**3. OAEs and MD**

It has been suggested that OAEs and, in particular, distortion product otoacoustic emissions (DPOAEs), may determine the important information about which cochlear regions have been involved in the first phase of MD characterized by recurrent hydropic crisis [25, 26]. Considering that the acoustic energy has to cross the middle ear structures twice, OAE response may be reduced or even suppressed due to imperfections of the middle ear transmission mechanism. In this context, inner ear disorders can influence the OAE response characteristics [27]. The endolymphatic hydrops (confined primarily in the cochlear duct and in the saccule [15]), increase the impedance at the level of the stapes, attenuating any forward or backward acoustic energy transmissions [28].
