Oval Window Transport of Gd-DOTA from Rat Middle Ear to Vestibulum and Scala Vestibuli Visualized by in vivo Magnetic Resonance Imaging

Abstract

Objectives: We tested our hypothesis that the oval window (OW) potentially functions as a route to carry substances from the middle ear to the vestibulum and then the scala vestibuli through the annular ligament across the stapediovestibular joint. Methods: Gd-DOTA was either injected into the lateral attic compartment of rats with a high-performance polyimide tube in a selective OW delivery group, or administered to the middle ear cavity of two groups of rats in which the OW was either sealed or not sealed. The dynamic uptake of Gd-DOTA in the inner ear was visualized with a 4.7-T magnetic resonance imaging machine. Results: In the selective OW delivery group, Gd-DOTA appeared in the vestibulum and in the basal turn of the scala vestibuli but not in the scala tympani on T1-weighted images acquired at 10 minutes after Gd-DOTA administration (the earliest available time point of magnetic resonance imaging). In the sealed-OW group, immediate uptake of Gd-DOTA was absent in the vestibulum and scala vestibuli. Measurement of the signal ratio of the vestibulum to that of the scala tympani showed that selective OW delivery induced the greatest signal ratio and that sealing of the OW induced the lowest signal ratio. Conclusions: The OW is a genuine and efficient pathway to transport Gd-DOTA from the middle ear to the vestibulum.