Dynamic mapping of the corticospinal tract in open cordotomy and myelomeningocele surgery

Spinal cord surgeries carry a high risk for significant neurological impairments. The initial techniques for spinal cord mapping emerged as an aid to identify the dorsal columns and helped select a safe myelotomy site in intramedullary tumor resection. Advancements in motor mapping of the cord have also been made recently, but exclusively with tumor surgery. We hereby present our experiences with dynamic mapping of the corticospinal tract (CST) in other types of spinal cord procedures that carry an increased risk of postoperative motor deficit, and thus could directly benefit from this technique.

Two patients with intractable unilateral lower extremity pain due to metastatic disease of the sacrum and a thoraco-lumbar chordoma, respectively underwent thoracic cordotomy to interrupt the nociceptive pathways. A third patient with progressive leg weakness underwent cord untethering and surgical repair of a large thoracic myelomeningocele. In all three cases, multimodality intraoperative neurophysiologic testing included somatosensory and motor evoked potentials monitoring as well as dynamic mapping of the CST.

CST mapping allowed safe advancement of the cordotomy probe and exploration of the meningocele sac with untethering of the anterior-lateral aspect of the cord respectively, resulting in postoperative preservation or improvement of motor strength from the pre-operative baseline. Stimulus thresholds varied likely with the distance between the stimulating probe and the CST as well as with the baseline motor strength in the mapped myotomes.