Acta Otorrinolaringol Esp 2005; 56: 322-327
Cochlear implants in obliterated or ossified cochleas
A. del Cañizo Alvarez, S. Santa Cruz Ruiz, A. Batuecas Caletrio, M. Gil Melcón, E. Coscarón Blanco
Servicio de ORL. Hospital Universitario de Salamanca
Abstract: We present the most recent cases of CI in ossification in the course of chronic otitis media. These
obliterated or ossified cochleas, describing the most observations were subsequently repeated by
appropriate surgical technique for the insertion of the Charachon5, Friedmann6 and Leroux-Robert7, whose
compressed or double electrode array, highlighting the histological preparations demonstrate the frequent
importance of the combined method (an endaural cochlear affectation in these processes, producing
approach with atticotomy and posterior tympanotomy) sclerosis and ossification. We add that, in the first era of
to obtain the best view of the promontory. The cochlear implants, when Chouard8 et al implanted their
advantages of this method are that it respects the Chorimac with independent electrodes, which were
posterior wall of the EAC in all cases and that it allows inserted, one by one, through perforations in the
the implant to be inserted easily. promontory, they described the eventuality of finding
an obliterated cochlear canal, affirming that this finding
Key words: Cochlear implants. Obliterated cochleas. Ossified. did not contraindicate the implant; as Chouard said, it’s
Surgical method. better to hear something than nothing.
Various types of electrodes have been designed
with a view to exploiting as far as possible the little
INTRODUCTION cochlear capacity offered in this situation. Some designs
shortened the electrode array, reducing the free space
In the case of the slightly permeable cochlea, the between the active plates, and others divided it9, that is
insertion of a conventional electrode array is partially or to say, doubling it or splitting it10. In some cases, the
absolutely impossible and in many cases cochlear cochlear problem is due to the continuance of an earlier
implantation is contraindicated1 for fundamental implant; we have been able to verify this in some of our
reasons. Firstly, this is due to the difficulty or near re-implantations, caused by defects or deterioration of
impossibility of introducing the electrode array safely; the system over time. The electrolytic phenomena
secondly, in the case of cochlear ossification, it is highly occasioned by the electrical stimulation produces a
unlikely, from the auditory point of view, that effective deposit of calcium and the development of a connective
electrical stimulation will be attained2; finally, net that makes the insertion of the new implant difficult.
histological observations seem to demonstrate the poor The objective of this peculiar implantation is to exploit
survival of the neurons of the spiral ganglion3, which the existing cochlea to its full advantage, although the
would make the insertion of the implant somewhat prognosis is uncertain and unpredictable with respect to
pointless. This occurs, fundamentally in the case of its results.
labyrinthitis ossificans caused by meningitis.
Nevertheless, it does not occur in cochleas ossified by INDICATIONS AND DIAGNOSIS
other causes and, of course, CI is not contraindicated and
total ossification is usually limited to the basal portion On the one hand the antecedents and duration of
of the cochlea, the rest of the canal being occupied by the deafness can lead us to suspect the existence of a
fibrous tissue. 100% non-permeable cochlea, above all if the patient has
We should remember the now historic observations suffered from meningitis or if we are dealing with an
of Schuknecht4, who demonstrated, morphologically old, cochlear-type otosclerosis. The CT will confirm the
and functionally, the etiology of sclerosis and labyrinth suspicion, although it should be taken into account that
this exploration is not conclusive and the help of the
MRI is needed. Once the malformation (almost always
Correspondence: A. del Cañizo Alvarez
Servicio de ORL. Hospital Clínico-Universitario de
at the level of the basal turn11) and the extent of the
Salamanca. cochlear obliteration have been confirmed, we will go
P º de San Vicente 58--182 on to choose which type of electrode array to use: the
37002 Salamanca compressed or the double array.
Fecha de recepción: 30-1-2004 There are authors12 who recommend using the
Fecha de aceptación: 20-5-2005 promontory test to evaluate the state of the nervous
tract, leading to a contraindication of implantation in
COCHLEAR IMPLANTS IN OBLITERATED OR SEMI-OSSIFIED COCHLEAS
the case of a negative response. We do not carry out this SURGICAL TECHNIQUE
test due to the common possibility of finding “false
positives”. The patient may report a hearing sensation, We use the Lenhardt or the Hannover incision and
confusing it with the electrical discharge. There was a the means of access to the cochlea does not differ, in
time when the promontory test was considered to be these cases, from the conventional, although in the case
compulsory13 for all possible candidates of a cochlear of implantation with the Nucleus system or the
implant. In the case of obliterated cochleas we should Advanced Bionics 90K, due to the characteristics of the
consider the usefulness of the promontory test, but not these devices, the minimal retro-auricular incision can
contraindicate the implant if the result is negative. We be made, with utmost ease. Draw attention to the
can only, in our opinion, consider it as relatively posterior tympanotomy, which must be wide, and pare
indicative with respect to the continuance and possible down as much as possible the posterior wall of the
integrity of the spiral ganglion. The validity of the canal, with the objective of obtaining the maximum
promontory test, in these cases, should be reviewed. visibility possible. On occasion, the excision of the incus
Nevertheless, there is an interesting study by Chouard14 and of the malleus head associated with the sectioning
et al in which they demonstrate the strong electrical of the tendon from the malleus to the stapes could be
resistance in these cases with respect to normal indicated if it is necessary to work on the promontory in
cochleas, drawing attention to the enormous its upper portion. The elimination of the posterior wall
subjectivity of their method and stimulating the round of the external auditory canal has even been described.
window, looking to avoid the osseous layer of the The greatest surgical difficulty lies in the
promontory and to better evaluate the response. identification of the area of the round window and we
We believe that the best way of evaluating the have to imagine where it would be found in normal
effectiveness of the promontory test is to accompany it conditions, as the niche of the window is often not
with a functional MRI. By means of this procedure, the recognizable; in these cases, the fundamental point of
test is no longer subjective (sensation of hearing), but reference is the oval window and we will make the
becomes, supposedly, “objective and more reliable”, as cochleostomy at some two mm from its lower edge.
is proposed by Neumann15 and Nishida16 in the updated Balkany (loc. cit.) has classified cochlear ossification
report edited by Kubo17 for the Asian Congress on in three degrees of obliteration: 1. Limited to the niche
Cochlear Implants. Obviously, according to what of the round window; 2. in the basal turn only, and 3.
emerges from the publications relating to this method, when the obliteration goes beyond this and reaches the
we will be able to make a neural tracing of the acoustic middle turn. In the first two cases, the cochlear lumen is
tract and rule out negatives. The use of a positron found after the drilling of the promontory, in an
emission tomography (PET scan) might also be valid18,19. ascendant direction, always bearing in mind its
When these methodologies are within the reach of all, anatomical situation. It can often be seen that the
many aspects of this controversy will undoubtedly be material that occupies the lumen is of a different
cleared up. composition to that of the otic capsule; it is softer and
We consider that the current implantation clearer in color and, on occasion, it can be extracted. On
techniques in the case of ossified cochleas allow for the other occasions, this tissue is compact and, therefore, it
insertion of the electrode array, in general lines, in the is impossible to view the cochlear lumen clearly and it is
totality of cases and the auditory benefit is always necessary to drill in an anteromedial direction until
greater than leaving the patient without an implant20. finding the lumen of the useful cochlear space.
We add that the present design of the electrode array Nevertheless, complete ossification is less frequent; in
facilitates the development of the technique and makes their series of 24 cases, Green11 et al only found it in
the insertion and use of all the channels possible. two. Furthermore, in their series, Cohen22 et al were
The view of the cochlear obstruction will depend on obliged to carry out a partial insertion of the implant in
the radiological explorations and surgical confirmation. 7% of the cases (out of 110) varying the number of active
Of the first, the most important test is the MRI, better in electrodes between 10 and 18 as they were dealing with
3-D, that will allow us to identify three eventualities, semi-obliterated cochleas with radiological images of
which have been very well defined by Chouard21. The normal appearance.
first, a greater density of the cochlear canal; secondly, When the ossification goes beyond the basal turn
images with beaded or fragmented irregularities, and; and reaches the middle turn, more aggressive
finally, the absence of liquids in which case the results techniques have been described. Both Gantz23 and
of the MRI imply total ossification. It should be Steenerson24 have proposed the creation of a
reiterated that the CT can provide images of apparent perimodiolar canal to hold the electrode array.
permeability. Subsequently, Telian25 described a similar procedure,
A. DEL CAÑIZO ET AL.
making use of a wide mastoidectomy and elimination of electrode array we will use; the reduced or shortest
the posterior wall of the canal to achieve a clear view, (compressed), or the split or double array guide. This
the widest possible, of the promontory. The obliteration was used in one of our cases.
of the cavity is achieved with an aponeurotic muscle If we opt for the split electrode array it is almost
flap or by sacrificing the membranous EAC as we do always feasible to insert both its components through
when we operate on tumors of the middle ear. the posterior tympanotomy. We will perform the
The best manner, without eliminating the posterior cochleostomy in the basal turn on the promontory at
wall of the canal, is to carry out a mixed or combined some 2 mm above the area of the round window. The
approach. (Figure 1). This combined method includes a cochleostomy in the middle turn will be made in front
posterior tympanotomy and, from the front, an of the oval window.
endaural approach, as proposed by Dr. Arauz26 of If we opt for the promontory implantation with a
Buenos Aires, based on the technique described by compressed electrode it is necessary to widen the access
Banfai27 et al for the insertion of their primitive 16- in an anterior direction, peeling away the membranous
channel extracochlear implant. Remember that this EAC and lifting, in a forward direction, the tympanous
author devised and promoted a device in the shape of a meatal flap, as is done in the tympanoplasty. This
plate that was placed directly on the promontory, as maneuver will give us ample visibility of the
Banfai said, to avoid endocochlear damage as a promontory, but we must widen it by sectioning the
consequence of implantation. This implant was not malleus head, the tendon of its muscle and eliminate the
widely used but we are indebted to Banfai for the incus, to obtain a more comfortable surgical field.
description of the technique and a magnificent study of Once the anterior view has been attained, the
cochlear anatomy28 in which its reference points are drilling made previously can be seen –through the
defined. posterior tympanotomy – of the area of the round
Once the mastoidectomy and the posterior window and, just above and in an ascendant direction,
tympanotomy have been carried out, the area of the we will cut a niche following a transversal line almost
round window is accessed; if it is not possible to parallel to the tube in its third portion, until reaching
identify the round window, the drilling will be carried the level of the stapes. We will then pass on to drill in
out at some 2 mm from the oval, in an anterior and the opposite direction and, finally, ascending towards
slightly ascendant direction, keeping in mind the the cochlear apex, we will have three lines cut in the
proximity of the carotid canal and the anatomical shape of a “Z”. While the formation of this cochlear
inclination of the cochlea. Whatever the ossification or neocanal is being carried out, it is very important to
partial obliteration should be, after the study of the data leave some osseous bridges that will impede the
provided by the CT and MRI, we must choose the subsequent displacement of the electrode array. The
other method is to cut the neocanal in the shape of a
“C”. To do this, from the area of the round window,
once the obliterated cochlear canal has been localized
(almost always full of fibrous tissue which can easily be
resected with the stilette) we will follow upwards until
we are 2 mm in front of the spoon-shaped apophysis, to
descend and arrive at 1 mm from the inferior edge of
the oval window.
We must warn that, should the cochlea be totally
ossified, it is advisable to make the cut in the shape of a
“Z” as there are no visible cochlear references. The
osseous bed for the receptor will then be made in the
mastoids and will be fixed in the conventional manner.
Holding the receptor in place will facilitate the surgical
maneuvers required for the insertion of the electrode
We should caution that partial insertions of
conventional electrode arrays should be avoided and
we would advise that an implant devised for the
particular purpose should be obtained22, with a view to
achieving maximum effectiveness. The initial insertion
Figure 1. Combined approach: transmastoid and transcanal of the device will be carried out from behind and
COCHLEAR IMPLANTS IN OBLITERATED OR SEMI-OSSIFIED COCHLEAS
through the posterior tympanotomy; we will then
change our approach to work from the front directly on
the promontory and introduce the electrode array in the
canal we cut earlier and beneath the osseous bridges
made previously. The manipulation of the system must
be very careful in order not to damage any microplate.
Finally, whichever device is used, it will be covered
with a fascia lamina secured with fibrin glue
(Tissucol®). The use of glue must be avoided as these
will damage the electrodes.
Figure 3. Implant with two Med-El GB 40+ electrode array guides.
OUR CASES Double cochleostomy on basal and middle turns.
Case 1: implanted patients, the patient being discharged after 48
A 72-year-old woman diagnosed with cochlear hours.
otosclerosis. The disease began when she was 20 and its In the telemetric revision all the electrodes had
evolution sped up after her second pregnancy, obliging good impedance, but the patient only obtained benefit
her to use a hearing aid from then on as a stapedectomy from the basal electrodes.
was not indicated due to the sensorial affectation of the
disease. She came to our Cochlear Implantation Center Case 2:
because her hearing aid did not help her in A 58-year-old male with right progressive profound
communication. Furthermore, she suffered from hearing loss since infancy, caused by recurrent
bilateral tinnitus. suppurative otitis media.
The CT and the MRI showed the existence in both He suffered from pneumococcal meningitis in
cochleas of obliterated or ossified tissue, giving a February, 1994, with sequelae of left-side hearing loss.
beaded cochlear image in the resonance image (Figure In 1995 a right-side cochlear implantation with a
2). Digisonic device was attempted; this was unsuccessful
It was decided to insert a Combi 40+ GB double due to the patient’s having fibrosis in the basal turn. A
cochlear implant in the right ear, with two electrode second operation was carried out 14 days later, as the
array guides (Figure 3): that of 7 mm in the basal turn MRI showed partial but sufficient cochlear
and that of 5 mm in the middle turn. The surgery was permeability, for which reason the cochleostomy was
carried out without major difficulties, with a widened in an ascendant and forward direction, and a
postoperative evolution similar to that of the majority of partial insertion was achieved.
Over the course of time, progressive deterioration
occurred in the CI, it was decided that the implant
should be replaced but this could not be done because
the cochlea was obliterated, without useful promontory
Figure 4. Complete bilateral cochlear obliteration: post-otitis in the right
Figure 2. CT and MRI: Partial beaded cochlear obliteration ear andpost-meningo labyrintitis in the left ear.
A. DEL CAÑIZO ET AL.
A three-year-old boy who was referred to us after
the failure of an attempted cochlear implantation for
profound bilateral hearing loss, after suffering from
pneumococcal meningitis a year and a half earlier,
complicated by subdural left-side parietooccipital
hygroma, which required neurosurgical treatment.
The temporal bone CT was repeated, showing
apparent normality in the cochlear permeability.
The child was operated on again and fibrosis and
complete cochlear ossification could be seen despite the
radiological reports, for which reason a “Z” was drilled
in the promontory, following a combined approach, and
a Nucleus 24 Contour was implanted. A response was
obtained with 8 electrodes. The post-operative evolution
was very good.
With reference to the functional results, we verified
that in the first case, in which a double electrode was
inserted, even with acceptable impedances, the first four
electrodes were not useful. The subsequent radiological
study showed good insertion of this portion of the
electrode array; it had not been pushed out as might
have been expected.
Disyllables: CI LL LL+CI
1st presentation 25% 50% 100%
2nd presentation 60% 55%
1st presentation 40% 60% 93%
2nd presentation 76% 66% 99%
In the second case the result was poor: the tests show
thresholds at 30 dB, but this only serves for the detection
Figure 5. Neocochlea on the promontory, with insertion of
compressed Med-El Combi 40+S electrode array. C40+ (24 electrodes across 27.4 mm)
surgical references. The MRI showed complete
obliteration (Figure 4). Given the circumstances we
decided for safety reasons to operate on the left ear,
with an obliterated cochlea, but with surgical references C40S (24 electrodes across 13.1 mm)
After the sectioning of the malleus head, the
incudostapedial disarticulation and the extraction of the
incus, a letter “Z” was drilled in the cochlea and a
Combi 40+S implant inserted through it (Figure 5). C40+ GB (14 electrodes across 6.6 mm)
This intervention is much more laborious than that (10 electrodes across 4.4 mm)
of the double cochleostomy. It is essential to take special
care to respect the carotid artery in the antero-inferior
portion of the promontory and the tympanic portion of
the facial nerve, in the upper part. Nevertheless the
post-operative evolution did not present any differences
with respect to other implants. Figure 6. Different types of electrodes.
COCHLEAR IMPLANTS IN OBLITERATED OR SEMI-OSSIFIED COCHLEAS
of sources of sound and for a slight improvement in the With respect to which technique to use, we
recognition of phrases with the help of lip-reading. recommend a mixed method combining an endaural
In the third case the result has been surprisingly approach with atticotomy and posterior tympanotomy,
good: the tests show thresholds at 42 dB; however, the to achieve easier access to the cochlear area and to better
child is advancing notably in acquiring auditory skills recognize the points of anatomical reference.
and is developing an oral language similar to that of It is usually impossible to insert a classical electrode
children of the same age with a cochlear implant. array; it is necessary to use a compressed or double
model, avoiding partial insertions of a conventional
DISCUSSION device (Figure 6).
We add that it is obligatory to carry out an MRI in
For the evaluation of the results and effectiveness of all cases, above all in those cases with a history of
the device, we believe it important to separate this meningitis, as the CT may offer false negatives.
group from that of normal implants and establish a
universal criteria of evaluation.
The mediocrity of the results obtained in these cases References
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