Discussion
Within the limits of the current study, Bioactive glass provides a safe and effective means of mastoid obliteration. We report outcomes in a group of patients who have undergone mastoid obliteration as an adjunct to a diverse group of procedures. Complications of the procedure are rare and outcomes good, irrelevant of surgical approach to initial mastoid surgery and concurrent procedures. Whilst concurrent or previous procedures may impact on the choice of covering graft, the most common complication suffered by patients is an increased frequency of attendance in the initial healing phase for ear dressing. This is to facilitate epithelialisation of the graft covering the bioactive glass.
We did not aim to assess the impact of obliteration on hearing outcomes within this retrospective study. Where the ossicular status was recorded, it did not preclude a decision to make use of Bioactive glass, nor did the Bioactive glass preclude the performance of an ossiculoplasty.
Where dehiscence of the lateral semicircular canal had occurred, surgical decision making was uniform in that all patients had a periosteal or fascial graft placed over the dehiscence prior to application of bioactive glass. In contrast in some cases bioactive glass was placed directly upon the dura and facial nerve in the event of their exposure. The duration of follow up is widely varied within our population. However, it is reassuring to note that none of these patients have had any late complications arising as a result of their obliteration during the follow-up period.
The issue of recurrence and recidivism has impacted upon the surgical technique used in obliterating the mastoid cavity. In the first few patients receiving Bioactive glass, the grafts were placed with temporalis fascia or muscular flaps providing both tympanic and covering grafts. In some of these early patients, the attic has retracted (Image 1). Our practice takes a number of measures to facilitate a successful obliteration and to attempt to prevent the position of clinical equipoise presented by a new retraction pocket in a previously operated ear. Firstly, when performing the mastoidectomy, the facial ridge is only lowered as far as needs be to ensure disease clearance. This is another advantage to the front-back approach, which was already preferred by surgeons reporting in this paper (Table I.). Secondly, when performing the reconstruction and obliteration, a small attic cavity is lined with a temporalis fascia graft, prior to using tragal cartilage to seal off the mastoid cavity from the attic and middle ear space. The mastoid may then be filled with Bioactive glass and covered appropriately. Once healed, the small attic cavity (Image 2) is easily examined and cleaned, should cleaning prove necessary. The retention of a small attic cavity and high facial ridge reduces the surface area of the covering graft. However, it has not obviated the problem of getting such a large graft to heal in the external ear canal. There have been a number of pedicled flaps described and utilised in mastoid obliteration.[3] The small number of local flaps performed as part of our series precludes comment on the efficacy when utilising Bioactive glass.
The current practices and techniques of surgeons beginning to make use of Bioactive glass, will likely determine both their patient and technique selection. Where a surgeon is confident in their disease clearance, primary obliteration may be undertaken but the long term benefits of reduced attendance at the outpatient department may just as well be achieved through a secondary procedure, at which time disease clearance may be confirmed. In secondary procedures, the potential to utilise the epithelium of the mastoid cavity, with its subdermal blood supply to cover the obliteration, is appealing but often impractical. The choice of grafts and flaps used during the obliteration will also likely depend upon the experience of the individual surgeon and indeed on what is available following previous procedures.
When consenting patients, they may expect that 90% of patients receive a benefit from the troublesome symptoms of mastoid cavity. However, it is important to inform them of a 1 in 5 chance of prolonged discharge and the need for repeat attendance until healing is complete. Bioactive glass provides a safe and effective means of mastoid obliteration. The role of obliteration in prevention of recurrence, the mechanism of its benefit, and the clinical outcomes achieved require further prospective study.
Figure 1. Frequency of covering graft material in Primary and Secondary Obliteration.
Figure 2. Frequency of common complications of mastoid cavity in patients who have underwent Mastoid Obliteration with Bioactive Glass. (AA – Atticoantrostomy, MRM – Modified Radical Mastoidectomy)
Image 1. Image showing retraction of attic in an early case where the attic was reconstructed with fascia as opposed to cartilage
Image 2. Image captured at endoscopic examination of the ear showing post-operative appearance
Table 1 : Surgery performed in primary and secondary procedures prior to obliteration.
Table 2: Ossicular status of ears undergoing exploration of the middle ear