Electrocochleography and brain stem responses used in the diagnosis of acoustic tumors

Electrocochleography (ECochG) and brain stem electric responses (BER) were obtained from 119 patients, 23 with confirmed vestibular Schwannomas (V-S) and 96 in which tumors were ruled out. Latency, amplitude, and waveforms of the EcochG response were considered from a diagnostic standpoint. Only the waveform held promise for the differential diagnosis of V-S. Analyses of these waveforms suggest two types of abnormality. However, comparison of these abnormal waves with those from non-tumor patients did not suggest the waveform to be of significant diagnostic value. It was concluded that ECochG is of little value in the differential diagnosis of acoustic tumors. Latency of the BER Jewett V wave was analyzed in two ways: Those from tumor patients were compared with the latency in normal patients; the latency obtained from each ear of the same patient was compared to obtain the interaural latency difference (ILD). The ILD was the preferred measure. Sources of error in using the ILD for screening to detect tumors are described. Unilateral conductive losses produced the most false positives, with head trauma, vascular insufficiency, Lues, and sudden losses also contributing false positives. Crossover responses from unilaterally deaf patients are described which show the need for masking of the contralateral ear. Two tumors missed by this method are discussed. An ILD of greater than 0.3 msec was considered abnormal. The ILD was found to be greater than 0.3 msec in 18 of 20 patients with V-S and in 34 of 96 non-tumor patients. An overall diagnostic efficiency of 76 per cent was calculated for this test. This efficciency ranks it as one of the best tests for the differential diagnosis of acoustic tumors.