67 / 224
781
into account audiometer output limits (for example, pre-
and post-implant thresholds of 60 and 75dB HL respec-
tively, with a 120dB HL output limit, would indicate 75%
hearing preservation). The authors suggested that pres-
ervation of
>
75% may be considered “complete” in terms
of practical implementation of EAS. The mean hearing
preservation recorded was 75% and 67% at 1 and 2 years
postoperative respectively (compared with 97% and 94%
in the non-implant ears). All subjects retained sufficient
hearing to use EAS at 24 months apart from four subjects
who had very poor preoperative hearing levels.
Several other studies have reported on hearing preserva-
tion with the SS electrode in smaller cohorts, generally
with similar findings. Lenarz (28) reported preservation
within 15dB of preoperative thresholds in 48% of 29
subjects implanted with the CI422 device after 6 months.
Mean preoperative low frequency thresholds were 63dB
HL and the median pre-postoperative increase in thresh-
olds was 15dB at 250Hz and 25dB at 500 Hz. Friedmann
et al. (21) reported a 21.5dB increase in low frequency
thresholds at initial activation in a group of twelve CI422
recipients, with a further 8.5dB deterioration by 12
months.
These studies have included a variety of surgical tech-
niques, patient types and follow-up times, but it can be
concluded that long-term low frequency hearing is typi-
cally preserved within 15–25dB of preoperative levels
when using the SS array, with the large majority of recip-
ients able to utilize EAS. Similar hearing preservation
outcomes have been reported for the 24mm MED-EL
FLEX
EAS
array (29,30). However, use of the full length
31mm MED-EL FLEXSOFT array in subjects with functional
preoperative hearing has been shown to be associated
with poorer hearing preservation and a higher incidence
of total hearing loss (31,32).
Factors predictive of good hearing preservation
Studies on specific electrode types have implanted a
variety of recipient types and used a variety of surgical
techniques, and it is likely that some of these factors have
contributed towards the variability in observed outcomes.
Several recent review articles have attempted to iden-
tify factors predictive of successful hearing preservation
by analyzing outcomes from a large number of studies.
However, while a few such factors have emerged, it is
probably reasonable to state that the reported influence
of many factors currently remains inconsistent.
Santa Maria et al. (33), Kopelovich et al. (34) and Causon
et al. (35) each examined a wide range of recipient
characteristics and surgical techniques and looked for
correlations with hearing preservation by meta-analysis
or multivariate regression analysis. The meta-analysis
of Santa Maria et al. (33) suggested better outcomes for
(i) cochleostomy insertion (rather than RW), (ii) poste-
rior tympanometry approach (rather than suprameatal),
(iii) insertion time of
>
30s, and (iv) use of postoperative
systemic steroids. Electrode parameters were not found to
be predictive of outcomes. Causon et al. (35) extracted low
frequency average hearing preservation reported for 110
patients in 12 studies. This review identified the use of
steroids, particularly when administered intraoperatively,
to be predictive of better outcomes, but reported supe-
rior outcomes from RW insertions. In addition, pre-curved
(perimodiolar) electrodes produced poorer outcomes and
hearing preservation was inversely correlated with inser-
tion angle. Regarding patient variables, stable hearing
loss appeared to be predictive of better hearing preser-
vation than progressive losses. Kopelovich et al. (34) anal-
ysed patient variables from the Cochlear Hybrid S FDA
trial (85 subjects). Low frequency hearing preservation 1
year post-implantation was clearly superior in subjects
implanted at a younger age (within a range from 17 to 84
years) and was significantly superior in females. Patients
with noise induced hearing loss were also found to suffer
from greater hearing loss than those with other aetiolo-
gies, though aetiology was unknown in 31% of the subjects.
Administration of steroids has become common in hearing
preservation surgery, but the route and timing of admin-
istration varies. The efficacy of pre-operative steroids
(usually dexamethasone, prednisolone or triamcinolone)
was recently reviewed by Kuthubutheen et al. (36), who
pointed out that although systemic administration at
various time points between induction and cochleostomy
has become commonplace, the efficacy of short dura-
tion steroid treatment is not well established from clinical
studies, though the evidence from animal studies is more
robust. The intracochlear steroid concentration may be
increased by local application to the round window during
surgery, and there is evidence that this can reduce surgi-
cally-related hearing loss (37). There is also some evidence
that extended exposure may be effective; Sweeney et al.
(38) reported better hearing preservation in patients who
received a 2-week oral corticosteroid (prednisolone) taper
commencing three days prior to surgery, though this study
was retrospective and non-randomized. Studies on long
term postoperative steroid application, using drug-eluting
electrode arrays (39) or via osmotic pumps (40) show
promise in reducing intracochlear fibrosis and hearing loss,
though these approaches currently remain in the experi-
mental stage.
[Electro-Acoustic Stimulation - an option when hearing aids are not enough - Herbert Mauch Biomed Eng. et al.]