Histopathology of the peripheral vestibular system after cochlear implantation in the human

The objective of this study was to describe the histology of the peripheral vestibular system in temporal bones from patients who in life had undergone cochlear implantation and to correlate the findings with previous reports of vestibular dysfunction after cochlear implantation. This is the first quantitative report of the impact of implantation on the vestibular neuronal end organ. METHODSThere were 19 temporal bones available for histologic study. Of these, 17 were suitable for the description of the morphology of the membranous labyrinth, 8 for counting Scarpa's ganglion cells, and 6 for measuring the densities of vestibular hair cells. The bones were fixed, cut, and stained according to previously published methods. Preferably, the implanted electrode was left in situ. Vestibular hair cells were counted with Nomarski's optics.

Differences in Scarpa's ganglion cell counts and hair cell densities between the implanted and nonimplanted sides were not statistically significant. In 59% of the implanted bones, the cochlea was hydropic, and in the majority of these bones the saccule was collapsed.

Cochlear implantation does not cause deafferentation of the peripheral vestibular system. Cochlear hydrops accompanied by saccular collapse is common and may cause attacks of vertigo of delayed onset, similar to Ménière's syndrome as previously reported in several clinical series. Hydrops could be caused by obstruction of endolymphatic flow in the ductus reuniens or in the hook portion of the cochlea or by damage to the lateral cochlear wall caused by implantation.