Hypothesis: The aim of this study was to show that a new auditory brain stem response (ABR) measure, the stacked derived-band ABR amplitude, can detect small acoustic intracanalicular tumors missed by standard ABR measures.
Background: Recent studies clearly have shown that standard ABR latency measures have inadequate sensitivity to detection of small intracanalicular acoustic tumors. Consequently, despite its relatively low cost and wide availability, the standard ABR test has been replaced as a diagnostic screening tool by magnetic resonance imaging (MRI) with gadolinium (GdDTPA) contrast. However, screening with MRIs can be problematic because of their high cost, limited availability, and impact on patient comfort. Thus, an ABR method capable of detecting small tumors with good specificity would be an invaluable cost-effective screening tool for reducing the number of patients without tumor imaged.
Methods: Derived-band ABRs were obtained to 63-dB normal hearing level (nHL) clicks using high-pass noise-masking procedures. The new measure is the wave V amplitude of a stacked ABR constructed by temporally aligning wave V of each derived-band ABR and then summing the time-shifted responses.
Results: In a series of 25 tumor cases, 5 small (< or = 1 cm) intracanalicular tumors, missed by standard ABR latency measures, were detected by this new stacked ABR method. The stacked wave V ABR amplitudes in all five cases were significantly lower than those obtained in a group of normal-hearing individuals without tumors.
Conclusions: A new ABR measure, the stacked derived-band ABR amplitude, is sensitive to the presence of small intracanalicular tumors in patients and has excellent specificity for the absence of tumors in normal-hearing individuals. This method, in combination with standard ABR measures, appears promising both as a cost-effective approach to reducing the number of patients without tumors imaged and as a method for acoustic tumor screening when MRI scans: 1) are unavailable; 2) are not appropriate because of patient comfort; and 3) need to be justified because of their cost.