SUCCESSFUL DETECTION OF SMALL ACOUSTIC TUMORS USING THE STACKED DERIVED-BAND AUDITORY BRAIN-STEM RESPONSE AMPLITUDE

Hypothesis: The aim of this study was to show that a new auditory brai n 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 stand ard ABR latency measures have inadequate sensitivity to detection of s mall intracanalicular acoustic tumors. Consequently, despite its relat ively low cost and wide availability, the standard ABR test has been r eplaced as a diagnostic screening tool by magnetic resonance imaging ( MRI) with gadolinium (Gd-DTPA) contrast. However, screening with MRIs can be problematic because of their high cost, limited availability, a nd impact on patient comfort. Thus, an ABR method capable of detecting small tumors with good specificity would be an invaluable cost-effect ive screening tool for reducing the number of patients without tumor i maged. Methods: Derived-band ABRs were obtained to 63-dB normal hearin g level (nHL) clicks using high-pass noise-masking procedures. The new measure is the wave V amplitude of a stacked ABR constructed by tempo rally aligning wave V of each derived-band ABR and then summing the ti me-shifted responses. Results: In a series of 25 tumor cases, 5 small (less than or equal to 1 cm) intracanalicular tumors. missed by standa rd ABR latency measures, were detected by this new stacked ABR method. The stacked wave V ABR amplitudes in all five cases were significantl y lower than those obtained in a group of normal-hearing individuals w ithout tamers. Conclusions: A new ABR measure, the stacked derived-ban d ABR amplitude, is sensitive to the presence of small intracanalicula r 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 app roach to reducing the number of patients without tumors imaged and as a method for acoustic tumor screening when MRI scans: I) are unavailab le, 2) are not appropriate because of patient comfort. and 3) need to be justified because of their cost.