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Abstract |
Gaetano Motta |
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Introduction Otosclerosis is
a degenerative process of the labyrinthine capsula that causes the onset of progressive
hearing loss. The osseous dysplasia mainly involves the platina of the stapes
and the stapedoovalar joint (Fig. 1). The stapes thus loses any possibility
of transmitting sound vibrations to the labyrinthine fluids. Various surgical
procedures have been put forward to resolve this deafness. Over the last
decade these have been fine-tuned and currently allow particularly satisfying
outcomes to be achieved in a high proportion of cases. The operation is
intended to restore the capacity of the ossicular chain of transmitting the
vibrations to the labyrinthine fluid. Surgery therefore permits recovery of
the transmission component of the acoustic damage, i.e. that part of the
deafness due to impairment of the ossicular chain functioning. On the other
hand the operation does not allow the resolution of any possible neurosensory
lesion. Audiometer
examination allows the accurate establishing of surgery indication and to
anticipate a valid prognostic judgement. The transmission component of
acoustic damage due to ossicular-tympanic system impairment is documented by
the gap, detectable by the audiogram, between the air passage and osteal
passage. The auditory damage provoked by a possible involvement of the
neurosensory apparatus - not susceptible to improvement with surgery - is
evidenced by the auditive loss through the osteal passage (Fig. 2a, b, c). The surgical
technique currently employed is stapedotomy: the crus of the stapes removed,
a hole is made on the platina of this bone. Then a “piston” prosthesis is
applied between the anvil and this hole, which permits sound vibrations to
spread to the labyrinthine fluid (Fig. 3). The stapedotomy
procedure has been an option since the latter 1950s (1), and has replaced
stapedectomy, which provided for the en bloc removal of all the stapes.
Stapedotomy has been progressively preferred for its simpler execution and
reduced occurrence of complications such as neurosensory hypacusia and
vertigo post-op (2, 3). Data from our previous
research (4) confirm this, showing in fact a reduced incidence of auditory
damage on the acute frequencies (stapedectomy: 13.8%; stapedotomy: 3.4%) and
of post-op anacusia (stapedectomy: 1.8%; stapedotomy: 0.7%). On the other
hand, in spite of technique refinements, it is necessary to point out, in
addition to the persistence of cases where perceptive hypacusia or an
instability might develop, the non-resolution of some problems relating to
vocal discrimination, hypacusia and the worsening of the acufens following
the surgery (5). To overcome such
drawbacks, a series of studies has been conducted on the possible
applications of laser energy in stapes surgery, starting from 1967 (6). The
preliminary experiments on the biological effects of lasers having different
wavelengths had indicated a high degree of safety for the use of visible
radiation (Neodynium, KTP and Argon) (7, 8), while pointed out at the same
time were the potential risks of heating the perilymph should the CO2 laser
be used (9). Therefore, the first clinical trials on stapes surgery were
performed using visible lasers. These allowed perforation of the platina with
a series of flashes grouped within a “rosette” pattern (9, 10). However, at the
beginning of the 1980s and based on the experimental data from studies by
Gardner, Shea (11) stated that: “The CO2 laser would appear to be less
potentially harmful to the inner ear”. This gave a new
boost to using this type of radiation in ear surgery. Indeed, it was
demonstrated that whereas the visible laser beam was only partially absorbed
by the fibrous and bone tissue (specifically by the platina) and could thus
be transmitted by the perilymph right to the pigmented cells of the inner
ear, a minimal layer (0.03 mm) of labyrinthine fluid was sufficient to absorb
up to 90% of the energy of the carbonic anhydride beam (12,13). The
employment of the latter, however, is further hindered by verification of
technical problems due both to the imprecise alignment of the laser beam and
to the difficulty in obtaining a spot having a diameter less than 1 mm (14). Only in 1989,
following the introduction of a new generation of equipment, could Lesinski
publish the positive results achieved in 137 cases of otosclerosis operated
with the CO2 laser (15, 16). More recently,
in 1996, House (17) expressed some doubts on the use of lasers to perforate
the platina, considering the micro-burr more reliable compared to radiant
energy. In fact, this
would have the limitation of being unable to create a suitable window in
cases where the stapes is particularly thick or in the presence of bleeding. Study
objective Since 1993 our
School has been introducing the CO2 laser to carry out stapedotomy, whether
traditional or combined with preservation of the stapes muscle tendon. Our
study objective was to assess the reliability of CO2 lasers in stapes surgery
and to compare the relative results with those obtained using the traditional
(micro-burr) operation. Survey
data The research was
based on 262 patients operated on for otosclerotic disorders between 1996 and
1998. These interventions were effected: - in 142 cases by employing the CO2 laser.
the stapes tendon was preserved in 85 of these (59.8%) (stapedotomy with
stapedoplasty) (Tab. I, group A); - in 120 cases
by a traditional technique (Tab. I, group B). Materials
and methods The operations
were performed using a Zeiss OPMI 1-H microscope having a focal length of 250
mm for the group A patients and 200 mm for group B. The lasers adopted were
the Sharplan 1030 and Zeiss OPMI CO2-50. The radiation produced by the latter
is the type T.E.M. 00 (Transverse Electromagnetic Mode) and therefore
presents the greater amount of energy concentrated within a restricted area. The beam is
emitted with a mechanical pulsating (chopped) at a frequency of 200 Hz with a
pulse duration of 1.25 msec and a pulse interval of 3.75 msec. The ratio
between the period of activity and duration of the cycle, and consequently
between the average power and peak power, is 1:4. The maximum energy supplied
by the laser with a peak power of 50 W is, therefore, 62.5 milliJoules (50 x
1.25 msec). Surgical
technique In all patients
the operation was carried out under local anesthesia after adequate sedation.
Access was through the classic endocanal route. Following the platinotomy,
used in all cases was a prosthesis of the “Platinum Fluoroplastic” type by
the Richards company having a diameter of 0.6 mm and length 4.50-4.75 mm. In the subjects
operated by traditional technique, a Richards mod. Shea micro-burr with a
micro-osteotribe of 0.7mm was used for the perforation of the platina. In the
patients subjected to the CO2 laser, a platinar opening of 0.7mm was made by
means of one or more spots repeated at intervals of at least 5 sec, depending
on the thickness of platina. Such spots were constituted by single
defocalised impulses of 0.05 sec and a power of 10-12 W in the case of the
Zeiss laser, or of 0.05 sec and 5 W, with a 'superpulse' modality where the
Sharplan equipment was used (Fig. 4). The radiation was suitably defocalized
to obtain an opening of 0.7 mm diameter. Concerning this, it is opportune to
point out that in order to achieve an optimal correspondence between the
spot's parameters (set beforehand) and the diameter of the platinotomy, the
laser beam has to be aimed with extreme precision in a perpendicular
direction. All the patients
underwent audiometer examination the day before the operation, and again
post-op at 12 months. In compliance with the most recent international
guidelines (18), the closure of the cochlear reserve was evaluated, expressed
as the difference between the average of the post-op limits per air passage
and per osteal passage, at the frequencies of 500, 1,000, 2,000 and 3,000 Hz.
On the basis of
the audiometric evolution phase of the otosclerosis, the patients were
further subdivided into two bands: the first included cases with
otospongiosis at stages I and II; the second was for those having a higher
impairment of osteal passage conduction, typical of stage III. The statistical
analysis of the results was carried out using the Student test. Results The pre-op
audiometer findings are analytically reported in Tab. II. With the post-op
audiometer check at 1 year, we found: a) In the 142 patients
operated with CO2 laser (group A): a transmission gap reduction in 140
subjects (98.6%); neurosensory hypacusia on the frequencies 500, 1000, 2000
and 3000 Hz, in two (1.4%). More precisely, in the 140 cases in whom no
worsening of the bony passage was found, there was a closing of the cochlear
reserve recorded on the considered frequencies, within 10 dB in 119 patients
(85%), between 11 and 20 dB in 20 (14.3 %) and over 20 dB in 1 case (0.7%)
(Fig. 5). Moreover, in 78 (91.8%) of the 85 patients operated with
stapedoplasty, there was a post op reduction of the bony passage-air passage
gap to within 10 dB; b) In the 120
cases that underwent traditional surgery (group B): an improvement in the
cochlear reserve in 108 patients (90%); neurosensory hypacusia in 4 (3.3 %);
and no significant change in the hearing loss in 8 (6.7%). In the 116
patients who did not report any post-op auditory damage to the bony passage
on frequencies 500, 1000, 2000 and 3000 Hz, there was a post-op bony
passage-air passage gap closure to within 10 dB in 84 patients (72.4%),
between 11 and 20 dB in 20 (17.2%) and over 20 dB in 12 (10.3%) (Fig. 5); c) There were no
cases of anacusia in either group in the study. Considerations Evaluation of
the functional outcomes allowed us to ascertain satisfactory hearing recovery
in almost all the patients in our study. In those cases where the CO2 laser
was used, cochlear reserve closure was achieved within 10dB in a
significantly higher proportion of cases compared to the patient group that
underwent the micro-burr technique (85%
vs. 72.4%). On the other
hand there were no significant differences detected on statistical analysis
between the subjects of the two groups regarding the incidence of post-op
neurosensory hypacusia. This data therefore
excludes the hypothesis according to which the use of CO2 lasers in stapes
could involve the risk of lesions to the inner ear structures (13). The
lesser labyrinthine traumatism of the stapedotomy carried out with CO2 is also
demonstrated by the reduced incidence of worsening of the osteal passage on
the frequencies of 4,000-6,000-8,000 Hz (0.7% Vs. 5%) and of post-op
vertiginous episodes (0% Vs. 10%) of a certain degree, in the patients who
underwent this technique. In the past, the
authors (9, 10) who had used lasers to perforate the stapes transmitted a
series of spots on to the platina, creating several tiny holes arranged
circularly, in “rosette” form. It was therefore subsequently necessary to use
traditional instruments for bringing the edges of these openings together and
obtain a perforation of the stapes, whose rims were often uneven (Fig. 6a).
We, on the other hand, have established a operational technique that, with a
single spot having a diameter adjusted to the prosthesis caliber (and if
necessary repeated), allows one to achieve a single platina opening with a
precise size and regular edge (Fig. 6b). Our procedure
offers other advantages too, especially the possibility to realize: - section of the
crura of the stapes by vaporization with the laser beam, without provoking
movement of the platina (an incident that is not exceptional when a micro-burr is used); - a precise
platina opening in cases where there has been an accidental fracture of the
platina or whenever one is found facing a horizontally pivoted stapes, as
described by authors elsewhere (19); - a
stapedoplasty operation preserving the tendon of the stapes muscle; this was
performed by ourselves in 85 (59.8%) of the 142 subjects operated with the
laser. Concerning this, we recall that stapedoplasty allows the ossicular
chain to be stabilized, post-op hypacusia to be reduced, vocal discrimination
to be improved and the incidence of necrosis of the long process of the incus
to be diminished, by preserving the vascular supply to the lenticular
apophysis (20). Conclusion Our research
shows that stapedotomy using the CO2 laser in the method we have described
allows improved functional outcomes to be achieved, in comparison with
traditional techniques. The absence of
post-op vertiginous episodes of a certain prominence and of neurosensory
hypacusia on acute frequencies excludes the fear that the CO2 laser might
cause damage to the inner ear structures. Luca Moscillo** *Istituto di Clinica Otorinolaringoiatria Seconda Universitą degli Studi di Napoli **Istituto di Clinica Otorinolaringoiatria Universitą degli studi di Napoli “Federico II” |
Gaetano Motta
Fig. 4: The
positioned prosthesis is seen, between the long process of the incus and the
hole of the stapes. In the upper panel, the platinectomy performed with the
CO2 laser is shown
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