Usadak u moždanom deblu (ABI)

Jokić, Karmela. (2015). Usadak u moždanom deblu (ABI). Diploma Thesis. Filozofski fakultet u Zagrebu, Department of Phonetics. [mentor Mildner, Vesna].

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Abstract

Hearing is one of the five primary human senses. Developing the sense of hearing is the main factor for speech and language development. Profound hearing loss resulting from illness or other kind of hearing damage is associated with a severe compromise in information exchange for human beings. Thanks to improvements in modern medical technology there is a number of hearing aids that can help hearing restitution or even development. Unfortunately, there are illnesses, like neurofibromatosis type 2, that can damage both hearing nerves so that standard hearing aids are useless. Neurofibromatosis type 2 (NF2) is characterized by benign tumors, neurinomas, that grow on the hearing and balance nerve. The microsurgical removal of the tumor damages the auditory nerve that conducts the neural signal from the inner ear to the brainstem and auditory cortex. This results in deafness. However, by studying the auditory pathway scientists have found other centers along the central auditory pathway that can be electrically stimulated resulting in hearing impressions. Electrical stimulation can be delivered to the second neuron of the auditory pathway at the brainstem – cochlear nucleus – through the Auditory Brainstem Implant (ABI). The first implantation of this neural prothesis was in 1979 at the House Research Institute in Los Angeles, California. The concept of auditory brainstem implant is similar to that of cochlear implant. ABI also has an internal part that consists of an electrode array and a receiver stimulator, and the external part that consists of the speech procesor, transmitting coil and a magnet. There are two main surgical approaches for the removal of an acoustic neurinoma and implanting the ABI electrodes: translabyrinthine and retrosigmoid/suboccipital approach. The site for electrode placement is cochlear nucleus complex. The hearing impressions with ABI are not as good as with cochlear implants, but auditory brainstem implant does improve lip reading and the distinction of environmental sounds. Open set speech is rarely gained. Because of that, scientists are trying to improve the existing implant by using penetrating microelectrodes that penetrate the cochlear nucleus complex. This neural prothesis is called PABI – Penetrating Auditory Brainstem Implant. For deaf patients who cannot sufficiently benefit from cochlear implant or ABI, there is Auditory Midbrain Implant (AMI) that stimulates the inferior colliculus. So far, the resulting hearing impressions have not been as good as expected. There are more than 2 000 ABI patients in the world today. The first ABI implantation in Croatia occurred in 1999. A deaf female patient was diagnosed with bilateral acoustic neurinomas. After the tumor removal, the auditory brainstem implant surgery was performed on the right side using the suboccipital approach. Post-operatively, the patient performed exceptionally well. According to the results of her audio rehabilitation at one speach and hearing rehabilitation clinic in Zagreb the patient could recognize up to 50 per cent of words in the open set and 80 per cent in the closed set, both without lip-reading. The results based on my own research experience with the same patient were very similar (50 per cent of words recognized in the open set and 70 per cent in the closed set). Patient's intelligibility depended on her psychophysical condition which became worse after the tumor recurrence (vestibular schwannoma on the right side, 22mm). She underwent another operation in 2002; after that we lost contact so further research could not proceed.

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