VBD is a disease of cerebrovascular variability with uncertain etiology. It develops in response to various vascular risk factors such as hypertension, arterial wall defects, and atherosclerosis. Current studies have speculated that its pathogenesis may be the dysfunction of vascular intimal matrix metalloproteinases, extensive defects of the endovascular elastic membrane, smooth muscle cell atrophy, and lack of mesial reticular fibers, resulting in the lengthening, dilation, and tortuosity of the wall of the vertebrobasilar artery under prolonged blood flow impact. VBD can lead to a variety of clinical symptoms. Wolters et al.15 reported that cranial nerve compression symptoms caused by VBD accounted for 10.3%, among which HFS was the most common16. HFS manifests as involuntary paroxysmal convulsions of unilateral facial expression muscles, which generally start from the eyelid to the corner of the mouth, progressively aggravates, and is unable to be self-healed. Microvascular decompression surgery has become the first choice for treating HFS because of its minimally invasive and high cure rate, especially its properties of preserving the function of blood vessels and nerves3,4,9,10.
Due to the dilatation and sclerosis of the VBA, it is often difficult to obtain satisfactory decompression effect of the facial nerve by simple decompression. According to preoperative imaging examination and intraoperative findings, in patients with HFS caused by VBD, the vast majority of VBA are usually indirectly responsible vessels, pushing the directly responsible vessels, such as AICA and PICA, to jointly compress the facial nerve3,5,8,9,12. Blindly padding Teflon cotton wool between the VBA and the facial nerve not only blocks the surgical field of view and prevents the exposure of the directly responsible vessels, but also the padded Teflon cotton wool can still transmit the pulsatile impact force of VBA to the facial nerve. Therefore, it is important to explore an appropriate decompression technique to achieve satisfactory decompression effect on the facial nerve. The interposition method is a simple and easy-to-operate surgical technique. After fully releasing the cerebrospinal fluid and sharply separating the arachnoid membrane around the posterior cranial nerves, we placed a slightly larger piece of Teflon cotton in the proximal end of the VBA (the caudal end of the vagus nerve) to displace it as a whole, and then, according to biomechanical principles, we placed several small pieces of Teflon cotton around the focus point of VBA and Teflon cotton to play a supportive role. At the same time, we explored the relationship between the responsible blood vessels that were pushed by the VBA and the facial nerve and fully decompressed them. We used the stepwise technique in 63 patients with VBD-related HFS. The immediate postoperative curative ratio was 87.3%, the efficacy rate was 96.8%, the long-term cure rate was 98.4%, and the recurrence ratio was 6.3% after 3 years of outpatient or telephone follow-up. Nonaka8 pointed out that the wedge technique is a simple and effective decompression technique for HFS caused by VBD without increasing the incidence of related complications and can also be used to manage other responsible vessels that are difficult to displace.
However, not all VBA can be successfully displaced due to tortuous dilatation of the vertebrobasilar artery9. In this study, 39 patients were difficult to displace due to high VBA tension, and we adopted the biomedical glue sling technique. The key point of this technique is that after the suspension point is determined, using low power bipolar electrocautery to cauterize the dura mater of the rock bone to make it easy to mark and to form a friction surface for the adhesion of the biological glue. We put a small amount of biological glue on a small piece of gelatin sponge and stick the responsible blood vessel with a gun-like forceps, and then push the responsible blood vessel towards the dura mater of the rock bone and apply a small amount of biological glue between the gelatin and the dura mater to make the two of them bonded together. Finally, the facial nerve REZ was investigated, and an appropriate amount of Teflon cotton was placed between the responsible blood vessel and the root of the facial nerve to complete decompression. However, the biomedical glue sling technique also has some disadvantages: ①The operation space of cerebellopontine angle is limited, and the anatomical structure is complex, which is difficult to operate, and it is difficult to shift again after VBA is fixed, which is a great test for the skill of the surgeons; ②biomedical glue sling technique is prone to neurovascular adhesion and chemical meningitis caused by glue spilling into subarachnoid space or leakage2, leading to ineffective surgery and even serious surgical complications. To avoid the above situation, we placed water-soaked gelatin sponges and brain sponges on the cerebellar hemisphere and adjacent nerves to ensure that the glue would not flow out beyond the adhesion point and cause damage. At the same time, the operation should be carried out carefully and slowly. In the transposition group, the immediate postoperative curative ratio was 89.7%, the efficacy was 97.4%, the long-term curative ratio was 97.4%, and the recurrence ratio was 7.7%. There was no statistically significant difference in the immediate curative ratio, efficacy, long-term curative ratio, and recurrence ratio between the two groups (P > 0.05). Shimano adopted the transposition method (fibrin glue) to treat HFS caused by bilateral vertebral artery compression and achieved good curative effect9. Lee reported that the bioglue-coated Teflon sling technique was a safe and effective surgical technique for HFS caused by the VA and none of the patients experienced recurrence during the 2 years follow-up7。
The common neurological complication risks of MVD for HFS are facial paralysis, hearing loss, dysphagia, hoarseness, cerebrospinal fluid leakage, intracranial hemorrhage, and other cranial nerve dysfunction2–4,8,9,11,14,15,17. Facial paralysis is a relatively common complication after MVD, with an incidence of 0.6%-1.2%6,7, which is related to unnecessary intraoperative manipulation of the facial nerve13. The interposition method or transposition method was applied to shift VBA as a whole at the proximal end, to fully expose the REZ area and reduce the overuse of Teflon felt in the REZ area of the responsible blood vessels and facial nerve and the unnecessary pulling of the facial nerve, thus minimizing the risk of postoperative facial paralysis. Postoperative hearing impairment is also one of the common complications4, which may be caused by inappropriate pulling on the cerebellum resulting in damage to the auditory nerve, vascular injury and compression by the Teflon felt. To avoid hearing damage, we need to pay attention to the direction of cerebellar traction, so that it is as vertical as possible to the auditory nerve, while protecting the blood vessels around the auditory nerve. In this study, there were no serious complications such as cerebral infarction, but one patient in the interposition group developed a small amount of subdural hematoma, which did not show any clinical symptoms and was absorbed spontaneously at the time of discharge. There was no statistically significant difference in the incidence of postoperative complications between the two groups (P > 0.05).
The application of intraoperative electrophysiological monitoring technology is very crucial. The disappearance of AMR is closely related to the removal of offending vessels in MVD. If the AMR wave completely disappears, it indicates that the facial nerve has been sufficiently decompressed. If the frequency or amplitude of the AMR wave decreases but does not completely disappear, it usually indicates that the decompression is not sufficient, or the compression vessels are missing. It is necessary to explore and check whether the implanted spacer is appropriate until the AMR wave completely returns to normal. In 6 patients in this study, after decompression of the facial nerve REZ, the frequency of AMR decreased under the same stimulation volume, but it did not completely disappear. The missed offending vessels were found, and the decompression was performed after the full-range exploration. Therefore, we advocate the use of AMR intraoperative monitoring to determine whether facial nerve decompression is possible adequacy.