had complete pain relief immediately following the procedure. Three patients (3.2%) had continued pain with reduced intensity. One of them was managed with low-dose carbamazepine (BNI 3b), and the other 2 were managed without drugs (BNI 2). Low-grade NRS (2–4) recurrent pain was seen in 8 cases (10.5%) during follow-up. Three of these cases were managed conservatively without drugs and the other 5 were managed with low-dose carbamazepine [Table 3]. Thus, immediate pain relief was seen in 96.8% (n = 93) patients, long-term pain relief in 89.4% (n = 76) patients, and 17 patients were lost follow-up over a period of 30 months. During the follow-up period of 18.8 months, the efficacy of the pain relief decreased from 96.8% to 89.4%. All the complications encountered were mild and not disabling to the patients [Table 4].{Table 3}{Table 4} Thirty-four patients (36.6%) had a low-grade headache following the procedure and were treated by foot elevation in supine position and adequate hydration with oral and intravenous fluids. The headache had a much lower intensity when the procedure was done with a small-bore lumbar puncture needle (21G). Seventy-two patients (77.4%) patients had an early and transient dysesthesia. Thirteen (14%) of them who had persistent and continuous dysesthesia gradually adjusted to it or the dysesthesia improved during a longer follow-up. Corneal hypoesthesia and delayed reflexes were seen in a few patients and 2 patients had corneal anesthesia. In patients with significant sensory changes and corneal reflex loss, prior procedures such as radiofrequency ablation and peripheral neurectomy were believed to be the contributing factors. Herpes reactivation was seen in 9 patients (9.2%) which is an expected complication with a procedure involving the Gasserian ganglion More Details. These patients presented on the 2nd or 3rd postoperative day with severe herpetic pain and rashes along the angle of mouth on the same side as the TN. They were treated with antiviral medication and had no residual complications. One patient who presented with meningitis like picture with fever, headache, and neck stiffness lasting for 1 week was treated with a full course of antibiotics and had no further sequelae.
TN is not a static disease and is usually characterized by remissions and exacerbations.[3] Its causation has been due to abnormalities of the trigeminal nerve, the Gasserian ganglion, or the root entry zone.[4] Jannetta had attributed the etiology of the neuralgic pain to vascular compression of the trigeminal nerve by arterial loops or veins [5] and has shown good results by MVD. However, Adams has contested this.[6] Several studies including that of Ramesh and Premkumar [7] have shown that the vascular contact and compression at the trigeminal root entry zone may be seen in a significant normal population also. Loeser et al., on the basis of their theory of presynaptic inhibition, have shown that TN could be due to focal changes in axon diameter or in myelination of the V th nerve.[8] The ignition hypothesis was also considered to account for the positive and negative symptoms of TN.[9] The hypothesis states that TN results from specific abnormalities of the trigeminal afferent neurons in the trigeminal root or ganglion. Lack of knowledge of the definitive etiopathogenesis of TN has led to confusion over the choice of treatment for refractory TN. Typical TN is usually responsive to initial medical management. The gold standard drug for treating TN is carbamazepine which is started at a low dose and gradually increased to a level where the pain is controlled with minimal side effects. A variety of procedures are available to treat refractory TN and for patients with intolerable side effects. Different procedures like balloon microcompression, radiofrequency rhizotomy, glycerol rhizotomy, and stereotactic radiosurgery work in different ways to induce axonal degeneration of the nerve.[10] These procedures do provide excellent pain relief; however, they are often associated with recurrence of the pain during follow-up, although late. MVD is also a popular procedure among neurosurgeons. This is an open surgical procedure which is more technically more demanding compared to the percutaneous procedures. Though the long-term results in terms of recurrence are marginally better compared to the other procedures, MVD has its own share of potential major complications. The choice of the procedure depends on the symptoms of the patient, medical co-morbidities, the age of the patient, prior treatment modalities, if any, and availability of the procedure. The goal of the treatment should be complete pain relief with an acceptable level of side effects. The patient should be free of pain and the fear of recurrence. Pollock has reported in his series of 98 patients that 73% were free of pain at some point following any surgical procedure, with the chance of remaining pain-free without medications at 61% and 50% after 1 and 3 years, respectively. His study shows that with almost all forms of treatment, the reported outcome is almost always comparable.[11] PRGR is considered as the first line of treatment for refractory TN by many surgeons because of the relative advantages it has over the other percutaneous procedures in terms of the lesser rates of postprocedure sensory deficits. Anhydrous glycerol chemically ablates the so-called pathological site on the axons. It is not clear how anhydrous glycerol acts to relieve the neuralgic attacks without producing the dense anesthesia which is seen after most neurolytic injections. But altered sensations in the form of dysesthesia or hypoesthesia, a sluggish corneal reflex, and temporary paresis of the V3 motor component in some of the patients have been observed. In our present study, 72 patients (77.4%) had an early and short-lived dysesthesia, and 13 patients (14%) had a persistent and continuous dysesthesia. In 2.3% patients, there was loss of corneal reflex also. This slight degree of sensory loss has been well tolerated by our patients. Motor paresis such as pterygoid weakness was seen in 1 case (1.2%). This finding is consistent with those of Lunsford et al.,[12] and Beck et al.[13] In our study, we had many younger patients than the usual age group. Rao and Dinakar [14] and Abraham and Chandy [15] have shown that it is quite common to see patients below the age of 40 years suffering from TN. The male preponderance may be because a larger number of male rather than female patients seek medical aid in India. Kalyanaraman and Ramamurthi reported more male patients compared to female patients suffering from TN in their series of 700 patients seen over 20 years.[16] A comparison with other studies in the published literature suggests that the results of our study were better in terms of immediate and long-term pain relief and recurrence of pain. However, the follow-up period has been shorter when compared to others studies [Table 5] and [Table 6]. Comparison between the different surgical modalities for treatment of recurrent TN have been reported in the literature but no clear evidence of one percutaneous method being better than the other has been shown.[25],[26],[27] MVD has been shown to be associated with slightly higher rates of long-term pain relief.[26],[27]{Table 5}{Table 6} The most common complications of PRGR are minor like development of a local hematoma, infection, sensory deficits, reactivation of labial herpes, and anesthesia dolorosa. Severe complications like chemical meningitis and infectious meningitis are rare.[10] The procedure is relatively safe and well tolerated by all patients irrespective of their age and comorbidities. PRGR can be done under local anesthesia with/without mild sedation, as an outpatient procedure with an X-ray or C-arm. The patient is back to his normal routine in a few days and is saved from long-term costly medications. We strongly recommend PRGR for patients with intractable TN and in those patients who cannot tolerate the medications, as it is simple, safe, and cost-effective with minimum complications. It has a high efficacy, and with recurrence rates comparable to that of other procedures. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.
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