High-resolution 3-D T2-weighted imaging in the diagnosis of labyrinthitis ossificans: emphasis on subtle cochlear involvement.

BACKGROUND: Meningitis is the most common cause of acquired sensorineural hearing loss (SNHL) in children. Labyrinthitis ossificans develops in a significant number of patients with meningitis-related SNHL. Reduced T2 signal on MRI within the membranous labyrinth is often noted in the fibrous and ossifying stages of labyrinthitis ossificans.

OBJECTIVE: The purpose of this study is to demonstrate the distribution and extent of involvement of the cochlea in children being evaluated for labyrinthitis ossificans; using high-resolution 3-D T2-weighted imaging, and to evaluate for subtle involvement of the scala tympani within the basal turn of the cochlea.

MATERIALS AND METHODS: A retrospective review from 2002 to 2012 was performed using a cochlear implant database and PACS search function. Twenty-four patients were found to have MR findings consistent with labyrinthitis ossificans, 13 previously reported. Axial 3-D T2-weighted sequences were obtained in all patients. The presence of abnormal decreased T2 signal within the scala tympani and vestibuli of the cochlea was noted and graded according to the extent. The electronic medical record was reviewed for audiometry and risk factors as well as correlative operative findings.

RESULTS: The average age at imaging was 4.2 years. M:F ratio = 5:1. Eighty-eight percent (21/24) of patients had bilateral SNHL. The most common risk factor for labyrinthitis ossificans was meningitis (19/24 or 79%). Eighteen (75%) patients had a history of bacterial meningitis. The mean age for the onset of labyrinthitis was 1.2 years with an average of 2.2-year interval to imaging. Nineteen patients (79%) underwent placement of a cochlear implant. Cochlear obstruction was documented in 83% (40/48) of the ears. Lower grade (1) cochlear obstruction was present in 14 ears and limited to the scala tympani. Statistical analysis was performed correlating MRI imaging and surgical findings.

CONCLUSION: Subtle, isolated involvement of the scala tympani within the proximal basal turn is a common finding in labyrinthitis ossificans and history typical for meningitis is not uniformly present. The extent of cochlear obstruction is important and has surgical implications.