Intraoperative localization of a cervicomedullary glioma from the killed end potential: illustrative case.

We recorded the intraoperative somatosensory evoked potentials directly from the upper cervical cord and medulla in a patient with an intrinsic tumor at the region of the cervicomedullary junction. The killed end potential, a large positive potential, was obtained at the caudal end of the tumor. This type of potential occurs when an impulse approaches but never passes beyond the recording electrode. Myelotomy guided by the killed end potential enabled appropriate spinal and medullary dissection and led to early encounter with the cervicomedullary tumor.