Intraoperative neurophysiological monitoring during resection of intradural extramedullary spinal cord tumors: experience with 100 cases.

BACKGROUND

Intradural-extramedullary spinal cord tumor surgery is common. Unlike intramedullary spinal cord tumor surgery, where intraoperative neurophysiological monitoring (IONM) has been described extensively, the application of IONM has not been described in this context, and its relevance has not been investigated.

METHODS

From 2001 to 2012, 100 patients underwent intradural-extramedullary spinal cord tumor resection with IONM. Preoperative and postoperative clinical evaluations were completed retrospectively, using a modified McCormick grading scale and correlated with IONM monitorability and dynamics. IONM consisted of transcranial motor evoked potentials (tcMEP), spinal (D wave) and muscle generators, somatosensory evoked potentials (SSEP), and electromyography (EMG). Both short-term and long-term clinical evaluations were performed. Patient demographics, tumor type, span, location, and morphologic complexity were analyzed.

RESULTS

Surgeries were performed for resection of schwannomas (33 %), meningiomas (22 %), ependymomas (12 %), and other pathologies (20 %); pathology was unknown in 13 % of patients. Tumor locations were cervical in 21 %, thoracic in 46 %, thoracolumbar in 7 %, lumbar 20 %, and not specified in 6 %. Tumors spanned an average of 2.2 spinal levels. Monitorability was 97 and 67 % with tcMEP and SSEP modalities respectively. D waves were monitorable in 73 % of attempts. Intraoperative tcMEP changes were reported in 29 cases with 14 resolved intraoperatively, There were one false-negative outcome and five true-positive outcomes. For SSEP, 13 changes were noted and three resolved; there were three false-negative results and one true-positive result. For D wave monitoring there were two intraoperative changes with none resolved leading to one false negative and one true positive result. With a multimodality approach incorporating any change in evoked potential, IONM demonstrated sensitivity of 0.82, specificity of 0.95, positive predictive value of 0.82, and a negative predictive value of 0.95.

CONCLUSIONS

IONM is feasible and useful in the context of intradural-extramedullary spinal cord surgery for identifying iatrogenic injury to the spinal cord.