Ménière's disease turn, is strongly associated with developing MD, but not everyone with EH develops MD: "The relationship between endolymphatic hydrops and Meniere's disease is not a simple, ideal correlation." Additionally, in fully developed MD the balance system (vestibular system) and the hearing system (cochlea) of the inner ear are affected, but there are cases where EH affects only one of the two systems strong enough to cause symptoms. The corresponding subtypes of MD are called "vestibular MD", showing symptoms of vertigo, and "cochlear MD", showing symptoms of hearing loss and tinnitus. The mechanism of MD is not fully explained by EH,
Inner ear its precise incidence cannot be determined. Birds have an auditory system similar to that of mammals, including a cochlea. Reptiles, amphibians, and fish do not have cochleas but hear with simpler auditory organs or vestibular organs, which generally detect lower-frequency sounds than the cochlea. In reptiles, sound is transmitted to the inner ear by the stapes (stirrup) bone of the middle ear. This is pressed against the oval window, a membrane-covered opening on the surface of the vestibule. From here, sound waves are conducted through a short perilymphatic duct to a second opening, the round window, which equalizes pressure, allowing