Intraoperative Neurophysiological Monitoring for Endoscopic Endonasal Approaches to the Skull Base: A Technical Guide

Abstract

Intraoperative neurophysiological monitoring during endoscopic, endonasal approaches to the skull base is both feasible and safe. Numerous reports have recently emerged from the literature evaluating the efficacy of different neuromonitoring tests during endonasal procedures, making them relatively well-studied. The authors report on a comprehensive, multimodality approach to monitoring the functional integrity of at risk nervous system structures, including the cerebral cortex, brainstem, cranial nerves, corticospinal tract, corticobulbar tract, and the thalamocortical somatosensory system during endonasal surgery of the skull base. The modalities employed include electroencephalography, somatosensory evoked potentials, free-running and electrically triggered electromyography, transcranial electric motor evoked potentials, and auditory evoked potentials. Methodological considerations as well as benefits and limitations are discussed. The authors argue that, while individual modalities have their limitations, multimodality neuromonitoring provides a real-time, comprehensive assessment of nervous system function and allows for safer, more aggressive management of skull base tumors via the endonasal route.

Intraoperative Evoked Potentials: A Review of Clinical Impact and Limitations

“…Even though sustained by little evidence, a similar conclusion was shown in brainstem auditory evoked potentials and motor evoked potentials [18].…”

“…In comparison, signal drop irreversibility (33.33%) was related to deterioration in Glasgow outcome scale at long term follow up. Some studies documented SSEP usefulness in postoperative neurological deficit detection, along with the fact that increasing MAP successfully reversed few false negatives and multiple altered waveforms [18,20,26].…”

“…Exceptionally, IONM may be rather useless during certain surgical procedures (i.e. pituitary adenoma resection without cavernous sinus invasion) [2,12,[15][16][17][18].…”

“…Furthermore, limb malpositioning, may cause peripheral nerve conduction failure which may resemble BFI; these situations are often concurrent with MEP signal deterioration. Peripheral sensitive evoked potentials may help to identify these problems [18,19].…”

“…This may lead to greater sensitivity and specificity when evaluating neural structures at risk during a technically demanding surgical approach [18].…”