A-trains for intraoperative monitoring in patients with recurrent vestibular schwannoma

Factors Related to the Deterioration of Postoperative Lower Back Pain in Hemilaminectomy Approach for Lumbar Spinal Schwannoma Resection

Objective

This study aimed to explore the related risk factors in patients who underwent hemilaminectomy for lumbar spinal schwannoma resection and who experienced deterioration of postoperative lower back pain in comparison to preoperative pain levels.

Methods

This retrospective study recruited 61 patients from the First Affiliated Hospital of An Hui Medical University between January 2018 and June 2019. All data were collected from clinical records and analyzed at 1-month and at 1-year follow-up. The visual analog scale (VAS) was used to evaluate pain, and neurologic function was assessed using the Modified McCormick Scale. Intraoperative neurophysiological monitoring was used to assess neuronal integrity and mitigate injury. Statistical analysis of the data was performed using the SPSS version 19 software.

Results

Preoperative pain improved dramatically in the 1-year follow-up (VAS: preoperative, 3.84±2.19; 1-year follow-up, 2.13±2.26; P<0.001). The pain-improved group and worsened group showed a significant difference at 1-month (VAS: 1.76±1.56; 5.54±1.26; P<0.05) and at 1-year (VAS: 0.83±1.09; 4.80±1.58; P<0.05) follow-up. The pain-improved and worsened groups had a significant difference in tumor size and hemilaminectomy removal segments at 1-month and 1-year follow-up, but A-train occurrence on electromyography could only be seen as a statistical difference in the 1-month follow-up. Logistic regression analysis revealed that tumor size was an independent risk factor for postoperative lower back pain deterioration.

Conclusion

The hemilaminectomy approach is a safe and effective method that can dramatically relieve pain in spinal lumbar schwannoma resection. Tumor size is an independent risk factor for postoperative lower back pain. A-train on spontaneous electromyography has been shown to be a reliable predictive factor for the evaluation of postoperative lower back pain. However, further detailed analysis of A-train characteristics can provide a more accurate warning during surgery.

Neural networks for estimation of facial palsy after vestibular schwannoma surgery

PURPOSE

Facial nerve damage in vestibular schwannoma surgery is associated with A-train patterns in free-running EMG, correlating with the degree of postoperative facial palsy. However, anatomy, preoperative functional status, tumor size and occurrence of A-trains clusters, i.e., sudden A-trains in most channels may further contribute. In the presented study, we examine neural networks to estimate postoperative facial function based on such features.

METHODS

Data from 200 consecutive patients were used to train neural feed-forward networks (NN). Estimated and clinical postoperative House and Brackmann (HB) grades were compared. Different input sets were evaluated.

RESULTS

Networks based on traintime, preoperative HB grade and tumor size achieved good estimation of postoperative HB grades (chi2 = 54.8), compared to using tumor size or mean traintime alone (chi2 = 30.6 and 31.9). Separate intermediate nerve or detection of A-train clusters did not improve performance. Removal of A-train cluster traintime improved results (chi2 = 54.8 vs. 51.3) in patients without separate intermediate nerve.

CONCLUSION

NN based on preoperative HB, traintime and tumor size provide good estimations of postoperative HB. The method is amenable to real-time implementation and supports integration of information from different sources. NN could enable multimodal facial nerve monitoring and improve postoperative outcomes.

EMG monitoring

While most neurophysiologists are familiar with electromyography (EMG) for the purpose of clinical diagnostics, this technique also has a long tradition for neuro-monitoring. In short, intra-operative use of EMG can be divided into stimulated EMG on the one hand and monitoring of the free-running EMG and its spontaneous activity on the other hand. Methods for utilization of stimulated EMG are covered elsewhere in this book. This chapter focuses on the monitoring of spontaneous, or, more correctly, "surgically evoked" EMG. The history and underlying physiologic principles of intra-operative EMG are covered in this chapter as well as a detailed overview of the methodology. Building up from the basis of this background, we describe examples of how EMG can be used to help in intra-operative detection of adverse events and also in the prediction of postoperative outcomes. In the opinion of the authors, EMG should not be used as a "standalone" technique in contemporary neuro-monitoring. Most of its significant potential may be realized when it is used in a complementary way together with other modalities, mainly motor evoked potentials. Bearing this in mind, we sketch out how such a complementary setup may be used for improved neuro-monitoring.

[Macroscopic and microscopic changes of the vestibulocochlear nerve after Gamma Knife treatment]

Wir berichten über einen Fall, bei dem makroskopische und mikroskopische Veränderungen des Verstibularnervs nach radiochirurgischer Behandlung eines intrameatalen Vestibularisschwannoms beobachtet wurden. Der Fallbericht zeigt das erste Mal ein morphologisches Korrelat der unerwünschten Effekte der Gamma-Knife-Therapie von Vestibularisschwannomen und unterstreicht, dass trotz eines deutlichen Abstands zum bestehenden Tumor degenerative Veränderungen der neuralen Strukturen erwartet werden können.

A-train clusters and the intermedius nerve in vestibular schwannoma patients

OBJECTIVE

EMG "A-train" activity correlates with postoperative facial palsy after vestibular schwannoma (VS) surgery. An intermedius nerve separate from the facial nerve increases A-trains without significant impact on function. We investigate occurrence of A-train "clusters", A-trains over a majority of channels within a short time frame.

METHODS

Data from 217 patients with first surgery for VS were evaluated retrospectively. Continuous EMG recorded with 9 channels was evaluated for A-train patterns. "Clusters" of A-trains were identified, i.e. A-trains within 3 seconds over a majority of channels. Relation to a separate intermedius, tumor size and facial palsy was evaluated.

RESULTS

Correlations between A-trains and postoperative facial palsy were higher in patients without separate intermedius (r = 0.562 versus r = 0.194). Clusters were identified in 107 patients (49.3%), separate intermedius in 109 (50.2%), with significant association of both (p < 0.001, Chi-Square test). Excluding clusters slightly increased correlation of A-trains to facial nerve function.

CONCLUSIONS

A-train clusters have limited relevance for predicting postoperative paresis. However, they should be regarded as warning signs, suggesting the presence of a separate intermedius nerve.

SIGNIFICANCE

A-train "clusters" are a sign of hyperactivity of the facial nerve due to a separate intermedius nerve and may confound intraoperative monitoring during VS surgery.

Continuous dynamic mapping to avoid accidental injury of the facial nerve during surgery for large vestibular schwannomas

In vestibular schwannoma (VS) surgery postoperative facial nerve (CN VII) palsy is reducing quality of life. Recently, we have introduced a surgical suction device for continuous dynamic mapping to provide feedback during tumor resection without switching to a separate stimulation probe. The objective was to evaluate the reliability of this method to avoid CN VII injury. Continuous mapping for CN VII was performed in large VS (08/2014 to 11/2017) additionally to standard neurophysiological techniques. A surgical suction-and-mapping probe was used for surgical dissection and continuous monopolar stimulation. Stimulation was performed with 0.05-2 mA intensities (0.3 msec pulse duration, 2.0 Hz). Postoperative CNVII outcome was assessed by the House-Brackmann-Score (HBS) after 1 week and 3 months following surgery. Twenty patients with Koos III (n = 2; 10%) and Koos IV (n = 18; 90%) VS were included. Preoperative HBS was 1 in 19 patients and 2 in 1 patient. Dynamic mapping reliably indicated the facial nerve when resection was close to 5-10 mm. One week after surgery, 7 patients presented with worsening in HBS. At 3 months, 4 patients' facial weakness had resolved and 3 patients (15%) had an impairment of CN VII (HBS 3 and 4). Of the 3 patients, near-total removal was attempted in 2. The continuous dynamic mapping method using an electrified surgical suction device might be a valuable additional tool in surgery of large VS. It provides real-time feedback indicating the presence of the facial nerve within 5-10 mm depending on stimulation intensity and may help in avoiding accidental injury to the nerve.

The intermedius nerve as a confounding variable for monitoring of the free-running electromyogram

OBJECTIVE

A-trains, a facial nerve EMG-pattern, are correlated with postoperative functional impairment. However, an unknown confounder is suspected to cause false positive monitoring results. The intermedius nerve contains motor fibers targeting lower facial muscles; their significance for facial nerve monitoring is yet unknown.

METHODS

Intraoperative videotapes and free-running 9-channel facial nerve EMG assessed from 87 patients undergoing surgery for vestibular schwannoma were evaluated, and presence/absence of an identifiable intermedius nerve was determined. The prognostic value of train time, a quantitative measure for A-train activity, was evaluated for both the groups with and without an identifiable intermedius nerve.

RESULTS

Correlation between traintime and outcome (Spearman's Rho) rose to 0.73 (p<0.001) when only patients without an identified intermedius nerve were considered, and fell to 0.43 (p<0.05) with the other patient group. This difference was statistically significant (p=0.036), was more prominent in the channels monitoring perioral facial muscles, and resulted from additional A-train activity in patients with an identifiable intermedius nerve.

CONCLUSIONS

A separate intermedius nerve may be more prone to manipulation, leading to A-train activity without clinical correlate, thus causing false positive monitoring results.

SIGNIFICANCE

For interpretation of the free-running EMG, the intermedius nerve needs to be taken into account as a confounder.