Polymorphous low-grade neuroepithelial tumor of the young: case report and review focus on the radiological features and genetic alterations

Pediatric-type diffuse low-grade gliomas

The World Health Organization's 5th edition classification of Central Nervous System (CNS) tumors differentiates diffuse gliomas into adult and pediatric variants. Pediatric-type diffuse low-grade gliomas (pDLGGs) are distinct from adult gliomas in their molecular characteristics, biological behavior, clinical progression, and prognosis. Various molecular alterations identified in pDLGGs are crucial for treatment. There are four distinct entities of pDLGGs. All four of these tumor subtypes exhibit diffuse growth and share overlapping histopathological and imaging characteristics. Molecular analysis is essential for differentiating these lesions.

Exploring a distinct FGFR2::DLG5 rearrangement in a low-grade neuroepithelial tumor: A case report and mini-review of protein fusions in brain tumors

We report the novel clinical presentation of a primary brain neoplasm in a 30-year-old man with a mass-like area in the anteromedial temporal lobe. Histopathological analysis revealed a low-grade neuroepithelial tumor with cytologically abnormal neurons and atypical glial cells within the cerebral cortex. Molecular analysis showed a previously undescribed FGFR2::DLG5 rearrangement. We discuss the clinical significance and molecular implications of this fusion event, shedding light on its potential impact on tumor development and patient prognosis. Additionally, an extensive review places the finding in this case in the context of protein fusions in brain tumors in general and highlights their diverse manifestations, underlying molecular mechanisms, and therapeutic implications.

Polymorphous Low-Grade Neuroepithelial Tumor of the Young (PLNTY): Scoping Review of Case Reports and Case Series

Polymorphous low-grade neuroepithelial tumor of the young (PLNTY) is considered one of the low-grade neuroepithelial tumors, as per the World Health Organization 2021 classification of brain tumors. First described in 2016, these morphologically variable tumors are characterized by oligodendroglioma-like cellular components, infiltrative growth patterns, and cluster of differentiation 34 immunopositivity. A literature search of the PubMed/MEDLINE, SCOPUS, ScienceDirect, and COCHRANE databases (from inception to 20th June 2022) was carried out to identify relevant studies. To identify additional studies, we performed a recursive search of the bibliographies of the selected articles and published systematic reviews on this topic. The search yielded a total of 64 results. After removing duplicates, 26 articles were eligible for the review. The diagnostic criteria for these glioneuronal variants, representing a broad neuropathological spectrum, are not distinct and hence impede proper diagnosis and prognosis. Frequent genetic abnormalities involving mitogen-activated protein kinase pathway constituents, such as B-Raf proto-oncogene or fibroblast growth receptor 2/3, are harbored by PLNTYs. Recent advances in molecular diagnostics have resulted in more accurate tumor classification systems, based on gene expression profiles and DNA methylation patterns. Gross total resection seems curative, with a low recurrence rate. Malignant transformation is rare; however, adjuvant radiation therapy and chemotherapy may be beneficial in selected cases.

Systematic review and cumulative analysis of clinical properties of BRAF V600E mutations in PLNTY histological samples

PURPOSE

Polymorphous low-grade neuroepithelial tumors of the young (PLNTY) represent a rare pediatric-type tumor that most commonly presents as medically refractory epilepsy. PLNTY has only recently been recognized as a distinct clinical entity, having been first described in 2016 and added to the World Health Organization classification of CNS tumors in 2021. Molecular studies have determined that PLNTY is uniformly driven by aberrant MAPK pathway activation, with most tumors carrying either a BRAF V600E mutation or activating FGFR2 or FGFR3 fusion protein. Although it is known that these driver mutations are mutually exclusive, little is known about differences in clinical presentation or treatment outcomes between PLNTY cases driven by these distinct mutations.

METHODS

We performed a systematic review and cumulative analysis of PLNTY cases to assess whether or not PLNTY tumors carrying the BRAF V600E mutation exhibit different clinical behaviors. By searching the literature for all cases of PLNTY wherein BRAF V600E status was characterized, we compiled a dataset of 62 unique patient instances. Using a logistic regression-based approach, we assessed a primary outcome of what factors of a clinical presentation were associated with BRAF V600E mutations and a secondary outcome of what factors predicted total seizure freedom post-surgical resection.

RESULTS

PLNTY cases carrying BRAF V600E mutations in the literature were strongly positively associated with adult patients (p = 0.0055, OR = 6.556; 95% Conf. Int. = 1.737-24.742). BRAF V600E status was also positively associated with tumor involvement of the temporal lobe (p = 0.0046, OR = 11.036; 95% Conf. Int. = 2.100-58.006). Male sex was also positively associated with BRAF V600E status, but the result did not quite achieve statistical significance (p = 0.0731). BRAF V600E status was not found to be associated with post-operative seizure freedom.

CONCLUSIONS

These findings indicate that BRAF V600E-positive PLNTY exhibit characteristic clinical presentations but are not necessarily different in treatment responsiveness. Non-BRAF V600E tumors are more commonly associated with young patients.

Diffuse Gliomas with FGFR3::TACC3 Fusion: Morphological and Molecular Features and Classification Challenges

FGFR3::TACC3 fusion is a driver, potentially targetable, genetic alteration identified in approximately 4% of high-grade diffuse gliomas and rare cases with low-grade histology. Herein, we review the genetic and epigenetic features of these tumors and highlight the challenges in their classification and grading. Diffuse gliomas with FGFR3::TACC3 fusion display unique histopathological and molecular features, including an oligodendroglioma-like appearance, calcifications, and CD34 extravascular immunoreactivity. High-grade tumors exhibit molecular alterations and a DNA methylation profile typical of glioblastoma, suggesting that they may represent a subtype clinically characterized by a slightly better prognosis. Tumors with low-grade morphology are genetically and epigenetically heterogeneous. Some, exclusive to adults, have molecular alterations typical of glioblastoma, although most do not match any methylation classes, using version 12.5 of the Heidelberg classifier. Another group, which mostly affects children or adolescents, lacks the molecular features of glioblastoma and has a DNA methylation profile similar to that of low-grade glioneuronal tumors. In conclusion, diffuse gliomas with FGFR3::TACC3 fusion do not constitute a distinct nosological entity, owing to their genetic and epigenetic diversity. Further studies are warranted to clarify the biological aggressiveness of tumors with low-grade histology to refine the grading and determine the optimal treatment strategy.

Expanding the Imaging Spectrum of Polymorphous Low-Grade Neuroepithelial Tumor of the Young in Children

Polymorphous low-grade neuroepithelial tumors of the young (PLNTY) are rare brain tumors first described in 2017 and recently included in the 2021 5th World Health Organization Classification of Tumors of the Central Nervous System. They typically affect children and young adults. Few pediatric cases have been reported in the literature. The most common imaging features described, include location within the temporal lobe, involvement of the cortical/subcortical region, coarse calcifications, and well-defined margins with solid and cystic morphology, with slight-or-no enhancement. However, there is limited information on imaging features in children. We present the imaging spectrum of neuroimaging features in a series of pediatric patients with a histologically and molecularly proved PLNTY diagnosis. Coarse calcifications are uncommon in children compared with the adult literature, and they may develop with time. The transmantle-like sign can be observed, and adjacent cortical dysplasia may be seen. Seizure recurrence may occur despite gross total resection of the tumor.

Pediatric CNS tumors and 2021 WHO classification: what do oncologists need from pathologists?

The fifth edition of the WHO Classification of Tumors of the Central Nervous System (CNS), published in 2021, established new approaches to both CNS tumor nomenclature and grading, emphasizing the importance of integrated diagnoses and layered reports. This edition increased the role of molecular diagnostics in CNS tumor classification while still relying on other established approaches such as histology and immunohistochemistry. Moreover, it introduced new tumor types and subtypes based on novel diagnostic technologies such as DNA methylome profiling. Over the past decade, molecular techniques identified numerous key genetic alterations in CSN tumors, with important implications regarding the understanding of pathogenesis but also for prognosis and the development and application of effective molecularly targeted therapies. This review summarizes the major changes in the 2021 fifth edition classification of pediatric CNS tumors, highlighting for each entity the molecular alterations and other information that are relevant for diagnostic, prognostic, or therapeutic purposes and that patients' and oncologists' need from a pathology report.

Polymorphous low-grade neuroepithelial tumour of young (PLNTY): the new kid on the block

INTRODUCTION

Polymorphous low grade neuroepithelial tumor of the young (PLNTY) is a newly described epileptogenic tumor first reported by Jason. T. Huse et al. in 2016. Only a very few cases have been reported so far and has been recently incorporated in the World Health Organization (WHO) Central Nervous System Classification of tumours, 5th edition, 2021. Here we report a rare case of PLNTY which closely resembles DNET (Dysembryoplastic neuroepithelial tumor) with plenty of interesting findings which would otherwise go unnoticed resulting in a nonspecific or misclassified diagnosis.

CASE REPORT

A 12 year old boy presented to the Neurosurgery OPD with seizures for the past five years and was given multiple antiepileptics for the same. Magnetic resonance imaging (MRI) showed a well-defined lobulated cortical mass with T1 hypo intensity and T2 hyperintensity in the left temporal lobe measuring 2.1 × 2 × 1.3 cm suggesting a DNET. Left temporal craniotomy and excision of the lesion was done. Frozen section showed features of a low grade glial neoplasm. Routine sections demonstrated polymorphous findings including oligodendroglia like features, neuronal nuclear pleomorphism, spindled astroglial elements, perivascular rosettes, calcification, and vascular mineralization. By immunohistochemistry (IHC), the tumor cells were diffusely positive for GFAP and CD34.Ki67 labelling index was low. A final diagnosis of PLNTY was made based on the above findings. The child has been epilepsy free since the past one-month post-surgery and is on follow up.

DISCUSSION/CONCLUSION

PLNTY is a newly discovered distinct pediatric low grade glial neoplasm which was earlier grouped into nonspecific forms of DNET. It is characterized morphologically and molecularly by the presence of oligodendroglial component, CD34 expression, BRAFV600E mutation and alterations in the MAP kinase pathway. They are known to behave in a low-grade fashion amenable to control by excision with occasional cases of recurrence reported. It is important to recognize and report similar tumors to determine the long-term risk of recurrence and create a more complete understanding on their radiology and molecular genetics.

Brain Tumor Imaging in Adolescents and Young Adults: 2021 WHO Updates for Molecular-based Tumor Types

Published in 2021, the fifth edition of the World Health Organization (WHO) classification of tumors of the central nervous system (CNS) introduced new molecular criteria for tumor types that commonly occur in either pediatric or adult age groups. Adolescents and young adults (AYAs) are at the intersection of adult and pediatric care, and both pediatric-type and adult-type CNS tumors occur at that age. Mortality rates for AYAs with CNS tumors have increased by 0.6% per year for males and 1% per year for females from 2007 to 2016. To best serve patients, it is crucial that both pediatric and adult radiologists who interpret neuroimages are familiar with the various pediatric- and adult-type brain tumors and their typical imaging morphologic characteristics. Gliomas account for approximately 80% of all malignant CNS tumors in the AYA age group, with the most common types observed being diffuse astrocytic and glioneuronal tumors. Ependymomas and medulloblastomas also occur in the AYA population but are seen less frequently. Importantly, biologic behavior and progression of distinct molecular subgroups of brain tumors differ across ages. This review discusses newly added or revised gliomas in the fifth edition of the CNS WHO classification, as well as other CNS tumor types common in the AYA population.

Glioma: bridging the tumor microenvironment, patient immune profiles and novel personalized immunotherapy

Glioma is the most common primary brain tumor, characterized by a consistently high patient mortality rate and a dismal prognosis affecting both survival and quality of life. Substantial evidence underscores the vital role of the immune system in eradicating tumors effectively and preventing metastasis, underscoring the importance of cancer immunotherapy which could potentially address the challenges in glioma therapy. Although glioma immunotherapies have shown promise in preclinical and early-phase clinical trials, they face specific limitations and challenges that have hindered their success in further phase III trials. Resistance to therapy has been a major challenge across many experimental approaches, and as of now, no immunotherapies have been approved. In addition, there are several other limitations facing glioma immunotherapy in clinical trials, such as high intra- and inter-tumoral heterogeneity, an inherently immunosuppressive microenvironment, the unique tissue-specific interactions between the central nervous system and the peripheral immune system, the existence of the blood-brain barrier, which is a physical barrier to drug delivery, and the immunosuppressive effects of standard therapy. Therefore, in this review, we delve into several challenges that need to be addressed to achieve boosted immunotherapy against gliomas. First, we discuss the hurdles posed by the glioma microenvironment, particularly its primary cellular inhabitants, in particular tumor-associated microglia and macrophages (TAMs), and myeloid cells, which represent a significant barrier to effective immunotherapy. Here we emphasize the impact of inducing immunogenic cell death (ICD) on the migration of Th17 cells into the tumor microenvironment, converting it into an immunologically "hot" environment and enhancing the effectiveness of ongoing immunotherapy. Next, we address the challenge associated with the accurate identification and characterization of the primary immune profiles of gliomas, and their implications for patient prognosis, which can facilitate the selection of personalized treatment regimens and predict the patient's response to immunotherapy. Finally, we explore a prospective approach to developing highly personalized vaccination strategies against gliomas, based on the search for patient-specific neoantigens. All the pertinent challenges discussed in this review will serve as a compass for future developments in immunotherapeutic strategies against gliomas, paving the way for upcoming preclinical and clinical research endeavors.

Clinical significance of molecular subgroups of polymorphous low-grade neuroepithelial tumor of the young (PLNTY): A small single institutional case series and integrated analysis

INTRODUCTION

Polymorphous low-grade neuroepithelial tumor of the young (PLNTY) is a recently described entity. The clinicopathological features and prognosis of the molecular subgroups of these rare tumors is poorly understood. In this study, we presented a small case series of three new cases and integrated the data with published cases in the literature to characterize the similarities and differences of molecular subgroups of PLNTY.

METHODS

We searched our institutional archive for PLNTY cases and searched PubMed and Web of Science for relevant data. Demographic, clinical, radiologic, histopathological, molecular, and follow-up data of our four cases with published cases were integrated for final analyses.

RESULTS

We identified three institutional cases of PLNTY. The median age of our patients was 17 years (range: 13-42). All patients had a prior history of chronic seizures and all had tumors affecting the temporal lobes. Histopathologically, all cases showed oligodendroglial-like morphology with intratumoral calcifications and at least partially infiltrative growth patterns. Tumor cells were immunoreactive with CD34 and GFAP. Genetically, all cases harbored BRAF V600E mutations. Integrated analyses, including a total of 67 cases, demonstrated that PLNTYs with FGFR2 mutation were significantly younger (median age 11.0 years) than those with BRAF V600E or FGFR3 fusions (median age 41.0 and 16.0 years, respectively). All BRAF V600E-positive PLNTYs were free of tumor recurrence, while four of PLNTYs in other molecular subgroups developed tumor recurrence by imaging.

CONCLUSION

Our study suggests that PLNTYs have distinct clinicopathological features and are driven by genetic alterations in the MAPK pathway. The molecular subgroups of PLNTYs share similar findings, but also demonstrate distinct patient demographics.

Polymorphous low-grade neuroepithelial tumor of the young with FGFR3-TACC3 fusion mimicking high-grade glioma: case report and series of high-grade correlates

Background

Polymorphous low-grade neuroepithelial tumor of the young (PLNTY) is a recently described entity that can mimic high-grade glioma (HGG) in histologic and molecular features; however, factors predicting aggressive behavior in these tumors are unclear.

Methods

We present an indolent neuroepithelial neoplasm in a 59-year-old female with imaging initially suggestive of HGG, and a series of adult patients with HGG harboring FGFR3-TACC3 fusions are also presented for comparison.

Results

Pathology in the case patient revealed low-grade cytomorphology, microcalcifications, unusual neovascularization, and a low proliferation index. The lesion was diffusely CD34+ and harbored an FGFR3-TACC3 fusion and TERT promoter mutation. A diagnosis of PLNTY was therefore favored and the patient was observed with no progression at 15-month follow-up. In patients with HGG with FGFR3-TACC3 fusions, molecular findings included IDH-wildtype status, absence of 1p19q codeletion, CDKN2A loss, TERT promoter mutations and lack of MGMT promoter methylation. These patients demonstrated a median 15-month overall survival and a 6-month progression-free survival.

Conclusion

PLNTY is a rare low-grade entity that can display characteristics of HGG, particularly in adults. Presence of FGFR3-TACC3 fusions and other high-grade features should raise concern for a more malignant precursor lesion when a diagnosis of PLNTY is considered.

Review on neuroimaging in pediatric-type diffuse low-grade gliomas

The fifth edition of the World Health Organization Classification of Tumors of the Central Nervous System (WHO CNS5) has identified a new classification system for tumors of the brain and spinal cord, highlighting the pivotal role of molecular diagnosis in accurately categorizing neoplasms. In addition to previous classifications, one of the key distinctions lies in categorizing pediatric-type diffuse low-grade gliomas (pDLGGs) and pediatric-type diffuse high-grade gliomas (pDHGGs) as distinct tumor types. Although similar in histology and morphology, pediatric diffuse gliomas are completely different from the adult type with respect to the molecular genetic characteristics, prognosis, and treatment strategies. pDLGG includes four tumor types, namely, diffuse astrocytoma, MYB- or MYBL1-altered; angiocentric glioma; polymorphous low-grade neuroepithelial tumor of the young (PLNTY); and diffuse low-grade glioma, MAPK pathway-altered, three types of which are newly recognized tumor types. Herein, we review the clinical characteristics, histopathological and molecular genetic characteristics, neuroimaging features, and prognosis of pDLGG and summarize the neuroimaging key points in diagnosing different tumor types. This review aims to evaluate and update the relevant pDLGG features and advances in neuroimaging that may assist in differential diagnosis, surgery planning, and prognostic determination of these tumor types and provide accurate diagnostic information for clinical colleagues.

Polymorphous Low-Grade Neuroepithelial Tumor of the Young (PLNTY): A Newly Described Entity of Special Radiological Significance

Intracranial granulomas are a major cause of seizures in India, the most common etiologies being neurocysticercosis and tuberculosis. However, other pathologies including rare low-grade tumors may mimic these granulomas on imaging. In this article, we presented the case of a young woman patient with drug-resistant epilepsy. On imaging, there was a small calcified lesion in the brain parenchyma. In view of concordant electroclinical and imaging data on presurgical evaluation, the lesion was excised and the patient was seizure free. On histopathological evaluation, it was found to be a polymorphous low-grade neuroepithelial tumor of the young (PLNTY) - a rare, recently reported entity that can mimic an intracranial granuloma on imaging.

Adult-type and Pediatric-type Diffuse Gliomas : What the Neuroradiologist Should Know

The classification of diffuse gliomas into the adult type and the pediatric type is the new basis for the diagnosis and clinical evaluation. The knowledge for the neuroradiologist should not remain limited to radiological aspects but should be based additionally on the current edition of the World Health Organization (WHO) classification of tumors of the central nervous system (CNS). This classification defines the 11 entities of diffuse gliomas, which are included in the 3 large groups of adult-type diffuse gliomas, pediatric-type diffuse low-grade gliomas, and pediatric-type diffuse high-grade gliomas. This article provides a detailed overview of important molecular, morphological, and clinical aspects for all 11 entities, such as typical genetic alterations, age distribution, variability of the tumor localization, variability of histopathological and radiological findings within each entity, as well as currently available statistical information on prognosis and outcome. Important differential diagnoses are also discussed.

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.

Pediatric and elderly polymorphous low-grade neuroepithelial tumor of the young: Typical and unusual case reports and literature review

Polymorphous low-grade neuroepithelial tumor of the young (PLNTY), one of the pediatric-type diffuse low-grade gliomas, is characterized by a diffuse infiltrating pattern of oligodendroglioma-like tumor cells showing CD34 positivity and harbors mitogen-activated protein kinase (MAPK) alteration, such as vRAF murine sarcoma viral oncogene homolog B1 (BRAF) p.V600E or fibroblast growth factor fusion genetically. It occurs mainly in pediatric and adolescents with seizures due to the dominant location of the temporal lobe. However, there have been a few cases of PLNTY in adult patients, suggesting the wide range of this tumor spectrum. Here, we describe two cases of PLNTY, one in a 14-year-old female and the other in a 66-year-old female. The pediatric tumor showed typical clinical course and histopathology with BRAF p.V600E mutation, whereas the elderly tumor was unusual because of non-epileptic onset clinically and ependymal differentiation histopathologically harboring KIAA1549-BRAF fusion. There might be unusual but possible PLNTY, as in our elderly case. We also compared typical pediatric and unusual elderly tumors by reviewing the literature.

Pearls & Oy-sters: Salt and Pepper Sign, PLNTY for Drug-Resistant Epilepsy

Drug-resistant epilepsy, defined as the failure of 2 or more antiseizure medications to achieve seizure freedom, is responsible for 2/3 of epilepsy cases. Tumors are responsible for up to 15% of all adult onset and up to 6% of childhood onset epilepsies. Among these tumors, commonly known subtypes DNET, ganglioglioma, and low-grade astrocytoma are often suspected. New advances in tumor classification have been made, with genetics playing a key role in tumor classification. Polymorphic low-grade neuroepithelial tumor of the young (PLNTY) is a highly epileptogenic subtype of tumors that may mimic low-grade gliomas but offer pathologic and genetic clues: oligodendroglioma-like cellular components and infiltration patterns and strong CD34-immunopositive stain. In addition, a key finding is radiologic: a unifocal abnormality best seen on MRI brain in FLAIR sequence as the "salt and pepper sign" and calcifications appreciated on CT head.

Newly Recognized CNS Tumors in the 2021 World Health Organization Classification: Imaging Overview with Histopathologic and Genetic Correlation

In 2021, the World Health Organization released an updated classification of CNS tumors. This update reflects the growing understanding of the importance of genetic alterations related to tumor pathogenesis, prognosis, and potential targeted treatments and introduces 22 newly recognized tumor types. Herein, we review these 22 newly recognized entities and emphasize their imaging appearance with correlation to histologic and genetic features.

Radiological and surgical aspects of polymorphous low-grade neuroepithelial tumor of the young (PLNTY)

BACKGROUND

Polymorphous low-grade neuroepithelial tumor of the young (PLNTY) is a low-grade epilepsy-associated tumor recently introduced in WHO 2021 classification. Since it has been recognized as an independent nosological entity, PLNTY has been mainly studied from a genetic and molecular perspective, not recognizing unique characteristic clinical and radiological features.

METHODS

A systematic literature research has been conducted aiming to identify all relevant studies about the radiological, clinical and surgical features of PLNTY. We described a representative case of a 45-year-old man treated with awake-surgery with confirmed diagnosis of PLNTY, reporting the radiological and surgical characteristics through imaging and intra-operative video. We performed a statistical meta-analysis attempting to assess the presence of relationships between surgical and radiologic tumor characteristics and clinical outcome and type of surgery.

RESULTS

A total of 16 studies were included in the systematic review. The final cohort was composed of 51 patients. Extent of resection (EOR) and outcome are not significantly associated with the different genetic profiling (p = 1), the presence of cystic intralesional component, calcification (p = 0.85), contrast-enhancing and lesion boundaries (p = 0.82). No significant correlation there is between EOR and remission or better control of epilepsy-related symptoms (p = 0.38). The contrast enhancement in the tumor is significantly associated with recurrence or poor control of epileptic symptoms (p = 0.07).

CONCLUSIONS

In PLNTYs, contrast enhancement seems to impact prognosis, recurrence, and seizure control much more than radiological features, genetic features and type of resection of the tumor.

Changes to pediatric brain tumors in 2021 World Health Organization classification of tumors of the central nervous system

New tumor types are continuously being described with advances in molecular testing and genomic analysis resulting in better prognostics, new targeted therapy options and improved patient outcomes. As a result of these advances, pathological classification of tumors is periodically updated with new editions of the World Health Organization (WHO) Classification of Tumors books. In 2021, WHO Classification of Tumors of the Central Nervous System, 5^th edition (CNS5), was published with major changes in pediatric brain tumors officially recognized including pediatric gliomas being separated from adult gliomas, ependymomas being categorized based on anatomical compartment and many new tumor types, most of them seen in children. Additional general changes, such as tumor grading now being done within tumor types rather than across entities and changes in definition of glioblastoma, are also relevant to pediatric neuro-oncology practice. The purpose of this manuscript is to highlight the major changes in pediatric brain tumors in CNS5 most relevant to radiologists. Additionally, brief descriptions of newly recognized entities will be presented with a focus on imaging findings.

Atypical presentation of polymorphous low-grade neuroepithelial tumor of young (PLNTY): a case report

The polymorphous low-grade neuroepithelial tumor of young (PLNTY) is considered as one among the low-grade neuroepithelial tumor; as per WHO-2021 classification of Brain Tumors in the fifth edition. The term PLNTY was first coined by Huse in 2016. These morphologically variable tumors are characterized by their oligodendroglioma-like cellular components, infiltrative growth pattern, and Cluster of Differentiation 34 (CD34) immunopositivity. Frequent genetic abnormalities involving mitogen-activated protein kinase pathway constituents like the BRAF proto-oncogene or fibroblast growth receptor 2/3 are harbored by PLNTYs. Radiologically, these are found to be well-circumscribed lesions with calcified and cystic components, affecting primarily temporal lobes. Clinically, they present with seizures/epilepsy in young adults (< 30 years). In the present manuscript we are reporting a case of 37-year-old male, presenting with a gradually progressive headache for 6 months, found to have a left frontal multiloculated cystic lesion with dystrophic calcifications. Based on the distinctive histopathological feature of the oligodendroglioma-like infiltrative lesion showing CD34 immunopositivity, a diagnosis of a polymorphous low-grade neuroepithelial tumor of young was made.

Clinico-pathological and epigenetic heterogeneity of diffuse gliomas with FGFR3::TACC3 fusion

BACKGROUND

Gliomas with FGFR3::TACC3 fusion mainly occur in adults, display pathological features of glioblastomas (GB) and are usually classified as glioblastoma, IDH-wildtype. However, cases demonstrating pathological features of low-grade glioma (LGG) lead to difficulties in classification and clinical management. We report a series of 8 GB and 14 LGG with FGFR3:TACC3 fusion in order to better characterize them.

METHODS

Centralized pathological examination, search for TERT promoter mutation and DNA-methylation profiling were performed in all cases. Search for prognostic factors was done by the Kaplan-Meir method.

RESULTS

TERT promoter mutation was recorded in all GB and 6/14 LGG. Among the 7 cases with a methylation score > 0.9 in the classifier (v12.5), 2 were classified as glioblastoma, 4 as ganglioglioma (GG) and 1 as dysembryoplastic neuroepithelial tumor (DNET). t-SNE analysis showed that the 22 cases clustered into three groups: one included 12 cases close to glioblastoma, IDH-wildtype methylation class (MC), 5 cases each clustered with GG or DNET MC but none with PLNTY MC. Unsupervised clustering analysis revealed four groups, two of them being clearly distinct: 5 cases shared age (< 40), pathological features of LGG, lack of TERT promoter mutation, FGFR3(Exon 17)::TACC3(Exon 10) fusion type and LGG MC. In contrast, 4 cases shared age (> 40), pathological features of glioblastoma, and were TERT-mutated. Relevant factors associated with a better prognosis were age < 40 and lack of TERT promoter mutation.

CONCLUSION

Among gliomas with FGFR3::TACC3 fusion, age, TERT promoter mutation, pathological features, DNA-methylation profiling and fusion subtype are of interest to determine patients' risk.

Brain and Spinal Cord Tumors Among the Life-Threatening Health Problems: An Introduction

As one of the global concerns, cancers, including brain and spinal cord tumors, are responsible for mortalities and irreversible morbidities in the affected patients. Although advancements in molecular pathology and imaging of tumors may have influenced the incidence rate due to higher diagnosis in early stages, exposure to environmental risk factors could be another explanation for increased incidence of these tumors over the past decades. Similar to many other tumors, the CNS tumors begin in cellular dimension with activation of different molecular pathways. Several genetic, epigenetic, and immunologic pathways and processes are already discovered to play roles in pathophysiology of these tumors, which mostly will eventually become symptomatic. Each of these tumors may exhibit imaging characteristics, making it possible to list a series of differential diagnosis before histopathologic examination. Advances in molecular pathology have resulted in better understanding and categorization of CNS tumors, leading to better decision-making on the most appropriate therapeutic approach for each category, as well as proposing new therapeutic modalities to treat these tumors. As an introduction to the 2-volume book, this chapter addressed different types of human brain and spinal cord tumors based on the fifth version of WHO classification of CNS tumors.

The landscape of common genetic drivers and DNA methylation in low-grade (epilepsy-associated) neuroepithelial tumors: A review

Low-grade neuroepithelial tumors (LNETs) represent an important group of central nervous system neoplasms, some of which may be associated to epilepsy. The concept of long-term epilepsy-associated tumors (LEATs) includes a heterogenous group of low-grade, cortically based tumors, associated to drug-resistant epilepsy, often requiring surgical treatment. LEATs entities can sometimes be poorly discriminated by histological features, precluding a confident classification in the absence of additional diagnostic tools. This study aimed to provide an updated review on the genomic findings and DNA methylation profiling advances in LNETs, including histological entities of LEATs. A comprehensive search strategy was conducted on PubMed, Embase, and Web of Science Core Collection. High-quality peer-reviewed original manuscripts and review articles with full-text in English, published between 2003 and 2022, were included. Results were screened based on titles and abstracts to determine suitability for inclusion, and when addressed the topic of the review was screened by full-text reading. Data extraction was performed through a qualitative content analysis approach. Most LNETs appear to be driven mainly by a single genomic abnormality and respective affected signaling pathway, including BRAF p.V600E mutations in ganglioglioma, FGFR1 abnormalities in dysembryoplastic neuroepithelial tumor, MYB alterations in angiocentric glioma, BRAF fusions in pilocytic astrocytoma, PRKCA fusions in papillary glioneuronal tumor, between others. However, these molecular alterations are not exclusive, with some overlap amongst different tumor histologies. Also, clustering analysis of DNA methylation profiles allowed the identification of biologically similar molecular groups that sometimes transcend conventional histopathological classification. The exciting developments on the molecular basis of these tumors reinforce the importance of an integrative histopathological and (epi)genetic classification, which can be translated into precision medicine approaches.

The 2021 World Health Organization Classification of Tumors of the Central Nervous System: What Neuroradiologists Need to Know

Neuroradiologists play a key role in brain tumor diagnosis and management. Staying current with the latest classification systems and diagnostic markers is important to provide optimal patient care. Publication of the 2016 World Health Organization Classification of Tumors of the Central Nervous System introduced a paradigm shift in the diagnosis of CNS neoplasms. For the first time, both histologic features and genetic alterations were incorporated into the diagnostic framework, classifying and grading brain tumors. The newly published 2021 World Health Organization Classification of Tumors of the Central Nervous System, May 2021, 5th edition, has added even more molecular features and updated pathologic diagnoses. We present, summarize, and illustrate the most salient aspects of the new 5th edition. We have selected the key "must know" topics for practicing neuroradiologists.

Polymorphous low-grade neuroepithelial tumor of the young: Rare tumor and review of the literature

Polymorphous low-grade neuroepithelial tumor of the young (PLNTY) is a recently described low-grade neuroepithelial tumor with an infiltrative growth pattern and oligodendrocyte-like cells that are CD34 immunopositive. Correlating histology and results from molecular testing is critical to correctly diagnosing PLNTY, as its histologic appearance is similar to oligodendrogliomas and shares genetic abnormalities common to other low-grade epilepsy associated tumors (LEATs). In this case report, we describe a 31-year-old female with intractable epilepsy found to have a temporal mass and diagnosed with PLNTY after histopathologic and molecular testing. We describe the radiographic, histologic, and genetic features in relation to the epileptic and oncologic outcomes for this patient. Then, we compare these features and outcomes to other cases of PLNTY described in the literature.

Clinical, Radiological, Pathological Features and Seizure Outcome With Surgical Management of Polymorphous Low-Grade Neuroepithelial Tumor of the Young Associated With Epilepsy

Objective

Polymorphous low-grade neuroepithelial tumor of the young (PLNTY) is a novel distinct epileptogenic neoplasm, and its clinical, imaging, histopathological, and molecular features were already known in the existing literature. We aimed to analyze the surgical management of PLNTY combined with these known characteristics.

Methods

Eight patients underwent surgical treatment in our center between December 2017 and December 2020, and the postoperative pathology was diagnosed as PLNTY. Their clinical data, imaging, pathological, molecular characteristics, and seizure outcome were retrospectively analyzed. Follow-up evaluations and a literature review were performed.

Results

The 8 patients included 1 woman and 7 men, aged between 5 and 51 years old (mean = 31.6, median = 29). The preoperative symptoms of all 8 cases were seizures. Four tumors were situated in the temporal lobes, and one of the four extratemporal tumors was in the occipital lobe and three were in the frontal lobe. Enlarged and gross total resections were performed in 2 cases and the other 6 cases, respectively. All cases exhibited intense labeling of CD34, and absence of 1p/19q codeletion and IDH1 or IDH2 mutation. B-Raf proto-oncogene (BRAF) V600E mutation was presented in 4 (66.7%) of 6 detected cases. The postoperative seizure outcome of Engel class I was achieved in 6 cases (75%).

Conclusion

PLNTY represents distinctive histologic, immunophenotypic and biomolecular features, and has high epileptogenicity. Early surgical intervention and enlarged resection of PLNTY associated with epilepsy will help to improve the postoperative seizure-free rate.

Neuroradiological features of the polymorphous low-grade neuroepithelial tumor of the young: five new cases with a systematic review of the literature

PURPOSE

Polymorphous low-grade neuroepithelial tumors of the young (PLNTY) is a newly recognized brain tumor with genetic abnormalities frequently involving either BRAF or FGFR2/FGFR3. There are few publications available about the neuroradiological features of PLNTY. In this systematic review, we assessed the demographic, clinical, and neuroradiological features of PLNTY.

METHODS

Literature data were extracted from database searches in MEDLINE and SCOPUS databases up to June 10, 2021. Studies reporting on pathologically proven PLNTY with neuroradiological findings were included. After reviewing 103 abstracts, 9 articles encompassing 19 cases met the inclusion criteria. We also added five patients from our hospital. The correlations between the presence of "transmantle-like sign" and the following three factors: duration of seizures; tumor size; and pathologically proven cortical dysplasia, were examined.

RESULTS

The median patient age was 15.5 years (range, 5-57 years), and 15/24 (62.5%) were female. All tumors were localized supratentorialy. The main radiological features included cortical or subcortical masses (95.8%) in the temporal lobe (66.7%), calcification (83.3%), well-defined margins (72.7%), solid and cystic components (66.6%), and T2-weighted imaging (T2WI) hyperintensity (50.0%). The duration of seizure was significantly longer (positive vs. negative (median [range]), 24 months [6 - 96 months] vs. 5 months [1 - 12 months], p = 0.042), and the presence of the cortical dysplasia was significantly more frequent (3/8 vs 0/16, p = 0.042) in the patients with transmantle-like sign.

CONCLUSION

PLNTY typically represents a calcified, well-defined mass in the supratentorial cortical or subcortical regions. The radiological findings defined here could facilitate the diagnosis of PLNTY.

A "polymorphous low-grade neuroepithelial tumor of the young (PLNTY)" diagnosed in an adult. Report of a case and review of the literature

Background:

Polymorphous low-grade neuroepithelial tumor of the young (PLNTY) is a rare neuropathological entity, recently introduced in neuro-oncology. These tumors, histologically similar to oligodendrogliomas, cause epilepsy, occurring in children and young adults. Only few cases of PLNTY have been described in literature and all reported cases invariably focused on the onset of these tumors in children and young adults.

Case Description:

We report the case of a 50-year-old woman suffering from epilepsy since the 1^st year of her life. Computed tomography scan and magnetic resonance imaging of the brain documented the presence of a calcified mass involving left temporal lobe. The tumor was surgically excised and the histological examination showed a hypocellular and massively calcified neoplasm with morphological and immunohistochemical features consistent with the diagnosis of “PLNTY.”

Conclusion:

A review of the literature revealed that there are 31 cases of PLNTY reported in literature, most of which are children or young adults. The present case represents the second PLNTY diagnosed in a middle-aged adult to the best of our knowledge, suggesting that PLNTY should always be included in the differential diagnosis of low-grade brain tumors, also in adult patients.

Polymorphous Low-Grade Neuroepithelial Tumor of the Young (PLNTY): Molecular Profiling Confirms Frequent MAPK Pathway Activation

Polymorphous low-grade neuroepithelial tumor of the young (PLNTY) is a recently described epileptogenic tumor characterized by oligodendroglioma-like components, aberrant CD34 expression, and frequent mitogen-activated protein kinase (MAPK) pathway activation. We molecularly profiled 13 cases with diagnostic histopathological features of PLNTY (10 female; median age, 16 years; range, 5-52). Patients frequently presented with seizures (9 of 12 with available history) and temporal lobe tumors (9 of 13). MAPK pathway activating alterations were identified in all 13 cases. Fusions were present in the 7 youngest patients: FGFR2-CTNNA3 (n = 2), FGFR2-KIAA1598 (FGFR2-SHTN1) (n = 1), FGFR2-INA (n = 1), FGFR2-MPRIP (n = 1), QKI-NTRK2 (n = 1), and KIAA1549-BRAF (n = 1). BRAF V600E mutation was present in 6 patients (17 years or older). Two fusion-positive cases additionally harbored TP53/RB1 abnormalities suggesting biallelic inactivation. Copy number changes predominantly involving whole chromosomes were observed in all 10 evaluated cases, with losses of chromosome 10q occurring with FGFR2-KIAA1598 (SHTN1)/CTNNA3 fusions. The KIAA1549-BRAF and QKI-NTRK2 fusions were associated respectively with a 7q34 deletion and 9q21 duplication. This study shows that despite its name, PLNTY also occurs in older adults, who frequently show BRAF V600E mutation. It also expands the spectrum of the MAPK pathway activating alterations associated with PLNTY and demonstrates recurrent chromosomal copy number changes consistent with chromosomal instability.

BRAF V600E mutation mediates FDG-methionine uptake mismatch in polymorphous low-grade neuroepithelial tumor of the young

We present a case of a 14-year old boy with tumor-associated refractory epilepsy. Positron emission tomography imaging demonstrated a region with heterogeneous high ¹¹C-methionine uptake and a region with homogenous low ¹⁸F-fluorodeoxyglucose uptake within the tumor. Histopathological and genomic analyses confirmed the tumor as BRAF V600E-mutated polymorphous low-grade neuroepithelial tumor of the young (PLNTY). Within the high-methionine-uptake region, we observed increased protein levels of L-type amino acid transporter 1 (LAT1), a major transporter of methionine; c-Myc; and constituents of the mitogen-activated protein kinase (MAPK) pathway. We also found that LAT1 expression was linked to the BRAF V600E mutation and subsequent activation of MAPK signaling and c-Myc. Pharmacological and genetic inhibition of the MAPK pathway suppressed c-Myc and LAT1 expression in BRAF V600E-mutated PLNTY and glioblastoma cells. The BRAF inhibitor dabrafenib moderately suppressed cell viability in PLNTY. Collectively, our results indicate that BRAF V600E mutation-activated MAPK signaling and downstream c-Myc induces specific metabolic alterations in PLNTY, and may represent an attractive target in the treatment of the disease.

BRAF V600E mutation mediates FDG-methionine uptake mismatch in polymorphous low-grade neuroepithelial tumor of the young

We present a case of a 14-year old boy with tumor-associated refractory epilepsy. Positron emission tomography imaging demonstrated a region with heterogeneous high ¹¹C-methionine uptake and a region with homogenous low ¹⁸F-fluorodeoxyglucose uptake within the tumor. Histopathological and genomic analyses confirmed the tumor as BRAF V600E-mutated polymorphous low-grade neuroepithelial tumor of the young (PLNTY). Within the high-methionine-uptake region, we observed increased protein levels of L-type amino acid transporter 1 (LAT1), a major transporter of methionine; c-Myc; and constituents of the mitogen-activated protein kinase (MAPK) pathway. We also found that LAT1 expression was linked to the BRAF V600E mutation and subsequent activation of MAPK signaling and c-Myc. Pharmacological and genetic inhibition of the MAPK pathway suppressed c-Myc and LAT1 expression in BRAF V600E-mutated PLNTY and glioblastoma cells. The BRAF inhibitor dabrafenib moderately suppressed cell viability in PLNTY. Collectively, our results indicate that BRAF V600E mutation-activated MAPK signaling and downstream c-Myc induces specific metabolic alterations in PLNTY, and may represent an attractive target in the treatment of the disease.