Discussion

Over the last decade, balloon dilatation of the Eustachian tube has emerged as a promising treatment for Eustachian tube dysfunction. The safety and utility of the procedure continues to be an area of active research. Eustachian tube balloon dilatation devices were approved by the Australian Department of Health in 2016. To our knowledge, since approval, no prospective study has analysed the use of Eustachian tube balloon dilatation in an Australian population. This study's results demonstrate significant improvements in the Eustachian Tube Dysfunction Questionnaire-7 scores of patients with normal middle ears for at least 12 months following Eustachian tube balloon dilatation. The rate and extent of score improvement was similar to those reported in other publications.^{Reference Hwang, Kok and Walton8,Reference Huisman, Verdam, Stegeman and de Ru10,Reference Froehlich, Le, Nguyen, McRackan, Rizk and Meyer11} Our results highlight the utility of Eustachian tube balloon dilatation in treating symptomatic patients that do not have objective evidence of negative middle-ear pressure, and therefore do not strictly meet dilatory Eustachian tube dysfunction diagnostic criteria.^{Reference Schilder, Bhutta, Butler, Holy, Levine and Kvaerner4,Reference Tucci, McCoul, Rosenfeld, Tunkel, Batra and Chandrasekhar12} This study also demonstrates the strong post-operative safety profile of Eustachian tube balloon dilatation, which is consistent with current literature.^{Reference Hwang, Kok and Walton8,Reference Huisman, Verdam, Stegeman and de Ru10,Reference Meyer, O'Malley, Schlosser, Soler, Cai and Hoy14,Reference Poe, Anand, Dean, Roberts, Stolovitzky and Hoffmann15}

The pre-operative middle ear may influence Eustachian Tube Dysfunction Questionnaire-7 scores following Eustachian tube balloon dilatation. A retrospective review of 62 patients by Cheng et al. assessed Eustachian Tube Dysfunction Questionnaire-7 scores six months to two years following Eustachian tube balloon dilatation.^{Reference Cheng, Saxby, Jufas, Kong and Patel17} The authors demonstrated that 83.9–100 per cent of patients without middle-ear disease had improvements in scores pre- and post-Eustachian tube balloon dilatation. Our data are similar to these figures. Additionally, Cheng et al. found that a subgroup of patients with middle-ear pathology had inferior improvements in Eustachian Tube Dysfunction Questionnaire-7 scores.^{Reference Cheng, Saxby, Jufas, Kong and Patel17} These preliminary findings may suggest that middle-ear disease can reduce the extent of symptom improvement post-Eustachian tube balloon dilatation. However, other studies have demonstrated that the presence of middle-ear pathology, such as chronic otitis media, independently predicts a greater likelihood of Eustachian Tube Dysfunction Questionnaire-7 score normalisation (Eustachian Tube Dysfunction Questionnaire-7 score < 2.1) following Eustachian tube balloon dilatation.^{Reference Yang, Alonso, Ishiyama, Gopen, Suh and Wang18} Limited studies have compared outcomes of Eustachian tube balloon dilatation in those with and without middle-ear disease. Further research is warranted to better understand predictors of symptom improvement and the effect of middle-ear status on post-operative Eustachian Tube Dysfunction Questionnaire-7 scores.

No patients in our study had tympanic membrane retraction. One patient (6.7 per cent) had a sustained type C tympanogram, pre- and post-Eustachian tube balloon dilatation. The remaining 93.3 per cent of participants, with no objective evidence of negative middle-ear pressure, all had statistically significant improvements in Eustachian Tube Dysfunction Questionnaire-7 scores post-operatively. These findings are consistent with current studies and underline the idea that symptomatic dilatory Eustachian tube dysfunction can be treated with balloon dilatation, regardless of normal tympanometry or otoscopic examination.^{Reference Xiong, Liang, Zhang, Xu, Ou and Chen13}

Using conventional interpretation where type A tympanograms are −100 to +25 daPa, type B tympanograms have no peak pressure and type C tympanograms are less than −100 daPa, tympanometry may lead to underdiagnosis of Eustachian tube dysfunction.^{Reference Parsel, Unis, Souza, Bartley, Bergeron and Master19} Additionally, the test may be unreliable when used to monitor the efficacy of Eustachian tube balloon dilatation or identify patients that may benefit from the procedure.^{Reference Froehlich, Le, Nguyen, McRackan, Rizk and Meyer11,Reference Meyer, O'Malley, Schlosser, Soler, Cai and Hoy14,Reference Yang, Alonso, Ishiyama, Gopen, Suh and Wang18–Reference Anand, Poe, Dean, Roberts, Stolovitzky and Hoffmann21} Although our data suggest Eustachian tube balloon dilatation may be performed on the sole basis of subjective measures, caution must be taken as this approach could greatly expand the number of surgical candidates. It is likely that a combination of subjective and objective measures is optimal to determine eligibility for Eustachian tube balloon dilatation and ongoing assessment of disease progression.

Several balloon catheter devices exist for dilatation of the Eustachian tube. These include the XprESS ENT Dilation System, the Bielefield system (Spiggle and Theis, Overath, Germany) and the Aera balloon catheter (Acclarent, Irvine, California USA). Variations exist amongst devices and surgical techniques, such as balloon sizes, inflation pressures, duration of inflation and the angle of catheter insertion.^{Reference Hwang, Kok and Walton8,Reference Froehlich, Le, Nguyen, McRackan, Rizk and Meyer11,Reference Schubert, Wilfling, Paasche, Lenarz, Schümann and Grabow22} For example, a prospective analysis of Eustachian tube balloon dilatation by Poe et al. used a shorter catheter (16 mm vs 18 mm) and inflated the device for less time (1 minute vs 2 minutes) in comparison to our approach.^{Reference Poe, Silvola and Pyykkö23} The subtle differences in operative techniques and device characteristics may play a significant role when evaluating Eustachian tube balloon dilatation efficacy, however, this role is yet to be studied.

Current literature emphasises that care must be taken to avoid catheter advancement into the bony Eustachian tube, in order to minimise the risk of carotid artery injury on balloon inflation.^{Reference Abdel-Aziz, Schröder, Lehmann, Gehl, Ebmeyer and Sudhoff24} In our study, the dilation device was bent at the 20 mm mark for Eustachian tube access, preventing overly deep catheter insertion. Serious, albeit rare complications, such as carotid artery dissection and stroke, surgical emphysema, and the development of patulous Eustachian tube dysfunction, following Eustachian tube balloon dilatation have been reported in the literature.^{Reference Merrill, Patel, Pool, Dornhoffer and Saadi25}

There are some limitations to this study. Given our small sample size and short-term follow up, further research is warranted to investigate long-term Eustachian tube balloon dilatation outcomes in larger Australian cohorts. Our post-operative data must be interpreted with caution as the Eustachian Tube Dysfunction Questionnaire-7 solely relies on subjective measures, which are difficult to validate against objective post-Eustachian tube balloon dilatation tests. The development of inner-ear hydrops and upper respiratory tract infection in patients during the follow-up period likely confounded the interpretation of pure tone audiometry results. Additionally, patients were free to use medical interventions (such as intranasal corticosteroids) following Eustachian tube balloon dilatation. Although these interventions have a limited role in Eustachian tube dysfunction management, this may have confounded study data.^{Reference Llewellyn, Norman, Harden, Coatesworth, Kimberling and Schilder6,Reference Mehta, Ma, Nguyen, McRackan, Meyer and Lambert7} Nevertheless, this study's prospective design had the advantage of longitudinally tracking changes in each patient's subjective and objective measures post-operatively.