EFFICACY OF AUDITORY BRAIN-STEM RESPONSE AS A SCREENING-TEST FOR SMALL ACOUSTIC NEUROMAS

Auditory brainstem response (ABR) has been advocated as a high sensiti vity screening test for acoustic neuroma. With the advent of magnetic resonance imaging (MRI), smaller size acoustic neuromas are now detect able. A prospective trial was performed to determine the sensitivity o f ABR in diagnosing small acoustic neuromas. One hundred five randomly selected patients with surgically proved acoustic neuromas underwent preoperative ABR tests within 2 months of their surgery. Patients with a histologic diagnosis other than acoustic neuroma were excluded from this study. A test was considered abnormal when the interaural wave I -V latency difference was greater than 0.2 ms, the absolute wave V lat ency was abnormally prolonged, or there was abnormal or absent wavefor m morphology. Of the 105 patients tested 92 (87.6%) had abnormal ABR t ests, and 13 (12.4%) had completely normal waveforms and wave latencie s. Eighteen patients had tumors over 2 cm in total diameter. Of these, 12 were 2.5 cm or larger and 6 were between 2.1 and 2.4 cm. All of th ese 18 patients had abnormal ABR tests. Of the 29 patients with tumors 1.6-2.0 cm in size, 25 (86%) had abnormal ABRs. In the 1.0-1.5 cm dia meter range there were 45 patients who underwent a preoperative ABR. O f these, 40 (89%) had abnormal ABRs. Of 13 patients with tumors 9 mm o r smaller, only 9 (69%) had abnormal ABR tests (p<.05). Thus, it appea rs that ABR sensitivity decreases with tumor size and is particularly inadequate for tumors of less than 1 cm in diameter. The authors concl ude that ABR is not a good screening test for smaller acoustic neuroma s and recommend MRI for patients with suspected acoustic neuroma.