Cochlear Implantation in Inner Ear Malformations

  

    
Type of IEM
    
Radiology
    
Audiology
    
Gusher
    
FN anomaly
    
Treatment modality
    
Electrode choice
  
  

    
Complete labyrinthine aplasia
    
Absent labyrinth
    
Profound SNHL
    

    
Yes
    
ABI
    
ABI
  
  

    
Rudimentary Otocyst
    
Incomplete milimetric otic capsule remnant
    
Profound SNHL
    

    
Yes
    
ABI
    
ABI
  
  

    
Cochlear aplasia
    
Absent Cochlea
    
Profound SNHL
    

    
Yes
    
ABI
    
ABI
  
  

    
Common cavity
    
Round or ovoid cystic structure for cochlea and vestibule
    
Profound SNHL
    
Rarey
    
Yes
    
CI or ABI
    
Transmastoid labyrinthotomy or double labyrinthotomy, AVOID MODIOLAR    HUDDING ELECTRODE
  
  

    
Cochlear hypoplasia
    
Cochlear size small, four types+
    
Conductive, mixed, SNHL
    
In CH-II Possible
    
Yes
    
HA, Stapedotomy, CI or ABI
    
Thin and short electrode
  
  

    
Incomplete partition-I
    
Cystic cochlea
    
Profound SNHL
    
50% of the cases
    
Possible
    
CI or ABI
    
Electrode with stopper
  
  

    
Incomplete partition-II
    
Cystic cochlear apex
    
Normal to profound mixed or SNHL, progressive
    
Always pulsation but gusher <10% of the cases
    
Not expected
    
HA or CI, NO ABI
    
Any electrode but electrode with stopper preferred
  
  

    
Incomplete partition-III
    
Modiolus absent, inerscalar septa present
    
Mixed or SNHL
    
100% of cases
    
Yes
    
HA or CI, NO Stapedotomy, NO ABI
    
Electrode with stopper AVOID MODIOLAR HUGGING ELECTRODES
  
  

    
Enlarged vestibular aqueduct
    
Normal cochlea with enlarged VA
    
Normal to profound mixed or SNHL, progressive
    
Always pulsation
    
Not expected
    
HA or CI, NO ABI
    
Any electrode but electrode with stopper preferred
  
  

    
Cochlear aperture abnotmalities
    
Narrow or absent cochlear aperture
    
Profound SNHL, OAE may be normal, profound SNHL
    
None
    
Not expected
    
CI for CN hypoplasia, or ABI if CN is absent
    
Standard CI or ABI
  
  

    
IEM: Inner Ear Malformatrion; SNHL: Sensorineural Hearing Loss; FN: Facial Nerve; VA: Vestibular Aquaduct;    CN: Cochlear Nerve; HA: Hearing Aid; CI: Cochlear Implantation; ABI: Auditory    Branistem Implantation; OAE: Otoacoustic Emissions 
  

Table 2: Various IEMs and their characteristics, operating risks and operating procedures [8].

CI was performed using a retroauricular incision, mastoidectomy, posterior tympanotomy, and oval window or cochleostomy approach under general anesthesia in all patients.

Various brands of cochlear implants were used.

The first implant tune-up was performed 1 month postoperatively. The patients were followed up monthly for 3–4 months and then scheduled for follow-up every 6 months.

All CI patients were evaluated with the Categories of Auditory Perception (CAP) [6] and Speech Intelligibility Rating (SIR) tests [7]. The CAP is an eight-point hierarchical scale that evaluates receptive auditory abilities and ranges from no awareness of environmental sound to telephone use with a familiar talker. The SIR is a five-point hierarchical scale that evaluates expressive abilities and ranges from no intelligible speech to connected speech intelligible to all listeners. The word lists were delivered in the free field at 40 dBSL and the patients were tested in an optimally aided condition with their implants.

Results

Patients’ Characteristics

Amongst the pediatric population that undergone cochlear implantation in our department 9 patients were diagnosed with IEM. The age range at cochlear implantation was between 2 years and 4 months and 5 years (average, 3.36 yr). Of the 9 children, 5 (55.5%) presented with enlarged vestibular aqueduct (LVA), 2 (22.2%) with incomplete partition (IP) Type II (IP II), 1 (11.1%) with IP Type I (IP I) and 1 (11.1%) with IP-III (Table 1).

The preoperative cochlear implantation assessment showed that every patient had severe-to-profound sensorineural hearing loss, without any improvement or residual benefit from well adapted hearing aids.

Regarding the deafness etiology, 4 children (44%) were born of a consanguineous marriage, 1 child (11.11) had suffered from meningitis and 4 children had unknown causes.

Surgical Findings and Postoperative Complications

In all patients, we performed CI surgery via the classical transmastoid-facial recess approach. In 3 patients, the vertical segment of the fascial nerve was located anteromedially toward the promontory, but we did not need to modify the surgical approach. Cochlear implant electrode placement into the scala tympani was performed using the round window technique in 6 (66%) patients and the cochleostomy technique in 3 (33%) patients. The Cochleostomy technique was used in 3 patients because the round window was hidden.

We implanted the Cochlear Nucleus in 6 patients, Oticon in 2 patients, and Advanced Bionics CI system in 1 patient.

CSF gusher was experienced by 3 patients (two with IP-II, one with IP-III, and one with EVA). CSF oozing was encountered in two patients (one with IP III and one with EVA). Cases with CSF gusher required 15–20 min of waiting and ceased completely only after cochlear implant insertion to the cochleostomy site. Full electrode insertion was achieved in all cases with CSF gusher and oozing. The selection of the appropriate electrode has played an important role in achieving this success.

None of the children with CSF gusher or oozing experienced dizziness, excessive vomiting, or CSF leakage in the postoperative period. One patient (IP-II) had meningitis in postoperative period.

Two patients had transient facial paralysis after surgery. One patient had an IP II anomaly (House–Brackmann score of 3) and one patient had EVA (House–Brackmann score of 3). Oral steroids were given to these two patients and tapered in the second postoperative week. All patients fully recovered within six months. The possible etiological factor was neural edema in these two patients. The burr made edema by working close to the nerve due to the narrowness of the window and caused the dissipated heat to reach the nerve.

Speech Perception

Every patient confirmed their cochlear implant daily usage. Post-implantation follow up time ranges from 6 to 45 months (average 25.7 months). After cochlear implantation, the performance of basic auditory skills such as patient response, voice discrimination, and voice recognition increased steadily after cochlear implantation. In the 12th month, basic skill improvement reached 80% in patients with vestibular anomalies and normal inner ear anatomic patients; this improvement was reached later in cochlear anomaly patients. All patients had increased CAP and SIR scores after implantation, those who presentend EVA show better scores than patients with IP-I or IP-II. The average percentage of open set speech recognition was 77% on the monosyllabic test, 100% on the number tests, 66% on the sentences test.

Discussion

Morphologically congenital sensorineural hearing loss can be splitted under two categories. The majority of congenital hearing loss causes (80%) are membranous malformations. Here, the pathology involves inner ear hair cells. There is no flagrant bony abnormality and, thus, in these cases high-resolution computerized tomography and magnetic resonance imaging of the temporal bone reveal normal findings. The remaining 20% have various malformations involving the bony labyrinth and, therefore, can be radiologically demonstrated [8].

This is going through the different weeks that we see these inner ear abnormalities. Basically, they appear during the first trimester between the third and eight week. They progress from complete abnormalities to incomplete abnormalities, and they start from bony abnormalities in the earlier weeks to membranous abnormalities in the later weeks. Also, the abnormalities that occur in the earlier stages of development tend to be more uncommon with about 20% of IEM, as opposed to the IEM that appear later in the development around 7/8 weeks [1].

Recently, owing to advancing technology and imaging methods, inner ear anomalies have been identified as a common cause of congenital hearing loss. For example, inner ear anomaly in the temporal bone has been reported in 20% of patients with congenital hearing loss [1].

Initially, the inner ear malformations were seen as a contraindication to cochlear implantation, but nowadays, this view has completely changed. Cochlear implant surgery can be performed in all patients with inner ear malformation except cochlear aplasia, Michel aplasia, and cochlear nerve agenesis.

3 patients with cochleovestibular anomalies in our study had abnormal facial nerve anatomy (33%). Sennaroglu et al [9] observed abnormal facial nerve anatomy in 4 out of 20 patients in their study (20%). This has been reporte more frequently in patients with inner ear anormalies than in normal patients [10].

Another problem that may be encountered in patients with inner ear malformations is perilymph fistulas. This usually occurs due to defects in the lateral end of the internal auditory canal. If perilymph gusher occurs during surgery, the cochleostomy should be closed completely around the electrode to avoid the risk of meningitis. In our study, gusher was observed in 3 patients with with IP-I and IP-II anomalies. Similar to Sennaroglu et al [9] and Au and Gibsons [11] studies. No gusher was observed in any of the patients with EVA in our study.

Meningitis is a life-threatening complication of cochlear implantation surgery. A study by Biernath et al [12] have shown that the risk of meningitis in patients with CI was 3-fold higher than in the normal population. We report one case of meningitis in our study (11%).

Postoperative hearing and speech rehabilitation programs are of utmost importance for all patients who get cochlear implants. With these programs, patients with cochlear anomalies can also develop their auditory performance at a level observed in patients with normal inner ear anatomy [13,14]. Current studies indicate that early implantation is necessary to gain better communication skills in bilateral total hearing loss. [15] Özdemir et al [16] found that there was a negative correlation between age at the time of operation and development of auditory performance: test scores have increased more rapidly in the small age group. Kim et al [17] have observed that cochlear implantation is beneficial for patients with inner ear malformations and that there was a slight delay in auditory skills in the early post-implantation period compared to normal inner ear anatomic patients. In addition, recent studies also have shown that patients with EVA and patients with normal inner ear anatomy have similar auditory performance [15]. Our study are in line with this, EVA patients show better perception skills.

Although most IEM patients fare well in speech perception 2–3 years after implantation, IEMs such as common cavity deformity or severe cochlear hypoplasia that disrupt cochlear architecture or cochlear nerve formation have limited improvement and tend to perform much worse in all speech perception tests [17,18]. Patients with milder forms of cochlear hypoplasia tend to perform better. Many studies suggest that earlier age of implantation resulted in better performance on open-set word speech perception tests [12].

We did not find severe inner ear malformations like common cavity, which may explain the excellent results presented above concerning speech perception and speech production.

The following conditions should be taken into account to avoid mortal complications such as meningitis: informing the patient’s relatives about all details and risks of the operation, interpreting radiological images carefully, vaccination before the operation, facial monitoring in the course of operation, close follow-up for rhinorrhea in the postoperative period.

Conclusion

There are certain challenges in the management of IEMs: 1. Cerebrospinal fluid gusher and risk for meningitis 2. Facial nerve anomalies 3. Decision making for the surgical approach and the type of electrode. As a result, auditory outcomes of cochlear implantation in patients with inner ear malformations can reach that of CI patients without inner ear anomalies in time. However, it should be known that the facial nerve anomalies and the risk of meningitis are higher in patients with inner ear malformations compared to CI patients without inner ear malformations.

References

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