The stapedius reflex test studied with laboratory and commercial equipment in acoustic neurinomas

Comparisons were made of contralateral stapedius reflex recordings obtained by means of two different electroacoustic impedance devices, the commercial Grason-Stadler 1723 (G-S 1723) impedance meter and a laboratory equipment, in patients with acoustic neurinoma. With the latter, acoustically elicited reflex responses were noted in 11 of the 21 tumour ears studied. The recordings with the G-S 1723 showed deflections indicating stapedius reflex responses in all 21 cases. Three of these deflections proved to be artefacts. The stapedius reflex threshold test indicated a retrocochlear lesion in all 21 pathological ears when the laboratory equipment was used. The G-S 1723 produced recordings indicating a cochlear lesion in two of these tumour ears. Furthermore, five of 15 normal contralateral ears were classified as having a retrocochlear lesion with the G-S 1723, as opposed to one with the laboratory equipment. The reflex decay test could be applied in 15 normal and six tumour ears. Only minor discrepancies in the degree of reflex decay were found between the two instruments. As the G-S 1723 displayed a low rate of detection for acoustic neurinomas (90%) and led to a large number of false-positive interpretations (33%), it is concluded that this instrument is less useful for diagnostic purposes than the laboratory equipment in differentiating between cochlear and retrocochlear lesions.