Ventricular entry during surgical resection is associated with intracranial leptomeningeal dissemination in glioblastoma patients.

PURPOSE: Glioblastoma (GBM) is associated with a poorer prognosis when leptomeningeal dissemination (LMD) occurs. Recently, the role of both ventricular entry (VE) during surgery and subventricular zone localization of tumors in promoting LMD in GBM patients has been debated. This article investigates the role of VE in causing LMD in GBM patients. METHODS: We conducted a retrospective analysis of GBMs operated on at our Institution between March 2018 and December 2020. We collected pre- and post-surgical images, anamnestic information, and surgical reports. RESULTS: Two hundred cases were collected. The GBM localization was periventricular in 69.5% of cases, and there was a VE during the surgical procedure in 51% of cases. The risk of post-surgical LMD in the case of VE was 16%. The rate of LMD was higher in the case of VE than not-VE (27.4% vs. 4%, p < 0.0001). The rate of LMD in periventricular GBM was 19% (p = 0.1131). CONCLUSION: According to our data, VE is an independent factor associated with a higher rate of post-surgical LMD, and the periventricular localization is not independently correlated to this negative outcome. Neurosurgeons should avoid VE when possible. The correct surgical strategy should be founded on balancing the need for maximal EOR and the risks associated with VE.

Radiomic Features Associated with Extent of Resection in Glioma Surgery.

Radiomics defines a set of techniques for extraction and quantification of digital medical data in an automated and reproducible way. Its goal is to detect features potentially related to a clinical task, like classification, diagnosis, prognosis, and response to treatment, going beyond the intrinsic limits of operator-dependency and qualitative description of conventional radiological evaluation on a mesoscopic scale. In the field of neuro-oncology, researchers have tried to create prognostic models for a better tumor diagnosis, histological and biomolecular classification, prediction of response to treatment, and identification of disease relapse. Concerning glioma surgery, the most significant aid that radiomics can give to surgery is to improve tumor extension detection and identify areas that are more prone to recurrence to increase the extent of tumor resection, thereby ameliorating the patients' prognosis. This chapter aims to review the fundamentals of radiomics models' creation, the latest advance of radiomics in neuro-oncology, and possible radiomic features associated with the extent of resection in the brain gliomas.

Functional outcomes, extent of resection, and bright/vague fluorescence interface in resection of glioblastomas involving the motor pathways assisted by 5-ALA.

BACKGROUND: 5-Aminolevulinic acid (5-ALA) fluorescence can maximize perirolandic glioblastoma (GBM) resection with low rates of postoperative sequelae. Our purpose was to present the outcomes of our experience and compare them with other literature reports to investigate the potential influence of different intraoperative monitoring strategies and to evaluate the role of intraoperative data on neurological and radiological outcomes in our series. METHODS: We retrospectively analyzed our prospectively collected database of GBM involving the motor pathways. Each patient underwent tumor exeresis with intraoperative 5-ALA fluorescence visualization. Our monitoring strategy was based on direct stimulation (DS), combined with cortical or transcranial MEPs. The radiological outcome was evaluated with CRET vs. residual tumor, and the neurological outcome as improved, unchanged, or worsened. We also performed a literature review to compare our results with state-of-the-art on the subject. RESULTS: Sixty-five patients were included. CRET was 63.1%, permanent postoperative impairment was 1.5%, and DS's lowest motor threshold was 5 mA. In the literature, CRET was 25-73%, permanent postoperative impairment 3-16%, and DS lowest motor threshold was 1-3 mA. Our monitoring strategy identified a motor pathway in 60% of cases in faint fluorescent tissue, and its location in bright/faint fluorescence was predictive of CRET (p < 0.001). A preoperative motor deficit was associated with a worse clinical outcome (p < 0.001). Resection of bright fluorescent tissue was stopped in 26%, and fluorescence type of residual tumor was associated with higher CRET grades (p < 0.001). CONCLUSIONS: Based on the data presented and the current literature, distinct monitoring strategies can achieve different onco-functional outcomes in 5-ALA-guided resection of a glioblastoma (GBM) motor pathway. Intraoperatively, functional and fluorescence data close to a bright/vague interface could be helpful to predict onco-functional outcomes.

Crossed Cerebellar Diaschisis in Patients With Symptomatic Unilateral Anterior Circulation Stroke Is Associated With Hemodynamic Impairment in the Ipsilateral MCA Territory.

BACKGROUND: In patients with steno-occlusive disease, recent findings suggest that hemodynamic alterations may also be associated with crossed cerebellar diaschisis (CCD) rather than a functional disruption alone. PURPOSE: To use a quantitative multiparametric hemodynamic MRI to gain a better understanding of hemodynamic changes related to CCD in patients with unilateral anterior circulation stroke. STUDY TYPE: Prospective cohort study. POPULATION: Twenty-four patients (25 datasets) with symptomatic unilateral anterior circulation stroke. FIELD STRENGTH/SEQUENCE: 3T/two sequences: single-shot (echo-planar imaging) EPI sequence and T2* gradient echo perfusion-weighted imaging study. ASSESSMENT: The presence of CCD was inferred from the cerebellar asymmetry index (CAI) of the blood oxygenation-level dependent cerebrovascular reactivity (BOLD-CVR) exam, which was calculated from the mean BOLD-CVR and standard deviation of the CAI of the healthy control group. For all perfusion-weighted (PW)-MRI parameters, the cerebellar and middle cerebral artery (MCA) territory asymmetry indices were calculated. STATISTICAL TESTS: Independent Student's t-test to compare the variables from the CCD positive(+) and CCD negative(-) groups and analysis of covariance (ANCOVA) to statistically control the effect of covariates (infarct volume and time since ischemia onset). RESULTS: CCD was present in 33% of patients. In the MCA territory of the affected hemisphere, BOLD-CVR was significantly more impaired in the CCD(+) group as compared to the CCD(-) group (mean BOLD-CVR ± SD [%BOLD signal/ΔmmHgCO2 ]: -0.03 ± 0.12 vs. 0.11 ± 0.13, P < 0.05). Moreover, the mean transit time (MTT) (asymmetry index (%) CCD(+) vs. CCD(-): 28 ± 23 vs. 4 ± 11, P < 0.05) and time to peak (TTP) (10 ± 10 vs. 2 ± 5, P < 0.05) in the MCA territory of the affected hemisphere were significantly prolonged, while cerebral blood volume was, on average, increased in the CCD(+) group (25 ± 15 vs. 4 ± 19, P < 0.05). DATA CONCLUSION: Our findings show that, in patients with symptomatic unilateral anterior circulation stroke, CCD is associated with hemodynamic impairment in the ipsilateral MCA territory, which further supports the concept of a vascular component of CCD. LEVEL OF EVIDENCE: 3 TECHNICAL EFFICACY STAGE: 3.

Intraoperative BOLD-fMRI Cerebrovascular Reactivity Assessment.

Blood oxygenation-level dependent cerebrovascular reactivity (BOLD-CVR) has gained attention in recent years as an effective way to investigate CVR, a measure of the hemodynamic state of the brain, with high spatial and temporal resolution. An association between impaired CVR and diverse pathologies has been observed, especially in ischemic cerebrovascular diseases and brain gliomas. The ability to obtain this information intraoperatively is novel and has not been widely tested. We report our first experience with this intraoperative technique in vascular and oncologic neurosurgical patients, discuss the results of its feasibility, and the possible developments of the intraoperative employment of BOLD-CVR.

How to avoid pneumocephalus in deep brain stimulation surgery? Analysis of potential risk factors in a series of 100 consecutive patients.

BACKGROUND: Accuracy of lead placement is the key to success in deep brain stimulation (DBS). Precise anatomic stereotactic planning usually is based on stable perioperative anatomy. Pneumocephalus due to intraoperative CSF loss is a common procedure-related phenomenon which could lead to brain shift and targeting inaccuracy. The aim of this study was to evaluate potential risk factors of pneumocephalus in DBS surgery. METHODS: We performed a retrospective single-center analysis in patients undergoing bilateral DBS. We quantified the amount of pneumocephalus by postoperative CT scans and corrected the data for accompanying brain atrophy by an MRI-based score. Automated computerized segmentation algorithms from a dedicated software were used. As potential risk factors, we evaluated the impact of trephination size, the number of electrode tracks, length of surgery, intraoperative blood pressure, and brain atrophy. RESULTS: We included 100 consecutive patients that underwent awake DBS with intraoperative neurophysiological testing. Systolic and mean arterial blood pressure showed a substantial impact with an inverse correlation, indicating that lower blood pressure is associated with higher volume of pneumocephalus. Furthermore, the length of surgery was clearly correlated to pneumocephalus. CONCLUSION: Our analysis identifies intraoperative systolic and mean arterial blood pressure as important risk factors for pneumocephalus in awake stereotactic surgery.

Development of machine learning models to prognosticate chronic shunt-dependent hydrocephalus after aneurysmal subarachnoid hemorrhage.

BACKGROUND: Shunt-dependent hydrocephalus significantly complicates subarachnoid hemorrhage (SAH), and reliable prognosis methods have been sought in recent years to reduce morbidity and costs associated with delayed treatment or neglected onset. Machine learning (ML) defines modern data analysis techniques allowing accurate subject-based risk stratifications. We aimed at developing and testing different ML models to predict shunt-dependent hydrocephalus after aneurysmal SAH. METHODS: We consulted electronic records of patients with aneurysmal SAH treated at our institution between January 2013 and March 2019. We selected variables for the models according to the results of the previous works on this topic. We trained and tested four ML algorithms on three datasets: one containing binary variables, one considering variables associated with shunt-dependency after an explorative analysis, and one including all variables. For each model, we calculated AUROC, specificity, sensitivity, accuracy, PPV, and also, on the validation set, the NPV and the Matthews correlation coefficient (ϕ). RESULTS: Three hundred eighty-six patients were included. Fifty patients (12.9%) developed shunt-dependency after a mean follow-up of 19.7 (± 12.6) months. Complete information was retrieved for 32 variables, used to train the models. The best models were selected based on the performances on the validation set and were achieved with a distributed random forest model considering 21 variables, with a ϕ = 0.59, AUC = 0.88; sensitivity and specificity of 0.73 (C.I.: 0.39-0.94) and 0.92 (C.I.: 0.84-0.97), respectively; PPV = 0.59 (0.38-0.77); and NPV = 0.96 (0.90-0.98). Accuracy was 0.90 (0.82-0.95). CONCLUSIONS: Machine learning prognostic models allow accurate predictions with a large number of variables and a more subject-oriented prognosis. We identified a single best distributed random forest model, with an excellent prognostic capacity (ϕ = 0.58), which could be especially helpful in identifying low-risk patients for shunt-dependency.

Feasibility and safety of intraoperative BOLD functional MRI cerebrovascular reactivity to evaluate extracranial-to-intracranial bypass efficacy.

Blood oxygenation level-dependent functional MRI cerebrovascular reactivity (BOLD-CVR) is a contemporary technique to assess brain tissue hemodynamic changes after extracranial- intracranial (EC-IC) bypass flow augmentation surgery. The authors conducted a preliminary study to investigate the feasibility and safety of intraoperative 3-T MRI BOLD-CVR after EC-IC bypass flow augmentation surgery. Five consecutive patients selected for EC-IC bypass revascularization underwent an intraoperative BOLD-CVR examination to assess early hemodynamic changes after revascularization and to confirm the safety of this technique. All patients had a normal postoperative course, and none of the patients exhibited complications or radiological alterations related to prolonged anesthesia time. In addition to intraoperative flow measurements of the bypass graft, BOLD-CVR maps added information on the hemodynamic status and changes at the brain tissue level. Intraoperative BOLD-CVR is feasible and safe in patients undergoing EC-IC bypass revascularization. This technique can offer immediate hemodynamic feedback on brain tissue revascularization after bypass flow augmentation surgery.

The Zurich Pituitary Score predicts utility of intraoperative high-field magnetic resonance imaging in transsphenoidal pituitary adenoma surgery.

BACKGROUND: It is currently unclear if there are subsets of patients undergoing transsphenoidal surgery (TSS) in which intraoperative high-field magnetic resonance imaging (3T-iMRI) is particularly advantageous. We aimed to investigate whether a radiological grading scale predicts the utility of 3T-iMRI in pituitary adenoma (PA) TSS. METHODS: From a prospective registry, patients who underwent endoscopic TSS for PA using 3T-iMRI were identified. Adenomas were graded using the Zurich Pituitary Score (ZPS). We assessed improvement after 3T-iMRI in terms of gross total resection (GTR), residual volume (RV), and extent of resection (EOR). RESULTS: Among 95 patients, rates of conversion to GTR after 3T-iMRI decreased steadily from 33% for grade I to 0% for grade IV adenomas, with a statistically significant conversion rate only for grade I (p = 0.008) and grade II (p < 0.001). All grade I adenomas were completely resected after 3T-iMRI. Median RV change was statistically significant for grades I to III, but not for grade IV (p = 0.625). EOR improvement ranged from a median change of 0.0% (IQR 0.0-4.5%) for grade I to 4.4% (IQR 0.0-9.0%) for grade IV, with a significant improvement only for grades I to III (p < 0.05). CONCLUSIONS: Interestingly, this study shows that clinical utility of 3T-iMRI is highest in the more "simple" adenomas (ZPS grades I-II) than for the more "complex" ones (ZPS grade III-IV). Grade I adenomas are amenable to GTR if 3T-iMRI is implemented. In grade III adenomas, EOR and RV can be improved to clinically relevant levels. Conversely, in grade IV adenomas, 3T-iMRI may be of limited use.

Utility of deep neural networks in predicting gross-total resection after transsphenoidal surgery for pituitary adenoma: a pilot study.

OBJECTIVEGross-total resection (GTR) is often the primary surgical goal in transsphenoidal surgery for pituitary adenoma. Existing classifications are effective at predicting GTR but are often hampered by limited discriminatory ability in moderate cases and by poor interrater agreement. Deep learning, a subset of machine learning, has recently established itself as highly effective in forecasting medical outcomes. In this pilot study, the authors aimed to evaluate the utility of using deep learning to predict GTR after transsphenoidal surgery for pituitary adenoma.METHODSData from a prospective registry were used. The authors trained a deep neural network to predict GTR from 16 preoperatively available radiological and procedural variables. Class imbalance adjustment, cross-validation, and random dropout were applied to prevent overfitting and ensure robustness of the predictive model. The authors subsequently compared the deep learning model to a conventional logistic regression model and to the Knosp classification as a gold standard.RESULTSOverall, 140 patients who underwent endoscopic transsphenoidal surgery were included. GTR was achieved in 95 patients (68%), with a mean extent of resection of 96.8% ± 10.6%. Intraoperative high-field MRI was used in 116 (83%) procedures. The deep learning model achieved excellent area under the curve (AUC; 0.96), accuracy (91%), sensitivity (94%), and specificity (89%). This represents an improvement in comparison with the Knosp classification (AUC: 0.87, accuracy: 81%, sensitivity: 92%, specificity: 70%) and a statistically significant improvement in comparison with logistic regression (AUC: 0.86, accuracy: 82%, sensitivity: 81%, specificity: 83%) (all p < 0.001).CONCLUSIONSIn this pilot study, the authors demonstrated the utility of applying deep learning to preoperatively predict the likelihood of GTR with excellent performance. Further training and validation in a prospective multicentric cohort will enable the development of an easy-to-use interface for use in clinical practice.

Predicting extent of resection in transsphenoidal surgery for pituitary adenoma.

BACKGROUND: The extent of resection (EOR) is a crucial outcome parameter in transsphenoidal pituitary surgery (TSS), and is linked to endocrinological outcome, postoperative morbidity, and mortality. We aimed to build a robust, quantitative, and easily reproducible imaging score able to predict EOR in TSS. METHODS: The ratio (R) between the maximum horizontal adenoma diameter and intercarotid distance at the horizontal C4 segment was used to stratify our patient series in four classes: class I R ≤ 0.75, class II 0.75 < R ≤ 1.25, and class III R ≥ 1.25. Class IV included adenomas which completely encased the internal carotid artery. The resulting score was internally validated for robustness. RESULTS: One hundred sixteen patients were included in the study, of which 96 (83%) for derivation and 20 (17%) for validation. EOR showed significant differences between grades (grade I, 100%; II, 97.9%; III, 94.2%; IV, 87.2%; all P < 0.05). The same applied to residual volume (RV) (grade I, 0 cm3; II, 0.08 cm3; III, 1.11 cm3; IV, 1.63 cm3; all P < 0.05). Differences in gross total resection (GTR) were statistically significant among classes I, II, and III (P < 0.05). The incidence of residual adenoma in the cavernous sinus increased also constantly from grade I up to grade IV although a significant difference was only found between grades III and II (P = 0.004). The score performed equally well in the validation cohort. Inter-observer agreement was high, with intraclass correlation coefficients > 0.89 for measurement of both the horizontal tumor diameter and the ICD among two independent raters (P < 0.001). CONCLUSIONS: The proposed score is a simple and reproducible tool which reliably predicts surgical outcome including EOR, RV, and GTR of pituitary adenoma patients undergoing TSS.

The changing sella: internal carotid artery shift during transsphenoidal pituitary surgery.

PURPOSE: Injuries to the internal carotid artery (ICA) are potentially lethal complications in transsphenoidal surgery (TSS) for pituitary lesions. The intercarotid distance (ICD) is thus a major parameter, determining the width of the surgical corridor in TSS. The purpose of the study is to investigate changes in ICD at different levels of the ICA during and after TSS using high definition intraoperative MRI (3T-iMRI). METHODS: Pre-, intra- and 3 months postoperative MRI images of 85 TSS patients were reviewed. ICD was measured at the horizontal (ICDC4h) and vertical (ICDC4v) intracavernous C4 segment as well as at the C6 segment (ICDC6). Association between ICD change at different levels and time points were compared and potential factors predicting ICD reduction were analyzed. RESULTS: ICD decreased intraoperatively at all three segments of ICA by -3% (median decreases: ICDC4h: -0.5 mm, ICDC4v: -0.7 mm ICDC6: -0.4 mm). At 3 months postoperative MRI, ICD reduced by a further -4%, -2% and -4% respectively (median decreases ICDC4h: -0.7, ICDC4v: -0.4 mm, ICDC6: -0.5 mm). Postoperative narrowing in ICD occurred independent of further resection after 3T-iMRI. ICD change correlated between different levels of the ICA indicating a uniform shift perioperatively. Preoperative ICD was significantly associated with the intraoperative reduction in ICDC4v and ICDC6. CONCLUSIONS: We have demonstrated a uniform narrowing in ICD at different levels of the ICA during and after TSS adenoma resection. Surgeons should be aware of this change since it determines the width of the surgical corridor and can thus influence the ease of surgery.

Unusual case of traumatic neuroma of the orbit.

Traumatic or amputation neuromas are neoformations developing after damage to a peripheral nerve. They are not proper tumors but rather a reactive process or a frustrated attempt of nerve regeneration. Traumatic neuromas are potentially found in every sensory peripheral nerve and often at the site of past surgical intervention, including orbital surgery. A 29-year-old Northern African migrant presented progressive exophthalmos and progressive loss of acuity in left eye, which had started about 6 months before after a cranio-facial trauma caused by a violent assault. MRI of the orbits showed a massive intra-orbital, intra-conical lesion, clearly compressing and dislocating the optic nerve and extending posteriorly to the orbital apex. Surgery was performed through lateral approach of Kroenlein and led to complete excision of the lesion. Histology revealed fibrotic, adipose and striated muscle tissues, a disordered, non-neoplastic overgrowth of small and large fascicles of nerves, inflammatory infiltrates, and fibrosis with sparse calcifications were diffusely observed in a background of fat, scar and striated muscle tissued. Patient was discharged on the fifth day in good health condition, without deficit of eye motion but without recovery of visual acuity. In conclusion, this case demonstrates that traumatic neuromas may arise in the orbit in patients with minor direct trauma to nerves and without previous surgical treatment.

Intraoperative seizures during neuro-oncological supratentorial surgery: the role of prophylaxis with levetiracetam and intraoperative monitoring in a consecutive series of 353 patients.

BACKGROUND: The aim of this paper was to understand the role of prophylaxis with levetiracetam at skin incision in preventing convulsive intraoperative seizures (IOS) during neurosurgical procedures with and without intraoperative neuromonitoring (IONM). METHODS: Authors retrospectively reviewed the Institutional database for cases of supratentorial brain tumors undergoing surgical resection performed from January 2021 to October 2022. Patients were operated on both under general anesthesia and awake, using motor-evoked potentials (MEP) and direct cortical stimulation for cortical mapping. 1000 mg ev of Levetiracetam before skin incision in case of a history of seizures was administrated. We excluded all infratentorial cases. RESULTS: Three hundred fisty three consecutive cases were retrieved. IOS occurred in 22 patients (6.2%). Prophylaxis with Levetiracetam was administered in 149 patients, and IOS occurred in 16 cases (10.7%) in this group of patients. The IOS rate in the case of no Levetiracetam prophylaxis administration (3.5%) was significantly lower (P<0.001, OR=3.38 [1.35-8.45], RR=3.12 [1.32-7.41]). The Penfield technique stimulation evoked seven of all 22 IOS reported (31.8%) (P=0.006, RR 5.4 [1.44 -20.58], OR 21 [2.3-183.9]), and the train-of-five technique stimulation caused two of all registered IOS (8.7%) (P=0.2, RR 2.3 [0.99-5.67], OR 6.5 [0.55-76.17]). Transcranial MEPs evoked no IOS. CONCLUSIONS: Under levetiracetam prophylaxis, the IOS rate was not significantly lower than in the group of patients without Levetiracetam prophylaxis, regardless of the histology of the tumor and IONM. Neither the transcranial stimulation (MEP) nor train-of-five technique stimulation increases the risk of convulsive IOS, as Penfield technique stimulation does.

Heads-Up Micronavigation Reliability of Preoperative Transcranial Magnetic Stimulation Maps for the Motor Function: Comparison With Direct Cortical Stimulation.

BACKGROUND AND OBJECTIVES: We aimed to assess the reliability of preoperative navigated transcranial magnetic stimulation (nTMS) maps for motor function as visualized intraoperatively with augmented reality heads-up display and to assess its accuracy via direct point-by-point comparison with the gold-standard direct cortical stimulation (DCS). METHODS: From January 2022 to January 2023, candidates for surgical removal of lesions involving the motor pathways underwent preoperative nTMS assessment to obtain cortical maps of motor function. Intraoperatively and before tumor removal, nTMS maps were superimposed on the cortical surface, and DCS was performed on positive points with increasing current intensity until obtaining a positive response at 16 mA. The outcome of each stimulation was recorded to obtain discrimination metrics. RESULTS: Twelve patients were enrolled (5 females [42%] vs 7 males [58%], mean age 62.9 ± 12.8 years), for a total of 304 investigated points. Agreement between nTMS and DCS was moderate (κ = 0.43, P < .005), with 0.66 (0.53-0.78) sensitivity, 0.87 (0.82-0.90) specificity, 0.50 (0.39-0.62) positive predictive values, 0.93 (0.89-0.95) negative predictive value, and 0.83 (0.79-0.87) accuracy. A loss of accuracy was observed with higher DCS current intensities. CONCLUSION: We performed a point-by-point validation of preoperative nTMS maps for motor function using augmented reality visualization. The high negative predictive value and low positive predictive values highlight nTMS reliability to visualize safe cortical zones but not to identify critical functional areas, confirming previous findings of nTMS maps for the language function and suggesting the need for combined use of nTMS maps and DCS for optimal maximal safe resection.

Brain tumor surgery guided by navigated transcranial magnetic stimulation mapping for arithmetic calculation.

OBJECTIVE: The onco-functional balance represents the primary goal in neuro-oncology. The increasing use of navigated transcranial magnetic stimulation (nTMS) allows the noninvasive characterization of cortical functional anatomy, and its reliability for motor and language mapping has previously been validated. Calculation and arithmetic processing has not been studied with nTMS so far. In this study, the authors present their preliminary data concerning nTMS calculation. METHODS: The authors designed a monocentric prospective study, adopting an internal protocol to use nTMS for preoperative planning, including arithmetic processing. When awake surgery was possible, according to the patients' conditions, nTMS points were used to guide direct cortical stimulation (DCS), i.e., the gold standard for cortical mapping. Navigated TMS-based tractography was used for surgical planning. Statistical analyses on the nTMS and DCS points were performed. RESULTS: From February 2021 to October 2023, 61 procedures for nTMS calculation mapping were performed. The clinical evaluation, including pre- and postoperative evaluations (3 months after surgery), demonstrated a good clinical outcome with preservation of arithmetic function and recovery (92.8% of patients). Between the awake and asleep surgery groups, the postoperative clinical results were comparable at the 3-month follow-up, with > 90% of the patients achieving improved calculation function. The surgical strategy adopted was aimed at sparing nTMS positive points in asleep procedures, whereas nTMS and DCS positive points were not removed in awake procedures. Overall, 62% of the positive points for calculation functions were exposed by craniotomy and 85% were spared during surgery. None of the patients developed nTMS-related seizures. Diffusion tensor imaging fiber tracking based on nTMS positive points for calculation was used. The white matter fiber tracts involved in calculation functions were the arcuate fasciculus (56%) and frontal aslant tract (22%). When nTMS and DCS points were compared in awake surgery (n = 10 patients), a sensitivity of 31.71%, specificity of 85.76%, positive predictive value of 22.41%, negative predictive value of 90.64%, and accuracy of approximately 69% were achieved. CONCLUSIONS: Based on the authors' preliminary data, nTMS can be an advantageous tool to study cognitive functions, aimed at minimizing neurological impairment. The postoperative clinical outcome for patients who underwent operation with nTMS was very good. Considering these results, nTMS has proved to be a feasible method to map cognitive areas including those for calculation functions. Further analyses are needed to validate these data. Finally, other cognitive functions (e.g., visuospatial) may be explored with nTMS.

A Diffusion Tensor Imaging-Based Prognostic Classification for Surgery of Intrinsic Lesions Involving the Motor Pathways.

BACKGROUND: The critical role of different adjuncts in improving the neurological outcome in intrinsic brain lesions affecting eloquent areas is demonstrated by their more diffuse utilization. Neurosurgeons often rely on preoperative and intraoperative diffusion tensor imaging tractography to improve the operative strategy and prognosis. We aimed to identify and validate a diffusion tensor imaging-based classification considering the relationship between the brain lesion and the corticospinal tract to predict a >50% reduction of motor evoked potentials (MEPs) during surgical excision of lesions involving the motor pathways. METHODS: We included patients consecutively enrolled at our institution between April 2020 and September 2022 with 3 patterns of increasing complexity according to the relationship between the lesion and the corticospinal tract as identified on preoperative diffusion tensor imaging. Outcome measures were >50% reduction in intraoperative MEPs and neurological outcome defined as unchanged, improved, or worsened. RESULTS: The study included 83 patients. A statistically significant linear trend between higher rates of reduction of MEPs and higher classification grades was observed (P = 0.001), with sensitivity 0.60, specificity 0.88, accuracy 0.83, and area under the curve 0.75. Higher grades were associated with worse neurological outcomes (P = 0.02). CONCLUSIONS: The classification proved reliable in anticipating reduction in intraoperative MEPs and in predicting neurological outcome. Using this classification in patients undergoing surgery for lesions involving the motor pathways could help in counseling the patient, surgical planning, enhancing teamwork of operating room personnel, and improving the patient's prognosis.

Intraoperative Mapping of the Sensory Root of the Trigeminal Nerve in Patients with Pontocerebellar Angle Pathology.

OBJECTIVE: The aim of the present study was to determine the position of the 3 sensory branches of the trigeminal nerve in the preganglionic tract using intraoperative neurophysiological mapping. METHODS: We included consecutive adult patients who underwent neurosurgical treatment of cerebellopontine angle lesions. The trigeminal nerve was antidromically stimulated at 3 sites along its circumference with different stimulus intensities at a distance of ≤1 cm from the brainstem. The sensory nerve action potentials (SNAPs) were recorded from each main trigeminal branch (V1 [ophthalmic branch], V2 [maxillary branch], and V3 [mandibular branch]). RESULTS: We analyzed 13 patients. The stimulation points at which we obtained the greatest number of congruous and exclusive SNAPs (SNAPs only on the stimulated branch) was the stimulation point for V3 (20.7%). The stimulation intensity at which we obtained the highest number of congruent and exclusive SNAPs with the stimulated branch was 0.5 mA. CONCLUSIONS: Using our recording conditions, trigeminal stimulation is a reliable technique for mapping the V3 and V1 branches using an intensity not exceeding 0.5. However, reliable identification of the fibers of V2 is more difficult. Stimulation of the trigeminal nerve can be a reliable technique to identify the V3 and V1 branches if rhizotomy of these branches is necessary.

Feasibility of Intraoperative Visual Evoked Potential Monitoring by Cortical Strip Electrodes in Patients During Brain Surgery: A Preliminary Study.

OBJECTIVE: The role of visual evoked potentials (VEPs) monitoring during neurosurgical procedure in patient remains unclear. The purpose of our study was to determine the feasibility of intraoperative VEP recording using a strip cortical electrode during surgical resection of intracranial lesions. METHODS: In this prospective, monocentric, observational study, we enrolled consecutive patients undergoing neurosurgical procedure for intracranial lesions. After dural opening, a cortical strip was positioned on the lateral occipital surface. Flash VEPs were continuously recorded using both subdermal corkscrew electrodes and strip electrodes. An electroretinogram was also recorded to guarantee delivery of adequate flash stimuli to the retina. RESULTS: We included 10 patients affected by different intracranial lesions. Flash VEPs were recorded using subdermal corkscrew electrodes in all patients except 1 in whom they were never identified during the recording. Flash VEPs were recorded using strip electrodes in all patients and showed a polyphasic morphology with a significantly larger amplitude compared with that of flash VEPs measured using subdermal corkscrew electrodes. No patient reported worsened postoperative vision and a >50% decrease in the VEPs amplitude was never registered. CONCLUSIONS: We have reported for the first time in the literature that VEP monitoring during a neurosurgical procedure is feasible via a cortical strip located on the occipital surface. The technique demonstrated greater stability and a larger amplitude compared with recordings with scalp electrodes, facilitating identification of any changes. Studies with more patients are needed to assess the clinical reliability of the technique.