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

The presence of a functioning cochlear nerve 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 ear 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 hearing loss (SNHL) for the presence of cochlear nerve deficiency, cochlear, vestibular or semicircular canal (SCC) anomalies, endolymphatic duct enlargement, and IAC stenosis. Generalized estimating equations (GEE) logistic regression models were used to determine the predictive factors of cochlear nerve deficiency. MRI demonstrated inner ear or IAC anomalies in 60 of 149 ears (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 bony labyrinth 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. 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 2013; 38: 43-50 MRi evaluation for predictive factors of cochlear nerve deficiency 44 J Radiol Sci June 2013 Vol.38 No.2 to be evaluated [4]. The absence of the cochlear nerve is considered an absolute contraindication for cochlear implantation. Lack of a visible cochlear nerve on magnetic resonance imaging (MRI) has been shown to be related to poor outcome of cochlear implantation [5]. The preoperative evaluation for cochlear implantation includes CT and MRI. High-resolution CT has been recommended by many authors as the imaging modality of choice for the initial work-up of children with SNHL [6, 7]. CT may provide good resolution for abnormalities of the bony labyrinth, internal acoustic canal (IAC), ossicular chain, facial nerve canal, and jugular bulb, and can assist in the planning of the operative route [8]. To detect cochlear nerve deficiency, MRI provides better soft tissue resolution and direct visualization of the cochlear nerve [9, 10], but has a higher cost and a longer examination time. Some authors have suggested that there may be a correlation between cochlear nerve deficiency and bony abnormalities of the labyrinth or IAC, which can be detected by CT [11-13], while others have suggested that the correlation is unreliable [14, 15]. Most of these studies were case series or of small patient numbers utilizing descriptive statistical methods. To the best of our knowledge, there have been no previous large-scale reports of multifactorial analysis for the predictive factors of cochlear nerve deficiency, especially imaging variables on MRI and CT. Figure 1. Normal and hypoplastic cochlear nerves 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. 1a