Letter: Prospective, Multicenter Clinical Study of Microvascular Decompression for Hemifacial Spasm.

Abstract

To the Editor: We read with great interest the recent article by Mizobuchi et al1 in Neurosurgery, which explored short-term and long-term outcomes and complications of microvascular decompression (MVD) for hemifacial spasm (HFS) through a multicenter, prospective, cohort study. They suggested that MVD is an effective and safe treatment for HFS under intraoperative neuromonitoring and expert guidance. Basically, we agree with this point of view. Information from intraoperative neuromonitoring has been considered to help prevent functional damage to those nerves in anaesthetized patients.2 We congratulate the authors for the excellent presentation of their results. Nevertheless, there are several queries and suggestions that we would like to communicate with the authors. The most common responsible vessels involved in HFS are anterior inferior cerebellar artery (AICA), posterior inferior cerebellar artery (PICA), and their branches, and decompression of these offending vessels is relatively easy and valid.3 The vertebral artery (VA) rarely directly compresses the root enter zone (REZ) and leads to HFS.4 It tends to generate indirect transmission of pulses on the REZ through other arteries, such as PICA or AICA.5,6 Mizobuchi et al1 confirmed this point and observed that 71.0% of the patients with HFS have non-VA type compressive pattern and 2.1% have merely VA compressive pattern. It is worth noting that treatment of VA-associated HFS (VA compresses the REZ directly or indirectly) is more challenging because of the larger size and greater elasticity of VA. Therefore, MVD for such patients is more likely to lead to unsatisfactory symptom relief. Curiously, the results of Mizobuchi et al1 showed that the VA type compressive pattern was associated with better long-term effects of MVD compared with non-VA type (P < .05). We try to explain this phenomenon from the aspect of the surgical technique. These techniques used during MVD generally fall into 2 main categories: “interposition” and “transposition.”7 The interposition method is relatively easily and traditional, often requiring an inserted prosthesis to separate the responsible vessels and the nerve.8 Regarding the latter method, various materials, including Teflon sling,9 biomedical glue,8 and vascular tape,10 are used to reposition the responsible vessels, sparing the nerves from any contact. For a small responsible vessel, such as AICA or PICA, the interposition technique is often adopted to achieve the desired decompression effect. For VA-associated HFS, considerable pulsatile pressure may continue to be transmitted to the facial nerve after inserting Teflon felt implants. Moreover, large volumes of Teflon felt can be responsible for additional pressure on the nerve. Therefore, the interposition method is despised by some authors,8-10 and they suggest that it is associated with insufficient decompression for the VA type compressive pattern, thus decreasing the efficacy of MVD. In this situation, transposition may be a more reasonable choice. The transposition method could prevent adhesion and granuloma formation near the REZ, which is considered to be a main reason for postoperative recurrence. Unfortunately, crucial information about the specific technique used in the 2 groups and what proportions were not specifically described in this study by Mizobuchi et al.1 From Table 2, it seems that the interposition technique is mainly used in this multicenter cohort study because prosthesis materials are involved in most patients. Indeed, this is not absolute. The prosthesis is also required in some transposition techniques such as Teflon sling technique. In addition, 51 (10.5%) people were demonstrated that prosthesis is not involved, so what technique was used in them? We believe that the information regarding the decompression modality used during operation is important. Further explorations may explain the seemingly unexpected phenomena presented in the Results section of this paper. In addition, we note that 5 people do not belong to either VA type group or non-VA type group B (Table 3). As described in the inclusion criteria, only HFS resulting from vascular compression of the facial nerve was included. This means that other factors that may cause HFS, such as arteriovenous malformation,11 Arachnoid bands,12 and cerebellopontine angle tumor,13 have been excluded. Therefore, what are the operative findings of these special 5 patients? What kinds of intraoperative treatments were used for them, and what was their effects? We appreciate the authors' contribution to functional neurosurgery and want to hear from them regarding the above comments.