Presurgical evaluation of language using functional magnetic resonance imaging in brain tumor patients with previous surgery

Functional MRI in Neuro-Oncology: State of the Art and Future Directions

Since its discovery in the early 1990s, functional MRI (fMRI) has been used to study human brain function. One well-established application of fMRI in the clinical setting is the neurosurgical planning of patients with brain tumors near eloquent cortical areas. Clinical fMRI aims to preoperatively identify eloquent cortices that serve essential functions in daily life, such as hand movement and language. The primary goal of neurosurgery is to maximize tumor resection while sparing eloquent cortices adjacent to the tumor. When a lesion presents in the vicinity of an eloquent cortex, surgeons may use fMRI to plan their best surgical approach by determining the proximity of the lesion to regions of activation, providing guidance for awake brain surgery and intraoperative brain mapping. The acquisition of fMRI requires patient preparation prior to imaging, determination of functional paradigms, monitoring of patient performance, and both processing and analysis of images. Interpretation of fMRI maps requires a strong understanding of functional neuroanatomy and familiarity with the technical limitations frequently present in brain tumor imaging, including neurovascular uncoupling, patient compliance, and data analysis. This review discusses clinical fMRI in neuro-oncology, relevant ongoing research topics, and prospective future developments in this exciting discipline.

Use of longitudinal functional MRI to demonstrate translocation of language function in patients with brain tumors

OBJECTIVE

The ability of functional MRI (fMRI) to localize patient-specific eloquent areas has proved worthwhile in efforts to maximize resection while minimizing risk of iatrogenic damage in patients with brain tumors. Although cortical reorganization has been described, the frequency of its occurrence and the factors that influence incidence are not well understood. The authors investigated changes in language laterality between 2 fMRI studies in patients with brain tumors to elucidate factors contributing to cortical reorganization.

METHODS

The authors analyzed 33 patients with brain tumors involving eloquent language areas who underwent 2 separate presurgical, language task–based fMRI examinations (fMRI1 and fMRI2). Pathology consisted of low-grade glioma (LGG) in 15, and high-grade glioma (HGG) in 18. The mean time interval between scans was 35 ± 38 months (mean ± SD). Regions of interest were drawn for Broca’s area (BA) and the contralateral BA homolog. The laterality index (LI) was calculated and categorized as follows: > 0.2, left dominance; 0.2 to –0.2, codominance; and < −0.2, right dominance. Translocation of language function was defined as a shift across one of these thresholds between the 2 scans. Comparisons between the 2 groups, translocation of language function (reorganized group) versus no translocation (constant group), were performed using the Mann-Whitney U-test.

RESULTS

Nine (27%) of 33 patients demonstrated translocation of language function. Eight of 9 patients with translocation had tumor involvement of BA, compared to 5/24 patients without translocation (p < 0.0001). There was no difference in LI between the 2 groups at fMRI1. However, the reorganized group showed a decreased LI at fMRI2 compared to the constant group (−0.1 vs 0.53, p < 0.01). The reorganized cohort showed a significant difference between LI1 and LI2 (0.50 vs –0.1, p < 0.0001) whereas the constant cohort did not. A longer time interval was found in the reorganized group between fMRI1 and fMRI2 for patients with LGG (34 vs 107 months, p < 0.002). Additionally, the reorganized cohort had a greater proportion of local tumor invasion into eloquent areas at fMRI2 than the constant group. Aphasia was present following fMRI2 in 13/24 (54%) patients who did not exhibit translocation, compared to 2/9 (22%) patients who showed translocation.

CONCLUSIONS

Translocation of language function in patients with brain tumor is associated with tumor involvement of BA, longer time intervals between scans, and is seen in both LGG and HGG. The reduced incidence of aphasia in the reorganized group raises the possibility that reorganization supports the conservation of language function. Therefore, longitudinal fMRI is useful because it may point to reorganization and could affect therapeutic planning for patients.

[Functional magnetic resonance imaging in neurosurgery]

The study is a short review of articles concerning functional magnetic resonance imaging (fMRI) and its practical application in neurosurgery. Advantages and disadvantages of the methods are considered, the results of surgical treatment of patients using functional navigation are presented. Separate attention is paid to fMRI precision, a new resting-state method of visualization. Practical advices of fMRI application in neurooncology and surgery of arteriovenous malformations are given.

[Functional magnetic resonance imaging in neurosurgery]

The review of publications on functional magnetic resonance imaging (fMRI) and its practical application in neurosurgery is presented. Advantages and disadvantages are selected taking pathogenesis into account. Results of surgical treatment with use of functional navigation are described. Separate attention is paid to fMRI precision by its comparing with direct cortical stimulation. New resting-state method of visualization is observed. Practical advices are given of fMRI application in neurooncology and surgery of arteriovenous malformations.

Characterization of cognitive function in survivors of diffuse gliomas using resting-state functional MRI (rs-fMRI)

As treatments for diffuse gliomas have advanced, survival for patients with gliomas has also increased. However, there remains limited knowledge on the relationships between brain connectivity and the lasting changes to cognitive function that glioma survivors often experience long after completing treatment. This resting-state functional magnetic resonance imaging (rs-fMRI) study explored functional connectivity (FC) alterations associated with cognitive function in survivors of gliomas. In this pilot study, 22 patients (mean age 43.8 ± 11.9) with diffuse gliomas who completed treatment within the past 10 years were evaluated using rs-fMRI and neuropsychological measures. Novel rs-fMRI analysis methods were used to account for missing brain in the resection cavity. FC relationships were assessed between cognitively impaired and non-impaired glioma patients, along with self-reported cognitive impairment, non-work daily functioning, and time with surgery. In the cognitively non-impaired patients, FC was stronger in the medial prefrontal cortex, rostral prefrontal cortex, and intraparietal sulcus compared to the impaired survivors. When examining non-work daily functioning, a positive correlation with FC was observed between the accumbens and the intracalcarine cortices, while a negative correlation with FC was observed between the parietal operculum cortex and the cerebellum. Additionally, worse self-reported cognitive impairment and worse non-work daily functioning were associated with increased FC between regions involved in cognition and sensorimotor processing. These preliminary findings suggest that neural correlates for cognitive and daily functioning in glioma patients can be revealed using rs-fMRI. Resting-state network alterations may serve as a biomarker for patients’ cognition and functioning.

Functional MRI Shows Altered Deactivation and a Corresponding Decrease in Functional Connectivity of the Default Mode Network in Patients with Gliomas

BACKGROUND AND PURPOSE

The default mode network normally decreases in activity during externally directed tasks. Although default mode network connectivity is disrupted in numerous brain pathologies, default mode network deactivation has not been studied in patients with brain tumors. We investigated default mode network deactivation with language task-based fMRI by measuring the anticorrelation of a critical default mode network node, the posterior cingulate cortex, in patients with gliomas and controls; furthermore, we examined default mode network functional connectivity in these patients with task-based and resting-state fMRI.

MATERIALS AND METHODS

In 10 healthy controls and 30 patients with gliomas, the posterior cingulate cortex was identified on task-based fMRI and was used as an ROI to create connectivity maps from task-based and resting-state fMRI data. We compared the average correlation in each default mode network region between patients and controls for each correlation map and stratified patients by tumor location, hemisphere, and grade.

RESULTS

Patients with gliomas (P = .001) and, in particular, patients with tumors near the posterior default mode network (P < .001) showed less posterior cingulate cortex anticorrelation in task-based fMRI than controls. Patients with both left- and right-hemisphere tumors, as well as those with grade IV tumors, showed significantly lower posterior cingulate cortex anticorrelation than controls (P = .02, .03, and <.001, respectively). Functional connectivity in each default mode network region was not significantly different between task-based and resting-state maps.

CONCLUSIONS

Task-based fMRI showed impaired deactivation of the default mode network in patients with gliomas. The functional connectivity of the default mode network in both task-based and resting-state fMRI in patients with gliomas using the posterior cingulate cortex identified in task-based fMRI as an ROI for seed-based correlation analysis has strong overlap.

Monolingual and bilingual language networks in healthy subjects using functional MRI and graph theory

Bilingualism requires control of multiple language systems, and may lead to architectural differences in language networks obtained from clinical fMRI tasks. Emerging connectivity metrics such as k-core may capture these differences, highlighting crucial network components based on resiliency. We investigated the influence of bilingualism on clinical fMRI language tasks and characterized bilingual networks using connectivity metrics to provide a patient care benchmark. Sixteen right-handed subjects (mean age 42-years; nine males) without neurological history were included: eight native English-speaking monolinguals and eight native Spanish-speaking (L1) bilinguals with acquired English (L2). All subjects underwent fMRI with gold-standard clinical language tasks. Starting from active clusters on fMRI, we inferred the persistent functional network across subjects and ran centrality measures to characterize differences. Our results demonstrated a persistent network "core" consisting of Broca's area, the pre-supplementary motor area, and the premotor area. K-core analysis showed that Wernicke's area was engaged by the "core" with weaker connection in L2 than L1.

Prior Neurosurgery Decreases fMRI Estimates of Language Laterality in Patients with Gliomas within Anterior Language Sites

The impact of previous surgery on the assessment of language dominance with preoperative fMRI remains inconclusive in patients with recurrent brain tumors. Samples in this retrospective study included 17 patients with prior brain surgery and 21 patients without prior surgery (38 patients total; mean age 43.2, SD = 11.9; 18 females; seven left-handed). All the patients were left language dominant, as determined clinically. The two samples were matched on 10 known confounds, including, for example, tumor laterality and location (all tumors affected Brodmann areas 44/45/47). We calculated fMRI language dominance with laterality indices using a whole-brain and region of interest approach (ROI; Broca’s and Wernicke’s area). Patients with prior surgery had decreased fMRI language dominance (p = 0.03) with more activity in the right hemisphere (p = 0.03) than patients without surgery. Patients with prior brain surgery did not display less language activity in the left hemisphere than patients without surgery. These results were replicated using an ROI approach in the affected Broca’s area. Further, we observed no differences between our samples in the unaffected Wernicke’s area. In sum, prior brain surgery affecting Broca’s area could be a confounding factor that needs to be considered when evaluating fMRI language dominance.

Functional Brain Anatomy

Knowledge of functional neuroanatomy is essential to design the most appropriate clinical functional MR imaging (fMR imaging) paradigms and to properly interpret fMR imaging study results. The correlation between neuroanatomy and brain function is also useful in general radiologic practice, as it improves the radiologist's ability to read routine brain examinations. Functional MR imaging is used primarily to determine the areas involved in functioning of movements, speech, and vision. Preoperative fMR imaging findings also play a key role in the neurosurgeon's decision to perform a biopsy, a subtotal resection, or a maximal resection using awake craniotomy.

Patient Preparation and Paradigm Design in fMRI

Functional magnetic resonance imaging (fMRI) is useful for localizing eloquent cortex in the brain prior to neurosurgery. Language and motor paradigms offer a wide range of tasks to test brain regions within the language and motor networks. With the help of fMRI, hemispheric language dominance can be determined. It also is possible to localize specific motor and sensory areas within the motor and sensory gyri. These findings are critical for presurgical planning. The most important factor in presurgical fMRI is patient performance. Patient interview and instruction time are crucial to ensure that patients understand and comply with the fMRI paradigm.

Methods of Analysis: Functional MRI for Presurgical Planning

There are many technical and nontechnical steps involved in a successful clinical functional MRI (fMRI) scan. The output from scanning and analysis can only be as good as the input, so task instruction and rehearsal are the most important steps during an clinical fMRI procedure. Properly pre-processed data significantly affects statistical analysis, which has a great impact on image interpretation. Even though there is general agreement on how to process clinical fMRI data, such as algorithms for head motion detection and correction, the theory and practicalities associated with data processing remain complex and constantly evolving.

The Problem of Neurovascular Uncoupling

Neurovascular uncoupling (NVU) is one of the most important confounds of blood oxygen level dependent (BOLD) functional magnetic resonance imaging (fMR imaging) in the setting of focal brain lesions such as brain tumors. This article reviews the assessment of NVU related to focal brain lesions with emphasis on the use of cerebrovascular reactivity mapping measurement methods and resting state BOLD fMR imaging metrics in the detection of NVU, as well as the use of amplitude of low-frequency fluctuation metrics to mitigate the effects of NVU on clinical fMR imaging activation.

Introduction to Functional MR Imaging

During the past decade, functional MR imaging has rapidly moved from the research environment into clinical practice. Preoperative functional MR imaging is now standard clinical practice not only in major academic institutions, but also in community neurosurgical and neuroradiologic practices. The clinical use of functional MR imaging will only increase in the years to come. Application of functional MR imaging (including resting-state functional MR imaging) to the context of neuropsychiatric diseases is likely to continue to advance.

Impact of Navigated Task-specific fMRI on Direct Cortical Stimulation

BACKGROUND AND STUDY AIMS

 Cortical mapping (CM) with direct cortical stimulation (DCS) in awake craniotomy is used to preserve cognitive functions such as language. Nevertheless, patient collaboration during this procedure is influenced by previous neurological symptoms and growing discomfort with DCS duration. Our study aimed to evaluate the impact of navigated task-specific functional magnetic resonance imaging (nfMRI) on the practical aspects of DCS.

MATERIAL AND METHODS

 We recruited glioma patients scheduled for awake craniotomy for prior fMRI-based CM, acquired during motor and language tasks (i.e., verb generation, semantic and syntactic decision tasks). Language data was combined to generate a probabilistic map indicating brain regions activated with more than one paradigm. Presurgical neurophysiological language tests (i.e., verb generation, picture naming, and semantic tasks) were also performed. We considered for subsequent study only the patients with a minimum rate of correct responses of 50% in all tests. These patients were then randomized to perform intraoperative language CM either using the multimodal approach (mCM), using nfMRI and DCS combined, or electrical CM (eCM), with DCS alone. DCS was done while the patient performed picture naming and nonverbal semantic decision tasks. Methodological features such as DCS duration, number of stimuli, total delivered stimulus duration per task, and frequency of seizures were analyzed and compared between groups. The correspondence between positive responses obtained with DCS and nfMRI was also evaluated.

RESULTS

 Twenty-one surgeries were included, thirteen of which using mCM (i.e., test group). Patients with lower presurgical neuropsychological performance (correct response rate between 50 and 80% in language tests) showed a decreased DCS duration in comparison with the control group. None of the compared methodological features showed differences between groups. Correspondence between DCS and nfMRI was 100/84% in the identification of the precentral gyrus for motor function/opercular frontal inferior gyrus for language function, respectively.

CONCLUSION

 Navigated fMRI data did not influence DCS in practice. Presurgical language disturbances limited the applicability of DCS mapping in awake surgery.

Decreased Hand Motor Resting-State Functional Connectivity in Patients with Glioma: Analysis of Factors including Neurovascular Uncoupling

Background Resting-state functional MRI holds substantial potential for clinical application, but limitations exist in current understanding of how tumors exert local effects on resting-state functional MRI readings. Purpose To investigate the association between tumors, tumor characteristics, and changes in resting-state connectivity, to explore neurovascular uncoupling as a mechanism underlying these changes, and to evaluate seeding methodologies as a clinical tool. Materials and Methods Institutional review board approval was obtained for this HIPAA-compliant observational retrospective study of patients with glioma who underwent MRI and resting-state functional MRI between January 2016 and July 2017. Interhemispheric symmetry of connectivity was assessed in the hand motor region, incorporating tumor position, perfusion, grade, and connectivity generated from seed-based correlation. Statistical analysis was performed by using one-tailed t tests, Wilcoxon rank sum tests, one-way analysis of variance, Pearson correlation, and Spearman rank correlation, with significance at P < .05. Results Data in a total of 45 patients with glioma (mean age, 51.3 years ± 14.3 [standard deviation]) were compared with those in 10 healthy control subjects (mean age, 50.3 years ± 17.2). Patients showed loss of symmetry in measures of hand motor resting-state connectivity compared with control subjects (P < .05). Tumor distance from the ipsilateral hand motor (IHM) region correlated with the degree (R = 0.38, P = .01) and strength (R = 0.33, P = .03) of resting-state connectivity. In patients with World Health Organization grade IV glioblastomas 40 mm or less from the IHM region, loss of symmetry in strength of resting-state connectivity was correlated with tumor perfusion (R = 0.74, P < .01). In patients with gliomas 40 mm or less from the IHM region, seeding the nontumor hemisphere yielded less asymmetric hand motor resting-state connectivity than seeding the tumor hemisphere (connectivity seeded:contralateral = 1.34 nontumor vs 1.38 tumor hemisphere seeded; P = .03, false discovery rate threshold = 0.01). Conclusion Hand motor resting-state connectivity was less symmetrical in a tumor distance-dependent manner in patients with glioma. Differences in resting-state connectivity may be false-negative results driven by a neurovascular uncoupling mechanism. Seeding from the nontumor hemisphere may attenuate asymmetry in patients with tumors near ipsilateral hand motor cortices. © RSNA, 2020 Online supplemental material is available for this article.

Paradoxical Activation in the Cerebellum During Language fMRI in Patients with Brain Tumors: Possible Explanations Based on Neurovascular Uncoupling and Functional Reorganization

The cerebellum is known for its crossed activation pattern with the contralateral cerebral hemisphere during language functional magnetic resonance imaging (fMRI) tasks in healthy patients. Crossed cerebro-cerebellar activation has been previously shown to occur in patients with brain tumors not affecting the activation areas. However, the presence of a tumor in left Broca's area in the inferior frontal gyrus is known to disrupt cerebral activation during language tasks. This study investigated if crossed cerebro-cerebellar activation patterns for language tasks would still occur in such patients. A total of 43 right-handed patients with a glioma affecting left Broca's area were examined for their cerebral and cerebellar activation during an fMRI language task. Only 13 of the 43 patients exhibited crossed cerebro-cerebellar activation patterns. Statistically significant differences of atypical cerebro-cerebellar activation patterns were found between cerebral right-dominant (RD) and cerebral co-dominant (CD) (p < 0.001) as well as cerebral RD and cerebral left-dominant (LD) patients (p < 0.01), while no differences were found when patients were divided based on cerebellar dominance (p > 0.75) or tumor grade (p > 0.5). No relation was found between the cerebellar and cerebral laterality index (LI) values (ρ = - 0.20; p = 0.21). Atypical activation patterns are suspected to have been caused by the tumor, perhaps a result of contralateral reorganization in some cases and false negative activation in left Broca's area from neurovascular uncoupling (NVU) in others. Cerebellar activation may also potentially indicate cerebral false negative behavior and future cerebral contralateral reorganization.

Image-guided surgery using near-infrared Turn-ON fluorescent nanoprobes for precise detection of tumor margins

Complete tumor removal during surgery has a great impact on patient survival. To that end, the surgeon should detect the tumor, remove it and validate that there are no residual cancer cells left behind. Residual cells at the incision margin of the tissue removed during surgery are associated with tumor recurrence and poor prognosis for the patient. In order to remove the tumor tissue completely with minimal collateral damage to healthy tissue, there is a need for diagnostic tools that will differentiate between the tumor and its normal surroundings. Methods: We designed, synthesized and characterized three novel polymeric Turn-ON probes that will be activated at the tumor site by cysteine cathepsins that are highly expressed in multiple tumor types. Utilizing orthotopic breast cancer and melanoma models, which spontaneously metastasize to the brain, we studied the kinetics of our polymeric Turn-ON nano-probes. Results: To date, numerous low molecular weight cathepsin-sensitive substrates have been reported, however, most of them suffer from rapid clearance and reduced signal shortly after administration. Here, we show an improved tumor-to-background ratio upon activation of our Turn-ON probes by cathepsins. The signal obtained from the tumor was stable and delineated the tumor boundaries during the whole surgical procedure, enabling accurate resection. Conclusions: Our findings show that the control groups of tumor-bearing mice, which underwent either standard surgery under white light only or under the fluorescence guidance of the commercially-available imaging agents ProSense® 680 or 5-aminolevulinic acid (5-ALA), survived for less time and suffered from tumor recurrence earlier than the group that underwent image-guided surgery (IGS) using our Turn-ON probes. Our "smart" polymeric probes can potentially assist surgeons' decision in real-time during surgery regarding the tumor margins needed to be removed, leading to improved patient outcome.

[Dynamics of functional MRI and speech function in patients after resection of frontal and temporal lobe tumors]

RATIONALE

There are no studies on application of functional MRI (fMRI) for long-term monitoring of the condition of patients after resection of frontal and temporal lobe tumors.

PURPOSE

The study purpose was to correlate, using fMRI, reorganization of the speech system and dynamics of speech disorders in patients with left hemisphere gliomas before surgery and in the early and late postoperative periods.

MATERIAL AND METHODS

A total of 20 patients with left hemisphere gliomas were dynamically monitored using fMRI and comprehensive neuropsychological testing. The tumor was located in the frontal lobe in 12 patients and in the temporal lobe in 8 patients. Fifteen patients underwent primary surgery; 5 patients had repeated surgery. Sixteen patients had WHO Grade II and Grade III gliomas; the others had WHO Grade IV gliomas. Nineteen patients were examined preoperatively; 20 patients were examined at different times after surgery. Speech functions were assessed by a Luria's test; the dominant hand was determined using the Annette questionnaire; a family history of left-handedness was investigated. Functional MRI was performed on an HDtx 3.0 T scanner using BrainWavePA 2.0, Z software for fMRI data processing program for all calculations >7, p<0.001.

RESULTS

In patients with extensive tumors and recurrent tumors, activation of right-sided homologues of the speech areas cold be detected even before surgery; but in most patients, the activation was detected 3 months or more after surgery. Therefore, reorganization of the speech system took time. Activation of right-sided homologues of the speech areas remained in all patients for up to a year. Simultaneous activation of right-sided homologues of both speech areas, the Broca's and Wernicke's areas, was detected more often in patients with frontal lobe tumors than in those with temporal lobe tumors. No additional activation foci in the left hemisphere were found at the thresholds used to process fMRI data. Recovery of the speech function, to a certain degree, occurred in all patients, but no clear correlation with fMRI data was found.

CONCLUSION

Complex fMRI and neuropsychological studies in 20 patients after resection of frontal and temporal lobe tumors revealed individual features of speech system reorganization within one year follow-up. Probably, activation of right-sided homologues of the speech areas in the presence of left hemisphere tumors depends not only on the severity of speech disorder but also reflects individual involvement of the right hemisphere in enabling speech function. This is confirmed by right-sided activation, according to the fMRI data, in right-sided patients without aphasia and, conversely, the lack of activation of right-sided homologues of the speech areas in several patients with severe postoperative speech disorders during the entire follow-up period.

Reducing task-based fMRI scanning time using simultaneous multislice echo planar imaging

PURPOSE

To maintain alertness and to remain motionless during scanning represent a substantial challenge for patients/subjects involved in both clinical and research functional magnetic resonance imaging (fMRI) examinations. Therefore, availability and application of new data acquisition protocols allowing the shortening of scan time without compromising the data quality and statistical power are of major importance.

METHODS

Higher order category-selective visual cortical areas were identified individually, and rapid event-related fMRI design was used to compare three different sampling rates (TR = 2000, 1000, and 410 ms, using state-of-the-art simultaneous multislice imaging) and four different scanning lengths to match the statistical power of the traditional scanning methods to high sampling-rate design.

RESULTS

The results revealed that ~ 4 min of the scan time with 1 Hz (TR = 1000 ms) sampling rate and ~ 2 min scanning at ~ 2.5 Hz (TR = 410 ms) sampling rate provide similar localization sensitivity and selectivity to that obtained with 11-min session at conventional, 0.5 Hz (TR = 2000 ms) sampling rate.

CONCLUSION

Our findings suggest that task-based fMRI examination of clinical population prone to distress such as presurgical mapping experiments might substantially benefit from the reduced (20-40%) scanning time that can be achieved by the application of simultaneous multislice sequences.

Clinical Concepts Emerging from fMRI Functional Connectomics

Recent advances in connectomics have led to a synthesis of perspectives regarding the brain's functional organization that reconciles classical concepts of localized specialization with an appreciation for properties that emerge from interactions across distributed functional networks. This provides a more comprehensive framework for understanding neural mechanisms of normal cognition and disease. Although fMRI has not become a routine clinical tool, research has already had important influences on clinical concepts guiding diagnosis and patient management. Here we review illustrative examples. Studies demonstrating the network plasticity possible in adults and the global consequences of even focal brain injuries or disease both have had substantial impact on modern concepts of disease evolution and expression. Applications of functional connectomics in studies of clinical populations are challenging traditional disease classifications and helping to clarify biological relationships between clinical syndromes (and thus also ways of extending indications for, or "re-purposing," current treatments). Large datasets from prospective, longitudinal studies promise to enable the discovery and validation of functional connectomic biomarkers with the potential to identify people at high risk of disease before clinical onset, at a time when treatments may be most effective. Studies of pain and consciousness have catalyzed reconsiderations of approaches to clinical management, but also have stimulated debate about the clinical meaningfulness of differences in internal perceptual or cognitive states inferred from functional connectomics or other physiological correlates. By way of a closing summary, we offer a personal view of immediate challenges and potential opportunities for clinically relevant applications of fMRI-based functional connectomics.

Cortical Plasticity in the Setting of Brain Tumors

Cortical reorganization of function due to the growth of an adjacent brain tumor has clearly been demonstrated in a number of surgically proven cases. Such cases demonstrate the unmistakable implications for the neurosurgical treatment of brain tumors, as the cortical function may not reside where one may initially suspect based solely on the anatomical magnetic resonance imaging (MRI). Consequently, preoperative localization of eloquent areas adjacent to a brain tumor is necessary, as this may demonstrate unexpected organization, which may affect the neurosurgical approach to the lesion. However, in interpreting functional MRI studies, the interpreting physician must be cognizant of artifacts, which may limit the accuracy of functional MRI in the setting of brain tumors.

Are nanotheranostics and nanodiagnostics-guided drug delivery stepping stones towards precision medicine?

The progress in medical research has led to the understanding that cancer is a large group of heterogeneous diseases, with high variability between and within individuals. This variability sprouted the ambitious goal to improve therapeutic outcomes, while minimizing drug adverse effects through stratification of patients by the differences in their disease markers, in a personalized manner, as opposed to the strategy of "one therapy fits all". Nanotheranostics, composed of nanoparticles (NPs) carrying therapeutic and/or diagnostics probes, have the potential to revolutionize personalized medicine. There are different modalities to combine these two distinct fields into one system for a synergistic outcome. The addition of a nanocarrier to a theranostic system holds great promise. Nanocarriers possess high surface area, enabling sophisticated functionalization with imaging agents, thus gaining enhanced diagnostic ability in real-time. Yet, most of the FDA-approved theranostic approaches are based on small molecules. The theranostic approaches that are reviewed herein are paving the road towards personalized medicine through all stages of patient care: starting from screening and diagnostics, proceeding to treatment and ending with treatment follow-up. Our current review provides a broad background and highlights new insights for the rational design of theranostic nanosystems for desired therapeutic niches, while summoning the hurdles on their way to become first-line diagnostics and therapeutics for cancer patients.

Infiltration of the basal ganglia by brain tumors is associated with the development of co-dominant language function on fMRI

Studies have shown that some patients with left-hemispheric brain tumors have an increased propensity for developing right-sided language support. However, the precise trigger for establishing co-dominant language function in brain tumor patients remains unknown. We analyzed the MR scans of patients with left-hemispheric tumors and either co-dominant (n=35) or left-hemisphere dominant (n=35) language function on fMRI to investigate anatomical factors influencing hemispheric language dominance. Of eleven neuroanatomical areas evaluated for tumor involvement, the basal ganglia was significantly correlated with co-dominant language function (p<0.001). Moreover, among patients whose tumors invaded the basal ganglia, those with language co-dominance performed significantly better on the Boston Naming Test, a clinical measure of aphasia, compared to their left-lateralized counterparts (56.5 versus 36.5, p=0.025). While further studies are needed to elucidate the role of the basal ganglia in establishing co-dominance, our results suggest that reactive co-dominance may afford a behavioral advantage to patients with left-hemispheric tumors.

The Contribution of Common Surgically Implanted Hardware to Functional MR Imaging Artifacts

BACKGROUND AND PURPOSE

Blood oxygenation level-dependent MR imaging is increasingly used clinically to noninvasively assess cerebrovascular reactivity and/or language and motor function. However, many patients have metallic implants, which will induce susceptibility artifacts, rendering the functional information uninformative. Here, we calculate and interpret blood oxygenation level-dependent MR imaging artifact impact arising from surgically implanted hardware.

MATERIALS AND METHODS

A retrospective analysis of all blood oxygenation level-dependent MRIs (n = 343; B0 = 3T; TE = 35 ms; gradient echo EPI) acquired clinically (year range = 2006-2014) at our hospital was performed. Blood oxygenation level-dependent MRIs were most commonly prescribed for patients with cerebrovascular disease (n = 80) or patients undergoing language or motor localization (n = 263). Artifact volume (cubic centimeters) and its impact on clinical interpretation were determined by a board-certified neuroradiologist.

RESULTS

Mean artifact volume associated with intracranial hardware was 4.3 ± 3.2 cm(3) (range = 1.1-9.4 cm(3)). The mean artifact volume from extracranial hardware in patients with cerebrovascular disease was 28.4 ± 14.0 cm(3) (range = 6.1-61.7 cm(3)), and in patients with noncerebrovascular disease undergoing visual or motor functional mapping, it was 39.9 (3)± 27.0 cm(3) (range = 6.9-77.1 cm(3)). The mean artifact volume for ventriculoperitoneal shunts was 95.7 ± 39.3 cm(3) (range = 64.0-139.6 cm(3)). Artifacts had no-to-mild effects on clinical interpretability in all patients with intracranial implants. Extracranial hardware artifacts had no-to-moderate impact on clinical interpretability, with the exception of 1 patient with 12 KLS-Martin maxDrive screws with severe artifacts precluding clinical interpretation. All examined ventriculoperitoneal shunts resulted in moderate-to-severe artifacts, limiting clinical interpretation.

CONCLUSIONS

Blood oxygenation level-dependent MR imaging yields interpretable functional maps in most patients beyond a small (30-40 cm(3)) artifact surrounding the hardware. Exceptions were ventriculoperitoneal shunts, particularly those with programmable valves and siphon gauges, and large numbers of KLS-Martin maxDrive screws.

Cortical Activation Through Passive-Motion Functional MRI

BACKGROUND AND PURPOSE

Functional brain mapping is an important technique for neurosurgical planning, particularly for patients with tumors or epilepsy; however, mapping has traditionally involved invasive techniques. Existing noninvasive techniques require patient compliance and may not be suitable for young children. We performed a retrospective review of our experience with passive-motion functional MR imaging in anesthetized patients to determine the diagnostic yield of this technique.

MATERIALS AND METHODS

A retrospective review of patients undergoing passive-motion fMRI under general anesthesia at a single institution over a 2.5-year period was performed. Clinical records were evaluated to determine the indication for fMRI, the ability to detect cortical activation, and, if present, the location of cortical activation.

RESULTS

We identified 62 studies in 56 patients in this time period. The most common indication for fMRI was epilepsy/seizures. Passive-motion fMRI identified upper-extremity cortical activation in 105 of 119 (88%) limbs evaluated, of which 90 (86%) activations were in an orthotopic location. Lower-extremity cortical activation was identified in 86 of 118 (73%) limbs evaluated, of which 73 (85%) activations were in an orthotopic location.

CONCLUSIONS

Passive-motion fMRI was successful in identifying cortical activation in most of the patients. This tool can be implemented easily and can aid in surgical planning for children with tumors or candidates for epilepsy surgery, particularly those who may be too young to comply with existing noninvasive functional measures.

Corpus Callosum Diffusion and Language Lateralization in Patients with Brain Tumors: A DTI and fMRI Study

BACKGROUND AND PURPOSE

Examining how left-hemisphere brain tumors might impact both the microstructure of the corpus callosum (CC) as measured by fractional anisotropy (FA) values in diffusion tensor imaging (DTI) as well as cortical language lateralization measured with functional MRI (fMRI).

METHODS

fMRI tasks (phonemic fluency and verb generation) were performed in order to detect activation in Broca's and Wernicke's area. Twenty patients with left-hemisphere brain tumors were investigated. fMRI results were divided into left dominant (LD), right dominant (RD), or codominant (CD) for language function. DTI was performed to generate FA maps in the anterior and posterior CC. FA values were correlated with the degree of language dominance.

RESULTS

Patients who were LD or RD for language in Broca's area had lower FA in the anterior CC than those who were CD for language (median for CD = .72, LD = .66, RD = .65, P < .09). Lateralized versus CD group level analysis also showed that CD patients had higher FA in the anterior CC than patients who displayed strong lateralization in either hemisphere (median for CD = .72, lateralized = .65, P < .05).

CONCLUSION

Our preliminary observations indicate that the greater FA in CD patients may reflect a more directional microstructure for the CC in this region, suggesting a greater need for interhemispheric transfer of information. Because brain tumors can cause compensatory codominance, our findings may suggest a mechanism by which interhemispheric transfer is facilitated during plasticity in the presence of a tumor.

Retrospective Analysis of Interobserver Spatial Variability in the Localization of Broca's and Wernicke's Areas Using Three Different fMRI Language Paradigms

PURPOSE

To determine interobserver spatial variability in language area localization using three commonly employed language tasks.

MATERIALS AND METHODS

With institutional review board approval, 125 fMRI time series from 50 different clinical language cases were retrospectively reviewed by three blinded readers who selected 3-dimensional points representing the perceived center of Wernicke's and Broca's areas using three language tasks (semantic decision, SD; sentence comprehension, SC; and silent word generation, WG). Point dispersion values were then calculated using the perimeter of the 3-dimensional triangle defined by the three readers' selections.

RESULTS

After resolving interobserver laterality disagreements, there was no difference in spatial variability between the three tasks (P = .069). The SD task had the fewest interobserver laterality disagreements (P = .028) and the SC task had fewer failed localizations for Broca's area (P = .050) and Wernicke's area (P = .013).

CONCLUSION

While there were no differences between interobserver spatial variability in language area localization between the three tasks, language task choice impacts the accuracy of fMRI language area identification because tasks vary in their rates of interobserver laterality disagreements and failed localizations. A combination of tasks including one with low laterality disagreements (eg, SD) and one with few failed localizations (eg, SC) may offer the best combination.

Special considerations/technical limitations of blood-oxygen-level-dependent functional magnetic resonance imaging

In this review, limitations affecting the results of presurgical mapping with blood-oxygen-level-dependent (BOLD) functional magnetic resonance imaging (fMRI) are discussed. There is a great need to standardize fMRI acquisition and analysis methods and establish guidelines to address quality control issues. Several national and international organizations are formulating guidelines and standards for both clinical and research applications of BOLD fMRI. Consensus regarding management of these issues will likely both improve the clinical standard of care and enhance future research applications of fMRI.

Verbal learning and memory in agenesis of the corpus callosum

The role of interhemispheric interactions in the encoding, retention, and retrieval of verbal memory can be clarified by assessing individuals with complete or partial agenesis of the corpus callosum (AgCC), but who have normal intelligence. This study assessed verbal learning and memory in AgCC using the California Verbal Learning Test-Second Edition (CVLT-II). Twenty-six individuals with AgCC were compared to 24 matched controls on CVLT-II measures, as well as Donders׳ four CVLT-II factors (i.e., Attention Span, Learning Efficiency, Delayed Memory, and Inaccurate Memory). Individuals with AgCC performed significantly below healthy controls on the Delayed Memory factor, confirmed by significant deficits in short and long delayed free recall and cued recall. They also performed less well in original learning. Deficient performance by individuals with AgCC during learning trials, as well as deficits in all forms of delayed memory, suggest that the corpus callosum facilitates interhemispheric elaboration and encoding of verbal information.

Clinical applications of functional MR imaging

Functional magnetic resonance (fMR) imaging for neurosurgical planning has become the standard of care in centers where it is available. Although paradigms to measure eloquent cortices are not yet standardized, simple tasks elicit reliable maps for planning neurosurgical procedures. A patient-specific paradigm design will refine the usability of fMR imaging for prognostication and recovery of function. Certain pathologic conditions and technical issues limit the interpretation of fMR imaging maps in clinical use and should be considered carefully. However, fMR imaging for neurosurgical planning continues to provide insights into how the brain works and how it responds to pathologic insults.

Effects of covert and overt paradigms in clinical language fMRI

RATIONALE AND OBJECTIVES

The aim of this study was to assess the intrasubject and intersubject reproducibility of functional magnetic resonance imaging (fMRI) language paradigms on language localization and lateralization.

MATERIALS AND METHODS

Fourteen healthy volunteers were enrolled prospectively and underwent language fMRI using visually triggered covert and overt sentence generation (SG) and word generation (WG) paradigms. Semiautomated analysis of all functional data was performed using Brain Voyager on an individual basis. Regions of interest for Broca's area, Wernicke's area, and their contralateral homologues were drawn. The Euclidean coordinates of the center of gravidity (x, y, and z) of the respective blood oxygenation level-dependent (BOLD) activation cluster, and the correlation of the measured hemodynamic response to the applied reference function (r), relative BOLD signal change as BOLD signal characteristics were measured in each region of interest. Regional lateralization indexes were calculated for Broca's area, Wernicke's area, and their contralateral homologues separately. Wilcoxon's signed-rank test was applied for statistical comparisons (P values < .05 were considered significant). Ten of the 14 volunteers had three repeated measurements to test intrasession reproducibility and intersession reproducibility.

RESULTS

Overall activation rates for the four paradigms were 89% for covert SG, 82% for overt SG, 89% for covert WG, and 100% for overt WG. When comparing covert and overt paradigms, language localization was significantly different in 17% (Euclidean coordinates) and 19% (BOLD signal characteristics), respectively. Language lateralization was significantly different in 75%. Intrasubject and intersubject reproducibility was excellent, with 3.3% significant differences among all five parameters for language localization and 0% significant differences for language lateralization using covert paradigms.

CONCLUSIONS

Covert language paradigms (SG and WG) provided highly robust and reproducible localization and lateralization of essential language centers for scans performed on the same and different days. Their overt counterparts achieved confirmatory localization but lower lateralization capabilities. Reference data for presurgical application are provided.

Single brain metastases from melanoma: remarks on a series of 84 patients

The authors report on 84 patients with single melanoma brain metastasis surgically treated from 1997 to 2007. There were 46 males and 38 females; mean age was 41 years (range 24-58 years). All patients were surgically treated, and 52 of them received postoperative adjuvant therapy consisting of whole-brain radiation therapy (36), radiosurgery (9), or a combination of these two techniques (7). Brain recurrences were observed in 44 cases, of which 9 were local. Of the latter, seven were re-operated while the remaining two were treated by radiosurgery. At 1-year follow-up, the survival rate was 52% (32 patients) whereas only 12 patients (14%) were still alive after 2 years. None of the patients in which removal was subtotal survived for more than 6 months after surgical treatment. Three years after the onset of the brain metastasis, five patients (6%) were still alive. Survival was significantly influenced by treatment with regard to overall survival reported in other series. A review of literature, together with our own series, suggests that radical surgical treatment of the lesion possibly employing the internal no-touch technique has significantly increased survival in our patients (p < 0.05) and that the association of postoperative radiotherapy and re-operation in the event of recurrent metastatic lesions is advisable even though statistical significance was not reached (p > 0.05).

Advanced imaging in brain tumor surgery

The advanced imaging techniques outlined in this article are only slowly establishing their place in surgical practice. Even a low risk of false information is unacceptable in neurosurgery, thus decision-making is necessarily conservative. As more validation studies and greater experience accrue, surgeons are becoming more comfortable weighing the quality of information from functional imaging studies. Advanced imaging information is highly complementary to established surgical "good practice" such as anatomic planning, awake craniotomy, and electrocortical stimulation; its greatest impact is perhaps on how neurosurgery is planned and discussed before the patient is ever brought to the operating room. Access to functional magnetic resonance (MR) imaging, diffusion tractography, and intraoperative MR imaging can influence neurosurgical decisions before, during, and after surgery. However, the widespread adoption of these techniques in neurosurgical practice remains limited by the lack of standardized methods, the need for validation across institutions, and the unclear cost-effectiveness particularly for intraoperative MR imaging. Before advanced imaging results can be used therapeutically, it is incumbent on the neurosurgeon and neuroradiologist to develop a working understanding of each technique's strengths and weaknesses, positive and negative predictive values, and modes of failure. This content presents several imaging methods that are increasingly used in neurosurgical planning. As these techniques are progressively applied to surgery, radiologists, medical physicists, neuroscientists, and engineers will be necessary partners with the treating neurosurgeon to bridge the gap between the experimental and the therapeutic.

fMRI assessment of language lateralization: an objective approach

Language lateralization based on functional magnetic resonance imaging (fMRI) is often used in clinical neurological settings. Currently, interpretation of the distribution, pattern and extent of language activation can be heavily dependent on the chosen statistical threshold. The aim of the present study was to 1) test the robustness of adaptive thresholding of fMRI data to yield a fixed number of active voxels, and to 2) develop a largely threshold-independent method of assessing when individual patients have statistically atypical language lateralization. Simulated data and real fMRI data in 34 healthy controls and 4 selected epilepsy patients performing a verbal fluency language fMRI task were used. Dependence of laterality on the thresholding method is demonstrated for simulated and real data. Simulated data were used to test the hypothesis that thresholding based upon a fixed number of active voxels would yield a laterality index that was more stable across a range of signal strengths (study power) compared to thresholding at a fixed p value. This stability allowed development of a method comparing an individual to a group of controls across a wide range of thresholds, providing a robust indication of atypical lateralization that is more objective than conventional methods. Thirty healthy controls were used as normative data for the threshold-independent method, and the remaining subjects were used as illustrative examples. The method could also be used more generally to assess relative regional distribution of activity in other neuroimaging paradigms (for example, one could apply it to the assessment of lateralization of activation in a memory task, or to the assessment of anterior-posterior distribution rather than laterality).