S. Butler et al., PHYSIOLOGICAL IDENTIFICATION OF THE AUDITORY-NERVE DURING SURGERY FORACOUSTIC NEUROMA, Clinical otolaryngology and allied sciences, 20(4), 1995, pp. 312-317
We report the design and clinical use of an electrode which can locate
the acoustic nerve fibres in the normal eighth nerve and also in eigh
th nerves deformed by acoustic neuromas. The improvement in facial ner
ve preservation during acoustic neuroma surgery is partly due to the u
se of a facial nerve stimulator to anatomically locate the fibres. Our
new acoustic nerve detector has the capability of anatomical location
of cochlear fibres which may help to improve hearing preservation in
selected cases of acoustic neuroma. The device functions by detecting
the compound action potential evoked by no frequency auditory simulati
on at 500 Hz. The 500 Hz compound action potential is detected with a
bipolar probe and then amplified and filtered. This results in a 500 H
z tone when the probe contacts the auditory nerve. Detection is virtua
lly instantaneous. The acoustic nerve detector (AND) is demonstrated i
n a normal eighth nerve complex and its use is then described in the t
otal removal of an acoustic neuroma with a 1 cm extracanalicular exten
sion in which useful hearing was saved post-operatively. The present p
rototype may not be sensitive enough to detect the very low signals th
at may result when cochlear fibres are widely distorted around a large
tumour or in cases where slight contusion of the nerve occurs during
dissection. In all other cases the real time anatomical information is
extremely helpful in guiding acoustic nerve dissection and also in mo
nitoring the effects of petrous bone drilling.