The Etiology of Endolymphatic Hydrops-Role of Spiral Ligament and Endolymphatic Sac-

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1)Labyrinthitis was induced by inoculation of keyhole limpet hemocyanin into the scala tympani of systemically sensitized guinea pigs, and inner ears were immunostained. Spiral ligament, spiral limbus, and blood vessels including the spiral modiolar vein were diffusely positive for IgG and albumin. Immunoreactivity for connexin 26 and Na-K-ATPase was decreased in the fibrocytes of the spiral ligament, however, endolymphatic hydrops was not induced.2)Changes in cochleas with experimental otitis media were investigated in mice. Otitis media was induced in all of the animals after the inoculation of Streptococcus pneumoniae into the middle ear cavity, and some of them showed inflammatory cells in the cochlea. Although other changes, including endolymphatic hydrops, were not obvious, cochleas showed positive immunostaining for fibrinogen. Immunostaining for connexin 26 was slightly decreased in the spiral ligament, accompanied by fibrinogen staining.3)Endolymphatic sacs of the guinea pigs … More were ablated to induce endolymphatic hydrops and processed for immunohistochemistry. Staining of type I fibrocytes in the spiral ligament, which are positive for vimentin and connexin 26, was decreased. However, immunostaining for extracellular matrix in the spiral ligament, which are positive for chondroitin 4-sulfate proteogly can and type II collagen, showed no changes.Because endolymphatic hydrops is not always obseved with the changes in the fibrocytes of the spiral ligament, it is suggested that the spiral ligament is not responsible for the production of endolymphatic hydrops. However, spiral ligament appears to be responsible for the cochlear malfunction, and immunostaining for fibrinogen or other blood constituents suggests that the blood-labyrinth barrier could disrupt in the spiral ligament by labyrinthitis or otitis media. The constant staining for the extracellular matrix with the experimental endolymphatic hydrops raises the possibility that changes in the spiral ligament has been underestimated by routine otopathologic observations. Less