Association of Pre-myelotomy Dorsal Column Mapping and Preservation of Somatosensory Evoked Potentials During Intramedullary Tumor Resection: A Case-control Study

Introduction: Iatrogenic injury is a risk during midline myelotomy in intramedullary tumor resection, especially when spinal cord anatomy is distorted. Mapping helps identify the midline between the dorsal columns while intraoperative somatosensory evoked potentials (SSEPs) provide real-time feedback on the function of the dorsal columns. However, the relationship between mapping and the maintenance of SSEPs is not well documented. This study aims to evaluate the impact of dorsal column mapping on maintaining SSEPs throughout intramedullary tumor resection.

Methods: We conducted a retrospective, case-control study of two groups: 5 patients who received dorsal column mapping between July 2022 and January 2023 and 5 patients who did not undergo mapping between December 2019 and March 2021. A linear mixed-effects model was used to compare SSEP amplitudes between study populations. Time-to-event analyses examined when significant SSEP amplitude decreases occurred. Preservation of SSEP amplitude throughout the procedure and the time until a significant SSEP decrease occurred post-myelotomy were analyzed as co-primary outcomes.

Results: Matching was performed based on tumor location, histology, and size. No significant difference in SSEP amplitudes between groups (p = 0.08) was evident before performing the myelotomy. Immediately after myelotomy and after tumor resection, SSEP amplitudes in the mapped group were significantly higher (p < 0.01, for both). Time-to-event curves did not differ significantly between cohorts (p = 0.18). However, the unmapped cohort had 3 significant SSEP decreases within 5 minutes of the myelotomy, and a fourth occurred 19 minutes after the myelotomy. The first significant SSEP decrease in the mapped cohort occurred 44 minutes after the myelotomy.

Conclusion : Using SSEP data, we have shown that mapping may protect the dorsal columns during intramedullary tumor resection. The mapped cohort had higher SSEP amplitudes immediately after the myelotomy and after tumor resection. While there was no significant difference in the time-to-event analysis, the mapped cohort had SSEP signal decreases later in the case during tumor resection. Further studies with large cohorts are needed to confirm these findings.