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The poor sensitivity of audiometric brain stem response for small vestibular schwannomas (acoustic neuromas) creates a dilemma for the physician evaluation a patient with sings and symptoms of retrocochlear disease. Magnetic resonance imaging is recognized as the gold standard for the evaluation of these problems, but it a complete examination of the internal auditory canals and head is done on every patient, the cost is high. Although less expensive, screening with audiometric brain stem response risks missing up to 33% of small tumors. Therefore we developed a focused magnetic resonance imaging sequence for evaluation of patients with asymmetric sensorineural hearing loss and or nonpulsatile tinnitus. The protocol includes a T1-weighted sagittal localizer pregadolinium and post-gadolinium –weighted 3-mm contiguous axial slice through the internal auditory canal and the region of the cerebellopontine angle, and t2 –weighted axial images through the entire brain. Total scanning time is about 12 minutes, and the estimated cost is $300 to $500. We retrospectively reviewed the imaging records of 485 screening examinations done during an 18-month period. Twenty-four patients had diagnoses definitely or probably producing the hearing loss for an overall positive rate of 5%. By eliminating the need for follow-up audiometric or electrophysiologic studies, we believe a focused magnetic resonance imaging-based diagnostic scheme is actually more cost-effective on a cost-per-patient basis.
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