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. 2022 Mar 4;119(9):135–141. doi: 10.3238/arztebl.m2022.0090

Auditory Brainstem Implants—Hearing Restoration in Congenitally Deaf Children

Robert Behr 1,*, Konrad Schwager 2, Erich Hofmann 3
PMCID: PMC9201461  PMID: 35012707

Abstract

Background

Children who are born deaf can learn to hear and to speak with the aid of a cochlear implant (CI). If the implantation of a CI is not possible for anatomical reasons, an auditory brainstem implant (ABI) is the only surgical option for auditory rehabilitation. It is estimated that about 5 to 45 children could potentially benefit from this treatment in Germany each year. In this article, we present and discuss the current state of the scientific evidence.

Methods

The PubMed and Embase databases were searched for relevant publications from 2010 onward. 15 articles reporting at least 10 cases with at least one year of auditory follow-up were included in the analysis. The results, including CAP (“categories of auditory performance”) scores on a scale of 0 to 7, are presented and compared with the authors’ own findings in a series of 38 patients.

Results

All of the publications show that children who do not suffer from impairments of other kinds hear significantly better with an ABI than those with additional handicaps. Early implantation is advantageous, under the age of three years if possible. The results vary widely across publications and from patient to patient. The mean CAP score in all publications is 3.57 (standard deviation [SD], 1.04). 38.24% of the patients (SD 18.68) achieved the ability to understand spoken language (CAP ≥= 5), more specifically, the ability to communicate in everyday life without lip reading, in person and some even succeed in conversing over the telephone.

Conclusion

ABI is a safe and effective treatment for sensorineural deafness in congenitally deaf children who cannot be treated with a cochlear implant. In particular, children without any other impairments have a good chance of developing the ability to understand spoken language, especially if the implantation is performed early.

cme plus

This article has been certified by the North Rhine Academy of Continuing Medical Education. Participation in the CME certification program is possible only over the internet: cme.aerzteblatt.de. The deadline for submission is 3 March 2023.

Conventional hearing aids rely on an intact connection between the peripheral auditory organ and the brain. Cochlear implants (CI), too, rely on an intact auditory nerve to restore the patient’s capacity for auditory communication, or even enable congenitally deaf children to hear (1– 3). Yet some children with congenital sensorineural deafness lack a cochlea in which a CI could be placed, or else suffer from aplasia or hypoplasia of the auditory nerves (or have both problems at once). Such persons make up 1–10% of the congenitally deaf; they can learn to hear if they are given an auditory brainstem implant (ABI).

As there is not even a CI registry in Germany, let alone an ABI registry, no precise statistics on CI or ABI surgery are available. In Switzerland, 45 children aged 0–3 years and 22 aged 3–12 years received a CI in 2015 (4). The population of Germany being some 10 times higher than that of Switzerland, we may roughly estimate, considering only children aged 0 to 3, that 450 congenitally deaf children in Germany would be eligible for a CI each year. Among these, then, an estimated 5 to 45 children might be provided with an ABI.

Unlike CI, the electrodes of an ABI are implanted directly on the surface of the cochlear nucleus of the brainstem, resulting in the creation of an electro-neural interface directly into the brain (figure 1). An audio processor transmits impulses via these electrodes into the cochlear nucleus, so that deaf children without any residual peripheral sensory input whatsoever can still learn to hear to a degree that promotes communication, i.e., they can still develop what is called functional hearing. Higher, integrative sensory function is enabled solely by technically generated impulses that flow directly into the brain.

Figure 1.

Figure 1

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intraoperative view of ABI implantation on the right side. At left, the quadripolar test probe is seen lying in the area of the cochlear nucleus. To the right of it is the prepared 12-polar stimulating electrode, with a dacron mesh for fixation in the lateral recess of the fourth ventricle.

The ABI was first developed for patients with neurofibromatosis type 2 (NF-2); its origins date back to 1979. House and Hitselberger successfully implanted the first, technically very simple ABI in an NF-2 patient (5, 6). Technical advancement led to electronically highly integrated, multichannel systems, which were used in NF-2 patients from the 1990s onward (7– 12) and in congenitally deaf children starting in the first decade of the 21st century (13) (for details see eMethods).

CI has seen widespread application to date: according to one estimate, 32 454 CI were implanted in Germany from 2005 to 2016 (4, 14). In contrast, ABI are still too rarely considered or even unknown, especially for children with prelingual deafness, i.e., deafness that began before language acquisition. In this article, we provide an up-to-date overview of the state of the scientific evidence on this topic.

Methods

The experience of the treatment team is a major determinant of the outcome of any type of therapy that is both highly specialized and rare. It follows that, in a cohort study, minimum case numbers must be set, in order for the findings to be valid and comparable across centers. We required at least ten cases per center. Moreover, each patient should have at least one year of auditory follow-up after implantation, as the hearing outcome changes markedly over time. We identified relevant studies by searching in the PubMed and Embase databases for the period from 1 January 2010 to 25 January 2021. The search criteria are given in Box 1.

BOX 1. Searching strategies.

  • cochlear OR cochlearis OR auditory OR acoustic OR acusticus OR vestibul OR cranial

  • aplasia OR hypoplasia OR disruption OR trauma OR neuroma OR ossification OR malformation OR dysfunction OR non-functional OR agenesis OR deficiency OR absent OR hypogenetic OR neuropathy OR otosclerosis OR avulsion OR fracture OR hyperostosis

  • neurofibromatosis OR NF2 OR schwannoma OR neurinoma OR neurilemoma OR meningioma OR hearing loss OR deaf OR cholesteatoma OR mastoiditis OR Cogan syndrome OR von Hippel Lindau OR Bourneville-Pringle

  • brainstem implant OR ABI OR no treatment

  • 1 AND 2

  • 5 OR 3

  • 6 AND 4

  • limit 7 to languages: English OR German

The PubMed search yielded 205 hits and 13 duplicates; all of the 99 references retrieved from Embase had already been found by the PubMed search. Among the hits from the searches, 48 publications were judged to be relevant to the topic and were then further narrowed down by the criteria of a minimum caseload (at least 10 cases) and a minimum duration of follow-up (at least one year); there remained 15 original papers meeting these inclusion criteria (15– 29). Not all of the publications were mainly concerned auditory outcomes. Some focused on complications, anatomic variants, quality of life, and intraoperative measurements. Hearing outcomes were sometimes reported only qualitatively, or with quantitative values as a range, without any average value. Nor was the duration of follow-up the same in all studies. All of the relevant and available quantitative information was extracted from the publications and is presented together with the qualitative data (table) as a comprehensive overview of the findings; in interpreting these findings, one must take the above limitations into account.

Table. Overview of the 15 scientific publications since 2010 with at least 10 cases and at least 1 year of auditory follow-up after ABI implantation. The findings in the authors’ own case series are also included at the bottom of the table.*1.

Ref. Case numbers, pathology (age range) Methods Results
15 N = 29 tumor and non-tumor patients (11 mo –16 yr) retrospective analysis of complication rate; comparison of tumor and non-tumor patients; adults and children. mFU: n.a.; d/o: n.a. more complications in tumor patients; complication rate in tumor patients comparable to CI, ca. 17%
16 aplasie/hypoplasia of CN VIII, N = 8 (1.5–18 yr); ossification of the cochlea, N = 3 (49–56 yr) retrospective analysis of hearing performance in non-tumor patients, mFU: 14 mo; d/o: 0 improved hearing over time;
mean CAP: 2.87; 3 max. CAP 4, 2 CAP 3
and 2 CAP 2, 1 CAP 1
17 aplasia/hypoplasia of CN VIII, N = 21 (mean for ABI: 3.41 ± 1.73 yr) retrospective analysis of failed CI followed by ABI. mFU: 5.2 yr d/o: 0 at 2 yr, 2 at 3 yr after CI: CAP 0–2, mean: 0.52 ± 0.68;
after ABI: CAP 4–7, mean: 4.33 ± 1.68;
CAP ≥ 5 = 42% (9/21)
18 aplasia/hypoplasia of CN VIII, N = 20 CI (1.3 ± 0.4 yr N = 20 ABI (1.4 ± 0.5 yr) retrospective analysis of two matched populations, ABI vs. CI. FU: up to 12 yr d/o: 0 at 1 yr, 11 at 3 yr Markedly better hearing outcome in the ABI group (CAP 3–7) than in the CI group (0–3).
CI at 2 yr CAP 0.7 ± 0.5
ABI at 2 yr 2.4 ± 1.3
CI at 8 yr 2 ± 0.8; ABI at 8 yr 6.1 ± 1
19 aplasia/hypoplasia of the auditory nerves; pediatric population overall, N = 64 (0.9–16 yr); aplasia/hypoplasia of CN VIII, N = 57 (0.9–10 yr) prospective study, with comparison across etiologies mFU: 6.9 yr d/o: 0 at 1 yr, 6 at 3 yr with cognitive impairment CAP: 1–5 (median 2);
without cognitive impairment CAP: 1–7, at 3 yr,
mean 4.47; CAP≥ 5 in 31% (20/64)
20 aplasia/hypoplasia of CN VIII, N = 36 (3–12 yr) retrospective study, FU: 1 yr d/o: 0 at 1 year all patients develop basic hearing ability; highly variable hearing outcomes;CAP 5 in 50%,
CAP 6 or higher in 16.6 %
21 aplasia/hypoplasia of CN VIII, N = 35 (1–5 yr) retrospective analysis. FU: 1 yr d/o: n.a. a majority achieved CAP 5; 12/35 (34%) achieved ≥ 50% open speech comprehension
22 aplasia/hypoplasia of CN VIII and/or cochlea N = 11 (2–18 yr) retrospective study of the effect of intraoperative E-BERA on hearing performance after ABI. FU: n.a.; d/o: n.a. E-BERA was helpful but an unreliable predictor of hearing performance; all 7 patients became able to hear after ABI; 5 could perceive LING Sounds*2, 2 scored 40% and 60% on a general sentence test
23 aplasia/hypoplasia of CN VIII, N = 12 (mean 43 mo) prospective study: the effect of floccular morphology on hearing performance after ABI. FU: 1 yr; d/o 0 at 1 yr no significant effect of floccular morphology was found; mean CAP at 1 yr 3.08
24 aplasia/hypoplasia of CN VIII, N = 11 (1–18 yr) retrospective study: long-term development of hearing and safety after ABI. mFU: 46.5 mo d/o: 3 at 1 yr 10/11 had improved hearing; mean CAP: 2.7; 2 of 10 patients (20%) achieved CAP 5
25 aplasia/hypoplasia of CN VIII, N = 12 (1.5–18 yr) retrospective study: speech perception, speech development and subjective quality of life after ABI; mFU: 3.05 yr; d/o: n.a. ABI had a beneficial effect on the quality of life, speech perception, and the development of hearing at a low level: LING Sounds*2, environmental noises, Cat 2 on the Early Speech Percept Test
26 cochlear ossification, N = 10 (3–56 yr) prospective study: ABI through an extended retrolabyrinthine approach in patients with postmeningitic deafness; mFU: 33.3 mo; d/o: 0 at 1 yr no auditory perception in 2 patients; 8/10 used ABI > 8 h per day and reported improved communication in everyday life. No open-set-speech recognition; 2/10 acheived closed-set hearing scores of 30 % and 40 %
27 aplasia/hypoplasia of CN VIII, N = 17 (8–64 mo) retrospective study of the utility of intraoperative
E-BERA at implantation;
FU: 1 yr; d/o: 0 at 1 yr		 E-BERA does not predict future hearing performance. CAP mean: 2.4 (1–4) at 6 mo. At 1 yr, 5 distinguished all 6 LING Sounds*2 without lip-reading
28 aplasia/hypoplasia of CN VIII, N = 24 (mean 4.1 yr) retro- and prospective single-center study: auditory and speech perception after ABI.
FU: 1 yr; d/o: 0 at 1 yr 		CAP mean 3.42
auditory and speech perception significantly better at 12 months
29 aplasia/hypoplasia of CN VIII, N = 11 (1–4 yr) retrospective study FU: 1–5 yr; d/o: n.a. CAP ≥ 5: 2/11 = 18%
Behr et al. aplasia/hypoplasia of CN VIII and/or cochlea, N = 38 (mean: 3.3 yr, 1.25–11 yr) retrospective analysis: congenitally deaf children with (+B) or without (–B) cognitive impairment:
mFU: 3.7 ± 1.4 yr (–B);
d/o: 0 at 1 yr, 8/29 at 3 yr (–B) 		72 % of -B patients (55% of the overall group)
acheived CAP 5–7 at 3 yr;
the mean CAP at 3 yr was 5.0 in the -B group and 3.14 in the +B group
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*1 Open speech comprehension is present when CAP ≥ 5. *2 LING Sounds are six sounds that are necessary for speech: a, i, o, sh, s, m. They are used together with pictures for initial auditory testing, particularly in children, and they serve as a basis for speech. Thus, they must be both produced and understood.

ABI, auditory brainstem implant; CAP, categories of auditory performance; CI, cochlear implant; CN VIII, eighth cranial nerve; d/o, dropout rate, i.e., the number of patients who were not followed up after a particular point in time; e-BERA, electrical brainstem evoked response audiometry; FU, follow-up duration; mFU, mean follow-up duration; mo, month(s); N, number of subjects; n.a., data not available or not stated; vs, versus; yr, year

Our patient cohort comprises 43 ABI operations in 41 children (two revisions) from 2009 to 2020. Data from 38 children were analyzed with the criteria described above. The mean age was 3.3 years (range, 1.25–11), and the mean follow-up duration (mFU) was 3.7 years (SD 1.4) – 2.7 (SD 1.2) years in the subgroup of children who had additional disabilities. The children’s parents or guardians gave their informed consent for the operations, subsequent follow-up visits, implant readjustments, and data analysis. Hearing outcomes were quantified on the widely accepted “categories of auditory performance” (CAP) scale (Box 2) (30). For statistical analysis, t-tests were used where applicable.

BOX 2. CAP categories*.

0) no awareness of environmental sounds

1) awareness of environmental sounds

2) responds to speech sounds

3) recognizes environmental sounds

4) discriminates at least two speech sounds

5) understands common phrases without lip-reading

6) understands conversation without lip-reading

7) can use the telephone

* categories of auditory performance after provision of an auditory implant

Results

The (Table) contains the main findings of the 15 studies, and of our own patient cohort, with respect to postoperative hearing performance, numbers of patients, age range, pathology, method, follow-up, and drop-out rates. There have been no prospective, randomized, controlled trials in this field—understandably, as these would be ethically problematic. The data are thus largely derived from retrospective cohort analyses. Three prospectively designed single-center studies (19, 23, 28) involved patients with varying pathologies who were followed up for as long as 12 years. The studies selected for the present analysis concerned a total of 366 congenitally deaf children who received an ABI.

Serious complications associated with ABI surgery in non-tumor patients included meningitis, cerebellar contusion, and local infection, in 1 of 29 patients each (15). No further infections were reported, and we did not encounter any in our own series. When major complications occurred, such as cranial nerve lesions, they were attributable to concomitant tumor removal (15). 17% of non-tumor patients with congenital deafness sustained minor complications, such as a wound seroma (in 4 of 29 patients) (15), which also occurs with CI (15). We expected ABI to be associated with a higher frequency of postoperative cerebrospinal fluid collections under the scalp than CI, because the electrode cable passes through the dura mater; five of our own patients developed this problem and could all be managed conservatively.

The duration of follow-up was variable, up to 12 years at the longest. Follow-up is most important in the year after implantation and the two years thereafter. At one year, a clear trend in the development of hearing was already apparent, and the hearing outcome could be almost definitively assessed at three years. It made a difference whether the children had an additional disability or a syndrome associated with deafness, e.g., CHARGE or Goldenhar syndrome: these patients responded markedly less well to treatment (19– 21). The timing of implantation was important as well: ABI before age 3 led to a better outcome (16, 19, 21, 24, 31). Similar results were obtained in our patient cohort (figure 2). The mean CAP was 5.5 (SD 0.75) in patients under age 3 and 4.73 (SD 0.64) in patients over age 3 (p < 0.05).

Figure 2.

Figure 2

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The effect of age on hearing outcome after ABI implantation in congenitally deaf children without other comorbidities. There is a clear correlation between early implantation and a better hearing outcome.

As shown in (Box 2) (30), CAP 4 is the lowest outcome score associated with the recognition and understanding of speech sounds and thus with the capacity for simple verbal communication. Persons with CAP 5 are capable of open language comprehension, i.e., correct understanding of previously unknown sentences without recourse to lip-reading.

The mean CAP score of all children with no further disability at their last evaluation, 1–3 years after implantation, was 3.57 (SD 1.04; median 3.33). There was a wide variation in mean CAP scores across studies, with a range of 2.4 to 5. For children with additional disabilities, CAP scores ranged from 2.0 to 3.14; no mean CAP scores were computed because of the sparseness of the data.

In our own cohort, the mean duration of follow-up (mFU) up to the last follow-up evaluation was 3.7 years, with mean CAP values of 5.05 (SD 0.80) without further disability and 3.14 (SD 0.66, p < 0.001) with additional disability (mFU 2.7 years in the latter patient group). The percentage of children with CAP 5 or better at last follow-up ranged from 18.2% to 72% across studies, with a mean of 38.24% (SD 18.68; median 34.28). The relatively large standard deviations are due to the variable follow-up intervals and large interindividual differences.

Discussion

Before the ABI era, CI was the only kind of surgical implant available to improve hearing. 1–10% of congenitally deaf children were doomed to permanent deafness, because they could not be helped with a CI. The first ABI procedures performed on children (13) were a controversial pioneer effort. As these patients did not require surgery for a tumor, the risk of an operation involving the brainstem was taken not to prolong survival, but rather just in the hope of generating auditory perceptions, whose potential functional utility could not be reliably predicted. Now that more experience has been gained with the technique, the probabilities of various outcomes a few years after implantation can be stated, but reliable prognostication is still impossible in the individual case. It is thus very important that these children’s parents or guardians should receive very comprehensive information before giving their informed consent to the procedure.

The available evidence must be assessed critically, in view of the limitations mentioned in the Methods section. The available studies are mostly retrospective, and hearing outcomes are not always recorded at the same time points, often at temporal intervals. In many publications, postoperative hearing rehabilitation are not explained in detail, and intraoperative problems, exclusion criteria, and drop-outs are not always addressed.

Nevertheless, the results show that this method led to a beneficial hearing outcome, up to the capacity for open speech comprehension, in 38% of cases. Moreover, the rate of complications was low in non-tumor patients.

The main complications were wound seromas, which arose in 4 of 29 patients (15), and cerebrospinal fluid (CSF) collections under the scalp. These problems are attributable to the passage of the ABI electrode cable through the dura mater, despite intensive intraoperative efforts to seal any potential sites of leakage, along with behaviors on the part of the treated children—crying, screaming, Valsalva maneuvers—that transiently raise the intracranial pressure and thereby promote the egress of CSF. The fluid collections were treated with puncture and pressure dressings where necessary. Most of the severe complications (32.3%), cranial nerve deficits in particular, arose in patients who were concomitantly undergoing tumor resection (15). The complication rates of ABI-only procedures were comparable to those of CI procedures (17% in both cases). Nonetheless, intracranial procedures generally carry a higher risk of severe complications. The consensus paper on ABI (32) therefore places an emphasis on the general and specific surgical experience of the implantation team, which is particularly important if a revision operation is needed. In rare cases, the stimulating electrode may become dislocated, or it may cease to function for technical reasons, e.g., after a fall. Determining the indications for revision is a difficult matter, and revisions are also more difficult to perform than primary operations, but they are highly effective in some cases (33). Robust study findings from large cohorts are not yet available.

The implants are magnetic resonance imaging- (MRI-) compatible in principle, but only if restricted MR sequences are used. Implant-related artefact that impairs the interpretability of the MRI is found exclusively in the posterior cranial fossa on the side of the implant. The remainder of the head, and the rest of the body, can be safely and usefully studied with 1.5 T MRI (34, 35). This option is especially important for children who have other medical conditions in addition to their deafness.

Bilateral ABI in children, analogously to bilateral CI (36), is also a matter of current discussion; some authors advocate it (37– 39). Bilateral ABI would enable exploitation of the full capacity of the auditory pathways, maximizing the input of information to the brain. It has been shown to be helpful in some patients with NF-2 (38, 39). In analogy to the improved cognitive performance after bilateral CI (e5), one may expect that bilateral ABI will yield better outcomes than unilateral ABI. This will only become possible if it is reimbursed by health-insurance carriers.

It has been found that practically all children treated with ABI develop the ability to hear, to a greater or lesser extent. Just over one-third (38%) of non-syndromic children achieved open language comprehension. Children with other disabilities in addition to deafness had a markedly worse outcome in all studies in which this question was addressed. Their CAP scores ranged from 2 to 3 (14), and they did not achieve open language comprehension. Nevertheless, they did benefit from auditory perception, in that they became able to perceive environmental sounds and to orient themselves better, as well as to use sounds to support nonverbal communication. Like hearing after CI (e5), hearing after ABI positively affects these children’s cognitive, mental, and social development. ABI has been found to improve children’s quality of life (25).

The average CAP scores and the percentages of open speech comprehension varied widely, both across studies and interindividually. Precise implantation, with intensive use of electrophysiological methods (electrical brainstem response audiometry, E-BERA), seems necessary for the best possible outcome. Precise placement leads to better pitch recognition, lower electrical stimulation intensity, and higher stimulation frequency for each individual electrode. These parameters are positively correlated with better open speech comprehension (40).

Hearing also improved over time, as described in almost all studies (15– 29). Among our patients, CAP scores improved from 0 to an average of 5 (implying open speech comprehension) after 24–36 months of ABI hearing experience. Children whose deafness was in the setting of a congenital syndrome achieved only CAP 3 (p < 0.001).

An important finding of the studies analyzed here, and of our own experience as well, is that hearing outcomes become significantly worse (p < 0.05) with increasing age at the time of implantation, from age 3 onward, even though the patients are still helped by ABI to some extent (figure 2). Some patients can still achieve open speech comprehension even after receiving an ABI after age 3. An analogous finding is already known from CI (31) and has to do with the development, plasticity, and maturation of the auditory pathway.

In view of these findings, another important aspect becomes apparent. CI has generally been preferred over ABI until now in cases where the presurgical diagnostic evaluation, with its limitations, does not conclusively reveal whether an auditory nerve is hypo- or aplastic, or whether the anatomy of the inner ear, which is often dysmorphic, would still be compatible with CI. Such decisions should be taken by an experienced CI otosurgeon as early as possible. If the patient, after receiving a CI, makes no discernible or only minimal progress, then an ABI should be considered as soon as possible, in order to promote the early development of the auditory pathway and the integration of neural functioning. Parents should be informed about this strategy from the very beginning of the otosurgical decision-making process. Studies from 2013 and 2014 (17, 18) show that early ABI after failed CI can markedly improve hearing if performed without an excessive delay in between. Parents may be understandably reluctant to have their child undergo a second operation, and a brain operation at that; yet studies have shown (15, 19, 21) that ABI is both effective and very safe. It can also be pointed out that, if no ABI is performed in such cases, then the preceding CI operation will have had no value either as a diagnostic test or as a treatment.

Intraoperative cochlear stimulation with electrical brainstem response audiometry (e6, e7) is a recently introduced aid for the determination whether a CI or ABI would be more beneficial to the patient, if other (presurgical) diagnostic tests cannot reliably answer this question. This technique requires a cochleostomy through which an atraumatic test probe is inserted. If stimulation yields positive responses, CI surgery proceeds as planned; if not, an ABI is indicated and the operation can be extended to auditory brainstem implantation.

It is clear that, in diagnostically difficult cases, the decision between primary CI and ABI must always be made by an experienced team, no matter whether it is made preoperatively or during the surgical procedure. The early recognition of a poor therapeutic response to a CI is crucial in this regard (17, 18). ABI after failed CI should be carried out in the child’s second year of life if possible, but no later than the third.

In conclusion, although ABI is not yet as widely known and established for children as it is for adult tumor patients, it is indeed a dependable therapeutic means of restoring hearing in special cases where CI is not an option.

Supplementary Material

eMethods

Patient selection and preoperative diagnostic testing

Neonatal auditory screening (e1) is widely performed and provides the first indication of a hearing problem, which must then be evaluated with further otological and audiological studies. Imaging should be carried out with high-resolution conventional or cone-beam computerized tomography of the petrous bones, and with magnetic resonance imaging employing sequences of the highest possible resolution to visualize the cranial nerves. These studies suffice to establish a diagnosis in 95% of cases. If it is hard to distinguish between hypoplasia and aplasia of the auditory nerves, a meticulous imaging study of the cochlear region at the fundus of the internal acoustic meatus can be of assistance. In cases where the diagnosis remain unclear, CI implantation is now recommended as the next step, as long as the operation is technically possible. If CI implantation yields no benefit for hearing, an ABI should be implanted at the earliest opportunity. The indication for an ABI is a team decision in all cases, requiring the combined expertise of neuro- and otosurgeons, neuroradiologists, and audiologists. An essential component of the decision-making process is the provision of full information to parents and caregivers, including the communication of realistic prospects of success.

Surgical technique

The operation is performed with the patient supine, under totally intravenous anesthesia (TIVA), and without muscle relaxation to enable intraoperative neuromonitoring. The head is turned to the side opposite the operative site and fixed in a Mayfield clamp. Neuromonitoring comprises somatosensory evoked potentials (SSEP), facial nerve function, and electrical brainstem evoked response audiometry (E-BERA).

A retrosigmoid craniotomy is performed with reimplantation of the bone flap. The lateral recess of the fourth ventricle is exposed and opened with microneurosurgical technique. We have encountered numerous large vessels at the implantation site in 75% of cases. The lateral recess of the fouth ventricle is often closed or partly closed (e2); this can make the implantation much more difficult, because the choroid plexus cannot be seen for surgical orientation. Inadequate or incorrectly located opening of the (supposed) lateral recess can easily lead to faulty implantation and brainstem injury. The glossopharyngeal nerve is a constant anatomical landmark that can show the way to the lateral recess.

A quadripolar test stimulation probe is used to check whether the cochlear nucleus is capable of auditory stimulation in principle; this is confirmed by the recording of reproducible E-BERA responses. The same technique is used to identify the optimal stimulation site with the 5 × 3.5 mm stimulating probe on the floor of the lateral recess of the fourth ventricle. The permanent stimulating electrode, which has the same surface area and incorporates 12 stimulating channels, is then implanted and fixed at this site. In recent years, it has been found that, in addition to fibrin glue, teflon as used in the Jannetta procedure (e3) is very useful for this purpose (e4). The titanium case containing the extracranial electronic components of the system is implanted subcutaneously in a bony bed behind the ear. After surgery, the patient is kept in the intensive care unit for 1–2 days.

Audiological follow-up examinations are performed at 1, 3, 6, and 12 months and at longer intervals thereafter. Experience has shown that patients with prelingual deafness who become able to hear only by electrical stimulation need several years to learn to hear, with much individual variation, and with variable outcomes, which also depend on the underlying disease or syndrome (if present). The same holds for the acquisition of speech. These children, therefore, need longer monitoring and more frequent adjustment of the electronic stimulating parameters.

Questions on the article in issue 9/2022: Auditory Brainstem Implants—Hearing Restoration in Congenitally Deaf Children.

The submission deadline is 3 March 2023. Only one answer is possible per question.

Please select the answer that is most appropriate.

Question 1

What does ABI stand for?

  1. advanced brainstem implant

  2. auditory brainstem implant

  3. auditory bilateral implant

  4. adapted brainstem implant

  5. advanced bilateral implant

Question 2

With what CAP scores can a patient be said to have open speech comprehension, i.e., to understand sentences without resorting to lip-reading?

  1. CAP ≤ 2

  2. CAP ≥ 3

  3. CAP ≤ 4

  4. CAP ≥ 5

  5. CAP ≥ 7

Question 3

What method should be used to ensure the maximal precision of implantation of an ABI?

  1. electrical brainstem evoked response audiometry (E-BERA)

  2. automatic brainstem response audiometry (A-BERA)

  3. electrical cochlear nerve response audiometry (E-CNRA)

  4. automated cochlear nerve response audiometry (A-CNRA)

  5. autotmated cochlear nucleus response audiometry (A-CNRA)

Question 4

What percentage of congenitally deaf children were doomed to remain deaf, i.e., had no available therapeutic options for hearing restoration, until ABI became available?

  1. 0.5–1 %

  2. 1–10 %

  3. 10–20 %

  4. 20–40 %

  5. 50–70 %

Question 5

Where are ABI electrodes inserted?

  1. in the cochlea

  2. along the cochlear nerve

  3. in the auditory cortex

  4. in the middle ear

  5. in the cochlear nucleus

Question 6

What is the best age for the implantation of an ABI in a congenitally deaf child?

  1. the first six months after birth

  2. in the third year of life at latest

  3. from age 3 onward

  4. before age 9

  5. from age 10 onward

Question 7

Hypoplasia or aplasia of which cranial nerve may be an indication for ABI implantation?

  1. CN I

  2. CN II

  3. CN IV

  4. CN V

  5. CN VIII

Question 8

As determined from a review of all relevant studies taken together, what is the likelihood that a child without any other type of disability besides deafness will be able to achieve open speech comprehension after receiving an ABI?

  1. approximately 14%

  2. approximately 28%

  3. approximately 38%

  4. approximately 49%

  5. approximately 72%

Question 9

In what anatomical region can a unilaterally implanted ABI produce an MRI artefact?

  1. in the posterior cranial fossa on the side of the implant

  2. in the posterior cranial fossa on both sides

  3. at the implant site and within a distance of 1 cm from it

  4. all over the head

  5. only in the brainstem region

Question 10

In general, how long after ABI implantation in a child is the hearing outcome nearly the same as the final outcome?

  1. after approximately six months

  2. after approximately one year

  3. after approximately two years

  4. after approximately three years

  5. after approximately ten years

Acknowledgments

Translated from the original German by Ethan Taub, M.D.

Footnotes

Conflict of interest statement

Prof. Behr has received support for database research, consulting fees, lecture honoraria, and reimbursement of meeting participation fees and travel expenses from MedEl, Innsbruck, Austria.The remaining authors state that they have no conflict of interest.

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Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

eMethods

Patient selection and preoperative diagnostic testing

Neonatal auditory screening (e1) is widely performed and provides the first indication of a hearing problem, which must then be evaluated with further otological and audiological studies. Imaging should be carried out with high-resolution conventional or cone-beam computerized tomography of the petrous bones, and with magnetic resonance imaging employing sequences of the highest possible resolution to visualize the cranial nerves. These studies suffice to establish a diagnosis in 95% of cases. If it is hard to distinguish between hypoplasia and aplasia of the auditory nerves, a meticulous imaging study of the cochlear region at the fundus of the internal acoustic meatus can be of assistance. In cases where the diagnosis remain unclear, CI implantation is now recommended as the next step, as long as the operation is technically possible. If CI implantation yields no benefit for hearing, an ABI should be implanted at the earliest opportunity. The indication for an ABI is a team decision in all cases, requiring the combined expertise of neuro- and otosurgeons, neuroradiologists, and audiologists. An essential component of the decision-making process is the provision of full information to parents and caregivers, including the communication of realistic prospects of success.

Surgical technique

The operation is performed with the patient supine, under totally intravenous anesthesia (TIVA), and without muscle relaxation to enable intraoperative neuromonitoring. The head is turned to the side opposite the operative site and fixed in a Mayfield clamp. Neuromonitoring comprises somatosensory evoked potentials (SSEP), facial nerve function, and electrical brainstem evoked response audiometry (E-BERA).

A retrosigmoid craniotomy is performed with reimplantation of the bone flap. The lateral recess of the fourth ventricle is exposed and opened with microneurosurgical technique. We have encountered numerous large vessels at the implantation site in 75% of cases. The lateral recess of the fouth ventricle is often closed or partly closed (e2); this can make the implantation much more difficult, because the choroid plexus cannot be seen for surgical orientation. Inadequate or incorrectly located opening of the (supposed) lateral recess can easily lead to faulty implantation and brainstem injury. The glossopharyngeal nerve is a constant anatomical landmark that can show the way to the lateral recess.

A quadripolar test stimulation probe is used to check whether the cochlear nucleus is capable of auditory stimulation in principle; this is confirmed by the recording of reproducible E-BERA responses. The same technique is used to identify the optimal stimulation site with the 5 × 3.5 mm stimulating probe on the floor of the lateral recess of the fourth ventricle. The permanent stimulating electrode, which has the same surface area and incorporates 12 stimulating channels, is then implanted and fixed at this site. In recent years, it has been found that, in addition to fibrin glue, teflon as used in the Jannetta procedure (e3) is very useful for this purpose (e4). The titanium case containing the extracranial electronic components of the system is implanted subcutaneously in a bony bed behind the ear. After surgery, the patient is kept in the intensive care unit for 1–2 days.

Audiological follow-up examinations are performed at 1, 3, 6, and 12 months and at longer intervals thereafter. Experience has shown that patients with prelingual deafness who become able to hear only by electrical stimulation need several years to learn to hear, with much individual variation, and with variable outcomes, which also depend on the underlying disease or syndrome (if present). The same holds for the acquisition of speech. These children, therefore, need longer monitoring and more frequent adjustment of the electronic stimulating parameters.

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