Hearing and hearing rehabilitation after obliteration of troublesome mastoid cavities

It is well known that chronically draining and troublesome canal wall down mastoidectomy cavities (CWDMCs) have a profound negative effect on those inflicted [1‐3]. Due to chronic drainage, conventional hearing aids (CHAs) are often not tolerated. Alternatives such as bone conduction devices (BCDs) and active middle ear implants (MEIs) have been propagated. However, functional hearing and speech discrimination of these devices are inferior to these criteria in CHAs [4]. Revision surgery and obliteration of CWDMCs with reconstruction of the ear canal have shown to ultimately address troublesome cavities and result in high rates of dry ears [5‐11]. Most publications state that in case of hearing thresholds post-operatively, a conductive or mixed hearing loss remains present. The feasibility to rehabilitate hearing post-operatively is, therefore, important and essential when counselling and selecting patients for such surgery. Unfortunately, this topic seems to be almost completely neglected in the available literature regarding revision CWDMC surgery [12]. Tolerance of CHAs can potentially be restored after surgery [12]. We evaluated various outcomes related to hearing in subjects who underwent revision CWDMC surgery including obliteration of the mastoid cavity to determine two relevant topics: first, which hearing thresholds are achieved after surgery; second, to which extent is successful CHA rehabilitation and tolerance achieved post-operatively.

Instable CWDMCs have been reported in 10 up to 40% of all cases [1, 5]. We report our outcomes of revision surgery including obliteration of the mastoid bowl of troublesome CWDMCs. High rates of dry, stable, and disease-free ears were achieved with comparable results to those reported in the literature [14‐16]. No residual disease was found in the obliterated area during MRI follow-up. We strongly advocate long-time follow-up with MRI to detect residual disease after obliteration. Our results strengthen the hypothesis that revision surgery and obliteration of troublesome CWDMCs is the preferred treatment modality for troublesome CWDMCs [17]. Despite the fact that we only reported on revision surgery, the surgical technique can also be used in rare primary cases in which the posterior ear canal needs to be removed during surgery. Yung et al. published earlier about this kind of surgery in both primary and revision cases [8]. Like every operation, revision surgery with obliteration has its learning curve. We presented all patients who were operated using this technique in our centre, so a learning curve is included in our data. Reduction in operating time and complication rate was seen after 20 patients (unpublished data). Vartiainen et al. showed that more experience is important in reduction of revision surgery rate and healing time in otological surgery [18]. Stankovic et al. confirmed these findings when they compared the early and late surgical experience of the same surgeon [19].

It remains debatable whether hearing thresholds of canal wall down mastoidectomy are worse when compared to canal wall up cases [20]. Ossiculoplasties and revision surgery in canal wall down status have shown to have unfavorable results when compared with canal wall up status [21, 22]. Although hearing thresholds improved significantly in our investigated cohort, they are small and are, therefore, considered clinically irrelevant. This is in concordance with the previous literature demonstrating that hearing loss (mostly of a mixed type) remains present after such surgery [12, 16]. We observed a significant improvement of the various types of ossicular chain replacements used. This finding shows that performing ossiculoplasty is advised even in these small middle ear spaces. Perhaps, the aeration of the middle ear space is restored/improved after chronic inflammation ceases and, therefore, results in a better hearing threshold. The usually reported superiority of PORP over TORP could not be supported [23]. A possible explanation could be that the middle ear space is still limited after surgery and the eardrum often retracts in these troublesome cases making any type of reconstruction more difficult. Perhaps, stapes fixation is more present in troublesome cavities due to prolonged inflammation. As these data were not present in our retrospective study cohort, we were not able to evaluate the hearing results in those patients without a bad middle ear status and/or fixed stapes. These details could add valuable information to pre-operative counselling in managing expectations on post-operative hearing.

Although hearing thresholds improved for the group as a whole, we also demonstrate that the group eligible for hearing rehabilitation remains nearly unchanged. In addition, one should note that some individuals demonstrate a deterioration in hearing thresholds and, therefore, the need for hearing rehabilitation remains pivotal.

Troublesome cavities are likely to result in a difficulty to wear CHAs. Other factors such as: a large post-operative meatus, altered resonance frequency of the ear canal, and inadequate aeration due to occlusion all complicate CHA usage in CWDMCs [12, 24]. One would expect that this topic would have been investigated thoroughly. Yet, it seems that, to date, only one report describing 20 cases descriptively is available [12]. From this manuscript, it was concluded that revision surgery including obliteration of the mastoid bowl of troublesome CWDMCs makes CHA usage feasible and generally well tolerated. The potential benefit of enabling CHA rehabilitation after this type of surgery was mentioned by others but not investigated [14, 16]. Our large cohort demonstrates a significant increase of CHA usage and tolerance after surgery. We also believe that contralateral hearing threshold should be considered when evaluating CHA usage. Therefore, it should be considered in pre-operative counselling.

We found a slight shift in BCD rehabilitation toward CHA. Our data suggest that one should consider to primarily perform revision surgery in troublesome cavities to enable CHA usage before advising BCD. We potentially introduce an inclusion bias as we performed our analysis regarding CHA usage and tolerance in a selected subgroup of the total cohort as this subgroup of patients had a complete data set. We still feel that this subgroup is representable of the whole group. In our center, a CHA is the favored device for hearing rehabilitation due to lower costs and no need for further intervention. However, some have advocated a BCD in large ABGs to perform better in case of speech recognition [25, 26]. Combination of SubTotal Petrosectomy (STP) with a BCD could, therefore, be another option in chronically draining CWDMCs [27]. Unfortunately, we often see that the operated ear has worse bone conduction level compared to the contralateral ear. Sound from a BCD would be heard in the contralateral ear which results in only contralateral hearing. Providing in the possibility to wear a CHA can result in bilateral hearing in these cases.

For counselling of an individual patient, we now can present the chance of hearing threshold change in regard to CHA indication (within the Dutch reimbursement system) (Fig. 2). One should be aware of managing expectations of post-operative hearing as only 12% of the patients were operated out of the CHA indication group. We also tried to make a pre-operative model using contralateral hearing threshold to predict the final hearing rehabilitation outcome of the operated ear, but cluster analysis of our data unfortunately did not support a viable model. It seems that the choice to use a CHA is dependent on more factors than hearing threshold alone.

Our study supports and strengthens the hypothesis that revision surgery and obliteration of CWDMCs enables successful CHA rehabilitation post-operatively. Hearing threshold improves significantly after such surgery, but the need for hearing rehabilitation remains necessary in most cases. Performing ossiculoplasty in troublesome CWDMCs seems to be beneficial. We supply a counselling diagram of the expected need for CHA rehabilitation postoperatively.