False negative auditory brainstem response findings in vestibular schwannoma: case reports

The false negative rate of the auditory brainstem response (ABR) for the detection of vestibular schwannoma (VS; acoustic neuroma) has been reported to range from 2 to 9 percent. The introduction of magnetic resonance with gadolinium contrast (Gd MRI) may be expected to raise the false negative rate, because smaller tumors can now be detected. We present two cases that illustrate some of the complex issues raised by the detection of small asymptomatic VS by Gd MRI that were missed by ABR. The role of ABR testing in the diagnosis and management of VS remains well established and will continue to evolve.