Individual Differences in the Permeability of the Round Window: Evaluating the Movement of Intratympanic Gadolinium Into the Inner Ear

Objective: Many recent studies have reported on intratympanic gentamicin therapy for the treatment of intractable Meniere's disease. Intratympanic administration of steroids has also been used to treat sudden sensorineural hearing loss. These intratympanic drug therapies are based on the assumption that the drug administered intratympanically enters the inner ear through the round window membrane. We used magnetic resonance imaging (MRI) to evaluate whether and how intratympanically administered gadolinium (Gd) enters the inner ear. Methods: GD hydrate was injected intratympanically through the tympanic membrane using a 23-G needle into 61 ears of 55 patients with inner ear diseases. The injected Gd was diluted 8-fold in saline for injection into 58 ears and 16-fold for 3 ears. Three-dimensional fluid-attenuated inversion recovery (3D-FLAIR) imaging was performed using a 3-Tesla MRI unit 1 day after the intratympanic injection. Results: In 53 of 61 ears, the Gd-containing inner ear was detected well as a high signal on 3D-FLAIR imaging. However, Gd was not visible in 2 ears with Meniere's disease and in 1 ear with profound deafness. The concentration of Gd in the perilymph was lower in 4 ears with Meniere's disease and 1 ear with delayed endolymphatic hydrops than after intratympanic administration of the 16-fold Gd dilution. Conclusion: Round window permeability was absent in 5% of ears, and 13% of ears had poor round window permeability. These results should be considered when planning intratympanic drug administration therapy to treat inner ear diseases.