Localized transcranial electrical motor evoked potentials for monitoring cranial nerves in cranial base surgery.

OBJECTIVE

To describe a novel monitoring technique that allows "functional" assessment of cranial nerve continuity during cranial base surgery.

METHODS

Facial motor evoked potentials (MEP) in 71 consecutive patients were obtained by localized transcranial electrical stimulation in all patients requiring facial nerve monitoring during the period from November 2002 to August 2004. With transcranial electrical stimulation localized to the contralateral cortex, facial nerve MEPs are obtained through stimulation of more proximal intracranial structures.

RESULTS

Logistic regression revealed that the final-to-baseline facial MEP ratio predicted satisfactory (House-Brackmann Grade 1 and 2 function) immediate postoperative facial function (0.005 > P > 0.0005). Contingency table analysis showed high correlation (chi2, P < or = 2 x 10(8)) and acceptable test characteristics using a 50% final-to-baseline MEP ratio.

CONCLUSION

Facial nerve MEPs recorded intraoperatively during cranial base surgery using the proposed technique predicts immediate postoperative facial nerve outcome. This technique can also be used to monitor other motor cranial nerves in cranial base surgery.