Intraoperative Monitoring for Cauda Equina Tumors: Surgical Outcomes and Neurophysiological Data Accrued Over 10 Years

Abstract

Objective: Cauda equina tumors affect the peripheral nervous system, and the validities of triggered electromyogram (tEMG) and intraoperative neurophysiologic monitoring (IOM) are unclear. We sought to evaluate the accuracy and relevance of tEMG combined with IOM during cauda equina tumor resection.

Methods: Between 2008 and 2018, an experienced surgeon performed cauda equina tumor resections using tEMG at a single institution. A cauda equina tumor was defined as an intradural-extramedullary or intradural-extradural tumor at the level of L2 or lower. The clinical presentation, extent of resection, pathology, recurrence, postoperative neurological outcomes, and intraoperative tEMG mapping and IOM data were retrospectively analyzed.

Results: One hundred three patients who underwent intraoperative tEMG were included; 38 underwent only tEMG (tEMG-only group), and 65 underwent a combination of tEMG and multimodal IOM (MIOM group). There were no significant differences between the neurologic outcomes, extents of resection, or recurrence rates of the 2 groups. No significant therapeutic benefit was observed; however, the accuracy of intraoperative predetection improved with the combination of IOM and tEMG (accuracy: tEMG-only group, 86.8%; MIOM group, 92.3%). When the involved rootlet was resected despite the positive tEMG result, motor function worsened in 3 of 8 cases. The sensitivity and specificity of tEMG were 37.5% and 94.7%, respectively.

Conclusion: tEMG is an essential adjunctive surgical tool for deciding on and planning for rootlet resection. If the tEMG finding is negative, complete resection, involving the rootlet, may be safe. The accuracy may be further improved by using a combination of tEMG and IOM.

Keywords: Cauda equina; Electromyogram; Neurological outcome; Neuromonitoring; Spinal cord tumors.

Fig. 1.

Triggered electromyogram (tEMG) method: meticulous dissection of the rootlet to preserve nerve function. A right-angle hook was used to pull the rootlet away from the surrounding tissue, including the tumor. After minimizing current interference with a cotton pattie, tEMG was performed using a bipolar stimulator (white dashed line: tumor; white dotted line: dura; yellow full line: rootlet; asterisk: cotton pattie).

Fig. 2.

Distribution of cauda equina tumors in each segment for the 103 cases. M, multilevel lesion.

Fig. 3.

(A) Preoperative magnetic resonance imaging of a 60-year-old woman who presented with radiating pain in the left leg shows a round intradural-extramedullary mass at the L3 level. (B) On intraoperative triggered electromyogram (EMG), action potentials were identified for the anus bilaterally (A7 & A8) and the left gastrocnemius (A5). A1 & A2, left and right vastus lateralis; A3 & A4, left and right tibialis anterior; A5 & 6, left and right gastrocnemius; A7 & 8, left and right sphincter ani externus.