Antidromic corticospinal tract potential of the brain

Objective: To describe a novel potential component (antidromic corticospina l tract potential, ACSP) of the brain after translaminar spinal stimulation of a relaxed patient during scoliosis surgery. To study the origin of this component and to compare its source to known sources of the somatosensory evoked potentials (SEPs). Methods: We studied 17 consecutive patients during posterior scoliosis surg ery. SEPs and ACSPs were elicited by translaminar spinal stimulation at the Th 2 and L 1 levels. ACSPs and SEPs were recorded on the scalp midline. Ne urogenic motor evoked potentials (NMEPs) were recorded on the popliteal spa ces. Preoperative tibial SEPs were also recorded. Results: ACSP was distinctly separated from the corresponding spinally evok ed cortical SEP that showed longer latency than the ACSP, ACSPs decreased a nd disappeared when stimulation was moved to the caudal direction in the co nus region while SEP persisted. In addition, the hemispheric origin of ACSP was confirmed with multichannel midline recordings of the scalp and neck. Thus there was no confusion to the response of nucleus gracilis, correspond ing the P 31 response of the tibial nerve SEP. Conclusions: The origin of ACSP seemed to be in the rostral part of the cor ticospinal tract. ACSP diminished in the conus region when stimulation was moved caudally and it disappeared when the stimulus was given to the root l evel. This proves that ACSP is not a response of the somatosensory tract, i nstead ACSP represents antidromic response of the pyramidal tract. ACSP can be used in monitoring of the motor tracts during scoliosis surgery togethe r with NMEPs. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.