Wenzel Angela, Ward Bryan K, Ritzl Eva K, Gutierrez-Hernandez Sergio, Della Santina Charles C, Minor Lloyd B, Carey John P
*Departments of Otolaryngology-Head and Neck Surgery, and †Neurology, Johns Hopkins School of Medicine, Baltimore, Maryland; and ‡Stanford University School of Medicine, Stanford, California, U.S.A.
Otol Neurotol. 2015 Jan;36(1):139-45. doi: 10.1097/MAO.0000000000000642.
Recent findings in patients with superior semicircular canal dehiscence (SCD) have shown an elevated ratio of summating potential (SP) to action potential (AP), as measured by electrocochleography (ECochG). Changes in this ratio can be seen during surgical intervention. The objective of this study was to evaluate the utility of intraoperative ECochG and auditory brainstem response (ABR) as predictive tools for postoperative hearing outcomes after surgical plugging via middle cranial fossa approach for SCD syndrome (SCDS).
This was a review of 34 cases (33 patients) in which reproducible intraoperative ECochG recordings were obtained during surgery. Diagnosis of SCDS was based on history, physical examination, vestibular function testing, and computed tomography imaging. Simultaneous intraoperative ECochG and ABR were performed. Pure-tone audiometry was performed preoperatively and at least 1 month postoperatively, and air-bone gap (ABG) was calculated. Changes in SP/AP ratio, SP amplitude, and ABR wave I latency were compared with changes in pure-tone average and ABG before and after surgery.
Median SP/AP ratio of affected ears was 0.62 (interquartile range [IQR], 0.45-0.74) and decreased immediately after surgical plugging of the affected canal to 0.42 (IQR, 0.29-0.52; p < 0.01). Contralateral SP/AP ratio before plugging was 0.33 (IQR, 0.25-0.42) and remained unchanged at the conclusion of surgery (0.30; IQR, 0.25-0.35; p = 0.32). Intraoperative changes in ABR wave I latency and SP amplitude did not predict changes in pure-tone average or ABG after surgery (p > 0.05).
This study confirmed the presence of an elevated SP/AP ratio in ears with SCDS. The SP/AP ratio commonly decreases during plugging. However, an intraoperative decrease in SP/AP does not appear to be sensitive to either the beneficial decrease in ABGs or the mild high-frequency sensory loss that can occur in patients undergoing surgical plugging of the superior semicircular canal. Future work will determine the value of intraoperative ECochG in predicting changes in vestibular function.
近期对上半规管裂（SCD）患者的研究发现，通过耳蜗电图（ECochG）测量，其总和电位（SP）与动作电位（AP）的比率升高。在手术干预过程中可观察到该比率的变化。本研究的目的是评估术中ECochG和听觉脑干反应（ABR）作为预测经中颅窝入路手术封堵SCD综合征（SCDS）后听力结果的工具的效用。
回顾性分析34例（33例患者）手术中获得可重复术中ECochG记录的病例。SCDS的诊断基于病史、体格检查、前庭功能测试和计算机断层扫描成像。同时进行术中ECochG和ABR检查。术前及术后至少1个月进行纯音听力测定，并计算气骨导差（ABG）。比较手术前后SP/AP比率、SP振幅和ABR波I潜伏期的变化与纯音平均听阈和ABG的变化。
患耳的SP/AP比率中位数为0.62（四分位间距[IQR]，0.45 - 0.74），在患侧半规管手术封堵后立即降至0.42（IQR，0.29 - 0.52；p < 0.01）。封堵前对侧的SP/AP比率为0.33（IQR，0.25 - 0.42），手术结束时保持不变（0.30；IQR，0.25 - 0.35；p = 0.32）。术中ABR波I潜伏期和SP振幅的变化不能预测术后纯音平均听阈或ABG的变化（p > 0.05）。
本研究证实SCDS患者患耳存在升高的SP/AP比率。封堵过程中SP/AP比率通常会降低。然而，术中SP/AP的降低似乎对ABG的有益降低或经上半规管手术封堵患者可能出现的轻度高频感觉丧失均不敏感。未来的研究将确定术中ECochG在预测前庭功能变化方面的价值。
