Intraoperative Neurophysiologic and Angiographic Techniques to Identify the Posterior Median Sulcus for Midline Myelotomy

Accurate midline myelotomy through the posterior median sulcus (PMS) is the key step to minimize surgical morbidity during intramedullary tumor removal.(1,2) When an intramedullary mass is present, the cord is usually rotated and it may be difficult to distinguish its sulci.(2-4) Inadvertent dissection through the dorsal columns exposes the patient to disabling postoperative deficits.(5) In recent years, together with the well-established neurophysiologic phase-reversal method, newer intraoperative angiographic techniques have been developed In order to illustrate the combination of the 2, we present the case of a 31-yearold man with a right claw hand syndrome who underwent surgical excision of a C6-D1 ependymoma (Video 1).(6,7) After localizing the tumor with ultrasound, somatosensory evoked potentials (obtained by stimulating the dorsal columns with the use of a bipolar handheld neurostimulator) were employed to identify the PMS by means of the phase reversal technique, which uncovered the silent central line corresponding to the PMS. Use of indocyanine green fluorescence (ICG) later confirmed with certainty the location of the spinal cord's midline by enabling identification of the dorsal medullary veins exiting the PMS. As expected, the midline was significantly laterally displaced by the tumor. After penetrating the PMS, gentle dissection between the 2 posterior chordae enabled the surgeon to reach and enucleate the tumor in a minimally traumatic fashion. No postoperative deficits were reported. This method represents a direct and effective way to reduce morbidity resulting from this type of surgery.