Preoperative nTMS and Intraoperative Neurophysiology - A Comparative Analysis in Patients With Motor-Eloquent Glioma

Abstract

BackgroundThe resection of a motor-eloquent glioma should be guided by intraoperative neurophysiological monitoring (IOM) but its interpretation is often difficult and may (unnecessarily) lead to subtotal resection. Navigated transcranial magnetic stimulation (nTMS) combined with diffusion-tensor-imaging (DTI) is able to stratify patients with motor-eloquent lesion preoperatively into high- and low-risk cases with respect to a new motor deficit.ObjectiveTo analyze to what extent preoperative nTMS motor risk stratification can improve the interpretation of IOM phenomena.MethodsIn this monocentric observational study, nTMS motor mapping with DTI fiber tracking of the corticospinal tract was performed before IOM-guided surgery for motor-eloquent gliomas in a prospectively collected cohort from January 2017 to October 2020. Descriptive analyses were performed considering nTMS data (motor cortex infiltration, resting motor threshold (RMT), motor evoked potential (MEP) amplitude, latency) and IOM data (transcranial MEP monitoring, intensity of monopolar subcortical stimulation (SCS), somatosensory evoked potentials) to examine the association with the postoperative motor outcome (assessed at day of discharge and at 3 months).ResultsThirty-seven (56.1%) of 66 patients (27 female) with a median age of 48 years had tumors located in the right hemisphere, with glioblastoma being the most common diagnosis with 39 cases (59.1%). Three patients (4.9%) had a new motor deficit that recovered partially within 3 months and 6 patients had a persistent deterioration (9.8%). The more risk factors of the nTMS risk stratification model (motor cortex infiltration, tumor-tract distance (TTD) ≤8mm, RMTratio <90%/>110%) were detected, the higher was the risk for developing a new postoperative motor deficit, whereas no patient with a TTD >8mm deteriorated. Irreversible MEP amplitude decrease >50% was associated with worse motor outcome in all patients, while a MEP amplitude decrease ≤50% or lower SCS intensities ≤4mA were particularly correlated with a postoperative worsened motor status in nTMS-stratified high-risk cases. No patient had postoperative deterioration of motor function (except one with partial recovery) when intraoperative MEPs remained stable or showed only reversible alterations.ConclusionsThe preoperative nTMS-based risk assessment can help to interpret ambiguous IOM phenomena (such as irreversible MEP amplitude decrease ≤50%) and adjustment of SCS stimulation intensity.

MRI-Based Risk Assessment for Incomplete Resection of Brain Metastases

“…The treating neurosurgeon decided about using intraoperative neuromonitoring (IOM) to ensure the integrity of the motor system based on a previously published risk stratification ( 21 , 22 ). Warning criteria were a decrease in MEP amplitudes >50% and a subcortical stimulation intensity <5mA which we described in detail elsewhere ( 23 ). No awake craniotomies were performed in this series.…”

Comparison of anatomical-based vs. nTMS-based risk stratification model for predicting postoperative motor outcome and extent of resection in brain tumor surgery

“…Another advantage is that the preoperative nTMS risk stratification facilitates the IOM (e.g. determining the subcortical stimulation intensity or interpreting heterogeneous phenomena such as a transient decrease of MEP amplitude) ( Rosenstock et al, 2021b ). In summary, recent studies showed several benefits for nTMS motor mapping and tractography, so patients with motor-eloquent brain tumors should ideally be treated at centers with experience in these techniques ( Ille and Krieg, 2021 ).…”

“…Tumor resections in motor eloquent regions were performed only by neurosurgeons with extensive experience in the field of neuro-oncologic surgery. Intraoperative neuromonitoring (IOM) such as transcranial motor evoked potentials and/or subcortical stimulation via the surgical aspirator took place if the distance of the tumor to the pyramidal tract was less than 1 cm ( Rosenstock et al, 2021b ). No awake surgeries were performed.…”

Diffusion tensor imaging, intra-operative neurophysiological monitoring and small craniotomy: Results in a consecutive series of 103 gliomas

“…Other preoperative tools have gained popularity in recent years, such as the preoperative transcranial magnetic stimulation (TMS) (71)(72)(73)(74)(75)(76). As a future perspective, our team aims at evaluating and validating the preoperative TMS as a useful tool to improve reduced invasiveness and reliable negative mapping.…”