Objectives: To describe the importance of imaging with the use of magnetic resonance (MR) or computed tomography (CT) during the diagnostic workup of a patient with sensorineural hearing loss to determine the status of the cochlear nerve.
Design: Retrospective review.
Setting: Tertiary care academic institution.
Methods: A pediatric database was used to find patients with diagnoses of absent cochlear nerve. A retrospective chart review was performed from July 1999 to July 2004 to evaluate the route to diagnosis and any concomitant factors. Patients who had presented at kindergarten screening were included. Review was made of the audiologic investigations undertaken: routine audiometry, auditory brainstem response (ABR), and distortion product otoacoustic emission (OAE). Radiologic investigations were also reviewed consisting of CT and/or MR scans.
Results: The database yielded 12 cases of cochlear agenesis. Four patients were excluded because they had absence of the entire inner ear structures ipsilateral to the aplastic cochlear nerve (two cases) and because they had multiple congenital anomalies (two cases). There were equal numbers of males and females. There was a slight left-sided preponderance (5:3), and ages ranged from 5 through 7 years. All children had failed the initial screening audiogram. Follow-up audiologic evaluation revealed either profound loss or dead ear or a failed ABR in the presence of normal OAE testing. All patients had internal auditory canals less than 1.4 mm or MR-compatible findings.
Conclusions: Agenesis of the cochlear nerve may be more common than previously thought, especially in an otherwise healthy, nonsyndromic, school-aged child. Although audiometric evaluation alone usually strongly suggests the diagnosis, definitive evaluation with MR remains the gold standard.