To Örebro University

OBJECTIVE: Gross total resection is strived for in intramedullary spinal cord lesion surgery. Intraoperative neurophysiological monitoring (IONM) is the gold standard, but there is no consensus on the optimal IONM workflow. This study details our institutional workflow.

METHODS: We retrospectively reviewed all adults who underwent intramedullary resection at Karolinska University Hospital, 2007-2021 (n = 70). Continuous multimodal IONM (somatosensory-evoked potentials (SSEP), motor-evoked potentials (MEP) and epidural D-waves) was conducted by an in-room neurophysiologist. Alarm thresholds were preset (≥ 50% SSEP amplitude drop/10% latency rise; ≥ 80% MEP reduction; ≥ 50% D-wave loss) and triggered a standardized four-step rescue protocol (halt manipulation, raise MAP to 80-90 mm Hg, topical papaverine, observation). Motor/sensory function, modified McCormick (mMC) grade, pain, and sphincter control were documented pre-operatively, at 3 months, and ≥ 12 months.

RESULTS: Seventy patients were included. Most harboured ependymoma (51%), hemangioblastoma (18%) and cavernoma (8.5%). A neurophysiologist was present during every procedure. A ≥ 50% intra-operative SSEP-amplitude decrease was not followed by a sensory deficit (OR:3.0, 95% CI 0.86-10.6; p = 0.085) or mMC deterioration (OR:1.6, 0.33-7.5; p = 0.57) at either short- or long-term follow-up. In contrast, complete SSEP loss markedly increased the risk of postoperative sensory deficit (3-months-OR:25.2, 4.7-135; p < 0.001; long-term-OR 11.0, 2.8-43.8; p < 0.001) and poorer mMC grade (3-months-OR:7.8, 2.0-31; p = 0.004; long-term-OR:11.0, 2.8-43.8; p < 0.001). Loss of MEPs predicted a decline in mMC at long-term follow-up (OR:4.0, 1.06-15.1; p = 0.041).

CONCLUSIONS: Live data from continuous intraoperative neurophysiological monitoring, expertly interpreted in the OR, could potentially be used to make surgical and anesthesiologic adjustments with the goal of minimizing the risk of negative neurological outcomes. Significant associations were found between decreased or lost IONM signals and poorer sensorimotor function and mMC score at short- and long-term follow-up. Implementation of the IONM workflow is suggested in all intramedullary surgery.