World Health Organization Grade II Gliomas and Subventricular Zone: Anatomic, Genetic, and Clinical Considerations

Prognostic Factors and Resectability Predictors in Insular Gliomas: A Systematic Review

BACKGROUND

 Insular gliomas (INGs) remain a surgically intimidating glioma subgroup encased by eloquent cortical parcels and white matter language tracts, and traversed by multiple middle cerebral artery branches. The predictive power of prognostic factors affecting overall survival (OS), progression-free survival (PFS), and resectability of INGs remain disputed. This comprehensive systematic review analyses prognostic factors and resectability predictors of INGs substantiating pragmatic management options.

MATERIALS AND METHODS

 A systematic review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Protocols (PRISMA-P) and the Cochrane Handbook of Systematic Reviews of Interventions guidelines. The PubMed, MEDLINE, and Embase databases were searched in April 2022. All clinical studies with ≥10 patients harboring INGs with any intervention and reporting predictors of OS, PFS, and tumor resectability in INGs were included. Molecular ING prognosticators were also included. Studies combining insular and other gliomas analysis, case studies, experimental and animal studies, conference abstracts, letters to the editor, and articles in other languages were excluded.

RESULTS

 Of the 2,384 articles returned, 27 fulfilled the inclusion criteria totaling 1,985 patients. The review yielded 18 OS and 17 PFS prognosticators. These were classified as preoperative (radiologic; clinical), intraoperative, and postoperative (molecular; histopathologic; clinical) prognosticators. In addition, 21 resectability predictors were categorized as preoperative (radiologic; clinical), intraoperative (surgical approach and assistive technology), and postoperative (histopathologic; clinical). The quality assessment revealed 24/27 studies had low risk of bias. One study with moderate and two studies with high risk of bias were included.

CONCLUSION

 Negative prognosticators reported in ≥2 studies included putaminal or paralimbic involvement and higher tumor grade, while seizures at presentation, isocitrate dehydrogenase (IDH) mutation, increased extent of resection, and higher Karnofsky Performance Status preoperatively and at 3 months postoperation were positive prognosticators. Resectability predictors reported in ≥2 studies included the positive predictors of zone I/zone IV tumor location and intraoperative imaging use and the negative predictor of encased lenticulostriate arteries. Paralimbic INGs are not a single entity with homogeneous prognosis. Integration of identified prognosticators in a prospective trial to devise a grading system for INGs can improve clinical decision-making.

Novel Galectin-3 Roles in Neurogenesis, Inflammation and Neurological Diseases

Galectin-3 (Gal-3) is an evolutionarily conserved and multifunctional protein that drives inflammation in disease. Gal-3's role in the central nervous system has been less studied than in the immune system. However, recent studies show it exacerbates Alzheimer's disease and is upregulated in a large variety of brain injuries, while loss of Gal-3 function can diminish symptoms of neurodegenerative diseases such as Alzheimer's. Several novel molecular pathways for Gal-3 were recently uncovered. It is a natural ligand for TREM2 (triggering receptor expressed on myeloid cells), TLR4 (Toll-like receptor 4), and IR (insulin receptor). Gal-3 regulates a number of pathways including stimulation of bone morphogenetic protein (BMP) signaling and modulating Wnt signalling in a context-dependent manner. Gal-3 typically acts in pathology but is now known to affect subventricular zone (SVZ) neurogenesis and gliogenesis in the healthy brain. Despite its myriad interactors, Gal-3 has surprisingly specific and important functions in regulating SVZ neurogenesis in disease. Gal-1, a similar lectin often co-expressed with Gal-3, also has profound effects on brain pathology and adult neurogenesis. Remarkably, Gal-3's carbohydrate recognition domain bears structural similarity to the SARS-CoV-2 virus spike protein necessary for cell entry. Gal-3 can be targeted pharmacologically and is a valid target for several diseases involving brain inflammation. The wealth of molecular pathways now known further suggest its modulation could be therapeutically useful.

The Diagnostic Value of Conventional MRI and CT Features in the Identification of the IDH1-Mutant and 1p/19q Co-Deletion in WHO Grade II Gliomas

RATIONALE AND OBJECTIVES

The classification of patients based on pathology and molecular features is important for improving WHO grade II glioma patient prognosis, especially for the initially diagnosed patients. Less invasive and more convenient methods for the prediction of the pathological type and gene status are desired.

MATERIALS AND METHODS

This study investigates the ability to use conventional magnetic resonance imaging (MRI) and computed tomography (CT) features for determining the Isocitrate Dehydrogenase (IDH)-mutant and 1p/19q-codeletion status, through a retrospective review of information obtained from 189 WHO grade II glioma patients. Diffuse astrocytoma (IDH-mutant), Diffuse astrocytoma (IDH- wildtype) and Oligodendroglioma (IDH-mutant and 1p/19q co-deletion) were included in this cohort. All patients were divided into IDH-mutant group and IDH-wildtype group according to the IDH R132H mutation status. Moreover, all patients were divided into 1p/19q co-deletion group and 1p/19q non-codeletion group according to the 1p and 19q chromosome status. Patients underwent pre-operative CT and MRI scans, followed by operation and histopathological analyses, including immunohistochemistry and polymerase chain reaction analysis for IDH mutants, and fluorescence capillary electrophoresis analysis for the 1p/19q co-deletion. The χ² test, logistical regression and receiver operating characteristic curve analysis were conducted for statistical analysis.

RESULTS

IDH-mutant group patients exhibited a higher calcification frequency (25.2% vs 2.4%, p = 0.006) and lower frequency of T1 enhancement (20.4% vs 38.1%, p = 0.028) comparing patients in IDH-wildtype group, while 1p/19q co-deletion group patients exhibited a higher calcification frequency (46.67% vs 2.6%, p < 0.001) and lower homogenous signal frequency in T2WI (12.0% vs 31.6%, p = 0.014), sharp lesion margins (14.7% vs 43.0%, p = 0.010), T2/fluid attenuated inversion recovery mismatch signs (22.7% vs 50.9%, p = 0.001), and subventricular zone involvement (64.0% vs 15.8%, p = 0.021) comparing patients in 1p/19q non-codeletion group. According to the results of receiver operating characteristic analysis, these features were observed to have certain diagnostic abilities, especially with regard to combination parameters, which had a high diagnostic capability, with an area under the curve of 0.848.

CONCLUSION

Conventional MRI and CT features, which still represent the most convenient and widely used predictive method, might be a promising noninvasive predictor for differentiating between varied WHO grade II gliomas. Patients with calcification and T1 nonenhancement are more likely to be IDH-mutant. Moreover, patients with noncalcification, homogenous signal, sharp lesion margins, subventricular zone involvement on T2 and T2/fluid attenuated inversion recovery mismatch signs are more likely to be 1p/19q non-codeletion.

Functional Mapping before and after Low-Grade Glioma Surgery: A New Way to Decipher Various Spatiotemporal Patterns of Individual Neuroplastic Potential in Brain Tumor Patients

Intraoperative direct electrostimulation mapping (DEM) is currently the gold-standard for glioma surgery, since functional-based resection allows an optimization of the onco-functional balance (increased resection with preserved quality of life). Besides intrasurgical awake mapping of conation, cognition, and behavior, preoperative mapping by means of functional neuroimaging (FNI) and transcranial magnetic stimulation (TMS) has increasingly been utilized for surgical selection and planning. However, because these techniques suffer from several limitations, particularly for direct functional mapping of subcortical white matter pathways, DEM remains crucial to map neural connectivity. On the other hand, non-invasive FNI and TMS can be repeated before and after surgical resection(s), enabling longitudinal investigation of brain reorganization, especially in slow-growing tumors like low-grade gliomas. Indeed, these neoplasms generate neuroplastic phenomena in patients with usually no or only slight neurological deficits at diagnosis, despite gliomas involving the so-called "eloquent" structures. Here, data gained from perioperative FNI/TMS mapping methods are reviewed, in order to decipher mechanisms underpinning functional cerebral reshaping induced by the tumor and its possible relapse, (re)operation(s), and postoperative rehabilitation. Heterogeneous spatiotemporal patterns of rearrangement across patients and in a single patient over time have been evidenced, with structural changes as well as modifications of intra-hemispheric (in the ipsi-lesional and/or contra-lesional hemisphere) and inter-hemispheric functional connectivity. Such various fingerprints of neural reconfiguration were correlated to different levels of cognitive compensation. Serial multimodal studies exploring neuroplasticity might lead to new management strategies based upon multistage therapeutic approaches adapted to the individual profile of functional reallocation.

Use of Preoperative Ependymal Enhancement on Magnetic Resonance Imaging Brain as a Marker of Grade of Glioma

Objectives:

Neural stem cells within the subventricular zone (SVZ) are thought to be responsible for the origin and the heterogeneous nature of the gliomas. The relationship of the gliomas to the SVZ can be appreciated as ependymal enhancement on contrast magnetic resonance imaging (MRI). This study evaluates the rate of ependymal enhancement and its association with the histopathological grade of gliomas.

Patients and Methods:

Seventy-five patients with radiological features of glioma were recruited. Preoperative MRI was evaluated for the presence of ependymal enhancement and fluid-attenuated inversion recovery (FLAIR) signal proximity of tumor to ependyma, and the association to grade was investigated.

Results:

Seventy-five patients studied showed a male predominance (62.66%) with a mean age of 44.91 ± 13.64 years. Evidence of ependymal enhancement was positive in 24% (n = 18), 46.67% (n = 35) showed no evidence, and in 29.33% (n = 22), assessment was inconclusive. According to WHO grading, 76% (n = 57) were high-grade gliomas (HGGs) including Grade III (n = 17) and Grade IV (n = 40) and 24% (n = 18) were low-grade gliomas (LGGs) Grade II. HGGs were significantly associated with ependymal enhancement (P < 0.01) and FLAIR signal proximity to the ependyma (P < 0.001). Among HGGs, rate of ependymal enhancement and FLAIR signal proximity was more in Grade IV than Grade III but was not statistically significant (P > 0.05).

Conclusion:

SVZ is associated with HGGs. These MRI features can be helpful in predicting the tumor grade preoperatively and by including LGGs, the role of SVZ in the heterogeneous disease process of glioma can be studied as a whole, not only in the glioblastoma (GBM).

The etiopathogenesis of diffuse low-grade gliomas

The origins of diffuse low-grade gliomas (DLGG) are unknown. Beyond some limited data on their temporal and cellular origins, the mechanisms and risk factors involved are poorly known. First, based on strong relationships between DLGG development and the eloquence of brain regions frequently invaded by these tumors, we propose a "functional theory" to explain the origin of DLGG. Second, the biological pathways involved in DLGG genesis may differ according to tumor location (anatomo-molecular correlations). The cellular and molecular mechanisms of such "molecular theory" will be reviewed. Third, the geographical distribution of diffuse WHO grade II-III gliomas within populations is heterogeneous, suggesting possible environmental risk factors. We will discuss this "environmental theory". Finally, we will summarize the current knowledge on genetic susceptibility in gliomas ("genetic predisposition theory"). These crucial issues illustrate the close relationships between the pathophysiology of gliomagenesis, the anatomo-functional organization of the brain, and personalized management of DLGG patients.

Differentiation between Solitary Cerebral Metastasis and Astrocytoma on the Basis of Subventricular Zone Involvement on Magnetic Resonance Imaging

Purpose

To determine the relationship between the subventricular zone (SVZ) and astrocytoma based on magnetic resonance imaging (MRI) and whether SVZ involvement can be used to distinguish solitary cerebral metastases (SCMs) from astrocytomas.

Methods

This retrospective study involved 154 patients with solitary low-grade astrocytoma (LGA), high-grade astrocytoma (HGA), and SCM, who underwent T1-weighted imaging (T1WI), Gd-DTPA–enhanced T1WI, and T2-weighted imaging (T2WI) or fluid-attenuated inversion recovery (FLAIR) T2WI. The spatial relationship between the tumor and SVZ was classified as “involvement” or “segregation” on contrast-enhanced T1WI for enhanced tumors and T2WI/FLAIR T2WI for non-enhanced tumors. Patient-based SVZ-contact rates were compared between the LGA, HGA, and SCM groups. The frequencies of involvement of various lateral ventricle regions by astrocytoma were compared. The correlation between SVZ involvement and tumor necrosis was analyzed.

Results

Patient-based SVZ-contact rates in SCM, LGA, and HGA were 24.1%, 68.8%, and 85.4%, respectively. Univariate analysis showed that the SVZ-contact rate was significantly different between SCM and astrocytoma (24.1% vs. 75.2% P < 0.001), also between LGA and HGA (68.1% vs. 85.4% P=0.037). After the tumor volume was adjusted as a covariate, SVZ-contact rates still differed between SCMs and astrocytomas (Odds ratio [OR]: 4.58, 95% Confidence interval [CI]: 1.65 to 12.8, P=0.004). Tumor volume differed between LGA and HGA (P< 0.001), and influenced the association between SVZ involvement and astrocytoma grade (P = 0.05). Among the lateral ventricle regions, the frontal horn was the most frequently involved by astrocytomas. SVZ-contact rates were higher in necrosis group compared with non-necrosis groups (83.9% vs. 50.0%, P < 0.001) among astrocytoma patients. Necrosis positively correlated with SVZ involvement in astrocytomas (r_s = 0.342, P < 0.001), but did not correlate with SVZ involvement in SCMs (P = 0.193).

Conclusions

Compared to SCMs, solitary cerebral astrocytomas exhibited spatial proximity to the SVZ, which might distinguish the supratentorial astrocytomas from SCMs.

Use of preoperative FLAIR MRI and ependymal proximity of tumor enhancement as surrogate markers of brain tumor origin

Neural stem cells proliferate in the subventricular zone and give rise to progeny that differentiate and migrate throughout the brain. We aimed to test the hypothesis that glioma behavior and grade may correlate with the identity of the tumor cell of origin. We evaluated three preoperative radiographic features (fluid attenuated inversion recovery [FLAIR] MRI characteristics, tumor proximity to ventricular ependyma, and subependymal representation) as surrogate markers of tumor origin using a retrospective cohort design. The medical records of 228 patients who underwent surgical resection of a glioma from January 2004 to August 2008 were reviewed. Average patient age was 54.5 years (standard deviation [SD] 15.3) with a male predominance (62.9%). World Health Organization glioma grades amongst the cohort were Grade IV (71.6%), Grade III (21.3%) and Grade II (7.1%). Mean survival was 11.2 months (SD 10.5) with a mean follow up of 12.8 months (SD 11.3). Glioma tumor grade was significantly correlated to FLAIR signal proximity to the ependymal surface (p<0.01) and inversely with proximity of tumor mass to the ependyma (p<0.01). The mean distance of tumor-associated FLAIR signal from the ependymal surface for glioblastoma multiforme (GBM) was 1.2mm (SD 3.3) compared to 4.8 (SD 6.5) for anaplastic astrocytomas and 6.6mm (SD 6.7; p<0.01) for low grade gliomas. Conversely, the mean distance of the enhancing tumor mass from the ependyma for GBM was 7.3mm (SD 9.4), Grade III glioma 2.3mm (SD 4.9), and Grade II glioma 3.8mm (SD 6.8; p<0.05). These findings suggest that higher grade gliomas might arise from less differentiated neuroepithelial cells in the subventricular zone that possess greater migratory potential.

Limbic Tumors of the Temporal Lobe: Radiologic-Pathologic Correlation

PURPOSE

The purpose of this study was to assess imaging and pathologic characteristics of limbic tumors. Our hypothesis was that temporal lobe limbic tumors have distinctive features from extralimbic tumors.

METHODS

This retrospective radiologic-pathologic correlation study of primary temporal lobe tumors (excluding glioblastoma) distinguished limbic from extralimbic tumors based on preoperative magnetic resonance imaging. Limbic tumors were categorized according to Yaşargil's classification into (1) mediobasal temporal (mbT), (2) insular-temporo-opercular (I-TO), and (3) fronto-orbital-insular-temporopolar (FO-I-TP).

RESULTS

A total of 50 cases with a mean age at diagnosis of 38 ± 19.9 years (14 women, 36 men) were included. Pathologic diagnoses were as follows: 20 anaplastic astrocytomas, 11 gangliogliomas, 8 astrocytomas (World Health Organization grade II), 3 pilocytic astrocytomas, 2 dysembryoplastic neuroepithelial tumors, 2 oligodendrogliomas (grade II), 2 anaplastic oligodendrogliomas, 1 low-grade glioneuronal tumor, and 1 atypical extraventricular neurocytoma. In all, 36 tumors were limbic and displayed consistent growth patterns (16 mbT, 11 I-TO, 8 FO-I-TP, and 1 pantemporal) and 14 were extralimbic. There were no differences between limbic and extralimbic tumors with regard to age, sex, pathologic diagnosis, and presentation with seizures. mbT tumors had more frequent neuronal differentiation (50 %) than I-TO (0 %) and FO-I-TP (25 %) tumors (chi-square = 7.8, df = 2, p = 0.02). Neuronal differentiation correlated with lower grade (r = 0.52, p < 0.01) and younger age (r = 0.52, p < 0.01).

CONCLUSIONS

Limbic tumors displayed consistent growth routes. mbT limbic tumors had more frequent neuronal differentiation, which may result from proximity to the neurogenic subgranular zone of the hippocampus. Neuronal differentiation was maximal in mbT and lowest in I-TO and FO-I-TP tumors and correlated with lower tumor grade and younger age at diagnosis.

Awake surgery for incidental WHO grade II gliomas involving eloquent areas

BACKGROUND

WHO grade II glioma (G2G) is a pre-malignant tumor, usually revealed by seizures in young patients living normal lives. G2G grows constantly and will inevitably become anaplastic. Surgical resection significantly increases the overall survival by delaying malignant transformation. Recently, a similar natural history was demonstrated in a patient with incidental G2G, with continuous growth and risk of anaplasia. Here, the aim was to study for the first time the functional results and extent of resection in a prospective series of patients who underwent resection for incidental G2G within eloquent areas.

METHOD

G2G involving functional regions in the left dominant hemisphere was incidentally diagnosed in 11 asymptomatic patients. Resection was achieved in all cases after demonstration of a volumetric increase on serial MRIs. Intraoperative awake mapping was performed in the 11 patients.

FINDINGS

There were no cases of mortality or permanent postoperative deficit. A subtotal, total or even "supratotal" resection was achieved in the 11 cases, with no partial resections. All patients resumed normal social and professional lives, with no seizures (KPS 100). Due to slow tumor re-growth in three patients with subtotal resection, adjuvant chemotherapy was administrated in two cases and radiotherapy in one. With a mean follow-up of 40 months since surgery, there was no anaplastic transformation.

CONCLUSION

These results show that surgery can be considered in incidental G2G, even in critical areas, with a minimal risk and optimal resection, thanks to intraoperative mapping. Such findings raise the question of an early detection.