Update on Circumscribed Gliomas and Glioneuronal Tumors

A Contemporary Approach to Intraoperative Evaluation in Neuropathology

CONTEXT.—

Although the basic principles of intraoperative diagnosis in surgical neuropathology have not changed in the last century, the last several decades have seen dramatic changes in tumor classification, terminology, molecular classification, and modalities used for intraoperative diagnosis. As many neuropathologic intraoperative diagnoses are performed by general surgical pathologists, awareness of these recent changes is important for the most accurate intraoperative diagnosis.

OBJECTIVE.—

To describe recent changes in the practice of intraoperative surgical neuropathology, with an emphasis on new entities, tumor classification, and anticipated ancillary tests, including molecular testing.

DATA SOURCES.—

The sources for this review include the fifth edition of the World Health Organization Classification of Tumours of the Central Nervous System, primary literature on intraoperative diagnosis and newly described tumor entities, and the authors' clinical experience.

CONCLUSIONS.—

A significant majority of neuropathologic diagnoses require ancillary testing, including molecular analysis, for appropriate classification. Therefore, the primary goal for any neurosurgical intraoperative diagnosis is the identification of diagnostic tissue and the preservation of the appropriate tissue for molecular testing. The intraoperative pathologist should seek to place a tumor in the most accurate diagnostic category possible, but specific diagnosis at the time of an intraoperative diagnosis is often not possible. Many entities have seen adjustments to grading criteria, including the incorporation of molecular features into grading. Awareness of these changes can help to avoid overgrading or undergrading at the time of intraoperative evaluation.

Development and External Validation of an MRI-based Radiomics Nomogram to Distinguish Circumscribed Astrocytic Gliomas and Diffuse Gliomas: A Multicenter Study

RATIONALE AND OBJECTIVES

The 5th edition of the World Health Organization classification of tumors of the Central Nervous System (WHO CNS) has introduced the term "diffuse" and its counterpart "circumscribed" to the category of gliomas. This study aimed to develop and validate models for distinguishing circumscribed astrocytic gliomas (CAGs) from diffuse gliomas (DGs).

MATERIALS AND METHODS

We retrospectively analyzed magnetic resonance imaging (MRI) data from patients with CAGs and DGs across three institutions. After tumor segmentation, three volume of interest (VOI) types were obtained: VOItumor and peritumor, VOIwhole, and VOIinterface. Clinical and combined models (incorporating radiomics and clinical features) were also established. To address imbalances in training dataset, Synthetic Minority Oversampling Technique was employed.

RESULTS

A total of 475 patients (DGs: n = 338, CAGs: n = 137) were analyzed. The VOIinterface model demonstrated the best performance for differentiating CAGs from DGs, achieving an area under the curve (AUC) of 0.806 and area under the precision-recall curve (PRAUC)of 0.894 in the cross-validation set. Using analysis of variance (ANOVA) feature selector and Support Vector Machine (SVM) classifier, seven features were selected. The model achieved an AUC and AUPRC of 0.912 and 0.972 in the internal validation dataset, and 0.897 and 0.930 in the external validation dataset. The combined model, incorporating interface radiomics and clinical features, showed improved performance in the external validation set, with an AUC of 0.94 and PRAUC of 0.959.

CONCLUSION

Radiomics models incorporating the peritumoral area demonstrate greater potential for distinguishing CAGs from DGs compared to intratumoral models. These findings may hold promise for evaluating tumor nature before surgery and improving clinical management of glioma patients.

Infiltration in Pilocytic Astrocytoma: A Diagnostic Pitfall

Glioma can be classified according to its infiltrative capacity into circumscribed and "diffuse"/infiltrative glioma. Pilocytic astrocytoma is typically grouped under the circumscribed astrocytic glioma in the 2021 World Health Organization (WHO) classification of central nervous system (CNS) tumors. The distinction of pilocytic astrocytoma from diffuse glioma is fundamental as it could be the difference between CNS WHO grade 1 and grade 4 glioma. This study aims to determine the infiltrative nature of pilocytic astrocytoma in different brain locations. All cases diagnosed as "pilocytic astrocytoma" were retrieved from 2008 to 2021. The clinical information (age, sex, location of the tumor), pathological description, and performed immunostaining were obtained from the pathological reports. The available pathological slides were retrieved and examined for the following features: diagnosis, infiltrative vs. circumscribed tumor, and immunostaining characteristics. There were 20 males and 19 females aged 17 months to 31 years. The diagnosis of pilocytic astrocytoma was confirmed in 38/39 cases, and in one case, the diagnosis changed to a dysembryoplastic neuroepithelial tumor. Histological infiltration is defined as the presence of neoplastic cells among the nonneoplastic brain parenchyma. Twenty cases were well-circumscribed with no evidence of infiltration histologically, while 18/38 cases showed apparent infiltration into adjacent brain tissue. The infiltration was not restricted to cerebellar pilocytic astrocytoma (12/24, 50%) but was also present in 3/7 supratentorial, single brainstem, and single spinal cord cases. In conclusion, cases with typical morphological features of pilocytic astrocytoma could show areas of brain infiltration, which should not affect the certainty of the diagnosis.

Role of Dynamic Parameters of 18F-DOPA PET/CT in Pediatric Gliomas

PURPOSE OF THE REPORT

PET with 18F-DOPA can be used to evaluate grading and aggressiveness of pediatric cerebral gliomas. However, standard uptake parameters may underperform in circumscribed lesions and in diffuse pontine gliomas. In this study, we tested whether dynamic 18F-DOPA PET could overcome these limitations.

PATIENTS AND METHODS

Patients with available dynamic 18F-DOPA PET were included retrospectively. Static parameters (tumor/striatum ratio [T/S] and tumor/cortex ratio [T/N]) and dynamic ones, calculated on the tumor time activity curve (TAC), including time-to-peak (TTP), slope steepness, the ratio between tumor and striatum TAC steepness (dynamic slope ratio [DSR]), and TAC shape (accumulation vs plateau), were evaluated as predictors of high/low grading (HG and LG) and of progression-free survival and overall survival.

RESULTS

Fifteen patients were included; T/S, T/N, TTP, TAC slope steepness, and DSR were not significantly different between HG and LG. The accumulation TAC shape was more prevalent in the LG than in the HG group (75% vs 27%). On progression-free survival univariate analysis, TAC accumulation shape predicted longer survival (P < 0.001), whereas T/N and DSR showed borderline significance; on multivariate analyses, only TAC shape was retained (P < 0.01, Harrell C index, 0.93-0.95). On overall survival univariate analysis, T/N (P < 0.05), DSR (P < 0.05), and TAC "accumulating" shape predicted survival (P < 0.001); once more, only this last parameter was retained in the multivariate models (P < 0.05, Harrell C index, 0.86-0.89).

CONCLUSIONS

Dynamic 18F-DOPA PET analysis outperforms the static parameter evaluation in grading assessment and survival prediction. Evaluation of the curve shape is a simple-to-use parameter with strong predictive power.

Updates in Pediatric Glioma Pathology

Gliomas are a diverse group of primary central nervous system tumors with astrocytic, oligodendroglial, and/or ependymal features and are an important cause of morbidity/mortality in pediatric patients. Glioma classification relies on integrating tumor histology with key molecular alterations. This approach can help establish a diagnosis, guide treatment, and determine prognosis. New categories of pediatric glioma have been recognized in recent years, due to increasing application of molecular profiling in brain tumors. The aim of this review is to alert pediatric pathologists to emerging diagnostic concepts in pediatric glioma neuropathology, emphasizing the incorporation of molecular features into diagnostic practice.