Intraoperative neurophysiological monitoring during the surgery of spinal arteriovenous malformation: sensitivity, specificity, and warning criteria

Objective: The incidence of spinal arteriovenous malformation (SAVM) is low, but its treatment is challenging. Intraoperative neurophysiological monitoring (IONM) for intramedullary tumors has been a benchmark in neurosurgery. This study aimed to determine the sensitivity, specificity, and warning criteria of IONM for SAVM surgeries. Materials and Methods: From November 2012 to January 2016, 55 patients underwent SAVM surgery with IONM at the Neurosurgery Department of Xuanwu Hospital of Capital Medical University, China. Modified McCormick grading scale was used to evaluate patients' function 3 days before and immediately, 1 week, 3 months, and 6 months after surgery. IONM was performed including somatosensory evoked potential (SEP), trans-cranial motor-evoked potential (tcMEP), and electromyography (EMG). All patients were followed up every 3 or 6 months. Results: The SAVM locations were cervical spine in 15 (27.3%) patients, thoracic in 24 (43.6%), thoracolumbar in 12 (21.8%), and lumbar in 4 (7.3%). TcMEP and SEP were could be monitored in 53 (96.4%) and 33 (60.0%) patients, respectively. Using > 80% irreversible amplitude reduction of the tcMEP as threshold, the sensitivity, specificity, and positive and negative predictive values were 77.3%, 87.1%, 81.0%, and 84.4%, respectively; using > 50% irreversible amplitude reduction of the tcMEP as the warning criterion, these values were 81.8% 74.2%, 69.2%, and 85.2%, respectively. Conclusion: In practical applications of tcMEP for SAVM surgeries, the 50% irreversible amplitude reduction of the tcMEP criterion can be used to warn the surgeon, while the > 80% criterion can be used to stop the operation in order to avoid neurological impairments.