Efficacy of auditory brainstem response as a screening test for small acoustic neuromas.

Auditory brainstem response (ABR) has been advocated as a high sensitivity screening test for acoustic neuroma. With the advent of magnetic resonance imaging (MRI), smaller size acoustic neuromas are now detectable. A prospective trial was performed to determine the sensitivity of 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 latency was abnormally prolonged, or there was abnormal or absent waveform morphology. Of the 105 patients tested 92 (87.6%) had abnormal ABR tests, and 13 (12.4%) had completely normal waveforms and wave latencies. 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 these 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 diameter range there were 45 patients who underwent a preoperative ABR. Of these, 40 (89%) had abnormal ABRs. Of 13 patients with tumors 9 mm or smaller, only 9 (69%) had abnormal ABR tests (p<.05). Thus, it appears that ABR sensitivity decreases with tumor size and is particularly inadequate for tumors of less than 1 cm in diameter. The authors conclude that ABR is not a good screening test for smaller acoustic neuromas and recommend MRI for patients with suspected acoustic neuroma