Glioma surgery : tailoring intraoperative neurophysiological strategies to clinical conditions enhances resection, extends indications, and keeps patient functional integrity

BACKGROUND: Glioma surgery has been changed from one,relying on anatomical references, to a new one aimed at recognizing, with the aid of intraoperative neurophysiology, the different neural structures on the basis of their functional properties, to maximally resect the tumor and preserve patient functional integrity. This approach called functional neurooncological surgery needs to be maximally and safely extended to enlarge the population of patients who will benefit from surgery. Intraoperative neurophysiology offers the surgeon various stimulation protocols, whose efficiency is based on the ability to recognize the essential sites at cortical and subcortical level, with the highest possible resolution in most clinical conditions. This ability faces the neural structures excitability that depends on patients characteristics and tumor features. The key point is the integration of the choice of the stimulation protocols with the clinical context. METHODS: Intraoperative neurophysiological protocols used in the study were the 60Hz-technique (Low Frequency-LF) and the train-of-five-or pulse technique (To5), delivered alternatively by bipolar or monopolar probe. In 620 patients with tumors involving the corticospinal-tract and in 450 patients with tumors involving language areas and tracts, the use of these stimulation protocols was tailored to the clinical context defined by patient characteristics (clinical history, seizures control, antiepileptic drug therapy, previous treatments) and tumor features (defined by MR-imaging: volume, location, degree of infiltration on volumetric FLAIR images, degree of tracts involvement in DTI-FT images). The effect was evaluated on the feasibility of mapping (number of cases in which a reliable mapping was feasible), number of intraoperative seizures, the impact on immediate and permanent morbidity, the extent of resection (by volumetric analysis), the number of patients treated, and by neuropsychological evaluation (immediately after surgery and at 3-6 months). RESULTS: By integrating the choice of the probe and the stimulating protocol with patient clinical history and tumor characteristics, the best “probe-frequency match” to be applied in different clinical conditions was identified. According to clinical and imaging criteria various risk groups of patients were identified (either in the group of tumors involving the motor or language tracts) and the most adequate stimulation protocols for each group was reported. This integrative approach allows increasing the extent of resection, keeping patient functional integrity, and strongly expanding the number of patients who benefit from surgery CONCLUSIONS: The integration of stimulation modalities with clinical context enhances resection extent and safety, and largely expands the population of patients who benefit from surgical treatment.