Motor-evoked potentials (MEP) during brainstem surgery to preserve corticospinal function

Abstract

Brainstem surgery bears a risk of damage to the corticospinal tract (CST). Motor-evoked potentials (MEPs) are used intraoperatively to monitor CST function in order to detect CST damage at a reversible stage and thus impede permanent neurological deficits. While the method of MEP is generally accepted, warning criteria in the context of brainstem surgery still have to be agreed on. Conclusions: Adjustment of surgical strategy contributed to good motor outcome in 33/39 patients. MEP monitoring may help significantly to prevent motor deficits during demanding neurosurgical procedures on the brainstem.

Facial nerve motor evoked potentials during skull base surgery to monitor facial nerve function using the threshold-level method

“…Gradually progressive threshold elevations were attributed to anesthetic fade, 11 and the baseline FNMEP threshold was adjusted. 6,16 Rapid threshold elevations were analyzed in the context of the surgical manipulations and were considered possibly pathological. Facial nerve MEPs were considered deteriorated, and the surgical team was notified whenever the FNMEP intensity threshold had to be elevated by more than 20 mA.…”

“…The criterion adopted in our study was motivated by values published for surgeries at the level of 16 This criterion led to a warning issued in 18 (53%) of 34 surgical interventions. However, one has to bear in mind that the 3 instances of warnings without ensuing House-Brackmann grade deterioration cannot strictly qualify as false-positive cases since action was taken intraoperatively with the aim to prevent paresis.…”

“…Also, high FNMEP stimulation intensity is needed to achieve maximal FNMEP response already at baseline so that subsequent response deterioration can be assessed. Inspired by promising findings in IONM of motor function during surgery at the level of the spine, 5 the cortex, 17 the brainstem, 16 and the facial nerve, 9 we propose here to monitor the increase in stimulation threshold needed to elicit FNMEPs to communicate with the surgeon and to predict postoperative facial nerve function.…”

Intraoperatives neurophysiologisches Monitoring verbessert das Outcome in der Neurochirurgie

“…Bei der ersten Gruppe von Verfahren, dem eigentlichen Monitoring, wird die Funktion der Nervenbahnen kontinuierlich überwacht [12,[14][15][16][17][18][19][20]. Die Messungen werden jeweils sofort ausgewertet, indem sie mit den Ausgangswerten zu Beginn der Operation verglichen werden (Abbildung 1).…”

“…Bei intrakraniellen Eingriffen wird schon eine Amplitudenreduktion als Warnzeichen angesehen [18]. Bei Eingriffen am Hirnstamm werden optimale Warnkriterien noch diskutiert [19,20,29] .…”