Objective: This study aimed to determine whether postoperative facial nerve
paralysis or surgical manipulation causing paralysis could be predicted on
train responses during intraoperative facial nerve monitoring in acoustic
Study Design and Setting: This was a prospective study performed at a terti
ary referral center.
Patients and Methods: Train responses were recorded on a floppy disk and co
mpared with postoperative facial nerve function in 51 patients who underwen
t enlarged translabyrinthine acoustic neuroma surgery.
Main Outcome Measures: The number, duration, frequency, and peak-to-peak am
plitude of train responses were analyzed and compared with postoperative fa
cial nerve function.
Results: Trains were observed in 42 of 51 patients. Six of seven patients w
ith high-amplitude trains more than 250 muV, and three of five patients wit
h bomber-type high-frequency trains elicited during tumor dissection from t
he facial nerve or stretching the nerve, showed severe facial nerve dysfunc
tion. On the other hand, seven of the nine patients with no trains also sho
wed severe facial nerve dysfunction.
Conclusions: The presence of high-amplitude or high-frequency trains elicit
ed by surgical manipulation to the facial nerve seems to indicate a critica
l situation for the facial nerve. However, certain types of mechanical trau
ma resulting in severe facial nerve paralysis cannot be identified by train