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Endoscopic Vascular Decompression vs. Microvascular Decompression of the Trigeminal Nerve
By M.S. Kabil., M.D, J.B. Eby M.D., H.K. Shahinian M.D.

Abstract

Microvascular decompression (MVD) is a highly accepted and effective method for treatment of patients with trigeminal neuralgia in whom compression of the nerve by a vascular structure is implicated in the pathogenesis of the disease. However, recent reports have highlighted the advantages of the endoscope in visualizing structures within the cerebellopontine angle. Additional research, using the endoscope to supplement the microscopic procedure, has demonstrated improved localization of neurovascular conflicts. In this report we present the results of our series utilizing a fully endoscopic vascular decompression (EVD) technique, and compare these results to those published for microvascular decompression.

From September 1999 till October 2004, 255 patients underwent endoscopic vascular decompression of the trigeminal nerve. These patients' records were retrospectively reviewed, and additional data from follow-up visits was collected and analyzed to ascertain success rates and review the incidence of complications.

From a total of 255 patients who underwent EVD of the trigeminal nerve we noted an initial, complete, postoperative success rate in 95% of patients. Initial, being defined as within the first 3 months postoperative, and "complete" being judged if the patient reported 98% relief of pain postoperatively without the need for medication (Barker's classification). Additionally, we documented a 93% complete success rate for 118 patients who completed at least a three-year follow-up period. Complication rates were compared to those reported for MVD. There were no serious complications or mortality in this series.

We conclude that EVD is a safe and effective method to remove neuro-vascular conflicts related to the trigeminal nerve. The results of this series demonstrate an improved rate of trigeminal neuralgia relief with EVD when compared to MVD, a lower incidence of complications and a better outcome.

Keywords
endoscopic, microvascular decompression, trigeminal neuralgia, facial pain

Introduction

Trigeminal neuralgia is a disease characterized by severe and often debilitating facial pain that occurs along the distribution of any of the three branches of the trigeminal nerve. As classically defined, attacks are intermittent and the quality of the pain is sharp, stabbing, or mimicking an electric shock. The mainstay of treatment for patients with trigeminal neuralgia prior to the modern surgical era was confined to either medical management of episodic symptoms, or sectioning of the trigeminal nerve.1-4

Microvascular decompression (MVD) of the trigeminal nerve, popularized by Jannetta in the late sixties and early seventies has become the gold standard surgical treatment for patients suffering from trigeminal neuralgia. Over the past thirty years several large studies of patients that underwent MVD have established that the overwhelming majority of cases of trigeminal neuralgia are due to compression of the root entry zone of the trigeminal nerve by ectatic vessels of the posterior circulation.5-19 Microvascular decompression has demonstrated a 70-80% long-term success rate with a minimal morbidity and almost no mortality.5-19

Notwithstanding the success of MVD, documented failures, recurrences, complications inherent to this operation.20-25 and a drive towards less invasive operations have led to a continued search for ways to improve and refine surgical outcomes and reduce the morbidity of this procedure.

Doyen first described the use of endoscopes in skull base surgery in 1917, when he performed trigeminal neurectomy under endoscopic guidance.3 However, it was not until the 1990's that endoscopic sinus surgery spurred a renewed interest in the application of endoscopy to intracranial pathology. This resurgence has paralleled recent advances in endoscopic technology. Advances in Technology such as endoscopes of varying diameters and angles of view, digital monitors and illumination sources, as well as the addition of irrigation sheaths and rigid holding arms, have enhanced the safety and versatility of endoscopic applications.26

Reports documenting the endoscopic anatomy of the cerebellopontine angle have highlighted the advantages of the endoscope over the operating microscope in visualizing structures of this region.27-29 Additionally, a recent report by Spencer quantified the superior volume of visualization provided by the endoscope compared with the operating microscope.30 Other early applications of endoscopy to assist microscopic decompression of the facial nerve demonstrated the improved accuracy of the endoscope in recognizing neurovascular conflicts.31

In 1997 our group began performing endoscope-assisted vascular decompression for the trigeminal nerve, and have reported our results.32 While performing the endoscope assisted procedure we determined that nearly 25% of neurovascular conflicts were missed during the regular MVD. In addition to the improved identification of conflicts, we also discovered that the endoscope allowed access to the trigeminal nerve with little or no cerebellar retraction and with minimal dissection. This led to our interest in converting to a fully endoscopic approach. In September of 1999 we converted to a fully endoscopic vascular decompression (EVD) surgical procedure and have published this technique.33 In the current study we report the results for our series of patients that have undergone EVD of the trigeminal nerve, and compare these results to data from several large MVD series.

Patients and Methods

Between September 1999 and October 2004 a total of 255 patients suffering from trigeminal neuralgia underwent EVD; all operations were performed by surgeons at the Skull Base Institute in Los Angeles, California. Patients' charts, retrospectively reviewed and information from follow-up visits was collected to assess operative success rates, and the incidence of complications.

Postoperative relief was graded as documented by Barker.[4] Relief was judged to be "complete" if a patient reported 98% pain relief without the need for medication, "satisfactory" if a patient reported greater than 75% relief with only intermittent use of pain medication and "none if a patient experienced less than 75% relief or required continual pain medication.

The incidence of complications was collected and compared for EVD vs. MVD. The category "temporary" referred to any deficit, which was completely resolved within three months postoperatively. Permanent deficits were further classified by severity. The incidence of facial numbness was graded as "mild" representing a diminution in fine touch sensation or two point discrimination. Patients with "severe" numbness demonstrated near complete or complete anesthesia in one or more branches of the trigeminal nerve. The category "moderate" encompassed all degrees of facial numbness, which fell between that of "mild" and "severe". Permanent hearing deficits were graded as: "profound" > 60 db hearing loss, whereas a 30-60 db deficit was graded as "mild". Permanent facial nerve palsies were graded using the House-Brackmann six point subjective grading scale and were divided into "mild" (grades II-III), and "severe" (grades IV-VI).

EVD results were compared to mean values calculated from several large MVD series that included over 1600 patients.5,7,9,15,19 The MVD series used for comparison included only those reports containing adequate data with regard to immediate relief, relief at one year post-op, as well as results for each of the specified complication categories.

Surgical Procedure

The technical aspects of the endoscope-assisted decompression operation performed during the early portion of this series have been described in a previous report.32 This procedure involved a complete microscopic examination of the nerve to determine all areas of vascular compression. This was followed by an endoscopic survey of the trigeminal nerve using both the 00 and 300 endoscopes to look for areas of compression missed by microscopic evaluation. The endoscopes were then used to guide decompression of the nerve and to confirm optimal placement of the pledgets between the nerve and vessels.

The fully endoscopic vascular decompression technique has been previously published 33 and will be briefly discussed in this report. The procedure begins with the patient in a park bench position. A 1.5cm retrosigmoid craniotomy is performed, and the CSF is slowly drained. The 00 endoscope is then guided into the cerebellopontine angle, without retraction and with minimal dissection to visualize the acoustico-facial bundle and the trigeminal nerve. Neuro-vascular conflicts affecting the trigeminal nerve are identified and gently dissected free from the nerve.

Once decompression is complete the 00 endoscope is removed and a 300 endoscope is advanced into this region to once again survey the nerve and surrounding structures to assess the adequacy of decompression. Additional conflicts were occasionally encountered, and were likewise separated from the nerve. Teflon pledgets are then placed between the nerve and offending vessel(s) and fibrin glue is used to secure the pledgets in position. The dura, soft tissues and the craniotomy are then closed in anatomical layers without the use of any drains, patients are then taken to the surgical intensive care unit or a step-down unit for overnight observation.

Results

A total of 255 patients underwent EVD for treatment of trigeminal neuralgia during the 61 month period of this study. Mean operative time was 52 minutes. Average length of hospital stay was 1.3 days, with 193 (76%) patients discharged within 24 hours postoperatively. Demographic information is presented in Table 1. There were 243 patients who experienced pain symptoms typical of trigeminal neuralgia, while 12 patients described atypical neuralgia pain. Twenty two additional patients were treated for atypical facial pain syndrome and were not included in this series.

We noted a female: male ratio of greater than 2:1, a mean age of 57 years, and a slightly higher distribution of left vs. right sided symptomatology. The mean duration of symptoms was just over 6 years. Fifty five patients had previously undergone destructive procedures for treatment of their trigeminal pain including 18 partial rhyzotomies, 16 Gamma Knife radio-surgeries and 21 radiofrequency ablations (RFA). Eleven patients had previous MVD operations. Five patients had multiple prior RFA procedures and 8 patients had multiple prior Gamma Knife treatment. Another two patients had undergone more than once a prior MVD operation.

All patients underwent magnetic resonance imaging and/or magnetic resonance angiography of the cerebellopontine angle preoperatively. In this series MR imaging identified vascular compression < 65% of cases. Intraoperatively vascular compression was identified in 100% of patients. Moreover, 20% of patients had more than one structure compressing the trigeminal nerve. Table 2 lists the vascular structures found to be compressing the trigeminal nerve at the time of surgery.

Outcome results are recorded in Table 3. 243/255 (95%) of patients experienced initial (within 3 postoperative months) "complete" pain relief, while 11/255 (4%) had an initial "satisfactory" relief; one patient had no relief. Another group (118 patients) included only those patients with at least a three-year follow-up period; 110/118 (93%) had "complete" relief while 6/118 (5%) had "satisfactory" relief , 2 patients (2%) had no relief.

Complications are depicted in Table 4; this table contains the analysis of complications for the entire group of patients with a mean follow-up of 39.6 months (range 2-61 months). Temporary facial nerve weakness was recorded in 2/255 (0.8%), none of the patients had persistent facial nerve deficit.

With regards to postoperative facial numbness, 17 patients had preoperative facial numbness from prior destructive procedures and were not included in our analysis of postoperative facial numbness. Out of the remaining 238 patients 212/238 (89%) patients never experienced postoperative facial numbness; 14/238 (6%) reported temporary facial numbness; 12/238 (5%) patients reported persistent facial numbness; the majority of which was reported as mild (7/238 patients - 3%), while 3/238 patients (1%) experienced moderate and 2/238 patients (<1%) noted severe facial numbness.

The incidence of CSF leakage was 6/255 (2%), of note that 5/6 leaks occurred during the early portion of our surgical experience. CSF leaks were noted in 5 out of the first 62 patients , whereas there was only 1 CSF leak noted in the last 193 patients (0.5%).

One patient with a pre-existing "mild" hearing loss had postoperative, unilateral, "profound" and permanent hearing deficit on the same side. There were no serious complications such as epidural or subdural hematomas, air emboli, brainstem infarction or death.

Discussion

Surgical approaches to the cerebellopontine angle have undergone a variety of modifications since early surgical pioneers first attempted sectioning of the trigeminal nerve in the early 1900's. Currently, the microvascular decompression operation represents the surgical procedure by which other techniques are compared.5-19

Recently, a shift toward minimally invasive skull base surgical techniques has ultimately fostered the application of endoscopy to access the narrow confines of the cerebellopontine angle. It must be noted however, that reducing the size of the incision and attempting to minimize complications through a minimally invasive approach must not come at the expense of surgical outcomes, thus, this report was designed to address the efficacy of EVD in comparision to MVD.

Relief of Neuralgia

The so-called "keyhole" approach is made possible by the excellent exposure provided by modern endoscopic technology. The flocculonodular lobe of the cerebellum, surrounding cranial nerves, and arachnoid adhesions often obscure the pathway to the cerebellopontine angle, hindering the direct forward view of the operating microscope. Moreover, without significant dissection and retraction, regions of the trigeminal nerve such as the medial and inferior aspects of the root entry zone, as well as the medial aspect of the nerve as it enters Meckel's cave are hidden from the operating microscopes view.

Previous studies have demonstrated that the 00 and 300 endoscopes provide a panoramic view of the trigeminal nerve from the pons to Meckel's cave; with illumination and exposure that is far superior to that of the operating microscope.27-29 The improved exposure of the endoscope has also been shown to result in improved rates of neurovascular conflict identification.31,32

A recent review by Lovely and Jannetta of over 2700 microvascular decompression operations, with an average of 4.4 years follow-up noted a 20-25% recurrence rate and an overall 6-38% failure rate.17 Several other reports have documented that between 10-86% of patients re-explored for persistent or recurrent trigeminal neuralgia after microvascular decompression are found to have areas of compression.21-24,34 These initial failures and recurrences are thought to result from incomplete identification of all neurovascular conflicts, or incomplete decompression at the time of the initial operation. 21-24,34

We believe that the improved visualization provided by the endoscope should in turn lead to better long-term surgical outcomes. Our results comparing EVD and MVD noted excellent outcomes for initial relief of neuralgia pain. Additionally, we documented a better outcome and a reduced recurrence at three-year postoperative follow-up, demonstrating complete relief in 94% of patients for EVD vs. 80% for MVD.5,7,9,15,19

Complications

The incidence of injury to the cranial nerves, brainstem or cerebellum using the microvascular approach is quite low. However, a smaller craniotomy, less dissection and the elimination of retraction should inherently lead to a further reduction in the number of complications. Our complication rates for this series compare favorably with those published for the microvascular procedure, and are well within the reported range for most MVD series (Table 4). 5,7,9,15,19

Manipulation of the trigeminal nerve is thought to be responsible for the occurrence of facial numbness following MVD.7 The endoscopic procedure provides improved visualization of the nerve therefore requiring less dissection to recognize conflicts. However, the identification of additional conflicts requires that these insults be dissected free to ensure complete decompression. This manipulation of additional vessels found to be compressing the trigeminal nerve might account for the slightly higher incidence of facial numbness in the EVD series. The majority of the postoperative facial numbness was graded as mild, and no patients suffered from painful dysesthesias. Of note, data from 2/5 MVD series was incomplete for the incidence and severity of facial numbness.

The endoscope enters the region of the cerebellopontine angle with minimal dissection and in most cases without the need for cerebellar retraction; it then provides excellent exposure of the trigeminal nerve. As a result, the incidence of complications such as retractor injury of the brainstem, cerebellum, and acoustico-facial bundle should diminish. No patient sustained a permanent facial nerve injury, and only 2 patients experienced mild, temporary facial nerve palsies. There were no instances of subdural, epidural, or cerebral/cerebellar infarction in this series, nor was there any mortality as a result of this procedure.

Our incidence of CSF leaks (2%) is lower than that reported for most MVD series. With experience, we have improved our closure technique. We often reinforce the dural closure with a fascial graft and close the subcutaneous tissues in multiple layers. These modifications have resulted in a significant reduction in the incidence of this complication, with only 1 CSF leak occurring in the last 193 patients for an incidence of 0.5%.

The minimally invasive approach results in less mastoid air cell disruption, which should decrease the incidence of meningitis and postoperative middle ear effusions. There were no instances of meningitis recorded in this series. We did not however, perform routine post-operative audiometry to document the incidence of middle ear effusions.

Conclusion

The advantages of the endoscope are numerous, and are expected to lead to improved outcomes and decreased morbidity. This series provides evidence as to the safety and convenience of this approach. In this series, EVD showed a significant advantage when compared to MVD with regards to outcomes and complications.

Moreover, the results in this series of EVD at three-year follow-up show a trend toward a reduction in recurrence rates. We believe that further long-term series results will confirm that EVD offers significant advantages over the current MVD technique.

During our endoscopic procedure we also noted a marked advantage of the endoscope in gaining access to the cerebellopontine angle, as we were able to enter this region with minimal dissection or retraction. This is in contrast to the microscope's straight line of sight view, which is frequently obscured by the narrow tortuous confines of this region, often requiring significant dissection and retraction for adequate exposure.

We believe that the less invasive exposure of this region using the endoscopic technique ultimately results in a lower incidence of complications. We found the endoscope offers several advantages over the operating microscope, including atraumatic access to the cerebellopontine angle, improved visualization of all neurovascular conflicts, as well as a more comprehensive evaluation of the adequacy of decompression.

The beneficial aspects of endoscopy are translated into better surgical outcomes. The fact that it is a more direct and a less invasive approach has lead to a shorter operative time (mean:52 minutes) and length of stay (mean:1.3days), leading us to conclude that fully endoscopic vascular decompression represents a step- forward in safe and effective surgical treatment of trigeminal neuralgia.

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