الفهرس 
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Abstract
Cochlear Implantation (CI) is the best standard for management of severe to profound hearing loss (HL) with unsatisfactory hearing aids. Injury to the vestibular organs may occur during surgery and result in vestibular dysfunction. Different mechanisms could lead to vestibular dysfunction during or after CI surgery. The first is direct trauma caused by electrode insertion. The second is acute serous labyrinthitis due to cochleostomy. The third mechanism is foreign body reaction with labyrinthitis. Fourthly, endolymphatic hydrops and finally, electrical stimulation from the implant itself. Vestibular evoked myogenic potentials (VEMPs) are small modulations in the electromyographic activity produced by acoustic stimulation of the otolith organs. Combined VEMPs recording is a convenient screening tool for assessing crossed vestibulo-ocular reflex and ipsilateral sacculo-collic reflex with shortened diagnostic test time. The otolith organs of the labyrinth are suited to detect linear acceleration. These organs play a major part in sensing gravitational input, in particular the perception of uprightness. SVV/SVH tilts are a sensitive sign of vestibular dysfunction. They have a potential use in measuring compensation, prognosis and recovery in various peripheral vestibular conditions. Thus, this work was designed to study the otolith function in unilateral cochlear implant patients using both cervical vestibular evoked myogenic potential and ocular vestibular evoked myogenic potential as well as subjective visual vertical test. The current study included sixty children divided into two groups: Control group (group I) 30 healthy children with age ranging from five to 18 years who had no auditory or vestibular complaints. Study group (group II) included 30 children with age ranging from five to 18 years with unilateral cochlear implant. All children underwent full audiological history, otological examination, basic audiological evaluation, dizziness handicap inventory (DHI) for children, pediatric vestibular symptom questionnaire (PVSQ), combined VEMPs, SVV and SVH tests. In the present study, none of the children in the control group had vestibular complaint. Comparison between both groups as regard results of Arabic Dizziness Handicap Inventory (DHI) questionnaire for children and results of Pediatric vestibular symptom questionnaire (PVSQ). There was a significant difference between both groups. These results indicate vestibular affection in CI children. Combined cervical and ocular VEMPs (Combined VEMPs) were recorded in both control and study groups. In control group, P13 and N23 were successfully recorded from all subjects. While in the study group (Implanted ears), cVEMPs were recorded in six ears (20.0%), and absent in twenty-four ears (80.0%). Moreover, in the non-implanted ears, cVEMPs were recorded in twenty-six ears (86.7%), and absent in four ears (13.3%). Comparing cVEMPs detectability results in control and study group was done. Results showed a statistically significant difference. Also, there was a statistically significant difference between the control and the study group (implanted side). Also, between implanted and the non-implanted sides as regard P13, N23 latencies and P13-N23 amplitude. As regard Ocular VEMPs, in the current work, N10 and P15 of oVEMPs in the control group were successfully recorded in all subjects. While in the study group (Implanted ears), oVEMPs were recorded in seven ears (23.3%) and absent in twenty three ears (76.7%). Moreover, in the Non-implanted ears, oVEMPs were recorded in eight ears (26.7%), and absent in twenty two ears (73.3%). Comparing oVEMPs detectability results in control and study group was done. Results revealed a statistically significant difference. While, there was no statistically significant difference between control and studied groups as regard N10, P15 latencies and N10-P15 amplitude. In the current study, all the subjects in the control group showed normal values of SVV&SVH tests. In the study group, eight (26.6%) children had a score outside the normal range of deviation in SVV test. In SVH test seven children (35%) had a score outside normal range of deviation. Comparing the SVV/SVH values in both the control and study groups was done. There was a statistically significant difference in SVV/SVH values between both groups. There was no correlation between age, duration of implantation, DHI, PVSQ and parameters of cVEMPs/ oVEMPs in the study group. There was a positive significant correlation between SVV results in study group and DHI , PVSQ scores. Also, between SVH results and DHI scores. As regards the results of this work, the functioning of the otolith organs gets even more impaired following CI surgery. This suggests that CI has a more negative impact on the functioning of the otolith structures. This was evidenced by the high prevalence of absent oVEMP and cVEMP as well as abnormalities in SVV/SVH in the study group. from the results of cervical VEMPs, implanted side was more affected than non-implanted side. According to ocular VEMPs, both implanted and non implanted sides were affected. As VEMPs assess only otolith organs other parts of vestibular system should be evaluated in children with CI.