Epidural D-Wave Recordings for Intramedullary Spinal Cord Tumors

Abstract

Direct or D-waves represent the direct activation of the corticospinal tract fibers that are recorded directly from the exposed spinal cord. While not as widely employed as the main intraoperative neuromonitoring motor function modalities such as motor evoked potentials (MEPs) or electromyography (EMG), epidural D-waves can provide just as much benefit to spinal monitoring cases. While MEPs and EMG record from the muscles, D-waves only record from the level of the epidural electrode on the spinal cord. While this may seem limited, D-waves have unique advantages (Figure 1). As a direct recording, the D-waves do not experience the same synaptic delay that MEPs experience at the ventral horn. Thus, there is little to no delay in the feedback of D-waves recordings. As a direct waveform, it requires little to no averaging, so there is less delay than for modalities that do. The single pulse stimulation needed to elicit a D-wave response also has less risk of causing patient movement, unlike MEPs, and thus can be run continuously without worry . This can detect warning changes potentially indicating compromised motor function sooner before it appears in the muscle recordings.