Intraoperative neuromonitoring during resection of cranial meningiomas and its effect on the surgical workflow.

PURPOSE: Resection of meningiomas adjacent to the central sulcus entails a high rate of morbidity. Explored for intra-axial lesion resection, intraoperative neuromonitoring intraoperative neuromonitoring (IONM) has been shown to decrease neurological deficits. The use of IONM is relatively uncommon and is not considered routine practice in the removal of extra-axial lesions. We sought to characterize IONM's impact on the surgical workflow in supratentorial meningiomas. METHODS: We retrospectively analyzed a prospectively collected database, searching cases in which IONM was used for resection of meningioma between 2017 and 2020. We classified the IONM effect on surgical workflow into 5 distinct categories of workflow changes (WFC). RESULTS: Forty cases of meningiomas with IONM use were identified. In 1 case (class 1 WFC), the operation was stopped due to IONM input. In 5 cases (class 2 WFC), the tumor was incompletely resected due to input from the IONM. In 14 cases (35%), IONM leads to an alteration of the resection process (alteration of approach, class 3 WFC). In 4 cases (10%), anesthesia care was modified based on IONM input (class 4 WFC). In 16 cases, no changes were made (class 5 WFC). In all patients in whom a change was made (24 cases, WFC 1-4), only 8.3% suffered a temporary deficit, and there were no permanent deficits, whereas when no change was made, there were 18.75% temporary deficit and 6.25% permanent deficit. CONCLUSION: IONM has an impact during resection of meningiomas in eloquent areas and may guide the surgical technique, approach to tumor resection, and extent of resection.

Intraoperative neurophysiology in pediatric supratentorial surgery: experience with 57 cases.

PURPOSE: Utilization of intraoperative neurophysiology (ION) to map and assess various functions during supratentorial brain tumor and epilepsy surgery is well documented and commonplace in the adult setting. The applicability has yet to be established in the pediatric age group. METHODS: All pediatric supratentorial surgery utilizing ION of the motor system, completed over a period of 10 years, was analyzed retrospectively for the following variables: preoperative and postoperative motor deficits, extent of resection, sensory-motor mappability and monitorability, location of lesion, patient age, and monitoring alarms. Intraoperative findings were correlated with antecedent symptomatology as well as short- and long-term postoperative clinical outcome. The monitoring impact on surgical course was evaluated on a per-case basis. RESULTS: Data were analyzed for 57 patients (ages 3-207 months (93 ± 58)). Deep lesions (in proximity to the pyramidal fibers) constituted 15.7% of the total group, superficial lesions 47.4%, lesions with both deep and superficial components 31.5%, and ventricular 5.2%. Mapping of the motor cortex was significantly more successful using the short-train technique than Penfield's technique (84% vs. 25% of trials, respectively), particularly in younger children. The youngest age at which motor mapping was successfully achieved was 3 vs. 93 months for each method, respectively. Preoperative motor strength was not associated with monitorability. Direct cortial motor evoked potential (dcMEP) was more sensitive than transcranial (tcMEP) in predicting postoperative motor decline. dcMEP decline was not associated with tumor grade or extent of resection (EOR); however, it was associated with lesion location and more prone to decline in deep locations. ION actively affected surgical decisions in several aspects, such as altering the corticectomy location and alarming due to a MEP decline. CONCLUSION: ION is applicable in the pediatric population with certain limitations, depending mainly on age. When successful, ION has a positive impact on surgical decision-making, ultimately providing an added element of safety for these patients.

The Transformation of Adaptation Specificity to Whisker Identity from Brainstem to Thalamus.

Stimulus specific adaptation has been studied extensively in different modalities. High specificity implies that deviant stimulus induces a stronger response compared to a common stimulus. The thalamus gates sensory information to the cortex, therefore, the specificity of adaptation in the thalamus must have a great impact on cortical processing of sensory inputs. We studied the specificity of adaptation to whisker identity in the ventral posteromedial nucleus of the thalamus (VPM) in rats using extracellular and intracellular recordings. We found that subsequent to repetitive stimulation that induced strong adaptation, the response to stimulation of the same, or any other responsive whisker was equally adapted, indicating that thalamic adaptation is non-specific. In contrast, adaptation of single units in the upstream brainstem principal trigeminal nucleus (PrV) was significantly more specific. Depolarization of intracellularly recorded VPM cells demonstrated that adaptation is not due to buildup of inhibition. In addition, adaptation increased the probability of observing complete synaptic failures to tactile stimulation. In accordance with short-term synaptic depression models, the evoked synaptic potentials in response to whisker stimulation, subsequent to a response failure, were facilitated. In summary, we show that local short-term synaptic plasticity is involved in the transformation of adaptation in the trigemino-thalamic synapse and that the low specificity of adaptation in the VPM emerges locally rather than cascades from earlier stages. Taken together we suggest that during sustained stimulation, local thalamic mechanisms equally suppress inputs arriving from different whiskers before being gated to the cortex.

Imbalance between excitation and inhibition in the somatosensory cortex produces postadaptation facilitation.

Adaptation is typically associated with attenuation of the neuronal response during sustained or repetitive sensory stimulation, followed by a gradual recovery of the response to its baseline level thereafter. Here, we examined the process of recovery from sensory adaptation in layer IV cells of the rat barrel cortex using in vivo intracellular recordings. Surprisingly, in approximately one-third of the cells, the response to a test stimulus delivered a few hundred milliseconds after the adapting stimulation was significantly facilitated. Recordings under different holding potentials revealed that the enhanced response was the result of an imbalance between excitation and inhibition, where a faster recovery of excitation compared with inhibition facilitated the response. Hence, our data provide the first mechanistic explanation of sensory facilitation after adaptation and suggest that adaptation increases the sensitivity of cortical neurons to sensory stimulation by altering the balance between excitation and inhibition.