Predicting the Extent of Resection in Low-Grade Glioma by Using Intratumoral Tractography to Detect Eloquent Fascicles Within the Tumor

Preoperative and intraoperative neuromonitoring and mapping techniques impact oncological and functional outcomes in supratentorial function-eloquent brain tumours: a systematic review and meta-analysis

Background

Supratentorial function-eloquent brain tumour surgeries challenge the balance between maximal tumour resection and preservation of neurological function. This study aims to evaluate the efficacy of preoperative and intraoperative mapping techniques on resection outcomes and post-operative deficits.

Methods

This systematic review and meta-analysis examined literature up to March 2023, sourced from PubMed, Embase, and Medline. Criteria for inclusion were studies on patients undergoing surgery for supratentorial brain tumours, comparing preoperative mapping only (POM), intraoperative neuromonitoring and mapping (IONM), and combined techniques (POM&IONM), excluding non-randomized controlled trials. Data extraction focused on rates of gross total resection (GTR) and focal neurological deficits (FNDs). The main outcomes, assessed through a random-effects model and Cochran's Q-test for subgroup analysis. The study protocol is published on PROSPERO CRD42024512306.

Findings

19 studies involving 992 patients were included. Systematic review with meta-analysis revealed a non-significantly higher average GTR rates for POM&IONM (49.13%) and POM (50.79%) compared to IONM alone (41.23%). Highest rates of GTR were achieved with tractography-guided resection in POM group (66.59% versus fMRI-20.00%, p = 0.0004), multimodal stimulation in IONM group (54.16% versus low frequency stimulation (LFS)-13.29%, p < 0.0001) and in POM&IONM group (65.88% versus LFS-37.77%, p = 0.0036). Within the same tumour histology-metastasis, high grade and low grade glioma-there are no differences in the GTR rates achieved in the different groups (p > 0.05). In language-eloquent tumours and in awake craniotomy techniques regardless of tumour functional eloquence, POM&IONM group had higher GTR when compared to IONM groups (language eloquent tumours-POM&IONM 43.31% versus IONM-15.09%, p = 0.022; awake craniotomy technique-POM&IONM-41.22% versus IONM-12.08%, p = 0.0006). Permanent FNDs were higher in the IONM group (IONM-73.0%; POM-29.6%; POM&IONM-33.7% of immediate postoperative deficits, p = 0.0010).

Interpretation

A combined POM&IONM approach is responsible for higher rates of GTR in patients with language eloquent tumours and in both awake and asleep craniotomy techniques regardless of the tumour functional eloquence. The tumour histology is not relevant for differences in GTR rates among different mapping and monitoring strategies. Permanent postoperative FNDs are more likely with standalone utilization of IONM.

Funding

Not applicable.

A Longitudinal Multimodal Imaging Study in Patients with Temporo-Insular Diffuse Low-Grade Tumors: How the Inferior Fronto-Occipital Fasciculus Provides Information on Cognitive Outcomes

BACKGROUND

Tractography allows the in vivo study of subcortical white matter, and it is a potential tool for providing predictive indices on post-operative outcomes. We aim at establishing whether there is a relation between cognitive outcome and the status of the inferior fronto-occipital fasciculus's (IFOF's) microstructure.

METHODS

The longitudinal neuropsychological data of thirty young (median age: 35 years) patients operated on for DLGG in the left temporo-insular cortex along with pre-surgery tractography data were processed.

RESULTS

A degraded integrity of the left (vs. right) IFOF (lower fractional anisotropy and length, p < 0.001; higher mean and axial diffusivity, p < 0.01) was found, with lower microstructural variables in the infiltration (vs. dislocation) group. Significant decreases immediately post-surgery vs. pre-surgery mainly occurred in lexico-semantics (p < 0.001), with significant improvements at follow-up in all the tests (p < 0.01 to p < 0.001), despite values in the range of 44% to 47.82% of patients with below cut-off scores regarding naming verbs and making visual lexical decisions. The status of left and right IFOFs is predictive of a decrease in immediate post-surgery performance for several tests (p < 0.05); similarly, it is predictive of better recovery in the follow-up performance for naming nouns, naming verbs, making phonological fluency lexical decisions, and the token test (p < -0.05). For the ROC analysis, a significant result was obtained for the verb-naming test, with a cut-off of 79%.

CONCLUSIONS

This study supports the role of the predictive value of pre-operative tractography for assessing the immediate post-operative result and at follow-up the risk of developing a cognitive deficit.

"False friends" in Language Subcortical Mapping: A Systematic Literature Review

BACKGROUND

Subcortical brain mapping in awake glioma surgery might optimize the extent of resection while minimizing neurological morbidity, but it requires a correct interpretation of responses evoked during surgery. To define, with a systematic review: 1) a comprehensive 'map' of the principal white matter bundles involved in awake surgery on language-related networks, describing the most employed tests and the expected responses; 2) In linguistics, a false friend is a word in a different language that looks or sounds like a word in given language but differs significantly in meaning. Similarly, our aim is to give the surgeons a comprehensive review of potentially misleading responses, namely "false friends", in subcortical language mapping.

METHODS

Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines were followed. Standardized data extraction was conducted.

RESULTS

Out of a total of 224 initial papers, 67 were included for analysis. Expected responses, common tests, and potential "false friends" were recorded for each of the following white matter bundles: frontal aslant tract, superior and inferior longitudinal fascicles, arcuate fascicle, inferior fronto-occipital fascicle, uncinate fascicle. Practical examples are discussed to underline the risk of intraoperative fallouts ("false friends") that might lead to an early interruption (false positive) or a risky surgical removal (false negative).

CONCLUSIONS

This paper represents a critical review of the present status of subcortical awake mapping and underlines practical "false-friend" in mapping critical crossroads in language-related networks.

Role of intraoperative ultrasound and MRI to aid grade of resection of pediatric low-grade gliomas: accumulated experience from 4 centers

PURPOSE

Pediatric low-grade gliomas (pLGG) are the most common brain tumors in children and achieving complete resection (CR) in pLGG is the most important prognostic factor. There are multiple intraoperative tools to optimize the extent of resection (EOR). This article investigates and discusses the role of intraoperative ultrasound (iUS) and intraoperative magnetic resonance imaging (iMRI) in the surgical treatment of pLGG.

METHODS

The tumor registries at Tuebingen, Rome and Pretoria were searched for pLGG with the use of iUS and data on EOR. The tumor registries at Liverpool and Tuebingen were searched for pLGG with the use of iMRI where preoperative CR was the surgical intent. Different iUS and iMRI machines were used in the 4 centers.

RESULTS

We included 111 operations which used iUS and 182 operations using iMRI. Both modalities facilitated intended CR in hemispheric supra- and infratentorial location in almost all cases. In more deep-seated tumor location like supratentorial midline tumors, iMRI has advantages over iUS to visualize residual tumor. Functional limitations limiting CR arising from eloquent involved or neighboring brain tissue apply to both modalities in the same way. In the long-term follow-up, both iUS and iMRI show that achieving a complete resection on intraoperative imaging significantly lowers recurrence of disease (chi-square test, p < 0.01).

CONCLUSION

iUS and iMRI have specific pros and cons, but both have been proven to improve achieving CR in pLGG. Due to advances in image quality, cost- and time-efficiency, and efforts to improve the user interface, iUS has emerged as the most accessible surgical adjunct to date to aid and guide tumor resection. Since the EOR has the most important effect on long-term outcome and disease control of pLGG in most locations, we strongly recommend taking all possible efforts to use iUS in any surgery, independent of intended resection extent and iMRI if locally available.

An update on tests used for intraoperative monitoring of cognition during awake craniotomy

PURPOSE

Mapping higher-order cognitive functions during awake brain surgery is important for cognitive preservation which is related to postoperative quality of life. A systematic review from 2018 about neuropsychological tests used during awake craniotomy made clear that until 2017 language was most often monitored and that the other cognitive domains were underexposed (Ruis, J Clin Exp Neuropsychol 40(10):1081-1104, 218). The field of awake craniotomy and cognitive monitoring is however developing rapidly. The aim of the current review is therefore, to investigate whether there is a change in the field towards incorporation of new tests and more complete mapping of (higher-order) cognitive functions.

METHODS

We replicated the systematic search of the study from 2018 in PubMed and Embase from February 2017 to November 2023, yielding 5130 potentially relevant articles. We used the artificial machine learning tool ASReview for screening and included 272 papers that gave a detailed description of the neuropsychological tests used during awake craniotomy.

RESULTS

Comparable to the previous study of 2018, the majority of studies (90.4%) reported tests for assessing language functions (Ruis, J Clin Exp Neuropsychol 40(10):1081-1104, 218). Nevertheless, an increasing number of studies now also describe tests for monitoring visuospatial functions, social cognition, and executive functions.

CONCLUSIONS

Language remains the most extensively tested cognitive domain. However, a broader range of tests are now implemented during awake craniotomy and there are (new developed) tests which received more attention. The rapid development in the field is reflected in the included studies in this review. Nevertheless, for some cognitive domains (e.g., executive functions and memory), there is still a need for developing tests that can be used during awake surgery.

Alterations in white matter fiber density associated with structural MRI and metabolic PET lesions following multimodal therapy in glioma patients

BACKGROUND

In glioma patients, multimodality therapy and recurrent tumor can lead to structural brain tissue damage characterized by pathologic findings in MR and PET imaging. However, little is known about the impact of different types of damage on the fiber architecture of the affected white matter.

PATIENTS AND METHODS

This study included 121 pretreated patients (median age, 52 years; ECOG performance score, 0 in 48%, 1-2 in 51%) with histomolecularly characterized glioma (WHO grade IV glioblastoma, n=81; WHO grade III anaplastic astrocytoma, n=28; WHO grade III anaplastic oligodendroglioma, n=12), who had a resection, radiotherapy, alkylating chemotherapy, or combinations thereof. After a median follow-up time of 14 months (range, 1-214 months), anatomic MR and O-(2-[18F]fluoroethyl)-L-tyrosine (FET) PET images were acquired on a 3T hybrid PET/MR scanner. Post-therapeutic findings comprised resection cavities, regions with contrast enhancement or increased FET uptake and T2/FLAIR hyperintensities. Local fiber density was determined from high angular-resolution diffusion-weighted imaging and advanced tractography methods. A cohort of 121 healthy subjects selected from the 1000BRAINS study matched for age, gender and education served as a control group.

RESULTS

Lesion types differed in both affected tissue volumes and relative fiber densities compared to control values (resection cavities: median volume 20.9 mL, fiber density 16% of controls; contrast-enhanced lesions: 7.9 mL, 43%; FET uptake areas: 30.3 mL, 49%; T2/FLAIR hyperintensities: 53.4 mL, 57%, p<0.001). In T2/FLAIR-hyperintense lesions caused by peritumoral edema due to recurrent glioma (n=27), relative fiber density was as low as in lesions associated with radiation-induced gliosis (n=13, 48% vs. 53%, p=0.17). In regions with pathologically increased FET uptake, local fiber density was inversely related (p=0.005) to the extent of uptake. Total fiber loss associated with contrast-enhanced lesions (p=0.006) and T2/FLAIR hyperintense lesions (p=0.013) had a significant impact on overall ECOG score.

CONCLUSIONS

These results suggest that apart from resection cavities, reduction in local fiber density is greatest in contrast-enhancing recurrent tumors, but total fiber loss induced by edema or gliosis has an equal detrimental effect on the patients' performance status due to the larger volume affected.

Predictors of tumor progression of low-grade glioma in adult patients within 5 years follow-up after surgery

Background

Glioma originates from glial cells in the brain and is the most common primary intracranial tumor. This study intends to use a retrospective analysis to explore the factors that can predict tumor progression in adult low-grade gliomas, namely WHO II grade patients, within 5 years after surgery.

Methods

Patients with WHO grade II glioma who were surgically treated in our hospital from February 2011 to May 2017 were included. According to the inclusion and exclusion criteria, 252 patients were included in the final analysis. According to the results of the 5-year follow-up (including survival and imaging review results), patients were divided into progression-free group and progression group. Univariate and multivariate analysis were conducted to investigate the related factors of tumor progression during the 5-year follow-up.

Results

The results of the 5-year follow-up showed that 111 (44.0%) cases had no progress (progression free group, PFG), 141 (56.0%) cases had progress (progression group, PG), of which 43 (30.5%) cases were operated again, 37 cases (26.2%) received non-surgical treatments. There were 26 (10.3%) all-cause deaths, and 21 (8.3%) tumor-related deaths. Univariate and multivariate analysis showed that age >45 years old (OR = 1.35, 95% CI, 1.07-3.19, P = 0.027), partial tumor resection (OR = 1.66, 95% CI, 1.15-3.64, P = 0.031), tumor diameter >3 cm (OR = 1.52, 95% CI, 1.14-4.06, P = 0.017) and no radiotherapy (OR = 1.37, 95% CI, 1.12-2.44, P = 0.039) were independent predictors of the progression of tumor during the 5-year follow-up period.

Conclusion

Age >45 years old, partial tumor resection, tumor diameter >3 cm, no radiotherapy are predictors for tumor progression for glioma patients after surgery.

Inferior fronto-occipital fascicle displacement in temporoinsular gliomas using diffusion tensor imaging

Background and Purpose

Brain tumors can result in displacement or destruction of important white matter tracts such as the inferior fronto‐occipital fascicle (IFOF). Diffusion tensor imaging (DTI) can assess the extent of this effect and potentially provide neurosurgeons with an accurate map to guide tumor resection; analyze IFOF displacement patterns in temporoinsular gliomas based on tumor grading and topography in the temporal lobe; and assess whether these patterns follow a predictable pattern, to assist in maximal tumor resection while preserving IFOF function.

Methods

Thirty‐four patients with temporal gliomas and available presurgical MRI were recruited. Twenty‐two had insula infiltration. DTI deterministic region of interest (ROI)‐based tractography was performed using commercial software. Tumor topographic imaging characteristics analyzed were as follows: location in the temporal lobe and extent of extratemporal involvement. Qualitative tractographic data obtained from directional DTI color maps included type of involvement (displaced/edematous‐infiltrated/destroyed) and displacement direction. Quantitative tractographic data of ipsi‐ and contralateral IFOF included whole tract volume, fractional anisotropy, and fractional anisotropy of a 2‐dimensional coronal ROI on the tract at the point of maximum tumor involvement.

Results

The most common tract involvement pattern was edematous/infiltrative displacement. Displacement patterns depended on main tumor location in the temporal lobe and presence of insular involvement. All tumors showed superior displacement pattern. In lateral tumors, displacement tendency was medial. In medial tumors, displacement tendency was lateral. When we add insular involvement, the tendency was more medial displacement. A qualitative and quantitative assessment supported these results.

Conclusions

IFOF displacement patterns are reproducible and suitable for temporoinsular gliomas presurgical planning.

Tractography methods and findings in brain tumors and traumatic brain injury

White matter fiber tracking using diffusion magnetic resonance imaging (dMRI) provides a noninvasive approach to map brain connections, but improving anatomical accuracy has been a significant challenge since the birth of tractography methods. Utilizing tractography in brain studies therefore requires understanding of its technical limitations to avoid shortcomings and pitfalls. This review explores tractography limitations and how different white matter pathways pose different challenges to fiber tracking methodologies. We summarize the pros and cons of commonly-used methods, aiming to inform how tractography and its related analysis may lead to questionable results. Extending these experiences, we review the clinical utilization of tractography in patients with brain tumors and traumatic brain injury, starting from tensor-based tractography to more advanced methods. We discuss current limitations and highlight novel approaches in the context of these two conditions to inform future tractography developments.

Risk Assessment by Pre-surgical Tractography in Left Hemisphere Low-Grade Gliomas

Background: Tracking the white matter principal tracts is routinely typically included during the pre-surgery planning examinations and has revealed to limit functional resection of low-grade gliomas (LGGs) in eloquent areas.

Objective: We examined the integrity of the Superior Longitudinal Fasciculus (SLF) and Inferior Fronto-Occipital Fasciculus (IFOF), both known to be part of the language-related network in patients with LGGs involving the temporo-insular cortex. In a comparative approach, we contrasted the main quantitative fiber tracking values in the tumoral (T) and healthy (H) hemispheres to test whether or not this ratio could discriminate amongst patients with different post-operative outcomes.

Methods: Twenty-six patients with LGGs were included. We obtained quantitative fiber tracking values in the tumoral and healthy hemispheres and calculated the ratio (H_IFOF–T_IFOF)/H_IFOF and the ratio (H_SLF–T_SLF)/H_SLF on the number of streamlines. We analyzed how these values varied between patients with and without post-operative neurological outcomes and between patients with different post-operative Engel classes.

Results: The ratio for both IFOF and SLF significantly differed between patient with and without post-operative neurological language deficits. No associations were found between white matter structural changes and post-operative seizure outcomes.

Conclusions: Calculating the ratio on the number of streamlines and fractional anisotropy between the tumoral and the healthy hemispheres resulted to be a useful approach, which can prove to be useful during the pre-operative planning examination, as it gives a glimpse on the potential clinical outcomes in patients with LGGs involving the left temporo-insular cortex.