INTRODUCTION
Trigeminal neuralgia (TN) is a neuropathic pain disorder characterized by paroxysms of stabbing or electric shock-like pain in the face [1]. TN is usually initially treated with drugs such as carbamazepine, oxcarbazepine, lamotrigine, or gabapentin [2]. However, in severe, medically refractory cases, and cases where the drugs’ side effects are severe, other treatments should be considered. Consequently, treatments such as microsurgery, percutaneous ablative surgery using glycerol or radiofrequency, radiation surgery, and percutaneous balloon compression are applied to patients of TN who are difficult to cure by drugs [3]. Among these treatments, microvascular decompression (MVD) for classic TN is known to be the surgical treatment of choice, as efficacy was reported to be generally high, with low complication rates [4]. In idiopathic TN, no clear offender of the trigeminal nerve may be present during microsurgery, resulting in procedures such as partial sensory root rhizotomy (PSR) or internal neurolysis [5,6]. However, several complications such as facial numbness or hypesthesia have been reported in these procedures [7,8]. Therefore, advancements in surgical techniques should be sought after for better clinical outcomes in microsurgery for TN in general.
In this study, we propose a modified surgical technique, Meckel’s cave compression with Teflon (Rhee’s method), which, when combined with MVD and/or PSR, could possibly show improved treatment outcomes with low complication rates in TN patients.
MATERIALS AND METHODS
Among patients diagnosed with TN in our institute from March 1996 to December 2014, 78 patients underwent microsurgery treatment. Fifty of these patients were treated with MVD only as a definite offending vessel was observed. The method of Meckel’s cave compression with Teflon was applied additionally with classical surgical procedures to the remaining 28 patients which either had no offending vessel, or the suspected vessel was doubted to be the only culprit. We investigated patient age, sex, distribution of pain, past medical history as well as the clinical outcome of combining the operative method with Meckel’s cave compression with Teflon.
Before surgery, patients with TN were examined with magnetic resonance imaging (MRI), computed tomography (CT) and skull X-rays. The vessels anterior to the brain stem could be observed through short range MRI. CT and CT angiography scans visualized the skull base and large arteries, which was useful for planning craniectomy. Simple skull X-rays, with a base skull view, showed sigmoid sinus grooves and mastoid air cells more precisely, providing further information in planning the surgical approach.
Operative method
The patient went through general anesthesia and was positioned in the lateral decubitus position (so-called park bench position). The neck was slightly inflected in order to ease the handling of the microscope and surgical instruments. A gel pad was placed opposite to the operation site to prevent compression of the jugular vein and maintain normal venous return from the brain. A linear skin incision was performed 2 cm behind the mastoid tip and about 6 cm from the hair line. A single burr hole was made 1 cm inferior to the asterion near the transverse-sigmoid junction. A craniectomy was carefully performed just posterior to the sigmoid sinus, and bone wax was used to block mastoid air cells when exposed. The dura mater was cut in a Y shape and the operation was continued through microscope view (Fig. 1). After sharp dissection of the arachnoid, the sensory and motor branches of the trigeminal nerve were exposed. If offending vessels were clearly observed, conventional MVD was conducted using Teflon while avoiding injuries to the superior petrosal vein by traction. Meckel’s cave compression with Teflon was conducted additionally if no offending vessel was observed, or the operator doubted the offending vessel to be the only culprit. For this method, trigeminal nerve roots forming a trigeminal ganglion entering Meckel’s cave were found and arachnoid layers enveloping the trigeminal nerve was dissected to provide space. Meckel’s cave was then carefully packed using Teflon (Fig. 1F). During this process, low blood pressure and bradycardia were carefully monitored, as parasympathetic nerve irritation can be generated from the pressure of the trigeminal ganglion [9].
For changes in clinical symptoms, pain intensity described by the Barrow Neurological Institute (BNI) pain intensity score was recorded during the hospitalization period [10]. Postoperative complications and symptoms including headache, facial numbness, tongue numbness, wound swelling, cerebrospinal fluid (CSF) leakage, dizziness, hearing disturbance, tinnitus, otitis media, V1 hyperesthesia and parasympathetic nervous system activation were also recorded. Follow-up observation after discharge was checked through inspections and interviews during outpatient visits. The subjects were 21 females (75.0%) and 7 males (25.0%). The average age was 54.3 years (range: 40 to 69 years), the mean symptom presentation period was 70.5 months (range: 5 to 360 months) and the mean follow-up period after surgery was 26 months (range: 1 to 77 months).
RESULTS
Clinical symptoms
The most frequent distribution of TN was V2+V3 (Table 1). Severity of TN was recorded based on the BNI pain intensity score (Table 2). On admission, three patients had mild facial palsy while one patient had facial palsy accompanied by homonymous hearing difficulty. For past medical histories, six patients (21.4%) had hypertension, one (3.6%) had tuberculosis, and one (3.6%) had hepatitis. Before surgery, 26 patients (92.9%) had undergone pharmacotherapy, and four (14.3%) had received percutaneous procedures for TN (3: glycerol rhizotomy, 1: supraorbital neurectomy).
Offending vessel
As shown in Table 3, many vessels were found to be associated with TN. We defined a definite offending vessel to be a vessel that crosses over and compresses the trigeminal root entry zone. Among the 28 cases, only seven cases (25.0%) appeared to have definite offending vessels. For the remaining cases, it was difficult to determine if vascular compression caused TN, especially if small nonspecific vessels were involved. One patient appeared to have no offending vessels.
Selection of surgical treatment method
In this study, 28 patients underwent Meckel’s cave compression with Teflon (Table 4). Ten cases (35.7%) were combined with MVD and one (3.6%) with PSR. Seventeen (60.7%) cases went through all three methods; Meckel’s cave compression with Teflon, PSR, and MVD. In the one patient that had no visible offending vessel whatsoever, PSR and Meckel’s cave compression with Teflon was conducted.
Clinical progress
After surgery, 22 patients (78.6%) saw immediate disappearance of TN. Two weeks after surgery, an additional four patients experienced a gradual alleviation of symptoms. BNI pain intensity scores recorded at the time of discharge showed 26 patients having reduced scores, and thus having a pain alleviation rate of 92.9% (Table 5). For the two patients who did not show symptom relief, one had both dolichoectatic basilar artery and anteroinferior cerebellar artery for culprit vessels, and the other patient had an abnormally large superior petrosal vein.
The mean follow-up period after discharge was 26 months (range: 1 to 76 months). Seven patients (25.0%), including the two patients who did not show symptom relief after surgery, required additional medical therapy during postoperative follow-up, but their symptoms were controllable by medical treatment. There were three cases of recurrence which included one patient who had initially been completely pain free, and two other patients who experienced only pain alleviation. Pain relapsed at 6 months, 6 months, and 11 months after surgery, respectively. No patients among the 28 subjects underwent re-surgery.
Complications
Eleven patients (39.3%) complained of persistent headaches unrelated to the operation site during hospitalization (Table 6). Four patients (14.3%) complained of facial dysesthesia, but showed gradual improvement during the follow-up period. Two patients (7.1%) complained of dysesthesia of the tongue. One patient (3.6%) showed infection at the operation site, but was relieved after a wound revision. One patient (3.6%) showed temporary hearing disturbance and one case (3.6%) was diagnosed with otitis media accompanied by CSF rhinorrhea. There was one case (3.6%) of hypotension accompanied by bradycardia during anesthesia when this technique was used, but was only transient. The patient immediately recovered during the operation and did not cause serious complications, and never reoccurred during hospital stay.
DISCUSSION
This study suggests that Meckel’s cave compression with Teflon, combined with MVD or PSR, showed favorable clinical outcomes in TN patients. Symptom relief rates were high, and complications were relatively observed to be low.
MVD is conducted on the assumption that TN is caused by the degeneration of trigeminal nerves due to vascular compression [11,12]. If there is no proof of vascular compression, procedures such as PSR are applied [5]. For actual surgery, MVD and PSR are applied either independently or simultaneously. The most important two factors in selecting microsurgery as the treatment method is that pain loss must continue without recurrence, and that it must be cured without any complications following surgery. Due to this reason, it should be definitely indicated whether the patients’ symptoms before surgery indicate typical TN. Moreover, accurate detection of the culprit vessel in TN is crucial for effective surgical treatment. However, as our study shows, during microsurgery, detecting a clear offending vessel or being sure if this is the only culprit that causes TN is not always possible. Therefore, when the operator is in doubt, further attempts to relieve TN with less complications should be done.
Meckel’s cave compression with Teflon conducted in this study uses Teflon to compress Meckel’s cave in the surgical view, if it is easily accessible. This idea was derived from the concept of percutaneous balloon compression for TN [13]. When there is no cause of vascular compression in the surgical view, or a definite vascular compression could not be confirmed even if there was an offending vessel, the combined method was performed for expectations of better treatment outcomes after conventional MVD and PSR. The reasons for combining this technique with the conventional operative methods were; it was relatively simple to perform, the occurrence of complications was not high, and conservative management was possible even if complications occurred.
As of now, there is no established hypothesis on what mechanism this artificial compression of the trigeminal ganglion has on the treatment of TN. In general, when pressure is applied to the trigeminal ganglion, large myelinated fibers are selectively injured and the emphatic transmission points disappear, which preserves the function of myelinated fibers and relieves pain [14-18]. On the other hand, complications by the compression of the trigeminal ganglion could include the suppression of the sympathetic nervous system and the stimulation of the parasympathetic nervous system. Unfortunately, this may cause bradycardia and hypotension [9]. Fortunately, among the 28 patients who underwent Meckel’s cave compression with Teflon, only one patient showed this phenomenon, and was transient.
The treatment results of MVD for TN show that the postoperative pain free rate varies from 62 to 96%, and the pain recurrence rate during the follow-up period is reported to be 3 to 32.3% [4,19-21]. Barker et al. [22] reported in their study of 1,204 patients, the pain free rate during a relatively long follow-up period of 6.2 years was 70%. Burchiel et al. [23] reported less than desirable results from their treatment of 40-year-old patients; during the follow-up period of 8.5 years 47% of the patients complained of persistent pain, and 31% of the patients experienced recurrence. The recurrence rate after surgery has been reported as 6 to 23%, and the clinical results vary according to differences in operative methods and follow-up periods [24]. Zakrzewska et al. [25] reported their treatment results after over 5 years of follow-up for a patient group who underwent MVD, and another patient group who underwent partial rhizotomy. They showed pain free rates of 90% and 88%, respectively, but the PSR group experienced more complications, so the satisfaction level of patients was higher among the MVD group. According to Kondo [26], the prognosis of TN treatment depended on the adequate localization of decompression material, how far the offending vessel was removed from the trigeminal nerve, and how well the surrounding arachnoid membrane was dissected. Sindou et al. [27] reported their treatment results for 360 patients with a long-term follow-up of 15 years, and the pain relief rate was 73.4%. The significance of Meckel’s cave compression with Teflon lies in the fact that it is a simple technique without risk, and thus we may expect better treatment results when combined with conventional therapies.
In idiopathic TN, where no definite cause of trigeminal nerve compression is observed, surgical decision making is still controversial. Cheng et al. [28] reported 28 cases of idiopathic TN patients who underwent surgical procedures of lysis of surrounding arachnoid, gentle compression of the nerve root for 10 seconds, and Teflon arrangement around the nerve root entry zone. Twenty patients (71.4%) showed immediate pain relief, but only 13 (46.4%) had pain relief at follow-up after discharge. PSR alone may also be a treatment option. Terrier et al. [5] reported 22 cases of TN patients who underwent PSR only. Of these patients, 86.4% reported complete pain relief, and 22.7% showed hypoesthesia. TN recurrence rate at 5 years was 31.5%. In contrast, Young and Wilkins [7] reported only 48% postoperative pain relief. Internal neurolysis by longitudinally dividing the fibers of the trigeminal nerve itself can also be performed. Li et al. [6] reported a 91.3% pain relief rate of 36 TN patients without vascular compression. Ko et al. [8] reported a 47% pain-free rate after 5 years of surgery. In our study, 22 patients (78.6%) saw immediate disappearance of TN, and at follow-up after discharge, 26 patients (92.9%) showed pain alleviation. Compared with other studies, we suggest that the addition of our technique to MVD and PSR could show enhanced pain relief rates. However, simply comparing the pain relief rates to other studies have major limitations, and thus a thorough study that compares clinical outcomes between surgical treatments that use and do not use our new technique should be performed in the future.
One disadvantage of operative treatment is that it has more complications than non-invasive techniques. Fortunately, at present, serious complications due to damage of the brainstem are rare thanks to the development of brainstem auditory evoked potential monitoring during operations [29]. Special care must be taken when retracting the cerebellum during an operation because if excessive force is applied, brain edema, brain contusion, and hemorrhage may occur after the operation. The occurrence of CSF leakage after posterior fossa operation is about 2%, and this is caused by the insufficient closure of cranial dura mater and inaccurate blocking of exposed mastoid air cells [30]. Of complications by operative method, facial sensory dysfunction by MVD is rare, but complications from PSR such as postoperative facial sensory deficits were reported to be more frequent [5,7]. According to the results of this study, the most frequent direct complication after our method was a persistent headache, and dizziness was reported in three cases as well. These symptoms gradually subsided during hospital stay. The four patients who experienced facial sensory dysfunction had also undergone simultaneous partial rhizotomy, and the patient who had transient hearing disturbance experienced pain relief during the outpatient follow-up period. Furthermore, only one patient suffered from transient hypotension and bradycardia by compression of the trigeminal ganglion during surgery. Therefore, even with combining Meckel’s cave compression with Teflon with MVD or PSR, complication rates seemed not to vary when compared with previously reported studies.
CONCLUSION
The results of this study showed that as a therapy for TN, compression through insertion of Teflon into Meckel’s cave achieved relatively good initial pain relief rates and pain free rates during the follow-up period. Additionally, the complication rates were also found to be as low as conventional surgical procedures. Meckel’s cave compression with Teflon may be an effective modified surgical technique for TN that can be performed without any serious difficulty when the Meckel’s cave is easily accessible in the surgical view.
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