Implementation of Intraoperative Neurophysiological Monitoring during Endovascular Procedures in the Central Nervous System

Abstract

Background and objective: Intraoperative monitoring (IOM) has been used in different surgical disciplines since the 1980s. Nonetheless, regular routine use of IOM in interventional neuroradiology units has only been reported in a few centers. The aim of this study is to report our experience, 1 year after deciding to implement standardized IOM during endovascular treatment of vascular abnormalities of the central nervous system.

Methods: Basic recordings included somatosensory-evoked potentials (SEPs) and motor-evoked potentials (MEPs). Corticobulbar motor-evoked potentials and flash-visual-evoked potentials were also recorded depending on the topography of the lesion. Intra-arterial provocative tests (PTs) with amobarbital and lidocaine were also performed. All patients except 1 were under total intravenous anesthesia. Clinical outcome was assessed prospectively and correlated with IOM events.

Results: Twelve patients and 15 procedures were monitored during the inclusion period. Significant IOM events were detected during 3 of the 15 procedures (20%). We observed temporary MEP changes in 2 cases which resolved after interruption of the embolization or application of corrective measures, leaving no postoperative neurological deficits. In 1 case, persistent SEP and MEP deterioration was detected secondary to a frontal hematoma, resulting in mild sensory-motor deficit in the right upper extremity after the procedure. Overall, 12 PTs (4 spinal cord and 8 brain abnormalities) were performed using lidocaine and sodium amytal injections. One positive result occurred after the injection of lidocaine. No false negatives were detected.

Conclusions: IOM may provide continuous real-time data about the functional status of eloquent areas and pathways of the central nervous system in patients under general anesthesia. It therefore allows us to detect early neurological damage in time to perform specific actions that may prevent irreversible neurological deficits.

Keywords: Central nervous system, vascular pathology; Endovascular treatment; Evoked potentials; Intraoperative neurophysiological monitoring; Provocative tests.

Fig. 1

Positive PT in a 50-year-old man diagnosed with a saccular aneurysm in the bifurcation of the right MCA, originating at the upper branch. a Baseline traces corresponding to the TES MEP of the left upper and lower limb muscles before injecting 40 mg lidocaine at 11:15. b A mild decrease of the left APB, TA, and AH MEPs 1 min after the injection. c Complete loss of the left MEPs 3 min after the lidocaine injection. d MEP recovery until reaching baseline value 19 min after the lidocaine injection. L = Left; EDC = extensor digitorum communi.

Fig. 2

Patient 9. Reversible MEP deterioration in a 38-year-old man diagnosed with a right frontal parasagittal AVM based on partial motor seizures in the left leg. a Baseline traces corresponding to the TES MEP of the left upper and lower limb muscles during a second Onyx injection. b Focal change restricted to a decrease in MEP amplitude of >90% in the left AH muscle (black arrow). c After 10 min, embolization was terminated, and the MEP returned to its baseline level with no increase in the stimulation threshold. L = Left; EDC = extensor digitorum communi; Qds = quadriceps.

Fig. 3

Patient 3. Reversible MEP deterioration in a 22-year-old woman diagnosed with a right cervical AVM (C6-C7). a The TES MEPs at about 20 min into the Onyx embolization. b The MEPs in the left APB and biceps disappeared almost completely. There was a significant decrease in amplitude in the right APB and both TA. The neuroradiologist was informed about the situation, and the procedure was aborted. c As the stimulus intensity was gradually increased to 180 V above baseline, we observed a progressive recovery of the affected MEPs, which reached their initial level after 20 min. L = Left; R = right.