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ORIGINAL ARTICLE
Year : 2015  |  Volume : 2  |  Issue : 1  |  Page : 1-4

High-resolution computerized tomography and Magnetic Resonance Imaging (MRI) in preoperative evaluation of cochlear implant patients


Department of Radiology, Bombay Hospital and Medical Research Centre, Mumbai, Maharashtra, India

Date of Submission03-Jan-2015
Date of Acceptance01-Apr-2015
Date of Web Publication15-Jun-2015

Correspondence Address:
Garge S Shaileshkumar
Room No. 1502, 15th Floor, Bombay Hospital, 12, New Marine Lines, Mumbai, Maharashtra - 400 020
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/2314-8667.158148

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  Abstract 

Context
Preoperative cross-sectional imaging evaluation of cochlear implant patients is critically important in deciding whether the patient is suitable for implantation and in choosing the side of implantation.
Aims
The aim of this prospective study was to determine the incidence of structural cochlear anomalies in patients with congenital profound bilateral sensorineural hearing loss, who were being evaluated for the feasibility of cochlear implantation.
Settings and design
This was a prospective observational nonrandomized study.
Patients and methods
A total of 26 patients with congenital profound bilateral sensorineural hearing loss, who were being evaluated for feasibility of cochlear implantation were included in this study. These patients were evaluated with high-resolution computerized tomography of the temporal bone and MRI for incidence of structural cochlear anomalies.
Results
The incidence of structural cochlear anomalies, excluding cochlear nerve aplasia, in patients with congenital profound bilateral sensorineural hearing loss, who were being evaluated for the feasibility of cochlear implantation was 50%.
Conclusion
This study highlights the importance of preoperative radiological scanning in the assessment of patients undergoing cochlear implantation. It provides vital information on cochlear status and in ruling out noncochlear causes where cochlear implantation is not feasible or contraindicated.

Keywords: cochlear implant, high-resolution computerized tomography, inner ear and cochlear nerve, MRI, sensorineural hearing loss


How to cite this article:
Pooja VD, Shaileshkumar GS, Deepak VD, Bushra RB, Nirav TR, Sunila JT, Inder TA. High-resolution computerized tomography and Magnetic Resonance Imaging (MRI) in preoperative evaluation of cochlear implant patients. Adv Arab Acad Audio-Vestibul J 2015;2:1-4

How to cite this URL:
Pooja VD, Shaileshkumar GS, Deepak VD, Bushra RB, Nirav TR, Sunila JT, Inder TA. High-resolution computerized tomography and Magnetic Resonance Imaging (MRI) in preoperative evaluation of cochlear implant patients. Adv Arab Acad Audio-Vestibul J [serial online] 2015 [cited 2017 Aug 18];2:1-4. Available from: http://www.aaj.eg.net/text.asp?2015/2/1/1/158148


  Introduction Top


The cochlear implant is a highly technological device that is surgically inserted in the cochlea of patients with severe-to-profound bilateral sensorial dysacusis and who have not benefited from conventional sound amplification hearing aids. The aim is to electrically stimulate auditory nerve fibers to partially replace cochlear function [1] .

Candidates for the cochlear implantation undergo preoperative assessment involving clinical, speech therapeutic, psychological, and social criteria. During this stage, imaging of the cochlear region is paramount in defining the etiology of hearing loss, in locating findings that may contraindicate surgery, in helping to select the ear to be implanted, in adequately evaluating the anatomy for surgery, and within limits in predicting possible complications [1] . Cochlear implantation in patients with proper indication results in great success, but in patients with improper etiology it results in catastrophe. Therefore, it is imperative to define the etiology of hearing loss preoperatively. High-resolution computerized tomography (HRCT) and Magnetic Resonance Imaging (MRI) are the two principal radiological investigations for cochlear implantation [2] .

The objective of this study was to determine the incidence of structural cochlear anomalies in patients with congenital profound bilateral sensorineural hearing loss, who were being evaluated for the feasibility of cochlear implantation.


  Patients and methods Top


This is a prospective observational study of 26 consecutive patients with congenital profound bilateral sensorineural hearing loss, who were being evaluated for feasibility of cochlear implantation between June 2011 and May 2013. Selection criterion was congenital profound hearing loss with thorough ENT examination. Patient with acquired hearing loss from causes such as viral diseases, meningitis, progressive hearing loss, ototoxicity, and temporal bone fracture were excluded from the study. All patients underwent complete audiological evaluation. Prior informed consent from parents of each patient was taken.

All candidates were evaluated using 64-slice MDCT scanner with 0.6 mm collimation 120 kVp (Somatom Sensation 64; Siemens Medical Solutions; Forchheim, Germany) and MRI scanner (Philips 1.5 T MRI scanner, Philips Healthcare, 3000 Minuteman Road, Andover MA, USA). For HRCT, patients were scanned in the axial and coronal (supine and prone) axis. Scout films were taken routinely in all patients. Scanning commenced from the lower margin of external auditory meatus and extended upward to the arcuate eminence of superior semicircular canal, as seen on the lateral topogram. Coronal images were obtained perpendicular to the axial planes from the cochlea to the posterior semicircular canal. Continuous 0.5-1 mm-thin slices were obtained at 1 mm interval using ultrahigh algorithm with a scan time of 20 s with a delay of 4 s at 120 kV tube voltage and 400 mAs. Intravenous contrast was administered to patients if needed. MRI protocol included brain T2-weighted imaging (T2WI) (DRIVE) and focused inner ear T2WI, Heavily T2WI (DRIVE), and T1-weighted. Postcontrast T1-weighted images were taken if needed. Brain T2-weighted sequences are compulsory to look for the anatomy from the cochlear nuclei to the temporal acoustic area. Focused inner ear T2-weighted (DRIVE) and pregadolinium and postgadolinium T1-weighted sequences were performed to display the cochlear anatomy and its anomalies. Heavily T2-weighted (DRIVE) delineate the endolymphatic and perilymphatic fluid and each part of the membranous labyrinth from the basal turn to the apical turn. Each nerve in the internal auditory meatus may be delineated by axial or sagittal T2 sequences.


  Results Top


A total of 26 patients were included in the study. All patients had congenital hearing loss as their chief complaint. The mean age of the participants was 7.4 years, with more than 50% (15 patients, 57.69%) of patients between 6 and 10 years of age. In our study, 14 patients were male and 12 were female, with male-to-female ratio of 1.1 : 1.

Out of 26 patients, six patients were completely normal and four patients had high jugular bulb. Among 16 patients with anomalies, four patients each had bilateral common cavity ([Figure 1]), three patients each had bilateral Mondini malformation ([Figure 2]) and cochlear nerve aplasia, two patients each had bilateral Michel deformity and dysplastic cystic dilation of the cochlea and the vestibule. One patient had right side Mondini malformation and left side common cavity, whereas the other patient had left side Mondini malformation and right side was normal.
Figure 1: (a, b) High-resolution computerized tomography of the temporal bone axial plane bone window at the level of the cochlea showed right (a) and left (b) common cavity deformity. (c) MRI of the brain T2-weighted axial image at level of the cochlea showed bilateral common cavity deformity.

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Figure 2: (a) High-resolution computerized tomography of the temporal bone axial plane bone window at the level of the cochlea showed bilateral one and half turns of the cochlea. (b, c) MRI of the brain T2-weighted axial (b) and coronal (c) image through the cochlea showed bilateral one and half turns of the cochlea in Mondini deformity.

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In our small observational study, the overall incidence of structural anomalies was 61.53%, whereas the incidence of structural cochlear anomalies excluding cochlear nerve aplasia was 50%.


  Discussion Top


A prospective observational study was conducted with the objective of evaluating the incidence of structural cochlear anomalies in patients with congenital profound bilateral sensorineural hearing loss, who were being evaluated for the feasibility of cochlear implantation.

Development of cochlear implant began in 1960s. It was Lo [3] who first recommended human implantation in 1969. After slow critical acceptance, cochlear implantation is now firmly established as an effective option in the rehabilitation of children with profound sensorineural hearing loss/hearing impairment.

Preoperative radiological evaluation of cochlear implant candidates is clinically important in deciding whether the patient is suitable for implantation and in choosing the side of implantation. HRCT and MRI are the two principal radiological investigations for cochlear implantation [2] . Some authors prefer computed tomography (CT) [3] , some favor MRI [4] , and some use both CT and MRI [5] before cochlear implantation. HRCT directly images the temporal bone structures while simultaneously imaging the soft tissues of the cochlea and its surroundings [6-9]. However, CT lacks detail as regards neural structures, inner ear fluid, and fibrosis, and when used alone is estimated to miss three out of five vestibulocochlear nerve hypoplasia [10] . MRI, however, is superior to CT in the demonstration of nerves in the internal auditory canal, retrocochlear pathologies, and membranous inner ear pathologies, which result in characteristic fluid changes. However, MRI's disadvantages include its inferiority to CT at determining bony anatomical details necessary for surgical planning and its cost [11] . It also complicates the monitoring and anesthetic management of patients who require sedation and is unable to differentiate clearly between fibrous and calcific obliteration of the membranous labyrinth (low signal output). In our study, combined HRCT and MRI scan was used for the preoperative evaluation of these patients as HRCT and MRI are complimentary to each other [12] . The classification of Jackler et al. [13] was used for bony malformations, which includes Michel's deformity, cochlear aplasia, cochlear hypoplasia, common cavity, and Mondini deformity.

In our small observational study of 26 patients, there were 14 male and 12 female patients, with male-to-female ratio of 1.1 : 1. Their ages ranged from 2 to 12 years, with a mean age of 7.4 years. Ten out of 26 patients included in the study were normal. Among 16 patients with anomalies, four patients had bilateral common cavity, three patients each had bilateral Mondini malformation and cochlear nerve aplasia, two patients each had bilateral Michel deformity and dysplastic cystic dilation of the cochlea and the vestibule. One patient had right side Mondini malformation and left side common cavity, whereas the other patient had left side Mondini malformation and right side was normal. These results are comparable to those reported in the study by Sennaroglu et al. [2] , in which 27 patients were studied.

The objective of this study was to determine the incidence of structural cochlear anomalies and to rule out noncochlear causes of congenital profound hearing loss. The importance of ruling out noncochlear causes has been demonstrated by Maxwell et al. [4] and Gray et al. [10] . They reported two cases of implant failure due to an absent cochlear nerve in patients with a narrow internal auditory canal. Both groups had to explant the device. Cochlear implantation in a patient with an absent cochlear nerve would be a catastrophe for the patient and the cochlear implant team. Therefore, it is imperative to diagnose etiology of the congenital profound hearing loss. The overall incidence of structural anomalies was 61.53%, whereas the incidence of structural cochlear anomalies excluding cochlear nerve aplasia was 50% in our small observational study.


  Conclusion Top


This study highlights the importance of preoperative radiological scanning in the assessment of patients undergoing cochlear implantation. It provides vital information on cochlear status and in ruling out noncochlear causes where cochlear implantation is not feasible or contraindicated.


  Acknowledgements Top


Conflicts of interest

There are no conflicts of interest.

 
  References Top

1.
Lima Júnior LR, Rocha MD, Walsh PV, Antunes CA, Dias Ferreira Calhau CM. Evaluation by imaging methods of cochlear implant candidates: radiological and surgical correlation. Braz J Otorhinolaryngol 2008; 74 :395-400.  Back to cited text no. 1
    
2.
Sennaroglu L, Saatci I, Aralasmak A, Gursel B, Turan E. Magnetic resonance imaging versus computed tomography in pre-operative evaluation of cochlear implant candidates with congenital hearing loss. J Laryngol Otol 2002; 116 :804-810.  Back to cited text no. 2
    
3.
Lo WW. Imaging of cochlear and auditory brain stem implantation. Am J Neuroradiol 1998; 19 :1147-1154.  Back to cited text no. 3
    
4.
Maxwell AP, Mason SM, O'Donoghue GM. Cochlear nerve aplasia: its importance in cochlear implantation. Am J Otol 1999; 20 :335-337.  Back to cited text no. 4
    
5.
Arriaga MA, Carrier D. MRI and clinical decisions in cochlear implantation. Am J Otol 1996; 17 :547-553.  Back to cited text no. 5
    
6.
Silberman B, Garabedian EN, Denoyelle F, Moatti L, Roger G. Role of modern imaging technology in the implementation of pediatric cochlear implants. Ann Otol Rhinol Laryngol 1995; 104 :42-46.  Back to cited text no. 6
    
7.
Phelps PD. The basal turn of the cochlea. Br J Radiol 1992; 65 :370-374.  Back to cited text no. 7
    
8.
Mueller DP, Dolan KD, Gantz BJ. Temporal bone computed tomography in the preoperative evaluation for cochlear implantation. Ann Otol Rhinol Laryngol 1989; 98 (Pt 1): 346-349.  Back to cited text no. 8
    
9.
Rosenberg RA, Cohen N, Reede DL. Radiographic imaging for the cochlear implant. Ann Otol Rhinol Laryngol 1987; 96 :300-305.  Back to cited text no. 9
    
10.
Gray RF, Ray J, Baguley DM, Vanat Z, Begg J, Phelps PD. Cochlear implant failure due to unexpected absence of the eighth nerve - a cautionary tale. J Laryngol Otol 1998; 112 :646-649.  Back to cited text no. 10
    
11.
Frau GN, Luxford WM, Lo WW, Berliner KI, Telischi FF. High-resolution computed tomography in evaluation of cochlear patency in implant candidates: a comparison with surgical findings. J Laryngol Otol 1994; 108 :743-748.  Back to cited text no. 11
    
12.
Jackler RK, Dillon WP. Computed tomography and magnetic resonance imaging of the inner ear. Otolaryngol Head Neck Surg 1998; 99 :494-504.  Back to cited text no. 12
    
13.
Jackler RK, Luxford WM, House WF. Congenital malformations of the inner ear: a classification based on embryogenesis. Laryngoscope 1987; 97 (Pt 2 Suppl 40): 2-14.  Back to cited text no. 13
    


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  In this article
   Abstract
  Introduction
  Patients and methods
  Results
  Discussion
  Conclusion
  Acknowledgements
   References
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