Aims: Intraoperative neuromonitoring (ION) aims to detect early neurophysiological changes
due to reversible alterations of nervous system to prevent irreversible deficits.
The present study aimed to determine the validity and reliability of ION based on
motor-evoked potentials (MEPs).
Methods: Data were analyzed according to five categories: supratentorial tumors, supratentorial
vascular, infratentorial, spinal pathologies, and epilepsy. Motor strength was evaluated
with the Medical Research Council Scale the day before the surgery, 1, 3, and 5 days
postsurgery, as well as 2, 3, and 6 months.
ION was conducted with the NimEclipse: MEPs were realized with transcranial electric
stimulation (5 pulses, 350 Hz, 0.4 ms phase duration, max 180 mA; corkscrew electrodes
at C1, C2, and 1 cm more anterior and lateral). MEPs could also be realized by direct
cortical stimulation (strips, same parameters, max 14 mA). MEPs were gathered through
subdermal electrodes (lower limbs: abductor halluces and anterior tibialis, gastrocnemius,
and vastus medialis if required; upper limbs: lumbrical and brachioradialis, biceps,
triceps, and thenar if required). The amplitude of MEPs was monitored; the alert criterion
was a 50% decrease.
Results: Between 2009 and 2011, 307 consecutive patients underwent neurosurgery with MEPs
in Geneva. MEPs were most often conducted for supratentorial tumor (32%), supratentorial
vascular (29%), spinal (22%), infratentorial (14.5%), and epilepsy surgeries (2.5%).
Distribution of true-negatives (no new deficit and none alert), true-positives (alert
and new deficit), false-positives (alert but no new deficit), and false-negatives
(new deficit but none alert) are described in Table 1.
|
% of 449 Contributive Limb MEPs |
Comments |
| TN, true-negatives; TP, true positives; FP, false-positives; FN, false-negatives;
MRI, magnetic resonance imaging; SMA; ION, intraoperative neuromonitoring. |
| TN |
83.5 |
|
| TP |
7.8 (6.2% of patients, n = 19) |
n = 16 recovery within max 3 mo |
| FP |
2 |
Brain sagging, decrease in mean blood pressure, or strip displacement if direct cortical
stimulation |
| FN |
6.7 (4.9% of patients, n = 15) |
n = 9 ischemic lesion, vasospasm, hematoma on postoperative MRI |
|
|
n = 2 SMA resection |
|
|
n = 4 ION technical reasons |
Except 1% of patients (n = 3/307, 1 spinal deterioration and 2 primary motor deterioration), all patients
fully recovered within 3 months. In addition, the surgeon was alarmed in 19% of supratentorial
vascular surgeries at the time of temporary artery occlusion or in cases of perforant
artery occlusion by an aneurysm clip.
Conclusion: In this group of 307 patients, MEPs contributed to prevent new permanent deficits,
changing the intraoperative strategy in supratentorial tumor or epilepsy surgery,
preventing damage to the primary motor cortex and to motor pathways; in vascular surgery,
limiting duration of temporary clipping or indicating the replacement of clips; in
infratentorial surgeries, preventing motor pathways; in spinal surgery by transient
interruption of surgery.
