CT and MR imaging for pediatric cochlear implantation: emphasis on the relationship between the cochlear nerve canal and the cochlear nerve.

BACKGROUND

Cochlear implantation has become an accepted treatment for deafness. As the frequency of cochlear implantation has increased, requests for images have also increased in the work-up for candidates. An absent cochlear nerve (CN) is a contraindication to cochlear implantation. Therefore, MRI is performed to evaluate the CN in patients with sensorineural hearing loss. Recently, some authors have reported the relationship between cochlear nerve canal (CNC) stenosis and CN hypoplasia.

OBJECTIVE

To review the relationship between CNC and CN.

MATERIALS AND METHODS

During a period of 78 months, 21 children (42 ears) with unilateral or bilateral sensorineural hearing loss underwent both HRCT and MRI of the cochlear nerve. We retrospectively reviewed two factors: the evaluation of inner ear malformations and the relationship between CNC stenosis and CN hypoplasia.

RESULTS

Inner ear malformations were recognized in ten ears. The mean CNC diameter was approximately 2 mm (ranging from 0.6 to 2.7 mm). CN hypoplasia was seen in eight of the 42 ears; all eight were associated with CNC stenosis (<or=1.5 mm). Of the 34 ears with normal CN, 32 had CNC >1.5 mm in diameter and the remaining two ears, with incomplete partition type I, had CNC stenosis.

CONCLUSION

Children with CNC stenosis had a high incidence of CN hypoplasia. CNC stenosis (<or=1.5 mm) suggests CN hypoplasia. On the other hand, CN hypoplasia was not seen in children with CNC diameter >1.5 mm. Therefore, we conclude that children with CNC stenosis or malformations on HRCT should receive MR imaging of the CN.