A prewarning sign for hearing loss by brainstem auditory evoked potentials during microvascular decompression surgery for hemifacial spasm

Predictive nomogram for hearing deficits after microvascular decompression treatment

We explored the impact of brainstem auditory evoked potentials monitoring, as well as anatomical characteristics, in relation to their influence on hearing deficits. A total of 851 patients diagnosed with idiopathic hemifacial spasm underwent microvascular decompression treatment were recruited in our study. A nomogram was developed based on the regression analysis. Nomogram performance was evaluated through receiver operating characteristic (ROC), decision curve analyses and calibration curve. The rate of positive wave V change was also higher in the hearing deficit group (71.8% vs no hearing deficit group, p < 0.001). Furthermore, greater retraction depth (0.78 ± 0.25 cm vs 0.55 ± 0.12 cm, p < 0.001), duration (74.43 ± 15.74 min vs 55.71 ± 7.01 min, p < 0.001) and retraction distance (4.38 ± 0.38 cm vs 4.17 ± 0.24 cm, p = 0.001) were evident in the hearing deficit patients. Multivariate logistic regression showed that positive wave V change (OR 5.43), greater retraction depth (OR 55.57) and longer retraction duration (OR 1.14) emerged as significant independent predictors of postoperative hearing deficit. The external validation cohort exhibited a favorable discrimination with an AUC of 0.88. The calibration curves further confirmed the reliability of the predicted outcome in relation to the observed outcome in the external validation cohort (p = 0.89). The decision curves demonstrated that the nomogram outperformed the All or None scheme when the threshold probability ranged from > 2% to < 60% in the external validation cohort. We constructed a nomogram, including wave V, retraction depth, and retraction duration, which can effectively predict the occurrence of hearing deficits and has good clinical applicability.

Outcomes after Microvascular Decompression for Hemifacial Spasm without Definite Radiological Neurovascular Compression at the Root Exit Zone

The purpose of this study was to investigate the outcome of microvascular decompression (MVD) in patients with hemifacial spasm (HFS) who have no definite radiological neurovascular compression (NVC). Sixteen HFS patients without radiological NVC on preoperative MRI underwent MVD surgery. The symptoms were left-sided in fourteen (87.5%) and right-sided in two patients (12.5%). Intraoperatively, the most common vessel compressing the facial nerve was the AICA (8, 44.4%), followed by arterioles (5, 27.8%), veins (4, 22.2%), and the PICA (1, 5.6%). The most common compression site was the cisternal portion (13, 76.5%) of the facial nerve, followed by the REZ (4, 23.5%). One patient (6.3%) was found to have multiple NVC sites. Arachnoid type (7, 50%) was the most common compressive pattern, followed by perforator type (4, 28.6%), sandwich type (2, 14.3%), and loop type (1, 7.1%). A pure venous compression was seen in two patients, while a combined venous-arterial "sandwich" compression was detected in two patients. Symptom improvement was observed in all of the patients. Only one patient experienced recurrence after improvement. Based on our experience, MVD surgery can be effective for primary HFS patients with no definite radiological NVC. MVD can be considered if the patient shows typical HFS features, although NVC is not evident on MRI.

Recent Advances in Intraoperative Brainstem Auditory Evoked Potential Monitoring during Microvascular Decompression Surgery for Hemifacial Spasm

Brainstem auditory evoked potential (BAEP) testing during microvascular decompression (MVD) is very important in the treatment of hemifacial spasm (HFS). The reason for this is that the vestibulocochlear nerve is located immediately next to the facial nerve, so the vestibulocochlear nerve may be affected by manipulation during surgery. BAEP testing for detecting vestibulocochlear nerve damage has been further developed for use during surgery. In most HFS patients with normal vestibulocochlear nerves, the degree of vestibulocochlear nerve damage caused by surgery is well-reflected in the BAEP test waveforms. Therefore, real-time testing is the best way to minimize damage to the vestibulocochlear nerve. The purpose of this study was to review the most recently published BAEP test waveforms that were obtained during MVD surgery to determine the relationship between vestibulocochlear nerve damage and BAEP waveforms.

Intraoperative Monitoring of the Facial Nerve during Microvascular Decompression for Hemifacial Spasm

This review article discusses the clinical significance of intraoperative neurophysiological monitoring (IONM), provides recommendations for monitoring protocols, and considers the interpretation of results in microvascular decompression (MVD) for hemifacial spasm (HFS). The lateral spread response (LSR) is an important monitoring parameter during MVD. It helps to identify the responsible blood vessel and confirms its thorough decompression from the facial nerve. The disappearance of the LSR during surgery is associated with favorable clinical outcomes. Standard and revised monitoring protocols and the confirmation of LSR persistence and disappearance are also discussed. The blink reflex and other facial nerve monitoring modalities, such as free-running electromyography, facial motor evoked potentials, F-waves, and the Z-L response, are further considered.

Advances in Intraoperative Neurophysiology During Microvascular Decompression Surgery for Hemifacial Spasm

Microvascular decompression (MVD) is a widely used surgical intervention to relieve the abnormal compression of a facial nerve caused by an artery or vein that results in hemifacial spasm (HFS). Various intraoperative neurophysiologic monitoring (ION) and mapping methodologies have been used since the 1980s, including brainstem auditory evoked potentials, lateral-spread responses, Z-L responses, facial corticobulbar motor evoked potentials, and blink reflexes. These methods have been applied to detect neuronal damage, to optimize the successful decompression of a facial nerve, to predict clinical outcomes, and to identify changes in the excitability of a facial nerve and its nucleus during MVD. This has resulted in multiple studies continuously investigating the clinical application of ION during MVD in patients with HFS. In this study we aimed to review the specific advances in methodologies and clinical research related to ION techniques used in MVD surgery for HFS over the last decade. These advances have enabled clinicians to improve the efficacy and surgical outcomes of MVD, and they provide deeper insight into the pathophysiology of the disease.

Prognostic Value of Lateral Spread Response Recorded 1 Month After Microvascular Decompression for the Treatment of Hemifacial Spasm

BACKGROUND

The predictive value of intraoperative disappearance of the lateral spread response (LSR) during microvascular decompression surgery for hemifacial spasm treatment is unclear. Studies evaluating the clinical implications of the LSR recorded during the postoperative period are also limited.

OBJECTIVE

To analyze the LSR 1 month postoperatively and to evaluate its prognostic value until 1 year postsurgery.

METHODS

In total, 883 patients who underwent microvascular decompression between 2016 and 2018 were included. LSR was recorded preoperatively, intraoperatively before decompression, intraoperatively after decompression, and 1 month postoperatively. The outcomes were evaluated at 1 week, 1 month, and 1 year postoperatively.

RESULTS

The presence of preoperative and intraoperative LSR after decompression did not predict the postoperative outcome at 1 year. In 246 patients (27.9%), the postoperative LSR at 1 month was not identical to that recorded intraoperatively after decompression. Postoperative LSR at 1 month was associated with a worse outcome at 1 month (P < .0001) and 1 year (P = .0002) postoperatively. Patients with residual symptoms and a LSR 1 month postoperatively were more likely to show residual symptoms 1 year postoperatively, with a positive predictive value of 50.7%.

CONCLUSION

Unlike the intraoperative LSR, the LSR at 1 month postoperatively showed prognostic value in predicting 1-year postoperative outcomes and was useful for identifying patients with a high risk of unfavorable outcomes. Thus, confirming the presence of postoperative LSR is necessary.

Monitoring cerebellopontine angle and skull base surgeries

Cerebellopontine angle (CPA) surgery represents a challenge for neurosurgeons due to the high risk of iatrogenic injury of vital neurological structures. Therefore, important efforts in improving the surgical techniques and intraoperative neurophysiology have been made in the last decades. We present a description and review of the available methodologies for intraoperative neuromonitoring and mapping during CPA surgeries. There are three main groups of techniques to assess the functional integrity of the nervous structures in danger during these surgical procedures: (1) Electrical identification or mapping of motor cranial nerves (CNs), which is essential in order to locate the nerve in their different parts during the tumor resection; (2) Monitoring, which provides real-time information about functional integrity of the nervous tissue; and (3) Brainstem reflexes including blink reflex, masseteric reflex, and laryngeal adductor reflex. All these methods facilitate the removal of lesions and contribute to notable improvement in functional outcome and permit on the investigation of their physiopathology in certain neurosurgically treated diseases. Such is the case of hemifacial spasm (HFS). We describe the methodology to evaluate the efficacy of microvascular decompression for HFS treatment at the end of this chapter.