O. Borysenko Effect of the Mastoid Cavity and External Auditory Canal Volume Changes in Sound Transmission

The main function of the middle ear is well-known. It serves as a mechanical transformer, designed for transmission of acoustic energy from the external air to the cochlea fluids. In the absence of such energy transformer of the vibrational motion of air particles will be reflected at the on the border with the labyrinth fluid. The appearance of the corresponding mechanical amplification leads to increase pressure and transfer of sound energy is lossless. In the literature there is a discussion about the factors affecting the transmission of sound in the middle ear. Otosurgeons often do not pay enough attention to the value of the resonance in the cavities of the middle ear and external auditory canal (EAC) in the planning of surgical intervention However, middle ear surgery in some degree alters the volume of these cavities, which could have a significant impact on the sound transmission by middle ear and, ultimately, on perception of hearing thresholds. The acoustic effect of changes in the volume of the cavities in different types of tympanoplasty is difficult to define clinically, since such surgery is performed while the restoration of the tympanic membrane and ossicular chain continuity also made. The combination of these stages of an operation does not allow it in the end determine the effect of only one change in the volume of the cavities of the middle ear and EAC. To the most significant anatomical changes in the middle ear leads three most common operations-canal wall down tympanoplasty (CWD), canal wall up tympanoplasty (CWU) and tympanoplasty with mastoid obliteration (MO). At the first intervention (CWD) posterior wall of the EAC is removed, aditus, antrum and mastoid’s cells are opened into the EAC. As a result the pneumatic cavity in the middle ear is represented only by the tympanic cavity and Eustachian tube and the EAC, combined with the mastoid, represent a large bowl in front of the eardrum (fig 1).