Effects of intraoperative motor evoked potential amplification following tetanic stimulation of the pudendal nerve in pediatric craniotomy

OBJECTIVE Monitoring the intraoperative motor evoked potentials (MEPs) in pediatric craniotomy is challenging because of its low detection rate, which makes it unreliable. Tetanic stimulation of the peripheral nerves of the extremities and pudendal nerves prior to transcranial electrical stimulation (TES) or direct cortical stimulation (DCS) amplifies the MEPs. The authors investigated the effects of MEP amplification following tetanic stimulation of the median and tibial nerve or the pudendal nerve in pediatric patients undergoing craniotomy. METHODS This prospective observational study included 15 patients <= 15 years of age (mean age 8.9 +/- 4.9 years) undergoing craniotomy. MEPs were obtained with TES (15 cases) or DCS (8 cases)-conventional MEP without tetanic stimulation (c-MEP) and MEP following tetanic stimulation of the unilateral median and tibial nerves (mt-MEP) or following tetanic stimulation of the pudendal nerve (p-MEP) were used. Compound muscle action potentials were elicited from the abductor pollicis brevis, gastrocnemius, tibialis anterior, and abductor hallucis longus muscles. The authors compared the identification rate and the rate of amplitude increase of each MEP. RESULTS For both TES and DCS, the identification and amplitude increase rates were significantly higher in cases without preoperative hemiparesis for p-MEPs than in those for c-MEPs and mt-MEPs. In comparison to patients with preoperative hemiparesis, p-MEPs displayed a higher identification rate, with fewer false negatives in DCS cases. CONCLUSIONS In pediatric craniotomy, the authors observed the amplification effect of MEPs with pudendal nerve tetanic stimulation and the amplification effect of DCS on MEPs without increasing false negatives. These findings suggested the likelihood of more reliable intraoperative MEP monitoring in pediatric cases.