The Role of Motor Evoked Potentials during Surgery for Intramedullary Spinal Cord Tumors

Abstract

MEP monitorability was a better predictor of functional outcome than the patient's preoperative motor status for the adult group. Significant predictors of MEP monitorability in the adult group were preoperative motor function (P < 0.01), history of no previous treatment (surgery or irradiation) (P < 0.01), and small tumor size (P < 0.05). Weak associations with monitorable MEPs existed for low-grade tumors (P = 0.09), the presence of baseline somatosensory evoked potentials (P = 0.10), and tumor pathological abnormalities (ependymoma) (P = 0.13). No associations were determined for sex (P > 0.4), associated syrinx (P > 0.3), or tumor location (P > 0.5). In the pediatric group, none of the examined factors were associated with MEP monitorability (P > 0.3). A decline of more than 50% in MEP amplitude during tumor removal should serve as a serious warning sign to the surgeon.

Feasibility and Predictability of Intraoperative Monitoring in Patients with Intradural Extramedullary and Epidural Metastatic Spinal Tumors

“…MEP was successfully obtained in 83% of ambulatory patients (motor grade 4-5) and the success rate significantly decreased to 39% in non-ambulatory patients (motor grade 0-3). Similar results were found in a study of MEP during surgery for intramedullary spinal cord tumours by Morota et al [6]. Although they did not calculate the MEP feasibility according to preoperative motor grade, we could retrieve the significant difference of MEP feasibility in patients with 'moderate-to-severe' preoperative deficit (motor grade 3 or lower.…”

“…underwent corrective spinal deformity surgery and the feasibility of MEP (51%) was far behind that of SSEP (93%) in these patients. The relative low feasibility of MEP could be attributed to vulnerable neuromuscular junction, relatively a few functional axon and sensitive anterior spinal cord function to ischemia, myelopathy from previous radiation and so on [6,12,13]. Also in our study, SSEP was more successfully obtained than MEP (93% vs 73%, p<0.01), and was still measurable in 83% of patients with preoperative motor grade 3 or less.…”

“…Meanwhile, in the surgery for intramedullary tumour, at which postoperative neurologic deficit occur at higher rate and wake-up test is rarely applicable, the sensitivity is still high but specificity comes out less accurately. Morota et al reported a MEP sensitivity of 100% in all 3 patients, who showed more than 50% decrease of MEP amplitude resulted in paraplegia at immediate postoperative period [6]. Cheng et al also presented 100% sensitivity of transcranial MEP in all 6 patients with MEP changes out of 12 paediatric patients with intramedullary tumours [7].…”

“…Later, MEP has played role in intramedullary spinal cord tumour surgery, where motor and sensory pathway could be separately dissected [6,7]. Among spinal tumours, intradural extramedullary (IDEM) and epidural (ED) metastatic spinal tumours are ideal for monitoring surgical manipulation of spinal cord as those tumours are free of both intrinsic pathologic condition of spinal cord and selective spinal cord dissection such as myelotomy.…”

Surgical outcomes in spinal cord ependymomas and the importance of extent of resection in children and young adults

“…We were unable to detect a difference in extent of resection or tumor recurrence rates among patients treated with intraoperative neuromonitoring compared with those without. In a prospective series of intramedullary spinal cord tumors, Morota et al 31 found that motor evoked potential monitoring was associated with good outcomes in adults, but not children, while other authors have commented on the extent to which intraoperative neuromonitoring changes drive intraoperative decision making. 22,23,47 Although some data have demonstrated the utility of intraoperative neuromonitoring, it should be considered as an adjunct during resection of all intramedullary spinal cord tumors, with a careful understanding of its limitations.…”