Techniques in cochlear implantation

Approach to Cochlear Implantation in Patients With Ventriculoperitoneal Shunts

OBJECTIVE

To evaluate the safety and outcomes of cochlear implantation (CI) in patients with ventriculoperitoneal (VP) shunts to inform clinical practice.

STUDY DESIGN

Historical cohort study.

SETTING

Tertiary referral centers.

METHODS

A multi-institutional historical cohort of patients with VP shunts and CI was identified and analyzed.

RESULTS

A total of 46 patients (median age 8 years [interquratile range, IQR: 2-46]) with VP shunts and CI were identified. Of these, 41 (89%) patients had a VP shunt prior to CI. Based on institutional preference and individual patient factors, CI was performed contralateral to a pre-existing VP shunt in 24 of these 41 cases (59%) and ipsilateral in 17 (41%). Furthermore, pre-CI relocation of the VP shunt was performed in 3 cases (7%), and 2 patients (5%) underwent planned revision of their VP shunt concurrent with CI. In total, 2 of 27 pediatric patients (7%) required unanticipated revision shunt surgery, both contralateral to CI device placement, given VP shunt malfunction. One of 19 adult patients (5%) required shunt revision during CI due to shunt damage noted intraoperatively. Among 43 patients with available follow-up, 38 (88%) are regular CI users, with a median consonant-nucleus vowel-consonant word: score of 58% (IQR: 28-72).

CONCLUSION

CI can be performed at low risk, either contralateral or ipsilateral, to a VP shunt, and does not mandate shunt revision in most cases. Additional considerations regarding CI receiver-stimulator placement are necessary with programmable shunts to mitigate device interaction. Preoperative planning, including coordination of care with neurosurgery, is important to achieving optimal outcomes.

Robotic Milling of Electrode Lead Channels During Cochlear Implantation in an ex-vivo Model

Objective: Robotic cochlear implantation is an emerging surgical technique for patients with sensorineural hearing loss. Access to the middle and inner ear is provided through a small-diameter hole created by a robotic drilling process without a mastoidectomy. Using the same image-guided robotic system, we propose an electrode lead management technique using robotic milling that replaces the standard process of stowing excess electrode lead in the mastoidectomy cavity. Before accessing the middle ear, an electrode channel is milled robotically based on intraoperative planning. The goal is to further standardize cochlear implantation, minimize the risk of iatrogenic intracochlear damage, and to create optimal conditions for a long implant life through protection from external trauma and immobilization in a slight press fit to prevent mechanical fatigue and electrode migrations.

Methods: The proposed workflow was executed on 12 ex-vivo temporal bones and evaluated for safety and efficacy. For safety, the difference between planned and resulting channels were measured postoperatively in micro-computed tomography, and the length outside the planned safety margin of 1.0 mm was determined. For efficacy, the channel width and depth were measured to assess the press fit immobilization and the protection from external trauma, respectively.

Results: All 12 cases were completed with successful electrode fixations after cochlear insertions. The milled channels stayed within the planned safety margins and the probability of their violation was lower than one in 10,000 patients. Maximal deviations in lateral and depth directions of 0.35 and 0.29 mm were measured, respectively. The channels could be milled with a width that immobilized the electrode leads. The average channel depth was 2.20 mm, while the planned channel depth was 2.30 mm. The shallowest channel depth was 1.82 mm, still deep enough to contain the full 1.30 mm diameter of the electrode used for the experiments.

Conclusion: This study proposes a robotic electrode lead management and fixation technique and verified its safety and efficacy in an ex-vivo study. The method of image-guided robotic bone removal presented here with average errors of 0.2 mm and maximal errors below 0.5 mm could be used for a variety of other otologic surgical procedures.

Round window accessibility during cochlear implantation

OBJECTIVE

To assess data regarding round window (RW) visibility and surgical approaches in cochlear implant cases, and to describe and analyze surgical steps relevant for the RW approach in cochlear implantation.

STUDY DESIGN

Prospective clinical study.

METHODS

A questionnaire was completed by surgeons after each of altogether 110 cochlear implantations. Round window membrane (RWM) visibility was graded according to the St Thomas Hospital (STH) classification.

RESULTS

Performing different surgical steps during the preparation of the RW niche, the RWM could be fully exposed (STH Type I) in 87%. A RW approach could be used for electrode insertion in 89% of the adult and 78% of the pediatric cases. The distribution of RW types differed significantly between adults and children. Drilling of the superior bony lip was the surgical step most frequently needed in adult as well as pediatric cases to obtain optimal RW exposure.

CONCLUSION

In children, optimized surgical exposure of the RW niche resulted in only 52% full RWM visibility; whereas in adults, this could be achieved in 87%. The facial nerve (FN) had to be exposed at the level of the posterior tympanotomy in more than 70% of pediatric cases with full RWM visibility; while in adult cases with 100% visibility, such specific exposure was necessary in only 33%. Thus, surgical preparation of the RW niche seems to be more demanding in children than in adults.

Anatomy of the Round Window Region With Relation to Selection of Entry Site Into the Scala Tympani

OBJECTIVES/HYPOTHESIS

The aim of cochlear implantation is to safely insert an electrode array into the scala tympani (ST) while avoiding damage to surrounding structures. There is disagreement on the optimal way of entering the ST-the round window (RW) approach versus cochleostomy. Regardless of the chosen approach, it is vital to understand the regional anatomy, which is complex, difficult to conceptualize, and rarely dissected in temporal bone courses. The goal of this study was to examine the anatomy of the RW to gain more in-depth knowledge on the local relationships of the anatomical structures and propose an approach for entering the ST in cochlear implant surgery tailored to the encountered anatomy.

STUDY DESIGN

Cadaveric prevalence study and expert opinion with literature review.

METHODS

Cadaveric temporal bone dissection (n = 13) by the first author assessing the RW anatomy.

RESULTS

The round window membrane (RWM) and the osseous spiral lamina (OSL) are curved structures, each with a horizontal and a vertical part. The two horizontal portions are very closely apposed. The relationship between the OSL and the RWM determines the best site for a cochleostomy, which if required is best placed anteroinferiorly to the RWM. The distance between the oval window inferior margin and the RW membrane is less than 2 to 3 mm. The ST initially extends inferiorly and medially to the RW.

CONCLUSIONS

The findings of our dissection have implications for cochlear implant surgery in aiming to avoid trauma to the OSL and basilar membrane and aid decision making in choosing the safest surgical approach.

LEVEL OF EVIDENCE

5. Laryngoscope, 131:E598-E604, 2021.

Long-term Outcomes in Down Syndrome Children After Cochlear Implantation: Particular Issues and Considerations

OBJECTIVE

The aim of the study was to analyze the long-term outcomes after cochlear implantation in deaf children with Down syndrome (DS) regarding age at the first implantation and refer the results to preoperative radiological findings as well as postoperative auditory and speech performance. Additionally, the influence of the age at implantation and duration of CI use on postoperative hearing and language skills were closely analyzed in children with DS.

STUDY DESIGN

Retrospective analysis.

SETTING

Referral center (Cochlear Implant Center).

MATERIALS AND METHODS

Nine children with Down syndrome were compared with 220 pediatric patients without additional mental disorders or genetic mutations. Patients were divided into four categories depending on the age of the first implantation: CAT1 (0-3 yr), CAT2 (4-5 yr), CAT3 (6-7 yr), and CAT4 (8-17 yr). The auditory performance was assessed with the meaningful auditory integration scales (MAIS) and categories of auditory performance (CAP) scales. The speech and language development were further evaluated with meaningful use of speech scale (MUSS) and speech intelligibility rating (SIR). The postoperative speech skills were analyzed and compared between the study group and the reference group by using nonparametric statistical tests. Anatomic abnormalities of the inner ear were examined using magnetic resonance imaging (MRI) and high-resolution computed tomography of the temporal bones (HRCT).

RESULTS

The mean follow-up time was 14.9 years (range, 13.1-18.3 yr). Patients with DS received a multichannel implant at a mean age of 75.3 months (SD 27.9; ranging from 21 to 127 mo) and 220 non-syndromic children from reference group at a mean age of 51.4 months (SD 34.2; ranging from 9 to 167 mo). The intraoperative neural response was present in all cases. The auditory and speech performance improved in each DS child. The postoperative mean CAP and SIR scores were 4.4 (SD 0.8) and 3.2 (SD 0.6), respectively. The average of scores in MUSS and MAIS/IT-MAIS scales was 59.8% (SD 0.1) and 76.9% (SD 0.1), respectively. Gathered data indicates that children with DS implanted with CI at a younger age (<6 years of age) benefited from the CI more than children implanted later in life, similarly in a control group. There were additional anomalies of the temporal bone, external, middle, or inner ear observed in 90% of DS children, basing on MRI or HRCT.

CONCLUSIONS

The early cochlear implantation in children with DS is a similarly useful method in treating severe to profound sensorineural hearing loss (SNHL) as in non-syndromic patients, although the development of speech skills present differently. Due to a higher prevalence of ear and temporal bone malformations, detailed diagnostic imaging should be taken into account before the CI qualification. Better postoperative outcomes may be achieved through comprehensive care from parents/guardians and speech therapists thanks to intensive and systematic rehabilitation.