Sheep as a large animal model for cochlear implantation

Abstract Introduction In surgical training, large animal models are more suitable as their anatomy is more similar to humans. In otology, there have been relatively few studies about large animal models for surgical training. Objective In this study, we aimed to do a neuroradiologic evaluation and surgical insertion of a cochlear implant electrode array on a sheep head model. Methods Twenty cadaveric sheep heads were studied. A computed tomography scan and neuroradiologic evaluation was performed on each head, obtaining measurements of the inner ear for each sheep. Sheep measurements were compared to those from temporal bone computed tomography scans from 20 female humans. Surgical procedures were first trained with 13 of the sheep temporal bones, after which cochlear implantation was performed on the remaining 7 temporal bones. The position of the inserted electrode array insertion was confirmed by computed tomography scan after the procedure. Results Neuroradiologic evaluation showed that, relative to the 20 female humans, the mean ratio for sheep was 0.60 for volume of cochlea, 0.70 for height of cochlea, 0.73 for length of cochlea; ratios for other metrics were >0.80. For the surgical training, the round window was found in all 20 sheep temporal bones. Computed tomography scans confirmed that electrode insertions were fully complete; the mean value of electrode array insertion was 18.3 mm. Conclusion The neuroradiologic and surgical training data suggest that the sheep is a realistic animal model to train cochlear implant surgery and collection of perilymph samples, but less so for surgical training of mastoidectomy due to pneumatization of the mastoid.

摘要：在外科手术培训中，大型动物模型因解剖结构与人类更为相似而更具应用价值。在耳科学领域，针对外科培训的大型动物模型相关研究相对匮乏。
研究目的：本研究旨在对绵羊头部模型开展神经影像学评估，并完成人工耳蜗电极阵列(cochlear implant electrode array)的外科植入操作。
研究方法：本研究纳入20例绵羊尸体头部标本。对每例标本均实施计算机断层扫描(computed tomography, CT)及神经影像学评估，测量每只绵羊的内耳结构参数，并将其与20例女性人类颞骨的CT测量结果进行对比。首先利用其中13个绵羊颞骨开展外科操作训练，随后对剩余7个颞骨实施人工耳蜗植入手术。术后通过CT扫描确认植入的电极阵列位置。
研究结果：神经影像学评估结果显示，相较于20例女性人类标本，绵羊的耳蜗容积均值比值为0.60，耳蜗高度均值比值为0.70，耳蜗长度均值比值为0.73；其余各项测量指标的比值均大于0.80。在外科训练过程中，20个绵羊颞骨均成功定位圆窗(round window)。CT扫描确认所有电极植入均完全完成，电极阵列植入深度均值为18.3 mm。
结论：本研究的神经影像学与外科培训数据表明，绵羊可作为开展人工耳蜗植入手术培训及外淋巴(perilymph)样本采集的合适动物模型，但由于其乳突(mastoid)气化特征，绵羊模型并不适用于乳突切除术(mastoidectomy)相关的外科培训。