Unilateral External Anal Sphincter MEP Monitoring in a Case of Conus Medullaris Tumor.

The use of intraoperative neurophysiological monitoring is a helpful tool during surgeries of conus medullaris tumors and helps in reducing the risk of post-operative functional compromise like paraparesis, sensory deficits, or urological dysfunctions. External anal sphincter (EAS) motor evoked potential (MEP) monitoring is usually done for monitoring sacral nerve roots and to prevent post-operative neurological deficits. Here we describe a case where unilateral motor cortical stimulation aided us to differentiate the laterality of TcMEP responses in EAS.