Introduction

Trigeminal neuralgia (TN), hemifacial spasm (HFS), and glossopharyngeal neuralgia (GPN) are caused by vascular compression at the root entry or exit zone of the cranial nerves. Microvascular decompression (MVD) performed via the lateral suboccipital approach is now the preferred method for treating these cranial nerve compression syndromes. MVD was introduced in the late 1960s and was largely popularized by Jannetta and colleagues [3, 8, 9, 18]. Since Jannetta’s original description, there have been several developments in the procedures and techniques, particularly in methods of keeping the offending vessel away from the nerve. In recent years, a variety of sling retraction techniques have been reported for securing vascular transposition [2, 5, 17, 19, 20, 24, 29, 30]. We have also utilized the stitched sling retraction technique to secure the transposition of the offending arteries [12]. However, few reports have systematically described the details of the optimal stitching point for effective transposition of the offending artery. In this paper, we introduce and describe surgical procedures and techniques for treating TN, HFS, and GPN with the stitched sling retraction method. We particularly focus on the stitching point for slinging the offending vessel in the appropriate direction and the surgical approach for obtaining a sufficient operative field from an anatomical viewpoint.

Patients and methods

Patient population

Between January 2007 and March 2009, 33 patients with TN, 36 patients with HFS, and 3 patients with GPN underwent MVD at our institution. Among them, the stitched sling retraction technique was employed in 28 patients (85%) with TN, 5 patients (14%) with HFS, and 3 patients (100%) with GPN.

Surgical procedures and stitching methods

We have adopted three different MVD approaches to treat the three main cranial nerve compression syndromes: (1) the infratentorial lateral supracerebellar approach for TN, (2) the lateral suboccipital infrafloccular approach for HFS, and (3) the transcondylar fossa approach for GPN. The details of these three approaches have been described in previous publications [7, 13, 14].

Trigeminal neuralgia

In cases of TN, the stitched sling retraction technique was employed to mobilize the superior cerebellar artery (SCA) and/or the anterior inferior cerebellar artery (AICA). We found that the SCA coursed medial to the trigeminal nerve and compressed the nerve from the superomedial side (Fig. 1a). To treat the condition, therefore, the SCA was transposed in a superomedial direction to free the compressed trigeminal nerve. Meticulous arachnoid dissection was performed to fully mobilize the SCA. We stitched 5–0 thread to the tentorium cerebelli to transpose the SCA superomedially, then passed it around the SCA, and knotted it to make a sling, ensuring that the vessel was not kinked (Fig. 1b). We placed the stitch at the center of the tentorium and used a long sling to transpose the SCA because the tentorial arteries and sinuses are located near the tentorial edge and in the dorsomedial part of the tentorium (Fig. 2). This helps to avoid hemorrhage from the tentorium and to perform the procedure in a shallow operative field. In the cases of compression of the AICA, the artery was transposed in the caudolateral direction because the AICA coursed caudal to the trigeminal nerve and compressed the nerve from the caudolateral side (Fig. 1a). We placed a stitch to the petrous dura (Fig. 3) to transpose the AICA inferolaterally (Fig. 1b). The petrous dura on the suprameatal tubercle is occasionally so thin that care should be taken not to tear the dura mater. Figure 4 demonstrates the intraoperative photographs of MVD for right TN.

Fig. 1
figure 1

Schematic drawings of MVD for TN caused by the SCA and AICA. a The SCA compresses the trigeminal nerve from the superomedial side, and the AICA compresses the nerve from the caudal side. b The SCA is transposed superomedially with a sling stitched to the tentorium cerebelli. The AICA is transposed caudolaterally with a sling secured to the petrous dura. SPV superior petrosal vein

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Fig. 2
figure 2

Cadaveric specimen showing the dural sinuses of the tentorium cerebelli. Tentorial sinuses are well-developed near the tentorial edge and in the dorsomedial part of the tentorium. The stitching point for transposition of the SCA is colored red where the tentorial sinuses are sparse

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Fig. 3
figure 3

Cadaveric specimen showing the lateral wall of the left cerebellopontine angle. The stitching point for transposition of the AICA in TN is colored yellow. The stitching points for the VA in HFS and the PICA in GPN are colored blue and green, respectively

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Fig. 4
figure 4

Intraoperative photographs of MVD in a 47-year-old woman with right TN. a The SCA compressed the trigeminal nerve from the superior side. b The SCA was transposed superomedially with a sling stitched to the tentorium cerebelli. In this case, a single hemoclip was used to make a sling

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Hemifacial spasm

In cases of HFS, we used the sling retraction technique to mobilize the offending vertebral artery (VA). The VA compressed the nerve from the ventral side. We made a stitch to the petrous dura near the jugular foramen (Fig. 3) and transposed the VA superolaterally away from the root exit zone of the facial nerve. Following this procedure, if necessary the ordinary prosthesis insertion with Teflon felt was added to dislocate the PICA or AICA. To inspect the root exit zone, the direction of view of the microscope should be turned to the brainstem side (Fig. 5a). To facilitate surgical access, it is important to expose sufficiently the inferolateral limit of the surgical field. On the other hand, to make a stitch to the petrous dura, the axis of view of the microscope should be turned to the petrous bone side (Fig. 5b). Therefore, the medial border of the surgical field should be enlarged. Figure 6 demonstrates the intraoperative photographs of MVD for left HFS.

Fig. 5
figure 5

Schematic drawings of MVD for HFS, caused by the PICA concomitantly with the VA. a The root exit zone (REZ) of the facial nerve is compressed by the PICA originating from the ectatic VA. b The VA is transposed superolaterally by a sling anchored to the petrous dura near the jugular foramen. Following this procedure, the ordinary prosthesis insertion with Teflon felt is added to dislocate the PICA. Ch Pl choroid plexus

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Fig. 6
figure 6

Intraoperative photographs of MVD in a 53-year-old woman with left HFS. a The VA compressed the root exit zone of the left facial nerve. b The VA was transposed superolaterally (arrowheads) with a sling

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Glossopharyngeal neuralgia

In cases of GPN, a loop of the PICA protruded into the supraolivary fossette and compressed the glossopharyngeal and vagal nerves from the caudal side (Fig. 7a). Therefore, the offending PICA was transposed caudally to free the compressed nerve. We made a stitch to the dura mater on the jugular tubercle (Fig. 3) and transposed the offending PICA inferolaterally (Fig. 7b). Figure 8 demonstrates the intraoperative photographs of MVD for left GPN.

Fig. 7
figure 7

Schematic drawings of MVD for GPN caused by the PICA. a The loop of PICA compresses the root of the glossopharyngeal nerve in the supraolivary fossette. b The loop of PICA is pulled out from the supraolivary fossette and repositioned inferolaterally by a sling stitched to the dura mater on the jugular tubercle

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Fig. 8
figure 8

Intraoperative photographs of MVD in a 42-year-old man with left GPN. a The PICA compressed the left glossopharyngeal nerve. b The loop of PICA was pulled out from the supraolivary fossette and repositioned with a sling

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Results

The demographics of the patients are summarized in Table 1.

Table 1 Summary of patients who underwent MVD using the stitched sling retraction technique
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Trigeminal neuralgia

Among the 28 patients with TN treated using the stitched sling retraction technique, the SCA was involved in 23 patients, the AICA in 1 patient, and the SCA and AICA were both involved in 4 patients. In 5 of the 33 patients undergoing MVD, the sling retraction technique was not employed: four patients exhibited no arterial compression and one patient had short perforators from the SCA to the brainstem. An excellent outcome (complete pain relief without medication) was obtained in 24 of 28 (86%) patients, and a good outcome (no or mild pain controlled with low-dose medication) was observed in the remaining four patients (14%). No recurrence was observed during postoperative follow-up periods of between 8 and 30 months. Complications were observed in four patients: One patient developed transient cerebellar ataxia due to venous infarction, and three patients showed cerebrospinal fluid leakage.

Hemifacial spasm

Among the five HFS patients treated with the stitched sling retraction technique, the VA alone was involved in one patient, the VA and AICA together in two patients, and the VA and PICA were involved together in two patients. All patients showed a complete resolution of their spasm and experienced no complications. Although the longest follow-up period was only 24 months, no patient suffered recurrence.

Glossopharyngeal neuralgia

In all three cases of GPN, the PICA alone was implicated. All patients recovered immediately after surgery. One patient suffered mild hoarseness. No recurrences were observed and each patient experienced complete relief during the 12, 18, and 29 months, respectively.

Discussion

Trigeminal neuralgia

Jannetta described an interposition technique that involved the insertion of a Teflon felt to keep the offending vessel off the nerve [1, 18]. However, long-term follow-up studies revealed that the efficacy of MVD for TN gradually decreased over time because of recurrence. The incidence of recurrence of TN has been reported to vary from between 3% and 30% [17]. The pathogenesis of recurrence in cases treated using the interposition method includes adhesions between the prosthesis–nerve complex [4] and inflammatory responses such as granuloma [23]. Thus, an ideal method should maintain a permanent separation between the nerve and the offending vessel, without any contact with the nerve itself [25, 30]. The transposition method may be more suitable than the interposition method for achieving this goal. Some authors have reported the use of a transposition method using adhesive glue [25]. Though an adhesive glue transposition technique is relatively easy to perform, the use of glue involves several problems, including adhesive strength, viral and prion disease transmission, and adhesion to the trigeminal nerve, which is considered to cause recurrence [21]. The technique of vascular transposition using a sling retraction was originally developed by Fukushima [5], and a variety of sling retraction techniques involving offending arteries have subsequently been reported using aneurysm clips [2], Gore-tex tape [29], or fascia strips [20]. To accomplish the sling retraction method successfully, an appropriate surgical approach must be used to obtain a sufficient operative field for placing a stitch at a suitable site and performing the stitching procedures safely.

We have utilized the infratentorial lateral supracerebellar approach for MVD in the treatment of TN [13]. The SCA, which is the most frequent offending vessel involved in TN, courses above the trigeminal nerve making a downward loop and compresses the nerve from the superior, superomedial or medial side [6, 13, 31]. Therefore, it is reasonable to transpose the SCA superomedially with a sling stitched to the tentorium cerebelli. This procedure can be facilitated using the infratentorial lateral supracerebellar approach. Moreover, the stitching procedure is both relatively easy and safe because the working space on the tentorial cerebellar surface obtained through this approach is sufficiently wide and is far from the seventh and eighth cranial nerves and the superior petrosal vein. Though some authors placed a stitch at the lateral part of the tentorium and repositioned the SCA superiorly [19, 20], unexpected bleeding can occur because tentorial sinuses are located in this area [16].

Hemifacial spasm

In cases of HFS, we employed a sling retraction technique to mobilize the VA. For dislocation of the AICA or PICA, however, we used the interposition method with Teflon felt because of difficulties in transposing these vessels due to the presence of short perforators in most cases. Compared with TN, the recurrence rate for HFS following the interposition method with Teflon felt is low, ranging from 1% to 10% [22, 26]. The main cause of recurrence of HFS is not attributed to adhesion. Rather, inadequate cushion effect of offending vessels is thought to be a frequent causative factor in HFS recurrence [26, 32]. The interposition method is sometimes insufficient to buffer a large pulsatile force caused by the VA; thus, we prefer the stitched sling retraction method for mobilizing the VA. We have also found Teflon sponges between the VA and brainstem useful to avoid excessive stress on the arterial wall. To obtain an adequate working space, a wide opening of the cerebellopontine fissure is essential. This can be facilitated using the lateral suboccipital infrafloccular approach.

Glossopharyngeal neuralgia

In cases of GPN, we have applied the transcondylar fossa approach [10, 14], in which the posterior part of the jugular tubercle is extradurally removed without injuring the atlanto-occipital joint [15]. This approach provides sufficient visualization of the entire course of the cisternal portion of the ninth and tenth cranial nerves with a slight retraction of the cerebellum and clearly shows its relationships with nearby arteries such as the PICA or VA. There have been only a few reports on the use of the sling retraction technique for the treatment of GPN. Sampson et al. repositioned the offending artery superolaterally with a Teflon sling that was attached to the petrous dura between the internal auditory meatus and jugular foramen [27]. We consider that inferior displacement of the vessel is more reasonable because the vessel usually arises from below and ventral to the nerves. The transcondylar fossa approach provides wide exposure of dura mater on the jugular tubercle; therefore, it is not difficult to reposition the offending artery in a caudal direction with this approach. Thus, the stitched sling retraction method through this approach seems to be the most suitable for MVD for GPN.

As a limitation, the sample size is not large enough for strong conclusion. The majority of previous reports insisting efficacy of the sling retraction method include a small number of patients, and data regarding the long-term outcome comparing the interposition method versus the sling retraction method are very limited [30]. Our method cannot apply to some cases in which short perforators originate from the offending artery, and the stitching points may not be generalized to every case due to individual variations. Nonetheless, it is clinically useful to understand the principle of the optimal stitching point because the anatomical relationships between the cranial nerves and the cerebellar arteries are similar in the majority of the cases. Recently, three-dimensional computer graphics with image fusion have been applied to preoperative simulation of MVD [11, 28]. With improvements in the software and the quality of the source images, this may become a powerful tool in the planning of the stitching points.

In summary, the stitched sling retraction method can be a safe and effective treatment for cranial nerve compression syndromes. It is vital to select the most suitable surgical approach and stitching point based on the surgical anatomy. Further evaluation in large series of patients with longer follow-up period is needed to assess the efficacy and safety of this method.