Focal Endolymphatic Hydrops as Seen in the Pars Inferior of the Human Inner Ear

Hypothesis: Endolymphatic hydrops of the human inner ear may be localized focally in the pars inferior of the human inner ear. Background: Endolymphatic hydrops may be found in the human inner ear in patients who in life had suffered from Ménière's syndrome or a variety of other disorders. The degree of endolymphatic hydrops may differ based on location in the inner ear. Methods: A computer-assisted search of all cases in the collection of the Massachusetts Eye and Ear Infirmary in which endolymphatic hydrops was found in the inner ear yielded 13 specimens in which there was good evidence for focal endolymphatic hydrops in the pars inferior. Temporal bones were prepared for light microscopy. Semi-serial sections were reviewed to generate localization data for endolymphatic hydrops and also to search for evidence of a previous inflammatory process, including fibrosis or new bone formation. Results: Endolymphatic hydrops was present in the saccule in 10 of 13 specimens. In the cochlear duct, there were segments of the cochlea in which there was no cochlear hydrops juxtaposed to other regions in which there was severe endolymphatic hydrops. Transition between hydropic and non-hydropic status in the cochlear duct was often abrupt. Evidence for a previous inflammation process was found in 6 of 13 specimens including fibrosis because of temporal bone fracture, or traumatic stapedectomy and in those cases in which the cause of hearing loss was idiopathic, fibrosis, and osteoid between the labyrinthine surface of the footplate and the hydropic saccular wall, and/or osteoid in the scala vestibuli, or in the proximate Rosenthal's canal. Evidence of a previous inflammatory process was uniformly seen in the perilymphatic compartment. Conclusions: Endolymphatic hydrops of the pars inferior in the human may have a focal distribution. This study suggests that the pathogenesis of endolymphatic hydrops is unlikely to be because of distal obstruction of longitudinal flow and was more consistent with the hypothesis that homeostasis of the endolymphatic and perilymphatic volumes occurs all along the cochlear duct. Other factors including variable distensibility of Reissner's membrane or disturbance of local solute homeostatic mechanisms may be responsible for wide variations in the degree of hydrops. A focal inflammatory process during life may be one cause of focal endolymphatic hydrops as seen histopathologically.

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