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