Discussion

The eustachian tube in adults is approximately 37.5 mm long, and consists of bony and cartilaginous portions, extending from the middle-ear cleft to the nasopharynx.Reference Cummings ¹⁵ It has several physiological functions, which include pressure equalisation, drainage of the middle ear and protection from the nasopharyngeal environment.Reference Cummings ¹⁵

Poor or inadequate eustachian tube function causes eustachian tube dysfunction, which is a physiological disorder that may be temporary and spontaneously resolving.Reference Adil and Poe ¹ Chronic eustachian tube dysfunction occurs when the dysfunction lasts for over three months; it is a poorly defined clinical entity, with variable diagnostic criteria based on clinical history, otoscopy and tympanogram results.Reference Norman, Llewellyn, Harden, Coatesworth, Kimberling and Schilder ² It can be a difficult pathology to manage, with debilitating symptoms affecting quality of life; current conventional treatments may not be effective.

A recent health technology assessment found that there was minimal evidence of effectiveness for current medical and surgical interventions, including nasal decongestants, topical and systematic corticosteroids, antihistamines, mechanical devices, and nasal surgery.Reference Norman, Llewellyn, Harden, Coatesworth, Kimberling and Schilder ² It identified only one study with a low risk of bias, a randomised, controlled trial, which found no improvement in eustachian tube dysfunction symptoms after six weeks of nasal steroids.Reference Gluth, McDonald, Weaver, Bauch, Beatty and Orvidas ¹⁶

In cases of chronic eustachian tube dysfunction refractory to conventional treatment, multiple insertions of ventilation tubes may be required. This can cause persistent perforation requiring dry ear precautions and/or myringoplasty. As a potential solution for this, eustachian tube balloon dilation (proposed as a treatment for chronic eustachian tube dysfunction) aims to ventilate and drain the middle ear by improving the physiological function of the eustachian tube.Reference Ockermann, Reineke, Upile, Ebmeyer and Sudhoff ^{6 ,} Reference Poe, Silvola and Pyykko ¹⁰

The initial papers by Ockermann et al. in 2010Reference Ockermann, Reineke, Upile, Ebmeyer and Sudhoff ^{5 ,} Reference Ockermann, Reineke, Upile, Ebmeyer and Sudhoff ⁶ and Poe et al. in 2011Reference Poe, Silvola and Pyykko ^{10 ,} Reference Poe and Hanna ¹⁷ focused on establishing the safety of eustachian tube balloon dilation by performing both cadaveric and clinical studies. The cadaveric studies revealed no evidence of fractures to the cartilaginous or bony lumen, and no damage to the internal carotid artery. Only minor mucosal lacerations at the eustachian tube orifice were noted.Reference Ockermann, Reineke, Upile, Ebmeyer and Sudhoff ^{5 ,} Reference Poe and Hanna ¹⁷

Since then, numerous prospective cohort studies have examined the role of eustachian tube balloon dilation. Pooled data analysis in this review revealed that the ability to perform a Valsalva improved from 8 per cent pre-eustachian tube balloon dilation to 72 per cent post-eustachian tube balloon dilation, while the rate of type A tympanograms increased from 5 to 61 per cent. Further statistical analysis is inappropriate because of the heterogeneity of the inclusion criteria, techniques and outcome measures in the papers included in this review.

The mechanisms by which eustachian tube balloon dilation improves eustachian tube function is an area of ongoing research, but appear to include both anatomical dilation of the cartilaginous eustachian tube and the initiation of histopathological changes.Reference Kivekas, Chao, Faquin, Hollowell, Silvola and Rasooly ⁷ A recent study examining the histopathological changes associated with eustachian tube balloon dilation found that the balloon had a crushing effect on inflammatory cells within the eustachian tube mucosa while sparing the basal layer, rapidly replacing the inflamed mucosa with a fibrous scar.Reference Kivekas, Chao, Faquin, Hollowell, Silvola and Rasooly ⁷

One major concern of eustachian tube balloon dilation is the theoretical risk of injury to a dehiscent carotid artery running adjacent to the bony eustachian tube;Reference Abdel-Aziz, Schroder, Lehmann, Gehl, Ebmeyer and Sudhoff ¹⁸ hence, computed tomography (CT) of the petrous temporal bones was routinely performed as a part of the pre-operative investigations. Abdel-Aziz et al.Reference Abdel-Aziz, Schroder, Lehmann, Gehl, Ebmeyer and Sudhoff ¹⁸ conducted a retrospective analysis of petrous temporal bone CT scans of 285 patients who underwent eustachian tube balloon dilation. The authors found that 24 eustachian tube balloon dilations were performed in 17 patients with carotid canal dehiscence, with no complications or technical difficulties. This suggests that routine petrous temporal bone CT is not indicated before eustachian tube balloon dilation.

Another area of concern for eustachian tube balloon dilation is its use in the paediatric population, where middle-ear disease is more prevalentReference Jenckel, Kappo, Gliese, Loewenthal, Lorincz and Knecht ¹⁹ because of a shorter, more horizontal eustachian tube, with a lumen that is less than half the size of an adult eustachian tube.Reference Cummings ¹⁵ Currently, there are 2 retrospective case series that describe eustachian tube balloon dilations in 33 children aged 5–14 years (mean, 9 years),Reference Jenckel, Kappo, Gliese, Loewenthal, Lorincz and Knecht ¹⁹ and in 66 children aged 4–14 years (mean, 8 years),Reference Maier, Tisch and Maier ²⁰ with no reported complications and an improvement in middle-ear symptoms.

Despite the aforementioned results of this review, BluestoneReference Bluestone ²¹ suggested, in 2014, that the efficacy of eustachian tube balloon dilation remains unverified. This is because the majority of studies have small numbers of patients, limited follow up, a weak definition of ‘cure’ and do not evaluate the direct effect of eustachian tube balloon dilation on eustachian tube function. This suggests that a more rigorous clinical trial is required.

Any future clinical trial on eustachian tube balloon dilation would require strict inclusion criteria and should use commonly accepted outcome measurements. The authors of this paper believe that the appropriate outcome measures should include: clinical measures of otoscopy and the ability to perform a Valsalva manoeuvre; objective measures of tympanometry, audiometry and/or tubomanometry; and patient-reported measures acquired using a verified questionnaire such as the seven-item Eustachian Tube Dysfunction Questionnaire.Reference McCoul, Anand and Christos ²²

Our evaluation of the evidence for eustachian tube balloon dilation is limited by the quality of the papers included, as the highest level of evidence available is prospective case series. Three papersReference Ockermann, Reineke, Upile, Ebmeyer and Sudhoff ^{6 ,} Reference Jurkiewicz, Bien, Szczygielski and Kantor ^{8 ,} Reference Poe, Silvola and Pyykko ¹⁰ had less than 20 patients, and only 2 papersReference Schroder, Reineke, Lehmann, Ebmeyer and Sudhoff ^{11 ,} Reference Silvola, Kivekas and Poe ¹² had an average follow-up period longer than 12 months. Also, there were significant variations in terms of the assessment of patients, indications for eustachian tube balloon dilation and assessment of outcomes.

The diagnosis, investigations and indications for eustachian tube balloon dilation were not standard across the papers. This standardisation is in part limited by the subjective clinical nature by which chronic eustachian tube dysfunction is diagnosed. Although all studies reviewed used clinical history, otoscopy and tympanometry to diagnose chronic eustachian tube dysfunction, the indications for eustachian tube balloon dilation differed. In some papers, eustachian tube dysfunction refractory to conventional treatment was required, while in others a diagnosis of chronic eustachian tube dysfunction was sufficient. In future evaluations of eustachian tube balloon dilation, diagnostic criteria that include objective measurements of tympanometry and the seven-item Eustachian Tube Dysfunction Questionnaire should be used.

In addition, the technique of eustachian tube balloon dilation differed across the nine papers, with the two main techniques being those described in the Results section. In both techniques, the target for balloon dilation is the 8–12 mm segment that acts as a valve within the cartilaginous eustachian tube, as this is where the physiological deficiency in chronic eustachian tube dysfunction is thought to originate.Reference Poe and Hanna ¹⁷ Hence, care is taken to not push the balloon catheter past the cartilaginous and bony isthmus, or to use a balloon size that is too large for the patient.

However, this has meant that a variety of balloon sizes and pressures have been employed, especially among those who use the Acclarent balloon catheters. No ‘best’ way to perform eustachian tube balloon dilation has yet been established; at the current early stages of evaluating its efficacy, the heterogeneity of techniques confounds the ability to draw conclusions.

Overall, this review found that eustachian tube balloon dilation is a procedure with a low rate of complications and may be considered for refractory chronic eustachian tube dysfunction in adults. More rigorous studies with standardised indications, techniques and outcomes are required to provide a higher level of evidence before its mainstream use. Nevertheless, the current data suggest a potential benefit of this procedure for a condition that can be difficult to manage.