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J Radiol Sci 2013; 38: 43-50

Magnetic Resonance Imaging Evaluation for Predictive Factors of Cochlear Deficiency in Pediatric Candidates

Yen-Ling Lin1 Che-Ming Wu2 Cheng-Hong Toh1,4 Mun-Ching Wong1,4 Sheung-Fat Ko3,4 Kar-Wai Lui1,4 Shu-Hang Ng1,4

Department of Medical Imaging and Intervention1 and Department of Otolaryngology2, Chang Gung Memorial Hospital Linkou Medical Center, Taoyuan, Taiwan Department of Radiology3, Chang Gung Memorial Hospital Kaohsiung Medical Center, Kaohsiung, Taiwan Department of Medical Imaging and Radiological Sciences4, Chang Gung University, Taoyuan, Taiwan

Abstract The presence of a functioning fiber is a crucial issue in the preoperative evaluation of pediatric cochlear implant candidates. Correlations between cochlear nerve deficiency and bony abnormalities of the labyrinth or internal acoustic canal (IAC) have not been well elucidated. The purpose of this study was to determine whether an inner or IAC anomaly could serve as a reliable predictive factor for the presence of cochlear nerve deficiency. We retrospectively reviewed magnetic resonance imaging (MRI) images of 88 patients with sensorineural loss (SNHL) for the presence of cochlear nerve deficiency, cochlear, vestibular or semicircular canal (SCC) anoma- lies, enlargement, and IAC stenosis. Generalized estimating equations (GEE) logistic regression models were used to determine the predictive factors of cochlear nerve deficiency. MRI demonstrated or IAC anomalies in 60 of 149 (40%) with SNHL, among which 37 presented with cochlear nerve deficiency, 16 had cochlear anomaly, 10 had vestibular/SCC anomaly, 28 demonstrated IAC stenosis, and 18 presented with endolymphatic duct enlargement. Multivariate GEE model demonstrated IAC stenosis and cochlear dysplasia to be positive predictive factors for cochlear nerve deficiency with odds ratios of 23.0 and 16.0, respectively. We concluded that most ears with cochlear nerve deficiency have concurrent anomaly of the or IAC. In those children with IAC stenosis or cochlear dysplasia which may be detected by CT in advance, MRI should be performed for evaluation of cochlear nerve deficiency.

Children with sensorineural (SNHL) candidates. Cochlear nerve deficiency implies an absence often present to otolaryngologists before adolescence. or hypoplasia of the cochlear nerve. A hypoplastic cochlear Early diagnosis and correction of the cause of SNHL are nerve is considered a relative contraindication for cochlear important in speech and language development for young implantation. Previous studies have shown that a reduction children [1]. Cochlear implantation is an effective treat- in the diameter of the cochlear nerve may be associated ment for selected patients with SNHL [2]. The presence with a reduced number of cells [3]; although of a functioning cochlear nerve becomes a crucial issue in the residual cochlear nerve fibers may still be effective, the the preoperative evaluation of pediatric cochlear implant extent of functioning nerve fiber is uncertain and needs

Correspondence Author to: Shu-Hang Ng Department of Medical Imaging and Intervention, Chang Gung Memorial Hospital Linkou Medical Center, Taoyuan, Taiwan No. 5, Fu-Shin Street, Kueishan, Kuei-Shan, Taoyuan 333, Taiwan

J Radiol Sci June 2013 Vol.38 No.2 43 MRi evaluation for predictive factors of cochlear nerve deficiency to be evaluated [4]. The absence of the cochlear nerve deficiency, MRI provides better soft tissue resolution and is considered an absolute contraindication for cochlear direct visualization of the cochlear nerve [9, 10], but has a implantation. Lack of a visible cochlear nerve on magnetic higher cost and a longer examination time. resonance imaging (MRI) has been shown to be related to Some authors have suggested that there may be a corre- poor outcome of cochlear implantation [5]. lation between cochlear nerve deficiency and bony abnor- The preoperative evaluation for cochlear implantation malities of the labyrinth or IAC, which can be detected by includes CT and MRI. High-resolution CT has been recom- CT [11-13], while others have suggested that the correlation mended by many authors as the imaging modality of choice is unreliable [14, 15]. Most of these studies were case series for the initial work-up of children with SNHL [6, 7]. CT or of small patient numbers utilizing descriptive statistical may provide good resolution for abnormalities of the bony methods. To the best of our knowledge, there have been no labyrinth, internal acoustic canal (IAC), ossicular chain, previous large-scale reports of multifactorial analysis for canal, and jugular bulb, and can assist in the the predictive factors of cochlear nerve deficiency, espe- planning of the operative route [8]. To detect cochlear nerve cially imaging variables on MRI and CT.

Figure 1

1a

1b 1c Figure 1. Normal and hypoplastic cochlear seen in 3DFT-CISS images through the IAC of a 6-year-old boy. a. Axial image showing the right cochlear nerve (arrow) in the right IAC with normal dimension. The left cochlear nerve (arrow) was poorly visualized in the left IAC. b. Oblique sagittal image through the right IAC showing that the right cochlear nerve (arrow) lay in the anteroinferior portion of the IAC. The diameter of the cochlear nerve was the same or larger than that of the adjacent facial nerve, suggesting a normal right cochlear nerve. c. Oblique sagittal image through the left IAC showing that the left cochlear nerve (arrow) was markedly smaller than the facial nerve, suggesting severe hypoplasia of the left cochlear nerve.

44 J Radiol Sci June 2013 Vol.38 No.2 MRi evaluation for predictive factors of cochlear nerve deficiency

The present study was performed to determine whether scanners (TR/TE/NEX, 5.42–12.25 ms/2.42–5.9 ms/1–2; FA, there are significant correlations between cochlear nerve 50°–80°; FOV, 120–160 mm; matrix size, 512), with near- deficiency and bony anomalies of the inner ear or IAC. The isotropic voxel sizes of 0.5 mm in length. Oblique coronal endpoint was to determine whether an inner ear or IAC and oblique sagittal CISS images of IAC were reformed by anomaly could serve as a reliable predictive factor for the the multiplanar reconstruction (MPR) procedure. presence of cochlear nerve deficiency. Image Analysis and Data Collection MR images were reviewed on a PACS station by a Materials and Methods board-certified neuroradiologist with 20 years of experi- ence, who was blinded to the side of hearing loss. Diameters Subjects of cochlear nerve, facial nerve, IAC, and endolymphatic A retrospective review of the medical records of duct were measured on PACS and recorded. The reviewer pediatric cochlear implant candidates during the period examined the images and recorded data for the presence of from June 2002 to June 2010 at our center was performed. cochlear nerve deficiency, cochlear, vestibular, or semicir- A total of 111 patients with MRI examinations for SNHL cular canal (SCC) anomalies, endolymphatic duct enlarge- were identified. Complete audiological data were available ment, and IAC stenosis. for 88 of the 111 patients, and these cases were included in Cochlear nerve deficiency implied an absence or hypo- this study. plasia of the cochlear nerve (Fig. 1). The cochlear nerve was considered hypoplastic if it was smaller in diameter than Imaging Acquisition that of the adjacent facial nerve at the level of the middle to MRI was performed with a pediatric vestibulocochlear lateral third of the IAC. The cochlear nerve was considered nerve protocol on two 1.5-T scanners. The protocol included aplastic if it was not visible on any plane of the MR images. axial unenhanced spin-echo (SE) T1-weighted imaging, The morphology of the was also assessed, which axial and coronal T2-weighted imaging, and high-resolu- was categorized as normal or dysplastic (including aplasia tion three-dimensional Fourier transformation-constructive and hypoplasia) (Fig. 2). Cochlear hypoplasia was defined interference in steady state (3DFT-CISS) imaging through as morphological malformation of the cochlea or a coch- the temporal bones as well as axial fluid-attenuated inver- lear duct with less than 2.5 turns. Common cystic anomaly sion recovery imaging of the entire . was included in the category of cochlear hypoplasia. If the Parameters for the CISS sequence varied by MR cochlea was not visible, the case was considered to be a

Figure 2

2a 2b Figure 2. Cochlear anomalies seen on axial 3DFT-CISS images through the IAC. a. Cochlear hypoplasia (arrow) was seen as a cochlea with smaller size. A dilated endolymphatic duct (arrowhead) was also noted. b. No visualization of cochlear turns in the temporal bone, suggesting cochlear aplasia (arrow). A severely stenotic IAC, deformed vestibule (arrowhead), and absence of were also noted.

J Radiol Sci June 2013 Vol.38 No.2 45 MRi evaluation for predictive factors of cochlear nerve deficiency

Figure 3

3a 3b Figure 3. Cochleovestibular anomalies seen on axial 3DFT-CISS images through the IAC. a. Cystic dilatation of the cochlea and vestibule (arrow). b. Absence of cochlear and cystic dilatation of the vestibule (arrow), suggesting cochlear aplasia and vestibular hypoplasia.

Figure 4

Figure 4. Axial 3DFT-CISS images through the IAC showing decreased diameter of the right IAC (arrow) < 3 mm and a normal-sized left IAC, suggesting right IAC stenosis.

Figure 5

Figure 5. Axial 3DFT-CISS images through the level of the showing dilatation of the bilateral endolymphatic ducts (arrows).

46 J Radiol Sci June 2013 Vol.38 No.2 MRi evaluation for predictive factors of cochlear nerve deficiency cochlear aplasia. Vestibular or SCC anomaly was consid- had unilateral SNHL, comprising a total of 149 ears with ered in cases with any morphological malformation of the SNHL. MRI demonstrated inner ear or IAC anomalies in vestibule or SCC (Fig. 3). IAC was considered stenotic if 60 of 149 ears (40%) with SNHL and IAC stenosis in only its narrowest dimension on axial or parasagittal oblique 2 of the 27 (7%) asymptomatic ears. Of the 62 ears with images was less than 3 mm [16, 17] (Fig. 4). Endolymphatic inner ear or IAC anomalies, 30 (48%) had at least one coex- duct dilatation was defined as a midpoint diameter larger isting anomaly. The specific type of anomaly, number and than 1.5 mm (Fig. 5). percentage of ears, and concurrent anomalies are summa- rized in Table 1. Statistical Analysis Of note, 10 ears (from 9 patients) had cochlear nerve Descriptive statistical analyses of the ears with deficiency but were not associated with any other anomaly cochlear nerve deficiency, inner ear anomalies, and IAC of the inner ear or IAC, considered isolated cochlear nerve stenosis were performed. Categorical data were calculated deficiency, which represented 6.7% of ears with SNHL. with frequency measurements. To determine the predic- As 10 (37%) of the 27 patients with cochlear nerve tive factors of cochlear nerve deficiency, generalized esti- deficiency presented with bilateral ear involvement, poten- mating equations (GEE) logistic regression models were tial correlations between the left ear and right ear of the used, taking into account the dependence between both same individual were considered. With respect to the pres- ears of the same individual. The outcome of interest (i.e., ence of cochlear nerve deficiency, the Pearson’s correlation the dependent variable) was cochlear nerve deficiency. coefficient between the bilateral ears was calculated to be Covariates (i.e., the predictor variables) included cochlear 0.42 (P < 0.001), indicating a medium positive correlation. dysplasia, vestibular/SCC anomaly, endolymphatic duct In the univariate GEE models (Table 2), after dilatation, and IAC stenosis. First, each of the possible adjusting for the sidedness of the ears, the presence of predictors was subjected to univariate analysis with a GEE cochlear dysplasia, vestibular/SCC anomaly, and IAC model. Then a multivariate GEE model was adopted with stenosis showed significant associations with cochlear respect to statistically significant results from univariate nerve deficiency, with calculated odds ratios for predic- analyses. Statistical analyses were performed using SPSS tion of 38.0, 31.7, and 30.2, respectively. Endolymphatic Version 18.0 (SPSS, Chicago, IL). In all analyses, P < 0.05 duct dilatation could not be evaluated by logistic regres- was taken to indicate statistical significance. sion analysis as there were no concurrent cases of cochlear nerve deficiency and endolymphatic duct dilatation in our study population. Results In the multivariate GEE model (Table 3), after adjust- ment for the sidedness of the ears, both cochlear dysplasia Among the 111 patients with SNHL undergoing and IAC stenosis showed significant correlations with temporal bone MRI over the 8-year study period, 23 were cochlear nerve deficiency. The odds ratios of cochlear excluded due to incomplete audiological data. Therefore, dysplasia and IAC stenosis for prediction of cochlear nerve 88 patients were included in the analysis (44 males and 44 deficiency were 16.0 and 22.8, respectively. The odds ratio females). The patients ranged in age from 6 months to 18 of vestibular/SCC anomaly was 1.4 and was not statistically years (mean age, 7.8 years). Among these 88 patients (176 significant. ears), 61 (69%) had bilateral SNHL and the other 27 (31%)

Table 1. Inner Ear and IAC Anomalies Detected by Magnetic Resonance Imaging in 149 Ears of Children with Sensorineural Hearing Loss

Type of Concurrent Anomalies, No/Total (%) Concurrent Anomalies, Anomaly Type Anomalies, No/Total (%) Cochlear nerve Cochlear Vestibule/ IAC Endolymphatic No/Total (%) deficiency anomaly SCC anomaly stenosis duct dilatation

Cochlear nerve deficiency 37/149 (25) 27/37 (73) - 13/37 (35) 9/37 (24) 23/37 (62) 0/37 (0)

Cochlear anomaly 16/149 (11) 16/16 (100) 13/16 (81) - 9/16 (56) 10/16 (63) 2/16 (13) Vestibule/SCC anomaly 10/149 (7) 10/10 (100) 9/10 (90) 9/10 (90) - 8/10 (80) 0/10 (0) IAC stenosis 28/149 (19) 24/28 (86) 23/28 (82) 10/28 (36) 8/28 (29) - 0/28 (0)

Endolymphatic duct 18/149 (12) 2/18 (11) 0/18 (0) 2/18 (11) 0/18 (0) 0/18 (0) - dilatation

J Radiol Sci June 2013 Vol.38 No.2 47 MRi evaluation for predictive factors of cochlear nerve deficiency

Table 2. Univariate GEE models for the prediction of cochlear nerve deficiency adjusting for sidedness of the ears

95% CI for OR Parameter OR P value Lower Upper Cochlear dysplasia =1 38.0 5.83 247.59 < 0.001 Cochlear dysplasia =0 1 - - Vestibular/SCC anomaly =1 31.7 7.71 130.02 < 0.001 Vestibular/SCC anomaly =0 1 - - IAC stenosis =1 30.2 10.93 83.64 < 0.001

IAC stenosis =0 1 - - Abbreviations: GEE, Generalized Estimating Equations; OR, odds ratio; CI, confidence interval

Table 3. Multivariate GEE model for the prediction of cochlear nerve deficiency adjusting for sidedness of the ears

95% CI for OR Parameter OR P value Lower Upper Cochlear dysplasia =1 16.0 1.81 140.27 0.012 Cochlear dysplasia =0 1 - - Vestibular/SCC anomaly =1 1.4 0.15 12.96 0.756 Vestibular/SCC anomaly =0 1 - - IAC stenosis =1 22.8 7.43 69.69 < 0.001 IAC stenosis =0 1 - - Abbreviations: GEE, Generalized Estimating Equations; OR, odds ratio; CI, confidence interval

Discussion odds of success for predicting cochlear nerve deficiency. In contrast, the presence of cochlear dysplasia had 16-fold IAC stenosis and cochlear dysplasia were positive greater odds of successful prediction for cochlear nerve predictive factors for cochlear nerve deficiency. In addition, deficiency than its normal counterpart. Therefore, IAC the odds ratio for success of predicting cochlear nerve defi- stenosis demonstrated a larger odds ratio than cochlear ciency was larger in the presence of IAC stenosis than for dysplasia, suggesting that it might be the most important cochlear dysplasia. predictor among all of the variables. To the best of our knowledge, there have been no In univariate GEE analyses, cochlear anomaly, previous reports of multivariate regression models for vestibular/SCC anomaly, and IAC stenosis showed possible predictors of cochlear nerve deficiency. In addition, the correlations with cochlear nerve deficiency. However, in potential correlation between both ears of the same indi- multivariate GEE analysis, the odds ratio of vestibular/SCC vidual has not been mentioned in previous reports. Our anomaly dropped and became statistically insignificant. study demonstrated that there is a positive correlation One possible explanation is that the weighting of correlation among the bilateral ears of the same individual with respect of vestibular/SCC anomaly with cochlear nerve deficiency to cochlear nerve deficiency. The GEE models were used is far smaller than those of either cochlear anomaly or IAC with correction for this within-subject variable. Future stenosis, so its influence is suppressed by the other two vari- studies should be performed to eluciadate for potential ables in multivariate analysis. Another possible explanation correlations among the ears of the same individual. is that there may be multicollinearity among the predictor In multivariate GEE analysis, both IAC stenosis variables. However, no significant multicollinearity was and cochlear dysplasia showed significant odds ratios for found in our study, because the value of variance inflation predicting cochlear nerve deficiency. Compared to normal factor (VIF) between the predictor variables was less than IAC, the presence of IAC stenosis had 23 times greater 10 (just slightly greater than 1).

48 J Radiol Sci June 2013 Vol.38 No.2 MRi evaluation for predictive factors of cochlear nerve deficiency

The overall incidence of inner ear or IAC anomaly was Previously, this was considered very rare [9, 13]. The devel- 40% in the ears with SNHL, falling at the high-end value opment of isolated cochlear nerve deficiency may be due to of the previously reported range of 20-41% [6, 7, 18]. The disturbance of the neuronal growth of cochlear nerve after most common inner ear anomaly identified in our study formation of the bony labyrinth and IAC. In the present was cochlear nerve deficiency (25%), the incidence rate of study, the incidence of isolated cochlear nerve deficiency which was higher than the values of 12–18% reported previ- was 6.7% in the ears with SNHL. Clinically, ENT surgeons ously [10, 18]. and radiologists should keep in mind that there is a small Embryonic development of the inner ear begins with percentage of cochlear nerve deficiency that cannot be the formation of the otic vesicle into a vestibular pouch and suggested by CT findings of abnormal bony labyrinth or a cochlear pouch (the future and ), which IAC, but can be determined by MRI. occurs between the fourth and fifth gestational week in In the present study, endolymphatic duct dilation humans [6, 19, 20]. The cochlear duct begins to extend from had an incidence of 12%, comparable to the previously the cochlear pouch late in the fifth gestational week, further reported incidence of 10-15% [18, 21]. In those both ears developing into cochlear turns in the seventh gestational with combined endolymphatic duct dilatation and cochlear week. The semicircular canals develop from the vestibular anomaly, the cochlear anomaly was presented with the pouch in the seventh gestational week. The developing milder form of cochlear deformity (cochlear hypoplasia) inner ear elicits a trophic effect on cochlear neurons with rather than the more severe form (cochlear aplasia). This nerve growth factor released from the otic vesicle, which observation was consistent with previous findings [23]. We is necessary for neuronal survival [9]. Disturbance of this did not find any deficient cochlear nerve in the ears with neurotrophic effect may lead to cochlear nerve hypoplasia, endolymphatic duct dilatation, although one such case was which may explain the positive predictive value of cochlear reported previously [11]. The vestibular aqueduct grows dysplasia for cochlear nerve deficiency observed in the throughout fetal life and continues postnatally until age 3 present study. or 4 years [24], which is different from the development As embryonic development of the vestibule precedes of the otic capsule and cochlear nerve early in embryonic that of the cochlea, vestibular anomaly suggests an earlier development. The difference in developmental chronicity embryological disturbance which may affect both the of cochlear nerve and vestibular aqueduct may explain the developing vestibule and cochlea with resultant more lack of concurrent endolymphatic duct dilatation and coch- severe labyrinthine malformation. Previously, vestibular lear nerve deficiency observed in our study. dysplasia was thought to be almost always in association In this study, most ears with cochlear nerve deficiency with other inner ear anomalies [21].Our study also demon- had concurrent structural anomaly that can be detected by strated that there was no isolated vestibular anomaly in our both CT or MRI. However, there were ten ears with isolated patients with SNHL. In addition, all the ears with vestibular cochlear nerve deficiency that could only be detected by anomaly were also associated more than two other types of MRI, which represented 27% of ears with cochlear nerve inner ear or IAC anomaly. deficiency. Clinically, children with SNHL who are candi- The development of IAC occurs by inhibition of carti- dates for cochlear implantation usually undergo MRI before lage formation at the medial side of the otic vesicle during final pretreatment evaluation. However, at times ENT fetal life. Previous studies have suggested that an inhibitory surgeons may prefer to order a HRCT of temporal bone first substance may be induced by the presence of the vestibulo- for an overall evaluation. Besides, parents may concern cochlear nerve [21, 22]. Glastonbury et al. further suggested about the risk of sedation for their children, and some that the degree of hypoplasia may children are not suitable for sedation due to medical issues. be related to the severity of IAC stenosis [11]. The results of CT has a number of advantages, including ready avail- the present study indicate that IAC stenosis is the strongest ability, lower cost, faster scan time that reduces the need statistically significant positive predictor of cochlear nerve for sedation of children, and better cortical delineation of deficiency, which supports the developmental theory of the the , bony labyrinths, facial nerve canal, and jugular cause-effect relationship between the cochlear nerve and fossa. CT findings can assist the surgeon in choosing the IAC. appropriate type and size of cochlear implant. This study There are four nerves contained in IAC, including suggests that if IAC stenosis or cochlear malformation is cochlear nerve, superior and inferior vestibular nerves, detected by CT, there is a higher risk of cochlear nerve defi- and facial nerve. The presence of a normal cochlear nerve ciency, and MRI is indispensable for definite results and within a stenotic IAC may be explained by deficiency of more cost-effective treatment in such cases. In contrast, if cartilage inhibitory substance resulting from hypoplasia of an enlarged vestibular aqueduct is detected by CT, there is facial nerve or vestibular nerves in the IAC [21]. a better chance of the presence of a normal cochlear nerve. The finding of isolated cochlear nerve deficiency is of In terms of choosing which ear for implantation, interest, which means a hypoplastic cochlear nerve within the ear without IAC stenosis or cochlear malformation is a normal IAC and without any labyrinthine deformity. preferred due to lower risk of cochlear nerve deficiency,

J Radiol Sci June 2013 Vol.38 No.2 49 MRi evaluation for predictive factors of cochlear nerve deficiency leading to a higher likelihood of successful implantation. 9. Casselman JW, Offeciers FE, Govaerts PJ, et al. Aplasia In the presence of cochlear nerve deficiency, the diameter and hypoplasia of the vestibulocochlear nerve: diagnosis of nerve fibers is also of clinical importance, which repre- with MR imaging. Radiology 1997; 202: 773-781 sents a disease spectrum ranging from nerve hypoplasia to 10. Parry DA, Booth T, Roland PS. Advantages of magnetic aplasia and correlates with the number of spiral ganglion resonance imaging over computed tomography in cell count [3]. It is important to remind the clinician of the preoperative evaluation of pediatric cochlear implant different extent of disease severity in the imaging report candidates. Otol Neurotol 2005; 26: 976-982 for better outcome of cochlear implantation. Further study 11. Glastonbury CM, Davidson HC, Harnsberger HR, to elucidate the relationship between severity of cochlear Butler J, Kertesz TR, Shelton C. Imaging findings of nerve deficiency and degree of congenital malformations cochlear nerve deficiency. AJNR Am J Neuroradiol may be considered. 2002; 23: 635-643 12. Shelton C, Luxford WM, Tonokawa LL, Lo WW, House WF. The narrow internal auditory canal in children: Conclusions a contraindication to cochlear implants. Otolaryngol Head Surg 1989; 100: 227-231 Congenital anomalies of the inner ear and IAC repre- 13. Sennaroglu L, Saatci I, Aralasmak A, Gursel B, Turan E. sent a spectrum of diseases that may be attributed to distur- Magnetic resonance imaging versus computed tomog- bance of the embryological development of the inner ear. raphy in pre-operative evaluation of cochlear implant Most ears with cochlear nerve deficiency have concurrent candidates with congenital hearing loss. J Laryngol Otol anomaly of the bony labyrinth or IAC. IAC stenosis and 2002; 116: 804-810 cochlear dysplasia were shown to be positive predictive 14. Adunka OF, Roush PA, Teagle HF, et al. Internal audi- factors for cochlear nerve deficiency with significant odds tory canal morphology in children with cochlear nerve ratios of 23.0 and 16.0, respectively. In those children with deficiency. Otol Neurotol 2006; 27: 793-801 IAC stenosis or cochlear dysplasia which may be detected 15. Nelson EG, Hinojosa R. Aplasia of the cochlear nerve: by CT in advance, MRI should be performed for evaluation a temporal bone study. Otol Neurotol 2001; 22: 790-795 of cochlear nerve deficiency. 16. Olivares FP, Schuknecht HF. Width of the internal auditory canal. A histological study. Ann Otol Rhinol Laryngol 1979; 88: 316-323 References 17. Sakashita T, Sando I. Postnatal development of the internal auditory canal studied by computer-aided three- 1. Osberger MJ. Cochlear implantation in children under dimensional reconstruction and measurement. Ann Otol the age of two years: candidacy considerations. Otolar- Rhinol Laryngol 1995; 104: 469-475 yngol Head Neck Surg 1997; 117: 145-149 18. McClay JE, Booth TN, Parry DA, Johnson R, Roland P. 2. Makhdoum MJ, Snik FM, van de Broek P. Cochlear Evaluation of pediatric sensorineural hearing loss with implantation in deaf children. Ann Saudi Med 1997; 17: magnetic resonance imaging. Arch Otolaryngol Head 533-539 Neck Surg 2008; 134: 945-952 3. Nadol JB, Jr., Xu WZ. Diameter of the cochlear nerve 19. Jackler RK, Luxford WM, House WF. Congenital in deaf humans: implications for cochlear implantation. malformations of the inner ear: a classification based on Ann Otol Rhinol Laryngol 1992; 101: 988-993 embryogenesis. Laryngoscope 1987; 97; Suppl 40: 2-14 4. Ylikoski J, Savolainen S. The cochlear nerve in various 20. Larsen WJ. Human Embryology. 3rd ed. New York: forms of deafness. Acta Otolaryngol 1984; 98: 418-427 Churchill Livingstone 2001 5. Morita T, Naito Y, Tsuji J, Nakamura T, Yamaguchi S, 21. Davidson HC. Imaging evaluation of sensorineural Ito J. Relationship between cochlear implant outcome hearing loss. Semin Ultrasound CT MR 2001; 22: and the diameter of the cochlear nerve depicted on MRI. 229-249 Acta Otolaryngol Suppl 2004: 551: 56-59 22. McPhee JR, Van de Water TR. Epithelial-mesenchymal 6. Lowe LH, Vezina LG. Sensorineural hearing loss in tissue interactions guiding otic capsule formation: the children. Radiographics 1997; 1079-1093 role of the otocyst. J Embryol Exp Morphol 1986; 97: 7. Simons JP, Mandell DL, Arjmand EM. Computed 1-24 tomography and magnetic resonance imaging in pedi- 23. Davidson HC, Harnsberger HR, Lemmerling MM, et al. atric unilateral and asymmetric sensorineural hearing MR evaluation of vestibulocochlear anomalies associ- loss. Arch Otolaryngol Head Neck Surg 2006; 132: ated with large endolymphatic duct and sac. AJNR Am 186-192 J Neuroradiol 1999; 20: 1435-1441 8. Mylanus EA, Rotteveel LJ, Leeuw RL. Congenital 24. Pyle GM. Embryological development and large vestib- malformation of the inner ear and pediatric cochlear ular aqueduct syndrome. Laryngoscope 2000; 110: implantation. Otol Neurotol 2004; 25: 308-317 1837-1842

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