Tumors of the central nervous system. Classification of the World Health Organization 2021. Towards a paradigm shift. / Tumores del sistema nervioso central. Clasificación de la Organización Mundial de la Salud 2021. Hacia un cambio de paradigma.

The study of central nervous system (CNS) tumors is a subject of great interest and such knowledge is of great importance in medical practice. The classifications of CNS neoplasms began in the mid-19th century, until the World Health Organization (WHO) published, in 1979, the first edition of a useful systematic review for the purpose of establishing a common language for all medical specialties. To date, 5 updated editions of neoplastic taxonomy have been published. The fifth edition, from 2021, consolidates the paradigm shift brought about by molecular advances, although the transition between morphological and molecular biological characterization is still in progress. In this article, the new modifications introduced in the different most frequent families of tumors in pediatrics are analyzed, emphasizing useful information for pediatricians in their daily practice and multidisciplinary consultations.

El estudio de los tumores del sistema nervioso central (SNC) resulta ser un tema de gran consideración y su conocimiento reviste una alta importancia en la práctica médica. Las clasificaciones de las neoplasias del SNC comenzaron a mediados del siglo XIX hasta que en 1979 la Organización Mundial de la Salud (OMS) publicó la primera edición de una sistemática útil con el objetivo de establecer un lenguaje común para todas las especialidades médicas. Al día de hoy, 5 ediciones actualizaron la taxonomía neoplásica. La quinta edición del año 2021 consolida el cambio de paradigma dado por los avances moleculares, si bien todavía la transición se encuentra en proceso entre la caracterización morfológica y la biológica molecular. En este artículo, se analizan las nuevas modificaciones incorporadas en las diferentes familias tumorales más frecuentes en pediatría haciendo hincapié en aquella información de utilidad para el médico pediatra en su práctica diaria y la consulta multidisciplinaria.

Intracranial Involvement of Systemic Hodgkin Lymphoma: A Case Report and Literature Review.

A 27-year-old male patient, previously diagnosed with Hodgkin lymphoma (HL), presented with gait disturbance. Brain MRI showed a 4.5 cm mass lesion in the right occipital lobe, suggesting either intracranial involvement of HL or a potential meningioma. Despite high-dose methotrexate and steroid treatment, the patient's symptoms persisted, and imaging showed an enlarging mass, leading to surgical intervention. Histopathological examination confirmed central nervous system (CNS) involvement of HL. Postoperatively, the patient underwent whole-brain radiotherapy and demonstrated marked clinical improvement. Our literature review from 1980 to 2023 identified only 46 cases of intracranial HL (IC-HL), underscoring its rarity. Lymphomas represent 2.2% of brain tumors, with 90%-95% being diffuse large B-cell lymphoma (DLBCL). In contrast, the incidence of CNS-HL patients is a mere 0.02%. Notably, IC-HL and intracranial DLBCL have differences in their typical locations and treatment strategies. Unlike DLBCL, which predominantly appears in the supratentorial region (87%), IC-HL is found there in 61.5% of cases. Additionally, 33.3% of IC-HL cases occur in the cerebellum, with 43.5% associated with posterior circulation regions. Furthermore, while biopsy followed by chemotherapy induction is a common strategy for DLBCL, 81.8% of IC-HL cases underwent surgical resection, and only 18.1% had a biopsy alone. The distinct characteristics of IC-HL tumors, including their larger size, attachment to the dura, and fibrotic nature with clear boundaries, might account for the preference for surgical intervention. The unique features of IC-HL compared to DLBCL highlight the need for distinct considerations in diagnosis and management.

Absence of enhancement in a lesion does not preclude primary central nervous system T-cell lymphoma: A case report.

BACKGROUND: Primary central nervous system lymphoma (PCNSL) is a non-Hodgkin lymphoma that originates in the central nervous system (CNS) and is exclusively limited to the CNS. Although most PCNSLs are diffuse large B-cell lymphomas, primary CNS T-cell lymphomas (PCNSTLs) are rare. PCNSTLs typically demonstrate some degree of enhancement on contrast-enhanced magnetic resonance imaging (MRI). To the best of our knowledge, non-enhancing PCNSTL has not been reported previously. CASE SUMMARY: A 69-year-old male presented to the neurology department with complaints of mild cognitive impairment and gradual onset of left lower leg weakness over a span of two weeks. Initial MRI showed asymmetric T2-hyperintense lesions within the brain. No enhancement was observed on the contrast-enhanced T1 image. The initial diagnosis was neuro-Behçet's disease. Despite high-dose steroid therapy, no alterations in the lesions were identified on initial MRI. The patient's symptoms deteriorated further. An MRI performed one month after the initial scan revealed an increased lesion extent. Subsequently, brain biopsy confirmed the diagnosis of PCNSTL. The patient underwent definitive combined chemo-radiotherapy. However, the patient developed bacteremia and died of septic shock approximately three months after diagnosis. CONCLUSION: The absence of enhancement in the lesion did not rule out PCNSTL. A biopsy approach is advisable for pathological confirmation.

A Multidisciplinary Skull Base Board for Tumour and Non-Tumour Diseases: Initial Experiences.

The skull base is the area where various cancerous and non-cancerous diseases occur and represents the intersection of several medical fields. The key is an integrated treatment by specialists of multiple disciplines. We prospectively analysed patients with a skull base disease between August 2022 and 2023 and presented to the Multidisciplinary Skull Base Board (MDT-SB), which takes place once a month hybridly (in-person and remotely). Thirty-nine patients (median age of 58.2 years) were included, of which twelve (30.8%) had a benign tumour, twelve (30.8%) had a malignant tumour, five had an infection (12.8%), and ten (25.6%) had other diseases. For each patient, at least two otorhinolaryngologists, a neurosurgeon, and a neuroradiologist, as well as an infectious disease specialist, a paediatrician, an oculoplastic surgeon, a maxillofacial surgeon, and a pathologist were involved in 10%, 8%, 8%, 3%, and 3% of cases, respectively. In fifteen patients (38%), the MDT-SB suggested surgical treatment; in fourteen (36%), radiological follow-ups; in five (13%), non-surgical treatments; in two, conservative treatments (5%); in two (5%), surgical and conservative treatments; and in one (3%), a biopsy. Non-cancerous and cancerous diseases of the skull base in adults and children should be presented to the MDT-SB, which consists of at least an otolaryngologist, a neurosurgeon, and a neuroradiologist.

Decoding the DNA methylome of central nervous system tumors: An emerging modality for integrated diagnosis.

The definitive diagnosis and classification of individual cancers are crucial for patient care and cancer research. To achieve a robust diagnosis of central nervous system (CNS) tumors, a genotype-phenotype integrated diagnostic approach was introduced in recent versions of the World Health Organization classification, followed by the incorporation of a genome-wide DNA methylome-based classification. Microarray-based platforms are widely used to obtain DNA methylome data, and the German Cancer Research Center (Deutsches Krebsforschungszentrum [DKFZ]) has a webtool for a DNA methylation-based classifier (DKFZ classifier). Integration of DNA methylome will further enhance the precision of CNS tumor classification, especially in diagnostically challenging cases. However, in the clinical application of DNA methylome-based classification, challenges related to data interpretation persist, in addition to technical caveats, regulations, and limited accessibility. Dimensionality reduction (DMR) can complement integrated diagnosis by visualizing a profile and comparing it with other known samples. Therefore, DNA methylome-based classification is a highly useful research tool for auxiliary analysis in challenging diagnostic and rare disease cases, and for establishing novel tumor concepts. Decoding the DNA methylome, especially by DMR in addition to DKFZ classifier, emphasizes the capability of grasping the fundamental biological principles that provide new perspectives on CNS tumors.

Cytological features of cranial and paraspinal nerve Tumours.

The 2021 World Health Organization Classification of Central Nervous System Tumours introduced significant revisions to the categorization of paraspinal and nerve sheath tumours. This updated system encompasses seven tumour types: schwannoma, neurofibroma, perineurioma, hybrid nerve sheath tumours, malignant melanotic nerve sheath tumour, malignant peripheral nerve sheath tumour and cauda equina neuroendocrine tumour. This review provides an image-rich cytologic reference of these tumours, with particular emphasis on intraoperative smear preparations. Knowledge of the key cytological features of these tumours and their differential diagnoses will help guide classification of these challenging entities.

Intracranial leptomeningeal CNS ganglioneuroblastoma. First report and review of the literature.

BACKGROUND: CNS ganglioneuroblastoma in an extremely rare embryonal tumour, specifically in the pediatric population. Bad prognosis is documented due to aggressiveness and absence of protocolized treatment at the moment. CLINICAL DESCRIPTION: We present the case of a 5-year-old boy who presented with sudden loss of consciousness. CT scan was performed showing a large posterior fossa lesion with several intraventricular focal lesions, suggesting metastases, the largest one located inside the III ventricle. The patient underwent a posterior fossa resection of the lesion and a subtotal resection of the III ventricle lesion, with adjuvant chemotherapy. The evolution was poor and the patient finally died 3 months after diagnosis. CONCLUSION: Ganglioneuroblastoma is extremely likely to recur quickly and extensively. There is little knowledge about treatment options but is documented that gross total resection followed by adjuvant radiotherapy and chemotherapy is the best management in these patients.

The 2021 WHO Classification for Gliomas and Implications on Imaging Diagnosis: Part 3-Summary of Imaging Findings on Glioneuronal and Neuronal Tumors.

The fifth edition of the World Health Organization classification of central nervous system tumors published in 2021 reflects the current transitional state between traditional classification system based on histopathology and the state-of-the-art molecular diagnostics. This Part 3 Review focuses on the molecular diagnostics and imaging findings of glioneuronal and neuronal tumors. Histological and molecular features in glioneuronal and neuronal tumors often overlap with pediatric-type diffuse low-grade gliomas and circumscribed astrocytic gliomas (discussed in the Part 2 Review). Due to this overlap, in several tumor types of glioneuronal and neuronal tumors the diagnosis may be inconclusive with histopathology and genetic alterations, and imaging features may be helpful to distinguish difficult cases. Thus, it is crucial for radiologists to understand the underlying molecular diagnostics as well as imaging findings for application on clinical practice. EVIDENCE LEVEL: 3 TECHNICAL EFFICACY: Stage 3.

Atypical teratoid/rhabdoid tumour with CDK6 amplification in a child: a case report and literature review.

Atypical teratoid/rhabdoid tumours (AT/RTs) are rare central nervous system neoplasms that frequently occur in infants and children and have a very poor prognosis. In recent years, molecular analysis of AT/RTs has shown that biallelic inactivation of SMARCB1 (INI1, SNF5, BAF47) or SMARCA4 (BRG1) frequently occurs. Here, we present a case of basal ganglia AT/RT with SMARCB1 gene deficiency and CDK6 gene amplification in a 5-year-old child. A 5-year-old boy was hospitalized due to a 1-week history of frontal and parietal headache. Magnetic resonance imaging (MRI) demonstrated a 3 cm × 2 cm × 1.5 cm heterogeneous enhanced mass located at the right basal ganglia that partially protruded into the right lateral ventricle. The lesion was successfully resected under electrophysiological monitoring and neuronavigation. The postoperative pathological examination implied an AT/RT diagnosis, with loss of SMARCB1 protein, SMARCB1 gene deficiency and CDK6 gene amplification. Unfortunately, the patient died due to respiratory and circulatory failure at 5 weeks after the operation. To date, standard regimens have not yet been established due to the lack of large-scale prospective studies for AT/RT. The p16-RB signalling pathway should be considered as a potential target for AT/RT treatment modalities. Apart from traditional regimens, targeted therapies, especially CDK4/6 inhibitors, are likely a promising therapeutic option for AT/RT treatment.

Exposição a agrotóxicos e o risco de tumores do Sistema Nervoso Central em crianças: revisão sistemática com metanálise / Pesticide exposure and risk of Central Nervous System tumors in children: a systematic review with meta-analysis

Resumo Os tumores do Sistema Nervoso Central (SNC) representam mais da metade das neoplasias infantis malignas que acometem crianças. Objetivou-se analisar o risco de exposição a agrotóxicos relacionado com o desenvolvimento de tumores do SNC em crianças. Realizou-se uma revisão sistemática da literatura nas bases de dados PubMed/MEDILINE, Embase, Web of Science, Scopus e CINAHL. Foram incluídos estudos de coorte e caso-controle sobre o desenvolvimento de tumores do SNC (todos os tipos histológicos do grupo III Classificação de Câncer Infantil) decorrentes da exposição a agrotóxicos em crianças de 0-14 anos. Na metanálise utilizou-se o modelo de efeito aleatório e o método estatístico de Mantel-Haenszel. A Razão de Chances (RC) ou Odds Ratio (OR) foi a medida de associação aplicada. A revisão foi registrada no International Prospective Register of Systematic Reviews (PROSPERO) sob o número CRD42021209354. A busca identificou 1.158 estudos, dos quais 14 compuseram a revisão. Verificou-se evidência de associação entre o desenvolvimento de astrocitomas e a exposição a todas as classes de pesticidas (OR 1,50; IC95% 1,15-1,96; p=0,03). A síntese dos resultados apontou para uma relação da exposição aos agrotóxicos com o desfecho de alguns tipos histológicos de tumores do SNC na infância.

Abstract Central Nervous System (CNS) tumors represent more than half of all childhood malignant neoplasms. The aim of this study was to determine the relationship between environmental exposure to pesticides and the development of CNS tumors in children. We conducted a systematic review of the literature in the PubMed/MEDILINE, Embase, Web of Science, Scopus, and CINAHL databases. The inclusion criteria were cohort and case-control studies investigating the association between exposure to pesticides and CNS tumors (all histological types included in group III of the WHO Classification of Childhood Cancer) in children aged 0-14 years. The meta-analysis was performed using a random effects model and the Mantel-Haenszel method. Strength of association was measured using odds ratios (OR). The review was registered in the International Prospective Register of Systematic Reviews (PROSPERO) under identification number CRD42021209354. The search identified 1,158 studies, 14 of which were included in the review. There was evidence of an association between the development of astrocytomas and exposure to all classes of pesticides (OR 1.50; 95%CI 1.15-1.96; p=0.03). The synthesis of the evidence pointed to a relationship between exposure to pesticides and some histological types of CNS tumors in childhood.

The 2021 World Health Organization classification of gliomas: an imaging approach.

The purpose of this pictorial essay is to describe the recommendations of the 2021 World Health Organization classification for adult-type and pediatric-type gliomas and to discuss the main modifications in relation to the previous (2016) classification, exemplified by imaging, histological, and molecular findings in nine patients followed at our institutions. In recent years, molecular biomarkers have gained importance in the diagnosis and classification of gliomas, mainly because they have been shown to correlate with the biological behavior and prognosis of such tumors. It is important for neuroradiologists to familiarize themselves with this new classification of central nervous system tumors, so that they can use this knowledge in evaluating and reporting the imaging examinations of patients with glioma.

O propósito deste ensaio iconográfico é descrever e discutir as novas recomendações da Organização Mundial da Saúde de 2021, referente aos gliomas dos tipos adulto e infantil, e suas principais diferenças com a classificação anterior (2016), exemplificadas com imagens de nove casos de pacientes atendidos nas nossas instituições. Recentemente, há uma crescente significância dos marcadores moleculares no diagnóstico e classificação dos gliomas e tumores do sistema nervoso central, principalmente pela correlação com o comportamento biológico e o prognóstico. É importante que os neurorradiologistas estejam familiarizados com a nova classificação dos tumores do sistema nervoso central para a prática clínica, na avaliação e emissão de laudos e opiniões nas imagens dos pacientes com gliomas.

Intradural Intramedullary Spinal Cord Glioblastoma: A Case Report.

Primary spinal cord glioblastoma multiforme (GBM) remains uncommon and typically affects males and patients during their fifth decade of life. Our case demonstrates a 77-year-old woman who initially presented with right arm paresthesia and limited range of motion and was subsequently diagnosed with primary spinal cord GBM. Our case illustrates an atypical and nonspecific neurological presentation highlighting that spinal cord GBM can have a more indolent course, unlike what current literature suggests. It also emphasizes the importance of considering a multimodal approach when managing atypical neurological symptoms and considering an early intervention, including magnetic resonance imaging, to rule out occult neoplasm in an appropriate clinical setting, thus preventing delay in the diagnosis. This case further emphasizes the role of molecular biomarkers of tumors, including isocitrate dehydrogenase mutation as well as methylguanine-DNA methyltransferase promoter methylation status, that can independently guide and affect the treatment outcomes in this patient population.

Mature T-cell and NK-cell lymphoma involvement of the central nervous system: a single center experience.

Mature T-cell and NK-cell lymphomas (MTNKL) are rare and heterogeneous lymphoproliferative disorders with poor clinical outcomes despite novel therapeutic advances. Although infrequent, central nervous system (CNS) involvement by MTNKL is associated with poor outcomes with a median overall survival (OS) of <12 months based on retrospective studies. We performed a retrospective analysis of patients who developed CNS involvement of MTNKL diagnosed at a single center from 1999 through 2020. Twenty-five patients were identified. Characteristics such as a diagnosis of adult T-cell leukemia/lymphoma, extranodal involvement, and poor performance status were associated with a higher risk of CNS involvement (p < 0.01). The median OS after diagnosis with CNS involvement was approximately 1 month (0.03-103.97 months). Patients exposed to novel therapeutics and/or clinical trial enrollment tolerated treatment without safety concerns and appeared to derive reasonable therapeutic benefit. Despite advances in the field, new therapeutic approaches are needed for patients with MTNKL with CNS involvement.

[Diagnosis of germ cell tumors]. / Diagnostik der Keimzelltumoren.

CLINICAL/METHODICAL ISSUE: Intracranial germ cell tumors are rare central nervous system (CNS) diseases in Europa and America. Because of their low frequency and lack of typical imaging features, they represent a difficult diagnosis for any radiologist. STANDARD RADIOLOGICAL METHODS: Magnetic resonance imaging (MRI) is a sensible diagnostic tool for the initial diagnosis of germ cell tumors, although it has limitations. METHODOLOGICAL INNOVATIONS: So far, no typical morphologic pattern as a red flag for germ cell tumors has been identified. Correlation with clinical symptoms and laboratory results is mandatory. PERFORMANCE: In certain cases, combining the location of the tumor and clinical findings may allow a diagnosis to be made even without histologic confirmation. PRACTICAL RECOMMENDATIONS: In addition to imaging, the radiologist needs the age, background, and laboratory findings to be able to make an accurate diagnosis.

A comprehensive genomic study of 390 H3F3A-mutant pediatric and adult diffuse high-grade gliomas, CNS WHO grade 4.

Malignant brain tumors, known as H3K27-altered diffuse midline glioma (DMG) and H3G34-mutant diffuse hemispheric glioma (DHG), can affect individuals of all ages and are classified as CNS WHO grade 4. We comprehensively characterized 390 H3F3A-mutant diffuse gliomas (201 females, 189 males) arising in pediatric patients (under 20 years old) and adults (20 years and older) evaluated by the CGP program at Foundation Medicine between 2013 and 2020. We assessed information from pathology reports, histopathology review, and clinical data. The cohort included 304 H3K27M-mutant DMG (156 females, 148 males) and 86 H3G34-mutant DHG (45 females, 41 males). Median patient age was 20 years (1-74 years). The frequency of H3K27M-mutant DMG was similar in both pediatric and adult patients in our cohort-48.6% of the patients were over 20 years old, 31.5% over 30, and 18% over 40 at initial diagnosis. FGFR1 hotspot point mutations (N546K and K656E) were exclusively identified in H3K27M-mutant DMG tumors (64/304, 21%; p = 0.0001); these tend to occur in older patients (median age: 32.5 years) and mainly arose in the diencephalon. H3K27M-mutant DMG had higher rates of mutations in NF1 (31.0 vs 8.1%; p = 0.0001) and PIK3CA/PIK3R1 (27.9% vs 15.1%; p = 0.016) compared to H3G34-mutant DHG. However, H3G34-mutant DHG had higher rates of targetable alterations in cell-cycle pathway genes (CDK4 and CDK6 amplification; CDKN2A/B deletion) (27.0 vs 9.0%). Potentially targetable PDGFRA alterations were identified in ~ 20% of both H3G34-mutant DHG and H3K27M-mutant DMG. Overall, in the present study H3K27M-mutant DMG occurred at similar rates in both adult and patient patients. Through our analysis, we were able to identify molecular features characteristic of DMG and DHG. By identifying the recurrent co-mutations including actionable FGFR1 point mutations found in nearly one-third of H3K27M-mutant DMG in young adults, our findings can inform clinical translational studies, patient diagnosis, and clinical trial design.

[Pediatric posterior fossa tumors]. / Infratentorielle Hirntumoren bei Kindern.

CLINICAL ISSUE: Tumors of the posterior fossa account for about 50-55% of brain tumors in childhood. DIAGNOSTIC WORKUP: The most frequent tumor entities are medulloblastomas, pilocytic astrocytomas, ependymomas, diffuse midline gliomas and atypical teratoid-rhabdoid tumors. Neuroradiological differential diagnosis with magnetic resonance imaging (MRI) is of considerable importance for preoperative planning as well as planning of follow-up therapy. PERFORMANCE: Most important findings for differential diagnosis of pediatric posterior fossa tumors are tumor location, patient age and the intratumoral apparent diffusion assessed by diffusion-weighted imaging. ACHIEVEMENTS: Advanced MR techniques like MRI perfusion and MR spectroscopy can be helpful both in the initial differential diagnosis and in tumor surveillance, but exceptional characteristics of certain tumor entities should be kept in mind. PRACTICAL RECOMMENDATIONS: Standard clinical MRI sequences including diffusion-weighted imaging are the main diagnostic tool in evaluating posterior fossa tumors in children. Advanced imaging methods can be helpful, but should never be interpreted separately from conventional MRI sequences.

The 2021 World Health Organization classification of gliomas: an imaging approach / Nova classificação das neoplasias gliais segundo a Organização Mundial da Saúde 2021, com enfoque radiológico

Abstract The purpose of this pictorial essay is to describe the recommendations of the 2021 World Health Organization classification for adult-type and pediatric-type gliomas and to discuss the main modifications in relation to the previous (2016) classification, exemplified by imaging, histological, and molecular findings in nine patients followed at our institutions. In recent years, molecular biomarkers have gained importance in the diagnosis and classification of gliomas, mainly because they have been shown to correlate with the biological behavior and prognosis of such tumors. It is important for neuroradiologists to familiarize themselves with this new classification of central nervous system tumors, so that they can use this knowledge in evaluating and reporting the imaging examinations of patients with glioma.

Resumo O propósito deste ensaio iconográfico é descrever e discutir as novas recomendações da Organização Mundial da Saúde de 2021, referente aos gliomas dos tipos adulto e infantil, e suas principais diferenças com a classificação anterior (2016), exemplificadas com imagens de nove casos de pacientes atendidos nas nossas instituições. Recentemente, há uma crescente significância dos marcadores moleculares no diagnóstico e classificação dos gliomas e tumores do sistema nervoso central, principalmente pela correlação com o comportamento biológico e o prognóstico. É importante que os neurorradiologistas estejam familiarizados com a nova classificação dos tumores do sistema nervoso central para a prática clínica, na avaliação e emissão de laudos e opiniões nas imagens dos pacientes com gliomas.

A Meningioma With Extensive Peritumoral Edema Mimicking Metastatic Brain Tumor: A Case Report.

Meningioma is the most common brain tumor among all histologically reported malignant and non-malignant tumors of the central nervous system. Angiomatous meningioma is one of the subtypes of meningioma that is rarely reported. In this paper, we present a case of a 67-year-old female patient who sought consultation due to seizure, cognitive decline, and parkinsonism. Contrast-enhanced MRI showed a well-defined tumor in the left frontal lobe convexity with extensive perilesional edema. A tumor excision was done and histopathology studies revealed an angiomatous meningioma subtype. This case is reportable because angiomatous meningioma is a recognized rare entity. It is important to share this entity with other medical professionals and start to consider this condition in differential diagnosis when diagnosing a patient with an intracranial mass with an extensive peritumoral edema. Furthermore, the patient's unusual presentation of parkinsonian features and its occurrence with colorectal cancer history suggest a possible association between these conditions.

The 2021 WHO Classification for Gliomas and Implications on Imaging Diagnosis: Part 2-Summary of Imaging Findings on Pediatric-Type Diffuse High-Grade Gliomas, Pediatric-Type Diffuse Low-Grade Gliomas, and Circumscribed Astrocytic Gliomas.

The fifth edition of the World Health Organization (WHO) classification of central nervous system tumors published in 2021 advances the role of molecular diagnostics in the classification of gliomas by emphasizing integrated diagnoses based on histopathology and molecular information and grouping tumors based on genetic alterations. This Part 2 review focuses on the molecular diagnostics and imaging findings of pediatric-type diffuse high-grade gliomas, pediatric-type diffuse low-grade gliomas, and circumscribed astrocytic gliomas. Each tumor type in pediatric-type diffuse high-grade glioma mostly harbors a distinct molecular marker. On the other hand, in pediatric-type diffuse low-grade gliomas and circumscribed astrocytic gliomas, molecular diagnostics may be extremely complicated at a glance in the 2021 WHO classification. It is crucial for radiologists to understand the molecular diagnostics and imaging findings and leverage the knowledge in clinical practice. EVIDENCE LEVEL: 3 TECHNICAL EFFICACY: Stage 3.

The 2021 WHO Classification for Gliomas and Implications on Imaging Diagnosis: Part 1-Key Points of the Fifth Edition and Summary of Imaging Findings on Adult-Type Diffuse Gliomas.

The fifth edition of the World Health Organization (WHO) classification of central nervous system tumors published in 2021 advances the role of molecular diagnostics in the classification of gliomas by emphasizing integrated diagnoses based on histopathology and molecular information and grouping tumors based on genetic alterations. Importantly, molecular biomarkers that provide important prognostic information are now a parameter for establishing tumor grades in gliomas. Understanding the 2021 WHO classification is crucial for radiologists for daily imaging interpretation as well as communication with clinicians. Although imaging features are not included in the 2021 WHO classification, imaging can serve as a powerful tool to impact the clinical practice not only prior to tissue confirmation but beyond. This review represents the first of a three-installment review series on the 2021 WHO classification for gliomas, glioneuronal tumors, and neuronal tumors and implications on imaging diagnosis. This Part 1 Review focuses on the major changes to the classification of gliomas and imaging findings on adult-type diffuse gliomas. EVIDENCE LEVEL: 3. TECHNICAL EFFICACY: Stage 3.