Image guidance and neuromonitoring in neurosurgery

Intraoperative neurophysiology in pediatric neurosurgery: a historical perspective

INTRODUCTION

Intraoperative neurophysiology (ION) has been established over the past three decades as a valuable discipline to improve the safety of neurosurgical procedures with the main goal of reducing neurological morbidity. Neurosurgeons have substantially contributed to the development of this field not only by implementing the use and refinement of ION in the operating room but also by introducing novel techniques for both mapping and monitoring of neural pathways.

METHODS

This review provides a personal perspective on the evolution of ION in a variety of pediatric neurosurgical procedures: from brain tumor to brainstem surgery, from spinal cord tumor to tethered cord surgery.

RESULTS AND DISCUSSION

The contribution of pediatric neurosurgeons is highlighted showing how our discipline has played a crucial role in promoting ION at the turn of the century. Finally, a view on novel ION techniques and their potential implications for pediatric neurosurgery will provide insights into the future of ION, further supporting the view of a functional, rather than merely anatomical, approach to pediatric neurosurgery.

The role of preoperative diffusion tensor imaging in predicting and improving functional outcome in pediatric patients undergoing epilepsy surgery: a systematic review

OBJECTIVE

Diffusion tensor imaging (DTI) is a useful neuroimaging technique for surgical planning in adult patients. However, no systematic review has been conducted to determine its utility for pre-operative analysis and planning of Pediatric Epilepsy surgery. We sought to determine the benefit of pre-operative DTI in predicting and improving neurological functional outcome after epilepsy surgery in children with intractable epilepsy.

METHODS

A systematic review of articles in English using PubMed, EMBASE and Scopus databases, from inception to January 10, 2020 was conducted. All studies that used DTI as either predictor or direct influencer of functional neurological outcome (motor, sensory, language and/or visual) in pediatric epilepsy surgical candidates were included. Data extraction was performed by two blinded reviewers. Risk of bias of each study was determined using the QUADAS 2 Scoring System.

RESULTS

13 studies were included (6 case reports/series, 5 retrospective cohorts, and 2 prospective cohorts) with a total of 229 patients. Seven studies reported motor outcome; three reported motor outcome prediction with a sensitivity and specificity ranging from 80 to 85.7 and 69.6 to 100%, respectively; four studies reported visual outcome. In general, the use of DTI was associated with a high degree of favorable neurological outcomes after epilepsy surgery.

CONCLUSION

Multiple studies show that DTI helps to create a tailored plan that results in improved functional outcome. However, more studies are required in order to fully assess its utility in pediatric patients. This is a desirable field of study because DTI offers a non-invasive technique more suitable for children.

ADVANCES IN KNOWLEDGE

This systematic review analyses, exclusively, studies of pediatric patients with drug-resistant epilepsy and provides an update of the evidence regarding the role of DTI, as part of the pre-operative armamentarium, in improving post-surgical neurological sequels and its potential for outcome prediction.

Optimizing Magnetoencephalographic Imaging Estimation of Language Lateralization for Simpler Language Tasks

Magnetoencephalographic imaging (MEGI) offers a non-invasive alternative for defining preoperative language lateralization in neurosurgery patients. MEGI indeed can be used for accurate estimation of language lateralization with a complex language task - auditory verb generation. However, since language function may vary considerably in patients with focal lesions, it is important to optimize MEGI for estimation of language function with other simpler language tasks. The goal of this study was to optimize MEGI laterality analyses for two such simpler language tasks that can have compliance from those with impaired language function: a non-word repetition (NWR) task and a picture naming (PN) task. Language lateralization results for these two tasks were compared to the verb-generation (VG) task. MEGI reconstruction parameters (regions and time windows) for NWR and PN were first defined in a presurgical training cohort by benchmarking these against laterality indices for VG. Optimized time windows and regions of interest (ROIs) for NWR and PN were determined by examining oscillations in the beta band (12-30 Hz) a marker of neural activity known to be concordant with the VG laterality index (LI). For NWR, additional ROIs include areas MTG/ITG and for both NWR and PN, the postcentral gyrus was included in analyses. Optimal time windows for NWR were defined as 650-850 ms (stimulus-locked) and -350 to -150 ms (response-locked) and for PN -450 to -250 ms (response-locked). To verify the optimal parameters defined in our training cohort for NWR and PN, we examined an independent validation cohort (n = 30 for NWR, n = 28 for PN) and found high concordance between VG laterality and PN laterality (82%) and between VG laterality and NWR laterality (87%). Finally, in a test cohort (n = 8) that underwent both the intracarotid amobarbital procedure (IAP) test and MEG for VG, NWR, and PN, we identified excellent concordance (100%) with IAP for VG + NWR + PN composite LI, high concordance for PN alone (87.5%), and moderate concordance for NWR alone (66.7%). These findings provide task options for non-invasive language mapping with MEGI that can be calibrated for language abilities of individual patients. Results also demonstrate that more accurate estimates can be obtained by combining laterality estimates obtained from multiple tasks. MEGI.

The role of diffusion tractography in refining glial tumor resection

Primary brain tumors are notoriously hard to resect surgically. Due to their infiltrative nature, finding the optimal resection boundary without damaging healthy tissue can be challenging. One potential tool to help make this decision is diffusion-weighted magnetic resonance imaging (dMRI) tractography. dMRI exploits the diffusion of water molecule along axons to generate a 3D modelization of the white matter bundles in the brain. This feature is particularly useful to visualize how a tumor affects its surrounding white matter and plan a surgical path. This paper reviews the different ways in which dMRI can be used to improve brain tumor resection, its benefits and also its limitations. We expose surgical tools that can be paired with dMRI to improve its impact on surgical outcome, such as loading the 3D tractography in the neuronavigation system and direct electrical stimulation to validate the position of the white matter bundles of interest. We also review articles validating dMRI findings using other anatomical investigation techniques, such as postmortem dissections, manganese-enhanced MRI, electrophysiological stimulations, and phantom studies with known ground truth. We will be discussing the areas of the brain where dMRI performs well and where the future challenges are. We will conclude this review with suggestions and take home messages for neurosurgeons, tractographers, and vendors for advancing the field and on how to benefit from tractography's use in clinical practice.

Diffusion Weighted/Tensor Imaging, Functional MRI and Perfusion Weighted Imaging in Glioblastoma-Foundations and Future

In this article, we review the basics of diffusion tensor imaging and functional MRI, their current utility in preoperative neurosurgical mapping, and their limitations. We also discuss potential future applications, including implementation of resting state functional MRI. We then discuss perfusion and diffusion-weighted imaging and their application in advanced neuro-oncologic practice. We explain how these modalities can be helpful in guiding surgical biopsies and differentiating recurrent tumor from treatment related changes.

3-T intraoperative MRI (iMRI) for pediatric epilepsy surgery

PURPOSE

Three-tesla intraoperative MRI (iMRI) is a promising tool that could help confirm complete resections and disconnections in pediatric epilepsy surgery, leading to improved outcomes. However, a large proportion of epileptogenic pathologies in children are poorly defined on imaging, which brings into question the utility of iMRI for these cases. Our aim was to compare postoperative seizure outcomes between iMRI- and non-iMRI-based epilepsy surgeries.

METHODS

We performed a comparative retrospective analysis of non-iMRI- versus iMRI-based epilepsy surgeries with 2-year follow-up. Patients were stratified into well-defined cases (WDCs), poorly defined cases (PDCs), and diffuse hemispheric cases (DHCs). Primary outcomes were rates of complete seizure freedom and surgical complications. Secondary outcomes included good (Engel class I/II) seizure outcome, extent of resection/disconnection, and operative duration. Regression models were used to adjust for confounding.

RESULTS

Thirty-nine iMRI-based and 39 non-iMRI-based surgeries were included. The distributions of age, sex, and lesion class in each era were similar, but the distributions of individual pathologies varied. Seizure freedom and complication rates at 2-year follow-up were not different between the groups, but Engel class I/II outcome was more common in the iMRI group. Extent of resection/disconnection and length of surgery were similar in both groups. PDCs had the worst outcomes, which were unchanged by the use of iMRI.

CONCLUSION

Three-tesla iMRI-based epilepsy surgery may have the potential to improve patient outcomes. However, we conclude that iMRI, in its current state of use at our institute, does not improve outcomes for children undergoing epilepsy surgery. Given that its use appears safe, further research on this technology is warranted, particularly for the most challenging PDCs.

Intra-operative neurophysiological mapping and monitoring during brain tumour surgery in children: an update

INTRODUCTION

Over the past decade, the reluctance to operate in eloquent brain areas has been reconsidered in the light of the advent of new peri-operative functional neuroimaging techniques and new evidence from neuro-oncology. To maximise tumour resection while minimising morbidity should be the goal of brain surgery in children as much as it is in adults, and preservation of brain functions is critical in the light of the increased survival and the expectations in terms of quality of life.

DISCUSSION

Intra-operative neurophysiology is the gold standard to localise and preserve brain functions during surgery and is increasingly used in paediatric neurosurgery. Yet, the developing nervous system has peculiar characteristics in terms of anatomical and physiological maturation, and some technical aspects need to be tailored for its use in children, especially in infants. This paper will review the most recent advances in the field of intra-operative neurophysiology (ION) techniques during brain surgery, focussing on those aspects that are relevant to the paediatric neurosurgery practice.

Clinical considerations and surgical approaches for low-grade gliomas in deep hemispheric locations: insular lesions

Insula and paralimbic region represent a common location for gliomas in adulthood. However, limbic and paralimbic tumors are rare in children. Reports of pediatric insular tumors are scarce in literature, and most of them are included in adult's series, so their management and outcome can be outlined only after extracting data from these reports. Due to their predominantly low grade, they usually have a benign course for some time, what make them ideal candidates for total resection. However, their intricate location and spread to key areas, including the temporal lobe, make them a surgical challenge. The transsylvian route, with or without resection of the frontal and/or temporal operculae, which requires exposure of part or all of the insula is commonly selected for insular tumor approaches. Intraoperative functional mapping is a standard procedure for resection of central region tumors in adults. In children and young individuals, awake craniotomy is not always possible and surgical planning usually relay on functional and anatomical preoperative studies. The main goal when approaching an insular tumor is to achieve the largest extent of resection to increase overall patient survival while preserving the functional status, minimizing postoperative morbidity and increasing the quality of life. The extent of resection seems to be correlated also with the control of associated (and usually intractable) epilepsy.

Pediatric infratentorial ganglioglioma

PURPOSE

Pediatric infratentorial gangliogliomas are exceedingly rare tumors; thus, the factors affecting their outcome are poorly understood and their optimal management has still to be defined.

METHODS

We reviewed the literature on pediatric gangliogliomas with a focus on those located in the posterior fossa to study treatment and outcome data. We added to this review some of our clinical cases.

RESULTS

We found 100 and 80 cases of brainstem and cerebellar pediatric ganglioglioma, respectively, in our literature review. The surgical management varied from biopsy to gross total resection, and adjuvant treatment was given after incomplete resection or at time of progression. A gross total resection should be attempted to remove the contrast enhancing part of the tumor, which may be possible in most of the cerebellar gangliogliomas and some of the brainstem lesions. The cervicomedullary ganglioglioma seems to be the most infiltrative and least amenable to complete resection. Chemotherapy has a limited role and BRAF mutation was reported in 38 to 54 % of cases. The use of radiotherapy exposes the patient to a risk of malignant transformation and should be reserved for unresectable tumors which progress.

CONCLUSION

Pediatric posterior fossa gangliogliomas are rare and challenging tumors due to their frequent infiltrative component involving the brainstem. To date, adjuvant therapy has a limited role that may evolve with time thanks to the use of targeted therapies against BRAF mutation. The surgical resection of well-defined contrast enhancing parts should be attempted even in staged surgeries and balanced with the risks of neurological deterioration.

MRI-guided stereotactic aspiration of brain abscesses by use of an optical tracking navigation system

BACKGROUND

Owing to the high risk of abscess drainage by craniotomy, imaging-guided stereotactic aspiration is considered an ideal choice in the management of brain abscesses. Interventional magnetic resonance imaging (MRI) represents a valuable technique for the treatment of brain abscess as a guiding modality.

PURPOSE

To evaluate the safety and efficacy of an interventional MRI system in performing the procedure.

MATERIAL AND METHODS

Thirteen brain abscesses in 11 patients were treated with percutaneous aspiration. All procedures were performed solely under the guidance of a 0.23-T open-configuration MRI scanner with optical tracking. Clinical and imaging follow-up was at 1 week, 1 month, 3 months, and 6 months. The changes of abscess, MRI features, and clinical symptoms were recorded. Procedure efficacy and safety were evaluated by success rate, procedure time, decrease of abscess, recovery rate, and complication. Descriptive statistical analysis was performed.

RESULTS

MRI-guided stereotactic aspirations were performed successfully in 13/13 (100%) abscesses. The mean operating time was 70 min (range, 45-100 min). Follow-up MRI at 1 week after the procedure showed average reduction of abscesses by 60% (2.1/3.5). And the abscesses continued to get smaller by up to 89.7% (3.14/3.5) at 1-month follow-up. All cavities resolved at the end of the 6-month follow-up period. The recovery rate was 100% for fever, headache, vomiting, papilledema, meningismus, altered sensorium, 75% (3/4) for hemiparesis, and 83.3% (5/6) for epilepsy. There were no complications.

CONCLUSION

Punctures of brain abscesses with subsequent aspiration can be performed safely and efficiently by monitoring the procedure using an open interventional MRI system.

Differences Between Generalized Q-Sampling Imaging and Diffusion Tensor Imaging in the Preoperative Visualization of the Nerve Fiber Tracts Within Peritumoral Edema in Brain

BACKGROUND:

Diffusion tensor imaging (DTI) tractography enables the in vivo visualization of white matter tracts inside normal brain tissue, which provides the neurosurgeon important information to plan tumor resections. However, DTI is associated with restrictions in the resolution of crossing fibers in the vicinity of the tumor or in edema. We find that generalized q-sampling imaging (GQI) can overcome these difficulties and is advantageous over DTI for the tractography of the fiber bundle in peritumoral edema.

OBJECTIVE:

To demonstrate the differences between GQI and DTI in the preoperative mapping of fiber tractography in peritumoral edema of cerebral tumors, and discuss the clinical application of GQI in neurosurgical planning.

METHODS:

Five patients with brain tumors underwent 3-T magnetic resonance imaging scans, and the data were reconstructed by DTI and GQI. We adjusted the parameters and compared the differences between DTI and GQI in visualizing the fiber tracts in the peritumoral edema of cerebral tumors.

RESULTS:

GQI and DTI showed substantial differences in displaying the nerve fibers in the edema surrounding the tumor. The GQI tractography method could fully display existing intact fibers in the edema, whereas the fiber tracts in edema displayed by DTI tractography were incomplete, missing, or ruptured.

CONCLUSION:

GQI can visualize the tracts in the peritumoral edema of cerebral tumors better than DTI. Although GQI has many limitations, its future in the preoperative guidance of brain tumor lesions is promising.

A systematic review of functional magnetic resonance imaging and diffusion tensor imaging modalities used in presurgical planning of brain tumour resection

Historically, brain tumour resection has relied upon standardised anatomical atlases and classical mapping techniques for successful resection. While these have provided adequate results in the past, the emergence of new technologies has heralded a wave of less invasive, patient-specific techniques for the mapping of brain function. Functional magnetic resonance imaging (fMRI) and, more recently, diffusion tensor imaging (DTI) are two such techniques. While fMRI is able to highlight localisation of function within the cortex, DTI represents the only technique able to elucidate white matter structures in vivo. Used in conjunction, both of these techniques provide important presurgical information for thorough preoperative planning, as well as intraoperatively via integration into frameless stereotactic neuronavigational systems. Together, these techniques show great promise for improved neurosurgical outcomes. While further research is required for more widespread clinical validity and acceptance, results from the literature provide a clear road map for future research and development to cement these techniques into the clinical setup of neurosurgical departments globally.

First preoperative functional mapping via navigated transcranial magnetic stimulation in a 3-year-old boy

Preoperative functional mapping in children younger than 5 years old remains a challenge. Awake functional MRI (fMRI) is usually not an option for these patients. Except for a description of passive fMRI in sedated patients and magnetoencephalography, no other noninvasive mapping method has been reported as a preoperative diagnostic tool in children. Therefore, invasive intraoperative direct cortical stimulation remains the method of choice. To the authors' knowledge, this is the first case of a young child undergoing preoperative functional motor cortex mapping with the aid of navigated transcranial magnetic stimulation (nTMS). In this 3-year-old boy with a rolandic ganglioglioma, awake preoperative mapping was performed using nTMS. A precise location of Broca area 4 could be established. The surgical approach was planned according to the preoperative findings. Intraoperative direct cortical stimulation verified the location of the nTMS hotspots, and complete resection of the precentral tumor was achieved. Navigated TMS is a precise tool for preoperative motor cortex mapping and is feasible even in very young pediatric patients. In children for whom performing the fMRI motor paradigm is challenging, nTMS is the only available option for functional mapping.

The evolution of imaging in cancer: current state and future challenges

Molecular imaging allows for the remote, noninvasive sensing and measurement of cellular and molecular processes in living subjects. Drawing upon a variety of modalities, molecular imaging provides a window into the biology of cancer from the subcellular level to the patient undergoing a new, experimental therapy. As signal transduction cascades and protein interaction networks become clarified, an increasing number of relevant targets for cancer therapy--and imaging--become available. Although conventional imaging is already critical to the management of patients with cancer, molecular imaging will provide even more relevant information, such as early detection of changes with therapy, identification of patient-specific cellular and metabolic abnormalities, and the disposition of therapeutic, gene-tagged cells throughout the body--all of which will have a considerable impact on morbidity and mortality. This overview discusses molecular imaging in oncology, providing examples from a variety of modalities, with an emphasis on emerging techniques for translational imaging.