Radiological classification of the mastoid portion of the facial nerve: impact on the surgical accessibility of the round window in cochlear implantation

Abstract

Background

Mastoid portion of the facial nerve plays an important role in the round window approach of cochlear implantation.

Objectives

This study aimed to predict the anterior displacement of the mastoid portion of the facial nerve in the preoperative HRCT coronal cuts. We also aimed to detect the implication of anterior displacement of MPFN on the R.W. accessibility through the posterior tympanotomy during cochlear implantation.

Materials and methods

It was a retrospective observational cohort study in tertiary referral hospitals. We included 246 pediatric patients who underwent cochlear implantation due to bilateral severe to profound SNHL through a posterior tympanotomy approach.

Results

Type I MPFN was present in 84 cases, type II MPFN was present in 149 patients, and type III MPFN was present in 13 cases. R.W. was inaccessible in 3 cases with MPFN type II and in 11 subjects with MPFN type III. There was a statistically significant difference regarding the R.W. accessibility between the three types of MPFN (p-value <.05). There was a strong statistically significant correlation between R.W. accessibility and the radiological type of the MPFN.

Conclusion

Mandour radiological classification of the mastoid portion of the facial nerve in the preoperative HRCT coronal offers an easily applicable method to detect the anterior displacement of the facial nerve by using easy and well-known landmarks. This classification can also predict R.W. accessibility through posterior tympanotomy during cochlear implantation with 97.97% accuracy.

Chinese abstract

背景：面神经乳突部分(MPFN)在人工耳蜗圆窗植入法中起重要作用。

目的：本研究旨在预测术前 HRCT 冠状切口中面神经乳突部分的前移, 并且在耳蜗植入过程中通过后鼓膜切开术检测 MPFN 前移对圆窗可及性的影响。

材料与方法：在三级转诊医院进行回顾性观察队列研究。我们纳入了 246 名因双侧严重至深度 SNHL通过后鼓膜切开法接受耳蜗植入的儿童患者。

结果：I型MPFN 84例, II型MPFN 149例, III型MPFN 13 例。 3 例 MPFN II 型患者和 11 名MPFN III 型患者, R.W.不可及。三种类型的 MPFN 之间, R.W. 可及性存在统计学的显著差异（p 值 <.05）。R.W. 可及性和 MPFN 放射学类型之间有很强的统计相关性。

结论：我们对术前 HRCT 冠的面神经乳突部分的放射学分类, 提供了一种易于应用的方法来检测面神经前移, 即, 通过使用简单且已知的标志。这种分类还可以在人工耳蜗植入过程中以 97.97% 的准确率, 通过后鼓膜切开术预测 R.W. 的可及性。

Keywords:

• Facial nerve
• cochlear implantation
• round window
• computed tomography scan

Disclosure statement

No potential conflict of interest was reported by the author(s).

Acknowledgments

The authors have no budget or financial relationships to disclose.