[Intraoperative monitoring of brainstem auditory evoked potentials during microvascular decompression of cranial nerves in cerebellopontine angle].

Brainstem auditory evoked potentials (BAEP) monitoring is a useful tool to decrease the danger of hearing loss during pontocerebellar angle surgery, particularly in microvascular decompression (MVD). Critical complications arising during MVD surgery are the stretching of the VIII nerve - the main cause of hearing loss - labyrinthine artery manipulation, direct trauma with instruments, or a nearby coagulation, and at end of the surgery neocompression of the cochlear nerve by the prosthesis positioned between the conflicting vessel(s) and the VIIth-VIIIth nerve complex. All these dangers warrant the use of BEAP monitoring during the surgical team's training period. Based on delay in latency of peak V, we established warning thresholds that can provide useful feedback to the surgeon to modify the surgical strategy: the initial signal at 0.4 ms is considered the safety limit. A second signal threshold at 0.6 ms (warning signal for risk) corresponds to the group of patients without resultant hearing loss. The third threshold characterized by the delay of peak V is at 1 ms (warning signal for a potentially critical situation). BAEP monitoring provides the surgeon with information on the functional state of the auditory pathways and should help avoid or correct manoeuvres that can harm hearing function. BAEP monitoring during VIIth-VIIIth complex surgery, particularly in MVD of facial nerves for HFS is very useful during the learning period.