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Intraoperative Neurophysiologic and Angiographic Techniques to Identify the Posterior Median Sulcus for Midline
Guglielmo Iess1, Giulio Bonomo1, Alessia Amato2
1Department of Neurosurgery, IRCCS Carlo Besta Neurological Institute Foundation, Milan, Italy; University of Milan, Milan, Italy.
Abstract:
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 to identify the PMS.1-4 In order to illustrate the combination of the 2, we present the case of a 31-year-old 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.
Insights
This study presents a combined neurophysiologic and ICG fluorescence technique to accurately identify the spinal cord midline during intramedullary tumor removal, minimizing surgical risks and preventing postoperative deficits.
Area of Science:
- Neurosurgery
- Spinal Cord Surgery
- Minimally Invasive Techniques
Background:
- Accurate identification of the posterior median sulcus (PMS) is critical for minimizing morbidity during intramedullary tumor removal.
- Intramedullary tumors often distort spinal cord anatomy, making sulci identification challenging and increasing the risk of iatrogenic injury to the dorsal columns.
- Established neurophysiologic phase-reversal methods and newer intraoperative angiographic techniques aim to improve PMS localization.
Observation:
- A 31-year-old male with a C6-D1 ependymoma presenting with right claw hand syndrome underwent surgical excision.
- Ultrasound localized the tumor, followed by somatosensory evoked potentials to identify the PMS via phase reversal, revealing a distinct central line.
- Indocyanine green (ICG) fluorescence confirmed the midline by visualizing dorsal medullary veins exiting the PMS, which was displaced by the tumor.
Findings:
- The combined phase reversal and ICG fluorescence technique accurately identified the spinal cord midline, even when distorted by the ependymoma.
- The posterior median sulcus (PMS) was successfully identified and utilized for minimally traumatic tumor enucleation.
- No postoperative neurological deficits were reported in the patient.
Implications:
- This combined approach offers a direct and effective method to reduce surgical morbidity associated with intramedullary tumor removal.
- Accurate midline identification is crucial for preserving neurological function and improving patient outcomes in spinal cord surgery.
- The integration of neurophysiology and advanced intraoperative imaging enhances surgical precision and safety.
