Release: May 12, 2000
Contact: Kenneth Satterfield, 407-238-4161 (as of 5/12/2000)
MRI RECOMMENDED FOR ANALYZING PEDIATRIC SENSORINEURAL HEARING LOSS
Orlando, FL -- Currently, the standard of care for imaging children with sensorineural hearing loss (SNHL) has been conducted by computed tomography (CT scan). Causes of pediatric SNHL are many, and determining the etiology of such losses can be difficult. Historical, clinical, audiometric, and serologic evaluation are often inadequate in establishing the diagnosis. Imaging techniques can evaluate for structural abnormalities, both congenital or acquired.
Background: Controversial issues surrounding temporal bone imaging in children with SNHL include yield, timing, cost effectiveness, clinical usefulness, and best technique. The diagnostic yield noted in previous studies of temporal bone high resolution CT (HRCT) for pediatric sensorineural hearing loss varies between 13-32 percent. Identifying patient factors which might predict positive imaging results, determining the frequency of neurotologic abnormalities, and distinguishing the temporal bone imaging techniques best able to identify abnormalities would be useful in addressing these issues
There have been several small series of studies reporting the results of magnetic resonance imaging (MRI) in evaluating both adults and children with sensorineural hearing loss and other neurotologic abnormalities. This is the first large scale analysis that compares the incidence and type of neurotologic studies found with an MRI to the findings of a temporal bone CT Scan. Identification of the type and incidence of abnormalities was performed, and an analysis of potential predictors of positive MRI scans completed. Where possible, comparison of -MRI findings with concurrently performed HRCT was made to distinguish the diagnostic yields between the two techniques.
The authors of the study, "High Resolution Magnetic Resonance Imaging in the Evaluation of Pediatric Sensorineural Hearing Loss: Can It Replace Computed Tomography?" are Mark Kriskovich, MD, Steven Kelly, MD, and Clough Shelton, MD, from the Department of Otolaryngology--Head and Neck Surgery; and H. Christian Davidson, MD, Department of Radiology, all from the University of Utah School of Medicine, Salt Lake City, UT. Their findings were presented before the Triological Society, meeting May 17-18, in Orlando, FL.
Methodology: One hundred ninety-eight consecutive children ages nine months to 16 years with SNHL who underwent screening MRI were evaluated retrospectively. MRI scans were performed using a 1.5 tesla super conducting MR scanner.
The scans were obtained using a three-inch dual phased-array coil centered over the external auditory canals. Acquisition time for this sequence was approximately 8 minutes. No contrast agent was required. Forty-four patients were also evaluated with HRCT, performed in the axial and coronal planes, 120 kvp, 400 mAs, one mm contiguous sections.
Inner ear, eighth nerve, and central abnormalities of the auditory pathways were considered significant radiographic findings. External auditory canal atresia, middle ear anomalies, inflammatory changes, and intracranial abnormalities not of neurotologic significance were not considered positive findings for the purpose of this study. HRCT and MRI results were compared for differences in those patients imaged by both modalities.
Results: Of the 198 MRIs performed, 62 (31.3 percent) had abnormalities of neurotologic significance Over 50 percent of patients had multiple anomalies either as bilateral lesions or different abnormalities occurring simultaneously.
(1) The most common radiological findings were large vestibular aqueduct, cochlear nerve aplasia or hypoplasia, cochlear dysplasia, modiolar deficiency, vestibular dysplasia, and labyrinthine ossificans.
(2) One hundred forty-one patients had adequate clinical and audiologic records available for review. The average age at time of scan was 6.9 years with an average age at diagnosis of hearing loss of 3.0 years. There was slight male predominance. The presence of family history of hearing loss, vertigo, progressive hearing loss, prematurity and low birth weight were not predictive of a positive scan.
(3) History of head trauma and meningitis were more likely to result in a positive imaging study. These approached statistical significance. Patients with severe, profound, asymmetrical, or unilateral hearing losses were statistically more likely to have abnormal MRIs.
(4) Forty-four patients had concurrent HRCTs performed in addition to MRI. Abnormalities noted on HRCT included the following: LVAS (8), labyrinthine ossificans (5), modiolar deficiency (4), cochlear dysplasia (2), vestibular dysplasia (2), high jugular bulb (1), temporal bone fracture (1), and internal auditory canal calcification (1). There were 19 discordant cases (43 percent) when comparing MRI to HRCT. Both techniques noted occasional inflammatory changes that may be missed by the other.
(5) HRCT did not detect the following significant abnormalities noted on MRI: cochlear nerve aplasia/hypoplasia (8), modiolar deficiency (3), temporal lobe atrophy (1), and facial nerve aplasia (1) . The only significant neurotologic abnormality noted on HRCT but not on MRI was one case of temporal bone fracture in a patient with a previous history of head trauma and known skull fracture.
The cost of MRI is actually less than HRCT at the host institution ($430 versus $700). There is also no radiation exposure. In comparison with standard MRI of the head, the scan time for the MRI is typically less than 20 minutes, and no intravenous contrast is required. The main disadvantage of MRI is loss of bony detail. Temporal bone fractures, when suspected, are better evaluated with HRCT.
Conclusion: High resolution MRI is sensitive in detecting abnormalities associated with pediatric SNHL. In this study MRI was superior to HRCT particularly for identification of cochlear nerve absence or hypoplasia and subtle cochlear abnormalities including modiolar deficiency. Whether to image all children with SNHL is a question yet to be answered. Patients with sever or profound asymmetric or unilateral hearing losses were more likely to have a positive MRI scan. Children with meningitis or head trauma may also be more likely to have abnormal studies. In many cases the imaging results have bearing on patient management including the feasibility of and planning for cochlear implantation.
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