Physiological alteration and anaesthetic drugs effects on intraoperative neurophysiological monitoring procedures

Intraoperative neurophysiological monitoring (IOM) and especially motor evoked potentials represents an important tool in the evaluation of the nervous system integrity and particularly of the motor tracts. A real and correct registration of the potentials with a proper interpretation of the modification is mandatory for an optimal outcome in eloquent areas, tumours, brainstem and medullary lesions. For all this to happen a suitable anaesthetic protocol must be used. Even though there is a large spectrum of anaesthetic agents at our disposal it is imperative to know their effect on the IOM signals recordings and the fact that some of them are dose-dependent. Drugs effects and physiological changes produced intraoperatively must be corrected before a shift in the direction of the surgical lesion resection it is taken. We present an overview of the action of the anaesthetic agents, most used protocols and the physiological alteration encountered in the operative theatre

The impact and causes of negative cortical mapping in primary motor area tumours

Introduction: Intraoperative neurophysiological monitoring is the golden standard for lesions located in eloquent areas of the brain. On the one hand, positive mapping offers a view of the relationship between the anatomo-functional cortical organisation of the patient and the lesion, facilitating the choice of the cerebrotomy entry point and the resection until the functional borders are found. On the other hand, negative mapping does not offer certainty that the absence of the motor response, from the operative field, is the real feedback or is the result of the false-negative response. In such a situation, a differentiation between those two must be done. Materials and methods: We evaluated the results of direct cortical stimulation of lesion located in or near the primary motor area, which were diagnosticated with contrast-enhancement head MRI and admitted to the Third Department of Neurosurgery, "Prof. Dr N. Oblu” Emergency Clinical Hospital, Iasi, Romania, between January 2014 and July 2018. Special attention was given especially to the negative mapping cases, regarding the histological type, imagistic localisation, symptoms and neurological outcome immediate postoperative, at 6 months and one-year follow-up. Results: From all 66 patients meeting the inclusion and exclusion criteria in 9,09% (6 cases) we did not obtain any motor response after direct cortical stimulation. The imagistic localisations of those cases were: 3 – Rolandic, 2 – pre-Rolandic and one retro-Rolandic. Tumors histological types were: glioblastoma, anaplastic astrocytoma, oligoastrocytoma and oligodendroglioma each one case and two cases of fibrillary astrocytoma. The intensity range was between 6 – 18mA, the mode – 12mA and the median – 10mA. Postoperatively the neurological condition of 3 patients worsened (4,54% from all the cases), while 3 had a favourable evolution with symptom remission. At 6monts and one-year follow-up in one case (1,51%), we observed no improvement in contrast with the other two, where dysfunction remission was highlighted. Conclusion: The possible technical, surgical and anesthesiologic causes of false-negative motor response must be eliminated to be able to differentiate from the real absence of the functional area from the operative field. In the first scenario, the resection may be associated with permanent postoperative neurologic deficit and major life quality alteration while in the second one the patient presents no motor dysfunction after surgery and the resection may be extensive with multiple oncological benefits

The evolution of eloquent located low-grade gliomas surgical approaches, their natural history and molecular classification

Low-grade glioma is characterized by slow growth, infiltrative pattern through white matter tracts and progression to a malignant tumour type. The traditional classification is newly replaced by molecular stratification. This reorganisation gathers glioma with similar prognosis and treatment protocols. The preferential location of that tumour in eloquent areas constituted, over time, a real challenge regarding the best surgical approach. Because of the high risk of postoperative neurological deficits initially a more conservative management was adopted. Once with the development of preoperative and intraoperative functional assessment techniques, a higher degree of resection was possible in the limits of cortico-subcortical eloquence, being well known that this is a statistically significant factor for survival. We present in this paper the natural evolution of low-grade glioma, their new molecular classification, prognostic factors and the various approach proposed for eloquent ones

Surgical management of Rolandic area meningioma in the era of intraoperative neurophysiological monitoring

Introduction: The advantages and the necessity of intraoperative neurophysiological monitoring (IOM) in the surgery of motor area infiltrative tumours is well known. The use of this technique for Rolandic meningioma is still debatable. The absence or the loss of the cleavage plan and an infiltrative border make the dissection exceedingly difficult and increase the risk of new postoperative motor disfunction. Materials and methods: We evaluated the impact of IOM, especially direct cortical stimulation on the degree of resection, new postoperative deficits, symptom remission and clinical-imagistic aspects at one-year follow up of 19 cases of Rolandic meningioma admitted in Third Department of Neurosurgery,” Prof. Dr N. Oblu” Emergency Clinical Hospital, Yassi, Romania, between January 2014 and July 2018. Results: More than half of the cases (57,88%) had epileptic manifestations as the main clinical symptom with the Jacksonian seizures being on the first place (31,57%), followed by progressive paresis (26,31%) and other nonspecific symptoms. Intraparenchymal preoperative oedema was observed in 36,84% of patients. The intensity of direct cortical stimulation was between 6-13 mA (median = 9mA; mode = 12mA). Simpson degree of resection was dominated by S3– 47,36% and S4 was obtained in 15,78% of cases. Postoperative the outcome was favourable for 73,68% patients with 5,26% motor aggravation and 10,52% new deficits. At one-year follow up no imagistic recurrence was observed and the permanent motor deficit was maintained in one of the three cases (5,26%). Conclusion: Even though meningiomas are extranevraxial lesions and those located on the convexity have a low risk of complication, the absence of a clear dissection plan between the tumour and the adjacent motor cortex is associated with a high risk for new postoperative neurological deficits. Therefore, it is important to perform cortical mapping for Rolandic meningioma, to determine the location of the primary motor area and to protect it from mechanical and vascular trauma, during tumour resection