Surgical Treatment for Trigeminal Neuralgia.

Various treatments for trigeminal neuralgia (TN) are known to yield initial satisfactory results; however, the surgical treatment has excellent long-term outcomes and a low recurrence rate. Surgical treatment addresses the challenge of vascular compression, which accounts for 85% of the causes of TN. As for surgical treatment for TN, microvascular decompression (MVD) has become the surgical treatment of choice after Peter J. Jannetta reported the results of MVD surgery in 1996. Since then, many studies have reported a success rate of over 90% for the initial surgical treatment. Most MVDs aim to separate (decompress) the culprit vessel from the trigeminal nerve. To increase the success rate of surgery, accurate indications for MVD and management of the offender vessels without complications are critical. In addition, if there is no vascular compression, partial sensory rhizotomy or internal neurolysis can be performed to improve surgical outcomes.

HISTORY

Trigeminal neuralgia (TN) is a debilitating neuropathic pain disorder characterized by spontaneous and elicited paroxysms of electric shock-like or stabbing pain in the face region [8,11,17]. It affects basic human psychological, physical, and social needs and activities, such as touching or washing the face, brushing teeth, and doing makeup, resulting in anxiety, depression, and social phobia in patients, thereby affecting their mental health[40,51].

TN is initially treated with drugs, but in medically refractory severe cases or cases where it is difficult to maintain the drug due to the side effect of the drug, other treatment is required. Many studies have recommended surgical treatment. In 1858, Carnochan first attempted surgical treatment for directly targeting the trigeminal ganglion [25]. Until the early 20th century, direct nerve sectioning was considered the most effective surgical treatment [57]. In 1929, Dandy has published the results of 88 patients on nerve sectioning and reported that the arterial loop sometimes obscures the surgical field [18]. Thus, he performed the first microvascular decompression (MVD) in neurosurgery without knowing it and not fully understanding the importance of these vascular loops. However, in his monumental paper in 1932, Dandy reported that TN could be caused by a tumor or an association with blood vessels [19]. He observed compression or alteration of the trigeminal nerve by an artery and indicated this to be the cause of the tic douloureux.

Dandy's idea brought a new wind for TN in Europe, but not in the United States. Taarnhøj, a young Danish neurosurgeon, encountered Dandy's hypothesis in the early 1950s and reported in 1954 that 41 out of 70 TN patients experienced complete pain relief and no permanent facial numbness or facial paralysis following decompression surgery [58,59].

After closely observing Taarnhøj's achievements, Gardner promptly perceived the paradigm shift in treatment that his research would bring. He quickly adopted the surgical technique on nine patients and published the results in 1953 [24]. Thereafter, he continued to practice, and in 1959, he published his famous thesis, including 112 patients. Thus, Gardner and Miklos [23] established the indications for vascular decompression surgery for TN. However, the absence of a surgical microscope made it difficult to fully substantiate the hypothesis.

Jannetta developed classical MVD surgery using a surgical microscope to prove that the compression of the arteries or veins can lead to TN. Over time, Janetta refined his surgical technique and eventually adopted the posterior fossa (retrosigmoid) approach [28]. He used Teflon padding to decompress the culprit vessel and trigeminal nerve because it was easy to handle and produced minimal arachnoid scarring. In addition, using this approach, he re-operated on many of Gardner's old patients, who were operated on by Gardner using a gel-foam that got absorbed over time with symptom recurrence. By reviewing Gardner's cases and honing his ideas, Jannetta was able to present evidence of the effectiveness of MVD. Finally, in 1996, 30 years after the initial MVD surgery, he reported a study with 1185 patients who underwent MVD from 1972 to 1991 at the Presbyterian University Hospital in Pittsburgh [6]. The initial success rate of the study was 82% for complete relief, with an additional 16% experiencing partial relief for a combined initial success rate of 98%. At the 10-year follow-up, 68% of patients reported excellent or good relief, whereas the remaining 32% experienced recurrent symptoms. After his great achievements, long-term follow-up studies were published over time, which showed the durability of MVD surgery. Finally, MVD was the surgical treatment of choice for TN.

SURGICAL OUTCOME

MVD is the first-choice surgery for patients with classical TN. A pooled analysis including 5149 patients showed that the MVD efficacy was generally high, as 62–89% of patients were pain-free at the follow-up (after 3–11 years) [9].

MVD shows excellent pain control results in most cases. Initial pain control after MVD was reported to be 80.3–96% [27,29,52,64]. In a prospective study, 92.5% of patients were pain-free without medication for an average of 28 months after surgery [13]. In another study, 85% of patients reported adequate pain control by an average of 38 months [10]. After 5 years post-surgery, 72–85% of patients showed relatively good results [13,52,64].

In a long-term follow-up study, 68% and 73.4% of patients reported complete pain relief after 10 years and 15 years postsurgery, respectively [6,53]. Postoperative pain relief usually occurs immediately after surgery; however, a delayed effect of 1 month or more is observed in some cases [20]. As a result of the study of 196 patients who underwent MVD for TN in our hospital, 157 patients (80%) had excellent outcome (Barrow Neurological Institute [BNI] pain intensity scale I-II) and 183 patients (93.3%) had good outcome (BNI pain intensity scale I-III) within 1 year after surgery (BNI pain intensity scale criteria; I, no pain; II, occasional pain, not requiring medication; III, some pain, controlled with medication; IV, some pain, not controlled with medication; and V, severe pain/no pain relief).

MVD is usually the most effective classical type of TN (type I). Conversely, surgical treatment for multiple sclerosis-related TN is ineffective, with 50% pain relief after 2 years [10]. Factors predicting a good prognosis after surgical treatment include proper neurovascular compression, trigger points for pain, male sex, absence of venous compression, and shorter disease duration [15,26,43,60]. In addition, some studies reported a low recurrence rate in elderly patients [47], while another study mentioned a shorter time to recurrence in patients over 60 years [4]. The recurrence rate might be related to the duration of the disease; however, this remains a controversial factor.

Moreover, sufficient surgical effect for the appropriate indication for repeated MVD is known to exist [3,16,30]. Although this is not as effective as the initial MVD, the initial pain relief rate is 90.3–93.3%, 67% after 12 months, and 42% after 10 years post-surgery with showing no pain [3,5,62].

COMPLICATIONS

Although MVD is a relatively invasive surgery, the complication rate reported due to the development of surgical techniques and specialized surgical skills is quite low [9]. The rates of serious complications, such as death, and intracerebral hemorrhage and stroke have been reported to be 0.3% and 0.6%, respectively [9]. In addition, complications, such as anesthesia dolorosa (0.02%) and meningitis (0.4%), have rarely been observed [9].

Various reports on cranial nerve-related complications are available. Approximately 1.6–22% of trigeminal nerve deficits have been reported, but about half are transient symptoms [7,52,63,66]. Facial weakness is reported to be 0.6–10.6%, but it improves over time [13,29,40,63]. Hearing loss is variously reported (1.2–6.8%) [53,60,63,64,66]; however, in large-scale studies, 1.8% experienced it [9]. Cerebrospinal fluid (CSF) leaks are found in 1.5–4% [21,32,56]. The relationships of the complications with age of the patients were evaluated to identify the risk factors; however, surgical site infections, cranial nerve disorders, and CSF leaks were not related to age [2,47].

In the case of re-MVD, the incidence of complications was higher than that in the initial MVD. Trigeminal nerve disorder was reported in 8.3–32% after reoperation, and hearing impairment occurred in 6.7% of cases [5,16,62].

DECOMPRESSION TECHNIQUE

Interposition technique

This technique is implemented in a conventional MVD. After a sharp dissection of the arachnoid, the blood vessel area associated with the trigeminal nerve gets clearly exposed. This method separates the culprit vessel from the area in contact with the trigeminal nerve using a decompression material [6]. Teflon is usually used as the decompression material (Fig. 1). However, sometimes, if bleeding occurs at the surgical site or if contact with the dura exists due to excessive Teflon insertion, recurrence of symptoms may occur due to granulation with Teflon after surgery [14,49].

Fig. 1.

A : The superior cerebellar artery (SCA) is compressing the back side of the trigeminal nerve (TN) (white arrow). The veins also contact the anterior part of the TN (white arrowhead). B : Decompression of SCA was performed using Teflon (black arrow). C : The vein was also decompressed using Teflon (black arrowhead).

Transposition technique

Recently, several studies have suggested that the offending vessel should be removed reliably and thoroughly from the neurovascular compression site rather than inserting a decompression material between the culprit vessel and trigeminal nerve (Fig. 2) [12,35,37,48,67]. This method, first proposed by Fukushima [22], completely separates the trigeminal nerve and the offending vessel. Sindou et al. [54] reported that this non-touching surgical technique had a better long-term prognosis than the touching one. A study suggested suturing of the culprit vessel to the surrounding dura mater with a 5-0 thread [38]. Other study showing good results using the transposition technique in patients who require repeated MVD have also been reported [41]. When the transposition is completely performed, inserting a decompression material is unnecessary and hence, complications related to materials can be prevented [49].

Fig. 2.

A : The superior cerebellar artery (SCA) was compressed to trigeminal nerve (white arrow). B : Transposition of SCA was performed (white arrow).

However, it is difficult to apply this technique to all TN MVDs because the transposition is too variable due to the diversity of the blood vessels. During transposition, damage to the offending vessels is likely to occur, and sometimes veins must be sacrificed for the workspace. Additionally, excessive movement of the blood vessels can lead to kinking or vasospasm eventually, resulting in stroke [42].

surgical glue or other surgical products, such as tachosil, have recently been used instead of suturing due to the complexity of this surgical technique [1,45,46]. these studies have been recently published, and although the initial effect is acceptable, the durability is controversial because there is not enough follow-up.

Vein offender

Most of the culprit vessels are arteries. However, research on veins has continuously been published over time [31,34,44,50]. A report suggest that in 5–18% of cases, veins are only the offenders [55]. Most studies have suggested the role of veins if symptoms recur or do not disappear after surgery [34]. Another group has suggested that if the culprit vessel of the TN is a vein, the vein must be sacrificed for a complete cure [39]. However, management of veins during MVD surgery is still controversial; many surgeons agree that it is the principle to preserve the veins whenever possible.

Partial sensory rhizotomy (PSR) and internal neurolysis

PSR is performed when no clear offending vessels are observed in the surgical field or preoperative examination. In the past, when anatomical knowledge about somatotrophy was lacking, various means of postoperative pain relief and sensory impairment were suggested [61]. However, these shortcomings have been partially resolved through recent anatomical studies. According to a recent study by Terrier et al. [61], 86.4% of patients reported complete pain relief, and 22.7% exhibited postoperative hypoesthesia following PSR, including secondary TN, in the patient group. In contrast, another study reported a 48% postoperative pain relief. Sensory deficit was reported in 67% of patients [65]. This difference is attributed to the variation in the cross-sectional area of the sensory root and the location of sectioning. As a result, the section of the ventrolateral two-thirds of the pars major of the trigeminal nerve at the pons provides favorable outcomes [61].

If there is no clear offender, internal neurolysis (nerve combing) can be performed. Usually, the trigeminal nerve itself is longitudinally divided along its fibers using a straight blunt-tip probe. Li et al. [36] reported 100% asymptomatic patients immediately after surgery due to internal neurolysis. Thereafter, pain relief was reported in 91.3% of cases. Severe facial numbness immediately after surgery was noted in 11% of patients, and it improved after 6 months post-surgery. Moreover, Ko et al. [33] reported the long-term outcome of internal neurolysis. A 47% pain-free rate was reported after 5 years post-surgery. Most patients (96%) experienced facial numbness or hypesthesia, but these symptoms did not affect the patient's quality of life.

CONCLUSION

The effect of MVD on TN has already been established. However, more advanced research is needed for clearer surgical indications, management of culprit vessels, and durability of the decompression materials. In the future, along with the continuous study on the pathophysiology of TN, a new MVD technique that is safer and can increase the cure rate should be developed.