Endoscopic evaluation of middle ear anatomic variations in autopsy series: analyses of 204 ears

Abstract Introduction Microsurgery of the ear requires complete evaluation of middle ear surgical anatomy, especially the posterior tympanic cavity anatomy. Preoperative assessment of the middle ear cavity is limited by the permeability of eardrum and temporal bone density. Therefore, middle ear exploration is an extremely useful method to identify structural abnormalities and anatomical variations. Objective The aim of this study is to determine anatomic variations of the middle ear in an autopsy series. Methods All evaluations were performed in the Forensic Medicine Institute Morgue Department. The cases over 18 years of age, with no temporal bone trauma and history of otologic surgery included in this study. Results One hundred and two cadavers were included in the study. The mean age was 49.08 ± 17.76 years. Anterior wall prominence of the external auditory canal was present in 27 of all cadavers (26.4%). The tympanic membrane was normal in 192 ears (94%) while several eardrum pathologies were detected in 12 ears (6%). Agenesis of the pyramidal eminence and stapedial tendon was found in 3 ears. While the ponticulus was bony ridge-shaped in 156 of 204 ears (76.4%), it was bridge-shaped in 25 ears (12.3%). The ponticulus was absent in 23 ears (11.3%). While complete subiculum was present in 136 of all ears (66.7%), incomplete subiculum was present in 21 ears (10.3%). Subiculum was absent in 47 ears (23%). Facial dehiscence was found in 32 ears and the round window niche was covered by a pseudomembrane in 85 ears (41.6%). A fixed footplate was present in 7.4% of all ears, and no persistent stapedial artery was seen in any cases. Conclusion The pseudomembrane frequency covering the round window niche was found different from reports in the literature. In addition, the frequency of the external auditory canal wall prominence has been reported for the first time.摘要 引言 耳显微外科手术需对中耳手术解剖结构进行全面评估，尤其需重点评估鼓室后部解剖结构。术前对中耳腔的评估受限于鼓膜（tympanic membrane）的通透性与颞骨骨质密度，因此中耳探查术是识别结构异常与解剖变异的极为有效的手段。 研究目的：本研究旨在明确尸检队列中的中耳解剖变异情况。 研究方法：所有评估均于法医学研究所尸检科完成。本研究纳入年龄18岁以上、无颞骨外伤史且无耳科手术史的病例。 研究结果：本研究共纳入102具尸体标本，平均年龄为49.08±17.76岁。27具尸体（26.4%）存在外耳道前壁隆起。192耳（94%）鼓膜正常，12耳（6%）检出鼓膜病变。3耳存在锥隆起与镫骨肌腱发育不全。204耳中，156耳（76.4%）的鼓室桥（ponticulus）呈骨嵴状，25耳（12.3%）呈桥状，23耳（11.3%）无鼓室桥。全部受试耳中，136耳（66.7%）存在完整鼓室亚突（subiculum），21耳（10.3%）存在不完整鼓室亚突，47耳（23%）无鼓室亚突。32耳存在面神经管裂缺（facial dehiscence），85耳（41.6%）的圆窗龛被假膜覆盖。7.4%的耳存在镫骨底板固定，所有病例均未发现永存镫骨动脉。 研究结论：本研究发现，圆窗龛被假膜覆盖的发生率与文献报道存在差异；此外，外耳道前壁隆起的发生率为首次报道。