摘要
先天性外中耳畸形是耳科一种较为常见的出生缺陷,发病率约为1/10000。本课题围绕这一疾病,对畸形耳各重要结构的解剖形态、畸形听骨链系统传声的力学行为特征及计算机辅助手术设计这三方面进行了深入的研究。对深入理解先天性外中耳畸形的形态学规律、畸形听骨链的微观生物力学机制与最优化手术方案的设计具有重要的理论指导意义。
先天性外中耳畸形可出现各重要结构的异位和畸形,给其诊断和治疗带来了很高的难度。为探究其形态结构的规律性,本研究基于近百例患者的HRCT的分析,比较耳廓与中耳畸形程度的相关性,发现耳廓畸形程度与鼓室大小、面神经位置、锤砧复合体畸形、乳突气化程度等具有显著的相关性,而与砧镫关节、镫骨存在、圆窗、卵圆窗的畸形无明显相关；测量面神经乳突段在畸形耳中的分布,发现其较正常耳有明显的前移倾向；在MIMICS快速三维重建的基础上发现了浮动颧弓、颧弓部分缺如、下颌支两突发育不全和颧弓部分缺如合并下颌骨发育不良四种伴发的颌面部畸形；通过重建15例畸形耳听骨链,发现畸形耳的砧镫关节角度为140.96°±16.99°,明显大于正常耳。
为探究畸形听骨链的传音特性及其与正常听骨链的差异,本文基于15例患者的HRCT提取畸形听骨链的形态学特征,并结合课题组前期基于Micro-CT与组织切片建立的精确的正常中耳形态学模型,首次构建了包括人造鼓膜、畸形听小骨、听关节、肌肉及韧带的较为完善的畸形耳的几何模型。应用ABAQUS软件,进行了谐响应分析。结果显示：在相同的声压条件下,畸形听骨链系统的镫骨足板位移曲线较正常听骨链系统明显偏低,转化成镫骨足板速度传递函数后两系统对比相差约20dB。在此基础上,分析了砧镫关节角度变化对听骨链系统声音传递功能的影响,发现当砧镫关节角度大于150度时,镫骨足板的响应峰值有较为明显的下降。
先天性外中耳畸形的耳廓、耳道一体化再造已成为趋势,但是三维耳廓软骨支架的制作、新建耳道的定位及耳廓、耳道位置的协调等问题依然是耳鼻喉科和整形科医生面对的难题。鉴于二维CT图像对显示空间结构关系方面的局限性,在MIMICS平台上,通过正常耳廓镜像及容积缩减处理,可以直接生成直观的耳廓软骨支架的三维模型,用于术中指导肋软骨的雕刻组装；基于HRCT影像资料重建出各重要结构的三维形态,将耳道近似为一直径为1.2cm的圆柱体,通过协调圆柱体与周围结构的关系,达到虚拟手术的目的,对判断手术的安全性及实现新建耳道的准确定位,避免损伤周围重要结构有重要作用；同时可以通过耳廓或耳道位置的微调,实现新建耳廓与耳道外口最佳位置匹配,达到整形手术与功能手术的协调统一。另外,利用Matlab软件编制完成EarCanalDriller计算软件,该软件可用于精确判断外耳道再造的可行性以及精确定位再造外耳道的方位,为临床手术提供参考。
Congenital aural atresia is a common birth defect in Otology with the incidence rate of approximately 1:10000. Focusing on this disease, the study investigated into the anatomical changes of the important structures, biomechanical roles of the malformed ossicular chains and the computer-aided surgery, which were of vital importance to understand the morphological and functional changes and choose the optimal surgical plan.
The malposition or deformity of the important structures, which may coexist with congenital aural atresia, adds lots of difficulty to the diagonosis and treatment of the disease. Based on HRCT, we studied into the relationship between the auricular malformation and the middle ear deformity. The malformations including middle ear space, facial nerve, malleus/incus complex, mastoid pneumatization were found out to be closely related to the auricular malformations. The mastoid portion of the facial nerve was measured in the malformed ears, and it was found to be more anteriorly located than the normal ears. With MIMICS, four kinds of maxillofacial malformations including floating arch, interrupted arch, mandibular processes hypoplasia and interrupted arch combined with severe maxillary malformation were found to coexist with aural atresia. With the 3D reconstruction and accurate measurement of the malformed ossicular chains, the angle of the incudostapedial joint was 140.96°±16.99°, and it was significant larger than that of the normal joint.
To explore into the biomechanical characteristics of the malformed ossicular chain, we developed the accurate 3D geometric model based on the information obtained from the HRCT of the patients and our previous model of the normal middle ear on the basis of Micro-CT and serial histological sections of the temporal bone. It was the first time that the malformed middle ear model which contained the artificial tympanic membrane, malformed ossicular chain, joint, musles and ligments was developed. With ABAQUS, we conducted harmonic response analysis. The result suggested that the stapes displacement of the malformed ear was significantly smaller than that of the normal ear, which was about 20dB when converted to stapes velocity transfer function (SVTF). On the basis of that, we extended investigation into the effects of the incudostapedial joint on the sound conduction fuction. And results suggested significant drop of the peak response when the angle was more than 150 degrees.
Combined auricular reconstruction and atresiaplasty has now been the trend. However, the fabrication of the delicate 3D auricular framework, the location of the new external auditory canal (EAC) and the spatial configuration of the two are still big challengs for otologists and plastic surgeons. For the limitations of 2D CT scans to show the spatial configuration, we used MIMICS to calculate 3D structures. Mirror of the contra-lateral normal auricle was used to design the appropriate model of the auricular cartilage frames, which could be used as template for rib carving and attaching during surgeries. New EAC was simulated by a cylinder with the diameter of 1.2cm. The position of the cylinder was adjusted to simulate the surgery, which was of great importance to assess the safety of the surgery and avoid damaging to the important structures. The appropriate relationship between the new EAC and the auricle could be adjusted for a better appearance. Furthermore, we developed EarCanalDriller on the platform of Matlab, with which the preoperative evaluation could be finished and the best location of the EAC could be calculated automaticly.
引文
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