Short-range axono-cortical evoked-potentials in brain tumor surgery: Waveform characteristics as markers of direct connectivity.

OBJECTIVE: Intraoperative measurement of axono-cortical evoked potentials (ACEP) has emerged as a promising tool for studying neural connectivity. However, it is often difficult to determine if the activity recorded by cortical grids is generated by stimulated tracts or by spurious phenomena. This study aimed to identify criteria that would indicate a direct neurophysiological connection between a recording contact and a stimulated pathway. METHODS: Electrical stimulation was applied to white matter fascicles within the resection cavity, while the evoked response was recorded at the cortical level in seven patients. RESULTS: By analyzing the ACEP recordings, we identified a main epicenter characterized by a very early positive (or negative) evoked response occurring just after the stimulation artifact (<5 ms, |Amplitude| > 100 µV) followed by an early and large negative (or positive) monophasic evoked response (<40 ms; |Amplitude| > 300 µV). The neighboring activity had a different waveform and was attenuated compared to the hot-spot activity. CONCLUSIONS: It is possible to distinguish the hotspot with direct connectivity to the stimulated site from neighboring activity using the identified criteria. SIGNIFICANCE: The electrogenesis of the ACEP at the hotspot and neighboring activity is discussed.

Technique and surgical outcomes of mesenterization and intra-operative neural monitoring to reduce recurrent laryngeal nerve paralysis after thoracoscopic esophagectomy: A cohort study.

BACKGROUND: Because the thoracic esophageal carcinoma has a high metastatic rate to the upper mediastinal lymph nodes, especially along the recurrent laryngeal nerves (RLN), it is crucial to perform a complete lymphadenectomy along the RLN without complications. Although intraoperative neural monitoring (IONM) during thyroid surgery has gained widespread acceptance as a useful tool for visual nerve identification, utilization of IONM during esophageal surgery has not become common. Here, we describe our procedures, focusing on a lymphadenectomy along the RLN utilizing the IONM. METHODS: Eighty-seven patients who underwent prone esophagectomy between December 2009 and September 2017 were included in this study. We divided patients into two groups: neural monitoring group (Nm, n = 31) and conventional method group without IONM (Cm, n = 56). We first dissect around the esophagus, preserving the membranous structure; mesoesophagus, which contains tracheoesophageal artery; RLN; and lymph nodes (mesenterization). In Nm group, we next identify the location of the RLN, which runs in the mesoesophagus using IONM before visual contact. Next, we perform lymphadenectomy around the RLN, preserving the nerve itself. Early surgical outcomes were retrospectively compared between two groups. RESULTS: In all 31 cases in the Nm group, we detected the location of the RLN before the visual contact. The sensitivity and specificity of the IONM to detect the RLN paralysis were 67% and 96%, respectively. Postoperative RLN paralysis was observed in 3 cases in the Nm group (9.7%), which was lower than that in the Cm group (32.1%, p = 0.03). Clavien-Dindo grade 2 and over aspiration were seen in 2 (Nm, 6.5%) and 16 (Cm, 28.6%) cases (p = 0.01), respectively. The postoperative hospital stay was shorter in the Nm group (22 days, median) than in the Cm group (39 days, median, p = 0.0002). The number of dissected mediastinal lymph nodes was similar in both groups (25 vs. 20, median, p = 0.12). CONCLUSIONS: The combination of IONM and the concept of the mesoesophagus have substantial advantages in allowing accurate and safe mediastinal lymphadenectomy during prone esophagectomy.