Fully implantable hearing device with transducer on the round window as a treatment of mixed hearing loss
Introduction
Conventional hearing aids are subject to many limitations, including occlusion of the ear canal, chronic irritation, acoustic feedback, sound distortion and other limitations [1]. Recently, implantable hearing devices have been developed to overcome some of these problems [1], [2], [3]. The Symphonix Vibrant Soundbridge was the first device to be used routinely, starting in February 1998 in Europe and August 2000 in United Stated [3]. It possesses an external auditory processor which transfers the information to the implant where the vibration is transmitted to the long process of the incus by a vibrating floating mass. The Middle Ear Transducer (MET) from Otologics LLC is also available on the market in EU as a semi implantable device. It is similarly composed of an external part containing the microphone, the battery and the sound processor, and of an internal part implanted in the middle ear whose vibrator is connected to the body of the incus [1], [2]. A new fully implantable hearing device has recently been made available by Otologics [1], [4]: the Otologics Middle Ear Transducer™ (also known commercially as the Carina™ fully implantable system) which is an available treatment for moderate to severe sensorineural hearing loss in adults. This system is registered and approved for sale in EU, and is in FDA clinical trials in the US.
Until recently, the transducers of the various devices have been attached to the various part of the ossicular chain. It has therefore been mandatory to implant a rather normal middle ear with a normally functioning ossicular chain. Recently, Colletti et al. have reported successful sound direct transfer to the inner ear through the round window membrane using the floating mass of the Vibrant Soundbridge [5].
The Otologics device is also indicated for mixed losses, and has been reported in a series of atresia patients [4], [6]. The end of the prosthesis is placed directly on the stapes footplate or directly on the round window if the oval window is completely obliterated by tissue and stapes footplate could not be identified [5]. As described, both the Soundbridge and the Otologics device have the potential to bypass the conductive hearing loss component to deliver vibratory stimulus to the cochlea. The development of these mixed loss applications can therefore offer a therapeutic option to patients whose other options may be limited.
We report the case of a patient with a mixed hearing loss who underwent a novel middle ear implantation surgery in which a vibratory transducer was placed in the round window niche, thus bypassing the damaged ossicular chain.
Section snippets
Case report
A 48-year-old woman suffered from a bilateral hearing loss: the right ear presented a mean PTA (pure tone average of 0.5, 1, 2 and 4 kHz thresholds) loss of 80 dB (Fig. 1) secondary to a cholesteatoma following three surgical procedures; the left ear presented a neurosensory hearing loss with mean PTA loss of 46.6 dB. The left tympanic membrane was normal and on the right tympanic membrane, no recurrence was demonstrated. She had a chronic bilateral irritation of the external ear canal. On the CT
Discussion
In a previous study of 282 patients, the Otologics MET ossicular stimulator was established to be safe and effective in treating moderate to severe sensorineural hearing loss in adults [1]. As demonstrated in the study, implantation of the electromechanical transducer should not result in a change of cochlear status and even if the transducer was attached to the ossicular chain, no change in bone conduction threshold was found [1], [2].
Recently, this application has been extended to patients
Conclusion
The mixed hearing loss described in this case was successfully treated by implantation of the Otologics fully implantable system, with vibratory stimulation direct to the round window. This is a promising new result, given the severity of the mixed loss treated and the fact that the stapes was obliterated by sclerotic tissue. For this patient, the fully implantable system was a suitable choice particularly because of the chronic ear canal irritation. It should be noted, however, that these are
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