| BackgroundDeafness is a functional disease that seriously affects the quality of human life.According to the latest report of the World Health Organization（WHO）,about 5%of the world’s population suffer hearing loss,and hearing loss affects about 466 million people around the world.The second sampling survey of the disabled shows that the number of people with hearing and speech disabilities is as high as 27.8 million,accounting for 27%of the total number of disabled people,and nearly 30,000 deaf children are born every year.Cochlear implant（CI）is the most effective method for the treatment of severe and profound sensorineural hearing loss（SNHL）.It is estimated that more than 30 million people worldwide need to regain hearing through CI surgery.Cochlear implant has significantly improved people’s quality of life from the aspects of hearing,understanding,speech,emotion,communication,behavior,cognition and social interaction,thus bringing profound clinical significance and social value.Cochlear implant is a special acoustic-electrical conversion electronic device.It directly electrically stimulates spiral ganglion cells（SGCs）of SNHL patients through the electrode stimulation to replace part of the function of hair cells that cannot work properly,so that patients can regain hearing.It is the most successful artificial sensory organ prosthesis in clinical practice at present.After decades of advances in CI products and implantation techniques,CI implantation has become a safe and minimally invasive surgery.Like any surgical operation,CI surgery also has certain complications.Among them,the effect of electrode implantation on inner ear function has gradually attracted clinical attention.During CI implantation,the electrode was implanted into the cochlea through the round window（RW）or cochleostomy.Because of vestibular end organs and cochlear together make up the inner ear,and communicate with each other by the potential lacuna between them,the electrode insertion and subsequently electrical stimulation can affect the function of vestibular end organs and cochlear function at the same time,leading to postoperative dizziness and residual hearing decline.Related researches in this area are increasing.The effects of CI electrode on vestibular organs mainly include postoperative vertigo,dizziness,balance disorder and vestibular organ dysfunction.Due to the importance of balance function to human life quality,clinicians gradually began to pay attention to the changes of vestibular function in patients after CI implantation.Studies have shown that the subjective description of vertigo after CI implantation is inconsistent,and only about 16-53%of adult patients describe vertigo after CI surgery.Postoperative vertigo can have different symptoms,characteristics,onset time and duration.The specific reasons of postoperative vertigo and balance dysfunction are not clear at present.Since the compensatory mechanisms can be rapidly established between bilateral vestibular sensors,subjective descriptions are often inaccurate.The objective test results can forecast and monitoring the change of vestibular dysfunction,especially for children who cannot accurately describe the symptoms of vertigo.Early identification of these injuries through objective tests is crucial to provide patients with more clinical attention,considering rehabilitation guidance,to avoid serious adverse outcomes,or to help clinicians comprehensively evaluate and determine treatment options when choosing to treat the contralateral ears in the future.However,there are still few reports on the changes in the results of comprehensive and systematic objective examination of vestibular function after CI implantation,especially in children.At present,the effects of CI electrode and electrical stimulation on cochlear function are mainly discussed around residual hearing（RH）.As the indications of CI implantation continue to expand,preoperative low-frequency residual hearing（LFRH）retention is also an indication for CI implantation.Most of these patients have hearing loss in high frequency and keep residual hearing in low frequency.Lehnhardt was the first to use soft surgery to preserve residual hearing,and subsequent studies have explored minimally invasive techniques to maximize the preservation of residual hearing in patients.Cochlear implant manufacturers are gradually developing thinner and softer electrodes.Surgeons are paying more attention to a range of minimally invasive implant methods,including the minimally invasive RW approach,electrode insertion depth,drug in preoperative period,and reduction of sudden changes in pressure in the cochlea during electrode insertion.These minimally invasive techniques are beneficial to the preservation of cochlear fine structure and keep the stable preservation of LFRH after surgery.Acoustic amplification of low frequency cues through hearing aids and electrical stimulation of middle and high frequencies（mainly above 750-1000 Hz）through CI stimulation can be realized simultaneously in the same ear of the patient,named electrical acoustic stimulation（EAS）device.In 1999,C von Ilberg first proposed the concept of residual hearing preservation surgery combined with EAS,which was suitable for patients with LFRH but had uselessness of hearing aid.In view of the limitations of CI encoding strategy in processing sound information,the use of EAS in patients with LFRH can significantly improve their speech recognition in the noisy environment,as well as their sound localization,tone discrimination and music appreciation ability to some extent.With the rapid development of bilateral simultaneous implantation,sequential implantation,minimally invasive implantation,and implantation for young children or elderly people,both clinicians and patients pay more attention to the two major problems after CI surgery,the postoperative vertigo symptoms and vestibular function impairment as well as postoperative LFRH loss and cochlear function damage.Many researchers are concerned about how the inner ear functions,including cochlea and vestibular functions,will be affected after the implantation of electrodes,and how to eliminate the negative effects as much as possible through technological advances,so as to achieve the goal of restoring hearing while reducing the impact on the inner ear functions.Effective utilization of low frequency residual hearing can improve speech,cognition,understanding,and remodeling of cerebral cortex at the same time.It is needed to timely evaluate and monitor the change of vestibular function,forecast vestibular dysfunction,offer certain rehabilitation guidance,so as to improve the quality of life in a real sense.According to the limitation of previous researches,this study is divided into three parts:The first part used cervical vestibular-evoked myogenic potential（cVEMP）,ocular vestibular-evoked myogenic potential（oVEMP）and video head impulse test（vHIT）to explore the effect of CI on the function of five vestibular terminal organs in children.The second part was the extension of the first part,and analyzed the influence of CI on vestibular function of children,a special group called enlarged vestibular aqueduct（EVA）.The first two studies discussed the effects of CI on the vestibular system.The third part discussed the influence of CI on cochlear function by summarizing the changes of LFRH after CI,which was similar to the previous two parts,and analyzed the influence of CI on LFRH in EVA patients.Part Ⅰ Influence of cochlear implantation on all five vestibular end organs in childrenObjectiveOur goal was to investigate the function of all five vestibular end-organs pre-and post-cochlear implantation in children.MethodsIn this retrospective cohort study,27 children（age 4-17 years）with bilateral severe to profound SNHL undergoing unilateral CI were included.Objective modalities to evaluate vestibular function included Caloric test,cVEMP test,oVEMP test,and vHIT test.All measurements were performed before surgery and 9 months after surgery.Results1.Mean age at CI was 8.6±4.0 years.The abnormal results of Caloric test,cVEMP,oVEMP,horizontal semicircular canal（HSC）tested by vHIT,superior semicircular canal（SSC）,and posterior semicircular canal（PSC）before surgery were 33.3%（9/27）,7.4%（2/27）,22.2%（6/27）,0%（0/27）,0%（0/27）,and 3.7%（1/27）respectively,while the abnormal results were 59.3%（16/27）,63.0%（17/27）,66.7%（18/27）,11.1%（3/27）,3.7%（1/27）,and 7.4%（2/27）when 9 months after implantation in the implanted side.We found a significant increase of overall abnormality rate in Caloric,cVEMP and oVEMP from pre-to post-CI（P<0.05）.In all three semicircular canals tested by vHIT,there were no statistically significant changes（P>0.05）.2.The deterioration rates were 38.9%（7/18）in Caloric test,60.0%（15/25）in cVEMP,57.1%（12/21）in oVEMP,11.1%（3/27）in HSC（vHIT）,3.7%（1/27）in SSC,and 7.7%（2/26）in PSC when 9 months after CI in children with normal preoperative results in the implanted side.The deterioration rate was higher in Caloric test than SSC and PSC tested by vHIT（P<0.05）.The deterioration rate was higher in Caloric test than HSC tested by vHIT,although there was no significantly statistic difference（P=0.067）.The deterioration rate was higher in VEMP than all the three semicircular canals（P<0.05）.The deterioration rate was higher in VEMP than Caloric,although there was no significantly statistic difference（P>0.05）.Conclusion1.In general,the saccule and utricle were the most affected peripheral vestibular sensors in children after cochlear implantation;2.The semicircular canal functions tested under high frequency stimulation were seldom influenced by CI surgery;3.We recommend the use of this vestibular function test battery for children with cochlear implantation,including Caloric test,cVEMP test,oVEMP test,and vHIT test.Part Ⅱ Influence of cochlear implantation on vestibular function in children with an enlarged vestibular aqueductObjectiveTo explore the influence of cochlear implantation on vestibular function in children with EVA.MethodsIn this retrospective case-control study,16 children with EVA and 16 children with a normal cochlea were recruited as the Study and Control Group,respectively.All children（mean age,10.3±4.4 years）had bilateral severe to profound SNHL and normal preoperative vestibular functions,and underwent unilateral CI.Otolith and canal functions were assessed before CI and 12 months thereafter.cVEMP,oVEMP,and vHIT were evaluated.ResultsFull insertion of the electrode array was achieved in all the 32 cases.1.Preoperatively,in the implanted side,no significant differences on parameters（PI latency,N1 latency,P1-N1 amplitude）in cVEMP between the Study and Control Group were revealed,although the amplitude was higher in Study Group（P>0.05）.In preoperative oVEMP,shorter N1 latencies（P=0.012）,shorter P1 latencies（P=0.010）,and higher amplitudes（P=0.001）were found in the Study than in the Control Group.2.In the implanted side,the Study Group had shorter P1 latency in cVEMP（P=0.033）,and had lower amplitude in oVEMP after implantation（P=0.030）.In the Control group,there were no significant differences in the parameters of cVEMP and oVEMP after surgery（P<0.05）.3.Statistically significant differences were not found in vestibulo-ocular reflex（VOR）gains of all three semicircular canals in the implanted sides before and after surgery（P>0.05）.4.In the implanted side,VEMP results revealed that the Control Group had significantly lower deterioration rates after CI（P<0.05）.5.The normal response rates of VEMP（cVEMP and oVEMP）were significantly lower than those of vHIT in the implanted side after surgery（P<0.05）.6.The surgical approach and electrode array had no statistically significant influence on the VEMP results in the implanted side（P>0.05）.Conclusion1.The oVEMP parameters differed between children with EVA and children with a normal cochlea before surgery;2.Systematic evaluations before and after CI showed that otolith function was affected,but all three semicircular canals functions were essentially undamaged after implantation;3.In contrast to subjects with a normal cochlea,children with EVA are more likely to preserve their saccular and utricular functions after CI surgery.Possible mechanisms include less pressure-related damage,less effect to air-bone gap（ABG）after surgery,or more sensitivity to acoustic stimulation.Part Ⅲ Residual hearing preservation after cochlear implantationObjectiveTo investigate the changes of LFPTA in patients after minimally invasive cochlear implantation,and to investigate the difference of postoperative LFRH between EVA and patients with a normal cochlea.MethodsA total of 45 severe to profound SNHL patients with unilateral CI were selected.The unaided thresholds at 250 Hz,500 Hz,1000 Hz,2000 Hz,4000 Hz,and 8000 Hz were tested in the implanted ears before CI surgery and 12 months after surgery.The threshold at 250 Hz or 500 Hz was less than or equal to 85 dB HL before surgery.The changes of 250 Hz,500 Hz,and the average results were compared.The hearing preservation rate was calculated according to Skarzynski formula.To compare the thresholds and RH between patients with EVA and a normal cochlea.Results1.The mean preoperative LFPTA（250-500 Hz average）was 70.83±12.71 dB HL,the postoperative result was 84.94±12.09 dB HL,and the PTA shift was 14.11±14.08 dB HL in the implanted ears.The difference was statistically significant（P<0.01）.2.The mean preoperative threshold at 250 Hz was 63.89±14.65 dB HL,the postoperative result was 78.78±15.64 dB HL,and the threshold shift was 14.89±15.43 dB HL in the implanted ears.The difference was statistically significant（P<0.01）.The mean preoperative threshold at 500 Hz was 77.78±13.76 dB HL,the postoperative result was 91.11±10.33 dB HL,and the threshold shift was 13.33±14.38 dB HL.The difference was statistically significant（P<0.01）.3.According to Skarzynski criteria,17（37.78%）implanted ears demonstrated complete hearing preservation,23（51.11%）partial hearing preservation,four（8.89%）minimally hearing preservation,and one（2.22%）exhibited no measurable acoustic hearing after surgery.In total,40（88.89%）patients demonstrated hearing preservation after CI surgery.4.One year after surgery,the average threshold of non-hearing pure tone at 250 Hz at the implanted side of EVA group was higher than that of the control group（82.83±12.04 dB HL compared with 71.00±19.20 dB HL）,but the difference was not statistically significant（P=0.073）.According to Skarzynski criteria,complete RH rate of EVA group was 34.78%（8/23）,partial RH rate was 43.48%（10/23）and limited RH rate was 13.04%（3/23）at 1 year after surgery.The overall RH rate was 78.26%.The complete RH rate and partial RH rate in control group were 53.33%（8/15）and 33.33%respectively.The limited retention rate was 13.33%（2/15）,and the overall retention rate of RH was 86.67%.By comparison,complete RH rate and overall RH rate in control group were higher than those in EVA group,but there were no significant differences（P>0.05）.Conclusion1.The majority of patients who underwent minimally invasive cochlear implantation preserved LFRH at 1 year after surgery,with less change of function in cochlea;2.The stable LFRH after a period use of cochlear implant providing the possibility for EAS in the future,in order to acquire an overall improvement in the auditory performance.3.EVA children and normal cochlea children acquired the similar RH rate after surgery. |
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