Microvascular Decompression for Trigeminal Neuralgia: Experience of a Tertiary Care Center in India and a Brief Review of Literature
Correspondence Address: Source of Support: None, Conflict of Interest: None DOI: 10.4103/0028-3886.315975
Source of Support: None, Conflict of Interest: None
Keywords: Headache, microvascular decompression, tic douloureux, treatment options, trigeminal neuralgia
Trigeminal neuralgia (TN), often known as tic douloureux, is “recurrent unilateral brief electric shock-like pains, abrupt in onset and termination, limited to the distribution of one or more divisions of the trigeminal nerve and triggered by innocuous stimuli”, as defined by the International Classification of Headache Disorders, 3rd edition.
Treatment options for TN include medical care (pharmacological therapy), surgical procedures, and radiosurgery including gamma knife radiosurgery. Of the surgical procedures, microvascular decompression (MVD) of the trigeminal nerve is a procedure commonly performed for TN as described initially by Dandy and later popularized and by Jannetta et al. However, the results of this procedure are often average due to inadequate cure complemented by recurrence of symptoms or associated surgical complications. Although some authors have tried to modify the MVD technique as well as emphasized on proper selection of patients who could benefit from the procedure,,, there is still a dearth of data in the literature regarding long-term clinical outcome after the procedure. In this study, we present our experience on 106 patients of TN managed by MVD over a period of 5 years and followed up for an average period of 32.6 months (range 1-year to 5-years) post-surgery.
Patient and selection criteria
Retrospective analysis of the database between January 2010 to December 2014 was carried out and 112 patients fulfilling the diagnostic criteria of idiopathic TN by ICHD3 and unresponsive to standard medical care (two drugs for at least three months each) were included in this study. Exclusion criteria included patients with atypical TN- like symptoms (those without severe paroxysmal pain around the trigeminal nerve distribution), those with the previous history of MVD and patients with bilateral pain distribution. All patients were evaluated on admission and detailed history and clinical examination including patient demographics, duration of complaints, trigger points, distribution and characteristic of pain and past medical treatment were performed. Contrast-enhanced magnetic resonance imaging (CE-MRI) was routinely performed in every patient pre-operatively to rule out cerebellopontine angle mass lesions and to delineate neurovascular compression as well as to exclude demyelinating diseases like multiple sclerosis. After this exclusion, 112 patients qualified for this study. Of them, six patients were lost in early follow-up (<1 year) and the final study population consisted of 106 patients who were followed up for at least 1 year up to 5 years (mean 32.6 months). Prior approval was taken from the institutional ethics committee for performing this study.
All the procedures were performed by a suboccipital retrosigmoid approach as described previously. The transverse and sigmoid sinuses were exposed, margins delineated and the dura was cut along the line bisecting the angle between the sinuses. Supracerebellar approach followed, CSF drained and the trigeminal nerve was exposed. This approach has the advantage of less traction on the 7th–8th cranial nerve complex. Cerebral decongestants (mannitol) or lumbar CSF drainage were avoided to prevent any anatomical alteration during exposure of the trigeminal nerve including anticipated traction on the petrous veins and care was taken to preserve them. Extreme care was taken to prevent unnecessary handling of the trigeminal nerve and it was carefully dissected free. Intraoperative monitoring was done using facial nerve electromyography and brainstem auditory evoked response in every case. The field was examined and any offending vessel compressing the nerve was identified and freed from the nerve and then mobilized off the trigeminal nerve by implanting Teflon sponge in all patients. All the surgical procedures were undertaken by an experienced senior neurosurgeon (DS) at one institution.
Outcome assessment and follow-up
Following the procedure, the patients were followed up on an outpatient basis to assess the symptom control or complications. Pain relief was assessed immediately after the surgery, then at 1st month, and then on yearly basis up to 5 years (mean 32.6 months). Postoperative pain relief was categorized as excellent, good, partial, or none. Patients were evaluated regarding recurrence of pain, the persistence of any facial sensory loss, dysesthesias, and occurrence of motor weakness in the masseters.
All statistical analysis was done using Statistical Package for Social Sciences (SPSS) version 19.0, IBM, Armonk, NY, USA. Categorical variables were presented as frequency values and continuous variables were presented as mean ± standard deviation and compared using a two-by-two Chi-square test. Pain-free outcome and pain recurrence was analyzed using Fischer test. The level of statistical significance was set at P < 0.05 and all the statistical analyses were two-tailed.
Of the 106 patients, 58 (54.7%) were female and 48 (45.3%) were male with a mean age of 55 years (range 22–75 years). The right side of the face was involved in 64 patients and left in 42. 98 (92.5%) patients had a history of previous medical treatment with at least one drug while 5 gave a history of ablative procedure done for the management of excruciating pain. The majority (42.5%) of the patients had pain in the distribution of both V2 and V3 division of the trigeminal nerve. The mean duration of symptom was 6.38 years prior to MVD and only two patients had a family history of TN [Table 1].
The common findings at the site of vessels compression were vessel touching the nerve, adhesions as well as indentation. Arterial compression was found in 87 (82%) patients while both artery and vein were the offending vessels in 15 (14.5%) and unidentified vessels were seen in four (3.8%) patients. The most common offending artery was the superior cerebellar artery (SCA) found in 56 patients while anteroinferior cerebellar artery (AICA) was the most common artery found in combination with one or more veins seen in eight patients. When veins were found, they were coagulated and sectioned and arteries repositioned.
The complications are mentioned in [Table 2]. There were no intra- or post-operative deaths or occurrence of any brainstem or cerebellar infarction in this study. Five patients developed ipsilateral facial numbness in the immediate postoperative period which was persisting in one patient, although not disabling. This patient had the indentation of the superior cerebellar artery and vein (dual compression) on the nerve along with adhesions and we suspect some degree of traumatization of the nerve during the relocation of the artery which may have lead to the numbness in the postoperative period [Figure 1]. CSF leak settled spontaneously in two patients in the postoperative period while in one patient it resolved by putting a lumber drain. Three patients had cerebellar hematoma of which two had to be reoperated for evacuation and postoperative recovery was uneventful in both patients. Facial weakness developed in two patients although it was transient and settled on facial exercise. One patient developed diplopia in the immediate postoperative period which was persisting and was likely due to trauma to the trochlear nerve while opening the dense arachnoid. Two patients had partial hearing loss and were followed up on regular basis and resolved over several months and none had persistent or significant hearing loss. One patient who was not relieved from surgery started developing severe tinnitus in 4th year of follow-up along with severe paroxysms of pain. Re-exploration was done in this patient and intraoperatively, the 5th cranial nerve was found to be badly sandwiched and thinned out and Teflon granuloma on the 7th–8th cranial nerve complex [Figure 2]. The granuloma had a mass effect causing vertebral artery compression on the 5th cranial nerve. The offending vessel was separated by placing a Teflon graft and the patient recovered significantly in the postoperative period.
Follow-up after MVD
Six patients were lost in follow-up and excluding them, follow-up results were obtained in 106 patients that ranged from 1 to 5 years (mean 32.6 months). The outcome was classified as excellent (complete relief from preoperative pain without medications), good (occasional low-intensity pain paroxysms that resolved without medications), partial (that required lower dosage of medications), and none (no relief from MVD and requiring continuous medications). Every patient was examined regarding the status of pain relief at the postoperative days (first 7 days) and then at the first month followed by a yearly basis at a mean duration of 32.6 months [Table 3]. In the immediate postoperative period, 55.7% of the patients had an excellent pain-free response of MVD, 15.1% had a good outcome, 23.6% had partial pain relief while no response from MVD was recorded in 5.7% of the patients. The best response was achieved at one month following the procedure where 85% of the patients showed excellent recovery which was statistically significant (P = 0.02) and only two patients (1.9%) had a poor response from MVD. At 1 year, there was a reduction in complete pain relief with 76.4% remaining pain-free while at more than 1 year follow-up, 73.6% of the patients had excellent control of pain while the good response was noted in 7.5% of the patients and partial relief of pain in 10.4% of the patients while 8.5% had no response from the procedure. Thus, the excellent pain-free outcome that was achieved in 85% of the patients at 1st a postoperative month had a decline to 73.6% when followed up for more than a year, however, this was not statistically significant (P = 0.124).
Predictors of outcome
The age of the patients at surgery was not related to the outcome. Of the 78 patients having an excellent outcome in the average follow-up period of 32.6 months, 42 (53.85%) were female and 36 (46.15%) were male but this gender difference was not statistically significant (P = 0.124). Of the nine patients who either had no relief or recurrence of preoperative symptoms in the follow-up period of more than 1 year, all of them had preoperative symptoms lasting more than 5 years, however, this was not statistically significant either (P = 0.2). 66 (84.6%) of the 78 patients having an excellent pain-free outcome in the follow-up had the presence of trigger points preoperatively which was statistically significant (P = 0.005). Intraoperatively, absence of adhesions (P = 0.02), indentations (P = 0.005) and distortion (P = 0.04; [Figure 2]) of trigeminal nerve were positive predictors of excellent outcome in the long run. The presence of a single named artery as the compressing vessel was another factor that was related to the statistically significant-excellent outcome as compared to the presence of both artery and vein or small unnamed vessels (P = 0.002). Immediate postoperative relief of symptoms was also significantly related to long-term pain-free outcomes (P = 0.03).
Our study suggests, MVD in the long run, is superior in terms of pain relief, safety, and overall patient satisfaction in TN. Complications following the procedure were mostly minor and not disabling to the patients. However, the subjects need to be followed up at regular intervals to look for complications that may arise later. Intraoperative presence of adhesions around the trigeminal nerve or any indentation/distortion of the nerve may suggest the occurrence of complications in the postoperative period. Teflon granuloma, although rare, should be kept in mind in patients with severe sensory/motor symptoms especially in the long-term follow-up.
Some previous studies, have suggested that the overall results of MVD in younger subjects differ from that of adults with TN. However, we could not find any association of age of patients at the surgery with operative outcomes. This finding supports another study that suggested the same findings hence MVD may be equally effective in both young and old patients with TN.
[Table 4] summarizes the literature on the efficacy of MVD on TN. Most of the studies reveal success rates ranging from 51.6 to 96.7% on long-duration follow-up after MVD. The results of our study suggest the same findings with a success rate of 86.6%. A recent study assessed the long-term effectiveness of MVD for idiopathic TN and found that pain relief maintained for at least 8 years in 71.2% of MVD cases. The study also found that typical clinical presentation, arterial neurovascular compression and older age are predictors of excellent long-term outcome while symptom duration and previous failed procedures had no effect on MVD prognosis.
John Fothergill in 1773 was the first who provided a modern analog of TN hence TN is also known as Fothergill's disease. The International Headache Society distinguishes TN as either idiopathic (classical/essential), where TN develops without apparent cause other than neurovascular compression, or atypical (symptomatic) where the pain occurs due to the presence of some structural lesion except for neurovascular compression. TN most commonly affects the second (maxillary) and third (a mandibular division of the trigeminal nerve and the pain distributes along with these divisions, usually on the right half of the face and less frequently on the left. The first (ophthalmic) division of the nerve is involved alone in only <5% of the cases.
Walter Dandy was the first who started the groundwork of managing TN by partial sectioning of trigeminal sensory nerve roots by posterior fossa approach in 1925, thus laying the foundation of MVD. By this route, he observed that in many cases there are compressing structures-arterial and venous loops as well as tumors that are responsible for symptoms. Peter Jannetta in the later years developed the MVD procedure based on this finding and described the technique in 1967.
Prevalence, presentation, and pathophysiology of TN
TN is a common condition having an incidence of new cases approximately 12 per 100,000 people per year and is seen most commonly in the 50–70 years age group. The condition affects more female than the male with a female-male ratio of 1.74:1. Patients usually describe the pain as sudden onset, excruciating, yet short-lasting that is limited to one or more branches of the trigeminal nerve. The patients are usually pain-free between the episodes but in some cases a dull background pain may persist. The pain in TN may be triggered by a stimulus like that of touch of a soft cloth, cold wind or water or even by simple touch and such trigger zones are seen in more than 90% of the cases.
The pathogenesis of TN remains controversial however several studies indicate a neurovascular conflict theory where named or unnamed vessels compress the trigeminal nerve as it exits the brainstem. The most common vessel involved is the superior cerebellar artery's rostroventral root which gives off the symptoms. This compression leads to the demyelination of sensory fibers of the trigeminal nerve in the long run which in turn leads to axonal degeneration, ephaptic transmission as well as the release of mediators which sensitize the peripheral nerve terminations causing increased excitability of the trigeminal nerve and its nuclei (central sensitization).,,
Surgical treatment options for TN
Variety of surgical procedures are available which are usually reserved for uncontrollable refractory pain after the trial of at least three drugs including carbamazepine inadequate doses. These can be divided into percutaneous ablative (destructive), minimally invasive stereotactic radiosurgery including gamma knife radiosurgery (GKRS) and MVD.
The percutaneous techniques target the Gasserian ganglion More Details causing mechanical and/or thermal/chemical response. These include balloon compression, glycerol/alcohol injection, and radiofrequency (RF) ablation and they have the advantage of being less invasive in nature and offer variable pain relief however, long-term success rate is inferior and the recurrence rate is higher than MVD. Balloon compression has a recurrence rate of 29.5% at 5-years as observed in one study. Significant dysesthesia, motor weakness, corneal ulcerations, and infections limit its use. Glycerol injection has an initial success rate and median pain-free time of 73–96% and 21 months respectively as observed in another study. and the main concern following this procedure is postoperative corneal hypoesthesia and significant dysesthesia. The RF ablation, although offers a high initial success rate approaching 100%, the probability of remaining pain-free at 2- and 11-years post-procedure is low (49%, and 26% respectively)., Moreover, RF ablation is associated with severe dysesthesia in 6%–9% of patients, corneal hypoesthesia in 1%–17%, and transient motor weakness in approximately 19%.
The stereotactic radiosurgery using gamma or cyberknife is a recently introduced procedure in the armamentarium of treatment options for TN, where a focused beam of radiation is addressed to the trigeminal nerve root at the posterior fossa. The target point lies either at the root entry zone of the trigeminal nerve or just proximal to the brain stem. The challenge lies incorrect recognition of the coordinates of the trigeminal nerve root where the radiation beams must be collimated to refrain from damaging the pons. The pain relief from GKRS is not immediate and there is a lag period that varies from few weeks to few months before the benefits of the procedure appear. Results from GKRS are better in typical TN involving single nerve distribution. 69% and 52% of the patients remain pain-free one year and at 3-year post-GKRS without additional medication, however, the long-term pain-free outcome is inferior to that of MVD. The recurrence rate following GKRS varies from 5-42%. The cyberknife is another modality that provides higher dose precision without damaging healthy tissues; the X knife radiosurgery also offers good pain relief with a low complication rate.
The widely used and time-tested treatment modality for TN that is unresponsive to medications, however, remains MVD. Here the compressing vessel is gently separated from the nerve and a Teflon sponge is implanted to keep the pulsating vessel away from the nerve. Significant pain relief is seen in 68-88% of the subjects at 1 to 2 years and 61-80% of the subjects at 4 to 5 years after the procedure. The average mortality rate from MVD varies from0.2% to 0.5% with up to 4% of patients develop complications like cerebrospinal fluid (CSF) leakage, infarcts or hematomas. MVD has been recommended in younger subjects as well as in healthy elderly.
Minimally invasive techniques are now a norm in many intracranial and spinal pathologies, and TN is no exception either. The advantages include better visualization of trigeminal nerve roots, smaller craniotomy, and lesser surgical time with better evaluation of completeness of decompression. A recent meta-analysis was conducted comparing patient outcome rates and complications for the open versus the endoscopic technique for TN and the authors concluded that fully endoscopic MVD affords clinical results comparable with those of an open MVD approach but with lower complication rates.
As a nonablative measure, MVD is a safe and effective method in selected cases of TN with high success rate and fewer complications and is a powerful weapon to treat this agonizing disorder. However, long term follow-up is warranted to look for recurrence and to avoid some unlikely complications.
Declaration of patient consent
A full and detailed consent from the patient/guardian has been taken. The patient's identity has been adequately anonymized. If anything related to the patient's identity is shown, adequate consent has been taken from the patient/relative/guardian.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3], [Table 4]