Fundamental and Clinical Study of Cochlear Synaptopathy

During functional surgery on the cerebellopontine angle, a ball electrode is placed on the human cochlear nerve to monitor hearing. Once the electrode is in place, clicks and random noise bands will be delivered in order to analyze the cochlear electrophysiological signal produced. Depending on the characteristics recorded, this signal can be used at a given frequency and intensity to identify the populations of auditory neurons mainly involved. Prior to surgery, each patient will have been examined by the audiologist in order to determine the auditory thresholds in silence and noise, in tone and in speech, to carry out the digit test and to perform an electrocochleography and distortion products. Each result analyzed will be the subject of a further analysis using the mathematic model of the human cochlea.

Inclusion criteria

Patients with normal hearing will be included:

• male or female
• over 18 and up to 70 years of age
• normal otoscopic examination
• due to undergo surgery on the cerebellopontine angle (microvascular decompression).
• free of neuro-sensory deafness, defined by mean hearing thresholds of less than or equal to 20 dB HL in pure tone audiometry in air conduction bilaterally on the side of the ear operated on and on the non-operated side from 0.25 to 8 kHz
• affiliated to a social security scheme
• have read the information note describing the study and have agreed in writing to take part by signing the informed consent form.

Patients with a hearing impairment will be included:

• male or female
• over 18 and up to 70 years of age
• normal otoscopic examination
• due to undergo surgery on the cerebellopontine angle (microvascular decompression).
• have a sensorineural hearing loss defined by hearing thresholds of 20 dB HL or better from 0.25 to 2 kHz and from 20 dB HL excluded to 55 dB HL at frequencies above 2 kHz.
• have read the information note describing the study and have agreed in writing to take part by signing the informed consent form.

Exclusion criteria

• Patients will be excluded from the study for whom the auditory nerve is not accessible during surgery, in particular because of complete tumour invasion of the cochlear nerve (stage III and IV neuroma, advanced meningioma) or because of a particular anatomical feature not identified during the preoperative examination, making it impossible to expose the nerve for recordings (protrusion of the posterior surface of the rock).