Prognostic Values of Motor Evoked Potentials in Insular, Precental, or Postcentral Resections

To determine the predictive values of motor evoked potentials (MEPs) on the muscle strength of patients undergoing insular and/or around precentral or postcentral neurosurgeries.

Neurosurgeries were performed in 104 patients with continuous MEPs elicited with direct cortical and/or transcranial stimulation (DCS, TES; alarm criterion: reproducible 50% decrease in the MEP amplitudes). Muscle strength was evaluated with the British Medical Research Council Scale, before and postoperatively (1-3 days, 3 months).

Permanent decreases in DCS-MEPs identified all new upper limbs deficits (sensitivity: 100%; TES-MEPs: 82.3% upper, 78.6% lower limbs). All MEP decreases predicted deficits (positive predictive value: 100%). None of the stable limbs were associated with MEP decrease (specificity: 100%). All unchanged DCS-MEPs predicted unchanged strength (negative predictive values: 100%; TES-MEPs: 95.3% upper, 95.5% lower limbs). The risks of paresis at 3 months were of 0% with none or MEP deterioration <50%; 1.1% (1/91 patients) with MEP deterioration (50%-90%); 7.7% (7/91 patients) with MEP loss. Deficits at 3 months were due to ischemia detected intraoperatively (4.8%, 5/104 patients) or consequent to postoperative hemorrhage (5.8%, 6/104 patients) or to disease progression (2.9%, 3/104 patients).

The primary motor cortex and corticospinal pathway can reliably be monitored to protect motor strength during insular, precentral, and postcentral resections under general anesthesia. Nevertheless, MEPs did not prevent subcortical ischemias that might be reduced with continuous subcortical mapping. For the preservation of complex motor functions, for example, bimanual coordination, not evaluated here, insular surgeries can be performed with awake surgeries for which decision to undergo remains to the patient, aware of possible shorter survival.