1Department of Neurosurgery, Kobe University Graduate School of Medicine, Kobe, Hyogo, Japan; and.
2Department of Neurosurgery, Kinki Central Hospital, Itami, Hyogo, Japan.
J Neurosurg. 2023 Jul 21;140(1):127-137. doi: 10.3171/2023.5.JNS23715. Print 2024 Jan 1.
Koos grade 4 vestibular schwannoma (KG4VS) is a large tumor that causes brainstem displacement and is generally considered a candidate for surgery. Few studies have examined the relationship between morphological differences in KG4VS other than tumor size and postoperative facial nerve function. The authors have developed a landmark-based subclassification of KG4VS that provides insights into the morphology of this tumor and can predict the risk of facial nerve injury during microsurgery. The aims of this study were to morphologically verify the validity of this subclassification and to clarify the relationship of the position of the center of the vestibular schwannoma within the cerebellopontine angle (CPA) cistern on preoperative MR images to postoperative facial nerve function in patients who underwent microsurgical resection of a vestibular schwannoma.
In this paper, the authors classified KG4VSs into two subtypes according to the position of the center of the KG4VS within the CPA cistern relative to the perpendicular bisector of the porus acusticus internus, which was the landmark for the subclassification. KG4VSs with ventral centers to the landmark were classified as type 4V, and those with dorsal centers as type 4D. The clinical impact of this subclassification on short- and long-term postoperative facial nerve function was analyzed.
In this study, the authors retrospectively reviewed patients with vestibular schwannoma who were treated surgically via a retrosigmoid approach between January 2010 and March 2020. Of the 107 patients with KG4VS who met the inclusion criteria, 45 (42.1%) were classified as having type 4V (KG4VSs with centers ventral to the perpendicular bisector of the porous acusticus internus) and 62 (57.9%) as having type 4D (those with centers dorsal to the perpendicular bisector). Ventral extension to the perpendicular bisector of the porus acusticus internus was significantly greater in the type 4V group than in the type 4D group (p < 0.001), although there was no significant difference in the maximal ventrodorsal diameter. The rate of preservation of favorable facial nerve function (House-Brackmann grades I and II) was significantly lower in the type 4V group than in the type 4D group in terms of both short-term (46.7% vs 85.5%, p < 0.001) and long-term (82.9% vs 96.7%, p = 0.001) outcomes. Type 4V had a significantly negative impact on short-term (OR 7.67, 95% CI 2.90-20.3; p < 0.001) and long-term (OR 6.05, 95% CI 1.04-35.0; p = 0.045) facial nerve function after surgery when age, tumor size, and presence of a fundal fluid cap were taken into account.
The authors have delineated two different morphological subtypes of KG4VS. This subclassification could predict short- and long-term facial nerve function after microsurgical resection of KG4VS via the retrosigmoid approach. The risk of postoperative facial palsy when attempting total resection is greater for type 4V than for type 4D. This classification into types 4V and 4D could help to predict the risk of facial nerve injury and generate more individualized surgical strategies for KG4VSs with better facial nerve outcomes.
Koos 分级 4 型前庭神经鞘瘤（KG4VS）是一种大型肿瘤，可导致脑干移位，通常被认为是手术治疗的候选者。很少有研究探讨 KG4VS 除肿瘤大小以外的形态学差异与术后面神经功能之间的关系。作者已经开发了一种基于解剖标志的 KG4VS 亚分类，可深入了解该肿瘤的形态，并可预测显微手术中面神经损伤的风险。本研究的目的是从形态学上验证这种亚分类的有效性，并阐明术前磁共振成像上桥小脑角（CPA）池内前庭神经鞘瘤中心的位置与接受显微切除的前庭神经鞘瘤患者术后面神经功能之间的关系。
在本文中，作者根据 KG4VS 中心相对于内听道垂直平分线在 CPA 池内的位置将 KG4VS 分为两种亚型，这是亚分类的解剖标志。KG4VS 中心位于标志前腹侧的被分类为 4V 型，而 KG4VS 中心位于标志后背侧的被分类为 4D 型。分析了这种亚分类对短期和长期术后面神经功能的临床影响。
本研究回顾性分析了 2010 年 1 月至 2020 年 3 月期间通过后路乙状窦入路手术治疗的前庭神经鞘瘤患者。在符合纳入标准的 107 例 KG4VS 患者中，45 例（42.1%）被分类为 4V 型（KG4VS 中心位于内听道垂直平分线前腹侧），62 例（57.9%）被分类为 4D 型（KG4VS 中心位于内听道垂直平分线后背侧）。4V 型组 KG4VS 向垂直平分线前腹侧的延伸明显大于 4D 型组（p<0.001），尽管最大的腹侧-背侧直径没有显著差异。4V 型组短期（House-Brackmann 分级 I 和 II）和长期（82.9%对 96.7%，p=0.001）面神经功能保留良好的比例明显低于 4D 型组。考虑到年龄、肿瘤大小和是否存在基底部液帽等因素，4V 型对术后短期（OR 7.67，95%CI 2.90-20.3；p<0.001）和长期（OR 6.05，95%CI 1.04-35.0；p=0.045）面神经功能有显著的负面影响。
作者描述了 KG4VS 的两种不同的形态学亚型。这种亚分类可以预测通过后路乙状窦入路显微切除 KG4VS 后的短期和长期面神经功能。与 4D 型相比，4V 型试图进行全切时发生术后面瘫的风险更大。4V 型和 4D 型的分类可以帮助预测面神经损伤的风险，并为面神经预后更好的 KG4VS 制定更个体化的手术策略。
