Department of Otolaryngology - Head and Neck Surgery, Harvard Medical School, Boston, MA, USA; Eaton Peabody Laboratories and Department of Otolaryngology - Head and Neck Surgery, Massachusetts Eye and Ear, Boston, MA, USA; Department of Otorhinolaryngology, Leiden University Medical Center, Leiden, the Netherlands; Department of Otorhinolaryngology, Amsterdam UMC, location Academic Medical Center, University of Amsterdam, the Netherlands.
Department of Otorhinolaryngology, Leiden University Medical Center, Leiden, the Netherlands; The Leiden Institute for Brain and Cognition, Leiden, the Netherlands.
Hear Res. 2022 May;418:108458. doi: 10.1016/j.heares.2022.108458. Epub 2022 Feb 7.
Hearing loss in patients with vestibular schwannoma (VS) is commonly attributed to mechanical compression of the auditory nerve, though recent studies suggest that this retrocochlear pathology may be augmented by cochlear damage. Although VS-associated loss of inner hair cells, outer hair cells, and spiral ganglion cells has been reported, it is unclear to what extent auditory-nerve peripheral axons are damaged in VS patients. Understanding the degree of damage VSs cause to auditory nerve fibers (ANFs) is important for accurately modeling clinical outcomes of cochlear implantation, which is a therapeutic option to rehabilitate hearing in VS-affected ears. A retrospective analysis of human temporal-bone histopathology was performed on archival specimens from the Massachusetts Eye and Ear collection. Seven patients met our inclusion criteria based on the presence of sporadic, unilateral, untreated VS. Tangential sections of five cochlear regions were stained with hematoxylin and eosin, and adjacent sections were stained to visualize myelinated ANFs and efferent fibers. Following confocal microscopy, peripheral axons of ANFs within the osseous spiral lamina were quantified manually, where feasible, and with a "pixel counting" method, applicable to all sections. ANF density was substantially reduced on the VS side compared to the unaffected contralateral side. In the upper basal turn, a significant difference between the VS side and unaffected contralateral side was found using both counting methods, corresponding to the region tuned to 2000 Hz. Even spiral ganglion cells (SGCs) contralateral to VS were affected by the tumor as the majority of contralateral SGC counts were below average for age. This observation provides histological insight into the clinical observation that unilateral vestibular schwannomas pose a long-term risk of progression of hearing loss in the contralateral ear as well. Our pixel counting method for ANF quantification in the osseous spiral lamina is applicable to other pathologies involving sensorineural hearing loss. Future research is needed to classify ANFs into morphological categories, accurately predict their electrical properties, and use this knowledge to inform optimal cochlear implant programming strategies.
前庭神经鞘瘤（VS）患者的听力损失通常归因于听神经的机械压迫，尽管最近的研究表明这种耳蜗后病理学可能会因耳蜗损伤而加重。尽管已经报道了 VS 相关的内毛细胞、外毛细胞和螺旋神经节细胞的损失，但尚不清楚 VS 患者的听神经周围轴突受损到何种程度。了解 VS 对听神经纤维（ANF）造成的损伤程度对于准确模拟耳蜗植入的临床结果非常重要，这是一种治疗 VS 影响耳朵听力的选择。对马萨诸塞州眼耳收藏夹中存档标本进行了人类颞骨组织病理学的回顾性分析。根据存在散发性、单侧、未经治疗的 VS，七名患者符合我们的纳入标准。用苏木精和伊红对五个耳蜗区域的切向切片进行染色，并用相邻切片对有髓 ANF 和传出纤维进行可视化。共聚焦显微镜检查后，在可行的情况下手动量化骨螺旋板内 ANF 的周围轴突，并使用适用于所有切片的“像素计数”方法。与未受影响的对侧相比，VS 侧的 ANF 密度明显降低。在上基底转，使用两种计数方法均发现 VS 侧与未受影响的对侧之间存在显著差异，这对应于调谐到 2000 Hz 的区域。即使是 VS 对侧的螺旋神经节细胞（SGC）也受到肿瘤的影响，因为大多数对侧 SGC 计数低于年龄平均水平。这一观察结果为单侧前庭神经鞘瘤对未受影响的对侧耳朵听力损失长期进展的临床观察提供了组织学见解。我们用于骨螺旋板中 ANF 定量的像素计数方法适用于涉及感音神经性听力损失的其他病理。需要进一步研究将 ANF 分类为形态学类别，准确预测其电特性，并利用这些知识为最佳耳蜗植入编程策略提供信息。
