| PurposeThis research systematically analyzes the anatomical characteristics of auricle and middle ear malformation of congenital microtia patients to compare its difference with normal anatomy and summarize significant variation pattern and correlation of anatomical structures. It is also useful for the improvement of clinical diagnosis classification and the instruction of surgery, could provide reference for series treatment of auricle reconstruction and auditory rehabilitation.3D finite element method is also adopted to analyze the acoustic change of microtia patients with CAA after auditory rehabilitation surgery. And finally, from the aspect of biomechanical analysis of materials for tympanic membrane, the optimal selection tendency of artificial materials for tympanic membrane is proposed.Materials and Methods1. Research ObjectsMicrotia patients were selected in the auricular Plastic and Aesthetic Center (Plastic Surgery Hospital) and ENT department (Chinese PLA General Hospital) from June,2009 to December,2009, and Own control study is carried out on them. There're 50 ears in study group, with 22 cases of unilateral malformation,22 ears (14right,8 left), and 14 cases of bilateral malformation,28 ears. They are generally 3 to 28 years old, with an average year of 12.44. The control group contains 22 healthy ears, and they are from the unilateral malformation cases (8 right,141eft). All the patients have neither history of middle ear and mastoid surgery, nor related Syndrome of acquired malformation and concomitant auricle and middle ear malformation.2. Research Methods2.1 Using Toshiba Aquilion 16 layers spiral CT for high-resolution scan of the temporal bone. Scanning Parameters:layer thickness 0.5mm,135kV,250mA, pitch11.0, speed5.50mm/rot. Taking acou-supraorbital line as the scanning baseline and carrying out axial plane scanning. Reconstruction Parameters:layer thickness 0.4mm, inernal value 2.0mm, window breadth 3584HU, window leve1600HU. Use source image input Mimics software to generate coronal, sagittal and 3D Reconstruction image. Measure the distances and degrees with the tools of the software.2.2 Evaluation Index2.2.1 Auricle classification:Max classification2.2.2 External Acoustic Meatus:In accordance with the malformation of external acoustic meatus, it is divided into bony atresia, bony stenosis and membranous atresia and membranous stenosis.2.2.3 Tympanic Cavity:Tympanic Cavity:Measuring the anteroposterior diameter and transverse diameter of tympanic cavity in the axial image; measuring the vertical diameter of the control group and study group in the coronal image.2.2.4 The. distances between the surface of atresia/stenosis and the attic, mesotympanum hypotympanum as well as the ossicular surface are measured in the coronal image. And in the axial image, the measurement of the distances between the surface of atresia/stenosis and the inner face of the lateral wall of tympanic sinus is carried out, so is that between the inner face of the lateral wall of tympanic sinus and the eminence of the canalis semicircularis lateralis.2.2.5Quantitative Measurement of the Following Parameters:the distance between the posterior surface of articular fossa of temporal bone and aditus ad antrum, and that between the posterior surface of articular fossa of temporal bone and tympanic cavity; the distance between ostium tympanicum tubae auditivae and aditus ad antrum; the auditory tube diameter, the distal internal diameter of aquaeductus vestibuli, vestibule, sigmoid sinus and the lateral wall of tympanic cavity to the external cortical bone of mastoid process, Prussak space, acoustic meatus length and the length-diameter of internal acoustic port.2.2.6Qualitative Observation of the Following Structures:fossa cranii media, tympanic baldachin, cerebral dura mate ptosis, bulbus venae jugularis, arteria carotis, Korner septum, mastoid process.2.2.7 The multi-planar reformation technology and Mimics software were used to reconstruct canal for facial nerve. The line feed of canal for facial nerve is described in rectangular coordinate system in reference to Takegosh methods. In reference to the connection between canal for facial nerve and fenestra vestibule, the shortest distance between fenestra vestibuli and tympanic segment is measured, so is the distance between cochlear window and mastoid segment.2.2.8 Auditory Ossicle:The identification and classification of types of auditory ossicles are respectively carried out on the two levels of axial and coronal cochlea and fenestra vestibuli.2.3 Statistical AnalysisUse statistical analysis software SPSS17.0 for windows to carry out T test/rank sum test when comparing two groups, and Variance Analysis/K-W test (Kruskal-Wallis Test) between multiple groups, and use SNK to compare two cases; use frequency and percentage to describe categorical variable and carry out Chi-square test (x2 test) when comparing two or multiple groups. If in all the test results P<=0.05, then the difference is of statistical significance.2.4 One case of unilateral microtia with CAA is selected and sacned by HRCT, and then the preprocessed data is inputted into Finite Element Analysis software Ansya. In this way the 3D finite element models of healthy ears and unhealthy ears after auditory rehabilitation surgery are established. Different elastic modulus of materials for artificial tympanic membrane is selected. To obtain the acoustic change at tympanic membrane, acoustic transmission is simulated.Result1. Microtia patients are classified according to Max to set up study group. The quantitative analysis is carried out on parameters, such as the anteroposterior diameter and the vertical diameter of tympanic cavity, the distance between the posterior surface of articular fossa of temporal bone and aditus ad antrum, the depth and breadth of sigmoid sinus, FL (the developmental condition of the mastoid segment of temporal bone). The qualitative analysis is carried out on parameters, such as the cover of. vestibule by facial nerve, mastoid pneumatization degree and the distribution of mastoid pneumatization classification. There's statistical difference between the study group and the control group.2. According to the acoustic analysis of the Finite Element model of unhealthy ears after the auditory rehabilitation surgery, the Maximum displacement is at the joint of artificial tympanic membrane and auditory ossicles, the minimum displacement is at the corpus incudis. And the Maximum pressure is at the lateral end of artificial external auditory canal while the minimum pressure is at the internal end of auditory ossicle. It is recognized that after surgery the acoustic characteristics of unhealthy ears are almost the same as that of healthy ears. The elastic modulus of materials for artificial tympanic membrane must be 100Mpa to 500Mpa, and the larger this value is, the more favorable it is for the improvement of the auditory of unhealthy ears.ConclusionThere's significant difference between partial morphology of microtia patients' tympanic cavity, temporomandibular joint, sigmoid sinus and facial nerve and that of healthy ears, which is correlated with Max classification and varies according to the degree of malformation.The result of 3D Finite Element Analysis indicates that after surgery the acoustic characteristics of unhealthy ears are almost the same as that of healthy ears. And in auditory rehabilitation surgery, the elastic modulus of materials for artificial tympanic membrane must be 100Mpa to 500Mpa.
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