Localized overexpression of alpha-internexin within nodules in multinodular and vacuolating neuronal tumors

Collision tumor: Multinodular and vacuolating neuronal tumor with isocitrate dehydrogenase-mutant diffuse astrocytoma

Herein, we report a case of a collision tumor involving a multinodular and vacuolating neuronal tumor (MVNT) and a diffuse astrocytoma. A collision tumor between these two entities has not previously been reported. The patient is a 35-year-old woman who presented with new-onset hearing loss and ringing in her right ear. Magnetic resonance imaging identified a non-enhancing mass involving the gray matter and subcortical white matter of the left middle frontal gyrus. Additionally, tiny clustered nodules were noted along the underlying subcortical ribbon and superficial subcortical white matter of the left superior frontal gyrus. The patient underwent a left frontal craniotomy and complete resection of the mass. Histologic examination of the resected specimen demonstrated a collision tumor consisting of a diffuse astrocytoma (isocitrate dehydrogenase [IDH] mutant, central nervous system [CNS] World Health Organization [WHO] grade 2) and an MVNT, with the latter demonstrating characteristic morphologic and immunohistochemical features.

Advanced multiparametric MRI and FDG-PET/CT in multinodular and vacuolating neuronal tumor: A pathologically confirmed case

Multinodular and vacuolating neuronal tumor (MVNT) is a relatively new disease concept proposed in 2013 and was classified as a separate tumor type in 2021 by the World Health Organization (WHO) classification. MVNT can cause seizures but is a benign disease, with no cases of enlargement or postoperative recurrence reported. Recent reports described advanced MRI features in MVNT cases, but the diagnosis of MVNT is usually based on characteristic MRI findings of clusters of nodules. Here, we report advanced multiparametric MRI and FDG-PET/CT findings in a case of MVNT with epileptiform symptoms that was pathologically confirmed by surgery.

Radiological and clinical features of multinodular and vacuolating neuronal tumor (MVNT)

Background

To investigate the imaging findings and clinical features of multinodular and vacuolating neuronal tumor (MVNT).

Methods

We retrospectively sought for cases that have suspicious imaging findings for MVNT through the hospital information system. The patients’ demographics and clinical symptoms were extracted. All available images were re-examined.

Results

Headache was the most common complaint (n = 7). Other complaints included seizure, stroke-like symptoms and numbness. Conventional MRI revealed that all lesions consisted of tiny, sharply marginated, round or ovoid nodules following the gyral contour. These nodules were hyperintense on T2 and FLAIR WI, hypointense on T1 WI. All lesions were characterized by a lack of enhancement and diffusion restriction. Mass effect and peripheral edema were not observed. MVNT presented as an incidental finding in one case who complained gynecomastia and had pituitary adenoma on pituitary MRI. All lesions were supratentorial—mostly on the right side (10/11)—and located in subcortical white matter. Follow-up MRI was available for 11 patients with a mean of 14.8 months (3–40 months). No change in lesion size and morphology was observed in these follow-up images.

Conclusions

Radiological and clinical follow-up data suggest MVNT may exhibit indolent behavior. If asymptomatic, patients can be followed by imaging alone. Surgery should be considered for symptomatic patients.

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.

Newly recognised Tumour Types in Glioneuronal tumours according to the 5th edition of the CNS WHO Classification

Glioneuronal tumours (GNT) are uncommon neoplasms, characterised by glial and neuronal differentiation.

In the 5th edition of the World Health Organization (WHO) Classification, they are grouped under the heading "Glioneuronal and neuronal tumours", which comprises fourteen different tumours, among which the diffuse glioneuronal tumour with oligodendroglioma-like cells and nuclear clusters (DGONC), myxoyd glioneuronal tumour (MGT) and multinodular and vacuolating neuronal tumour (MNVNT) are new types.

MGT and MNVNT are classified WHO grade 1 and may be recognised and diagnosed by peculiar clinical-pathological features. DGONC was not assigned a WHO grade and was only provisionally included among GNT, due to the possibility that it rather represents an embryonal tumour type or subtype. Although the histopathological characteristics may be useful for its identification, the specific methylation profile is an essential diagnostic criterion for DGONC.

Emerging glioneuronal and neuronal tumors: case-based review

Glioneuronal and neuronal tumors (GNTs) are rare heterogeneous central nervous system tumors characterized by slow growth and favorable outcomes, but are often associated with diagnostic difficulties. A thorough analysis of three rare and recently recognized GNTs was performed in the context of clinicopathological features and molecular genetic characterization. The current spinal diffuse leptomeningeal glioneuronal tumor (DLGNT) was characterized with oligodendroglioma-like tumor with chromosome 1p/19q codeletion without IDH mutations and KIAA1549:BRAF fusion. The current occipital multinodular and vacuolating neuronal tumor (MVNT) was characteristic of the variable-sized vague nodules consisted of gangliocytic tumor cells with intracytoplasmic and pericellular vacuolation and the next-generation sequencing (NGS) revealed MAP2K1 p.Q56_V60del. A diffuse glioneuronal tumor with oligodendroglioma-like features and nuclear clusters (DGONC) of the amygdala was characterized by oligodendroglia-like cells and nuclear clusters, and monosomy 14. From the current cases and literature review, we found that DLGNT commonly occurs in the spinal cord and can make mass and more commonly have KIAA1549:BRAF fusion; MVNT is a neoplasm rather than malformation and MAP2K1 deletion is one of the hallmarks of this tumor; although DGONC may require a methylation profile, we can reach a diagnosis through its unique histology, monosomy 14, and exclusion diagnosis without a methylation profile.

Neuropathology of the temporal lobe

Neuropathological examination of the temporal lobe provides a better understanding and management of a wide spectrum of diseases. We focused on inflammatory diseases, epilepsy, and neurodegenerative diseases, and highlighted how the temporal lobe is particularly involved in those conditions. Although all these diseases are not specific or restricted to the temporal lobe, the temporal lobe is a key structure to understand their pathophysiology. The main histological lesions, immunohistochemical markers, and molecular alterations relevant for the neuropathological diagnostic reasoning are presented in relation to epidemiology, clinical presentation, and radiological findings. The inflammatory diseases section addressed infectious encephalitides and auto-immune encephalitides. The epilepsy section addressed (i) susceptibility of the temporal lobe to epileptogenesis, (ii) epilepsy-associated hippocampal sclerosis, (iii) malformations of cortical development, (iv) changes secondary to epilepsy, (v) long-term epilepsy-associated tumors, (vi) vascular malformations, and (vii) the absence of histological lesion in some epilepsy surgery samples. The neurodegenerative diseases section addressed (i) Alzheimer's disease, (ii) the spectrum of frontotemporal lobar degeneration, (iii) limbic-predominant age-related TDP-43 encephalopathy, and (iv) α-synucleinopathies. Finally, inflammatory diseases, epilepsy, and neurodegenerative diseases are considered as interdependent as some pathophysiological processes cross the boundaries of this classification.

[Neuropathology of epilepsy]

The neuropathology of epilepsy aims at diagnosing the cerebral lesions underlying epilepsy that are obtained from epilepsy surgery, or rarely from biopsy or autopsy. The main histopathological and immunohistochemical characteristics of several entities are described: epilepsy-associated hippocampal sclerosis, long-term epilepsy-associated tumours, cortical malformations, vascular malformations, glial scars, encephalitides, and focal neuronal lipofuscinosis. The diagnostic approach, the differential diagnosis and the histochemical and immunohistochemical tools are detailed in order to provide the pathologist with a summarized toolkit to handle the broad range of epileptogenic lesions.

Multinodular and vacuolating neuronal tumor of the cerebrum: Two cases and review of the literature

BACKGROUND

Multinodular and vacuolating neuronal tumor (MVNT) recently described as a purely neuronal tumor. Although its nature as a genuine tumor is controversial, this new entity assumed benign lesion and mostly affecting adults. Herein, we introduce two cases of MVNT presumed low grade glial tumor (LGG) and focal cortical dyplasia (FCD) as a differential diagnosis.

CASE DESCRIPTION

Case 1 has admitted to our hospital with headache which frequency and severity has increased within two months. Radiological examination revealed hyperintensity on T2-WI and T2 FLAIR images. Microsurgical resection was performed and histopathological findings were compatible with MVNT instead of low grade glial tumor as we thought. Case 2, who presented at our hospital with one episode seizure. MRI showed T2 hyperintensity and T1 hypointensity without contrast enhancement. We suspected FCD, thus performed microsurgical gross total resection with frontal craniotomy. Pathological findings confirmed MVNT as a diagnosis. Both cases were discharged on the 3rd day after surgery without any complications and with no regrowth of tumor at the 9-months and 3-months follow-up respectively.

CONCLUSIONS

Radiological hallmarks may be helpful to prevent from aggressive treatment in case of patient is asemptomatic. Nevertheless further studies are necessary for the adoption of 'wait and see' philosophy and give a verdict about benign nature of these tumors.

cIMPACT-NOW update 6: new entity and diagnostic principle recommendations of the cIMPACT-Utrecht meeting on future CNS tumor classification and grading

cIMPACT-NOW (the Consortium to Inform Molecular and Practical Approaches to CNS Tumor Taxonomy) was established to evaluate and make practical recommendations on recent advances in the field of CNS tumor classification, particularly in light of the rapid progress in molecular insights into these neoplasms. For Round 2 of its deliberations, cIMPACT-NOW Working Committee 3 was reconstituted and convened in Utrecht, The Netherlands, for a meeting designed to review putative new CNS tumor types in advance of any future World Health Organization meeting on CNS tumor classification. In preparatory activities for the meeting and at the actual meeting, a list of possible entities was assembled and each type and subtype debated. Working Committee 3 recommended that a substantial number of newly recognized types and subtypes should be considered for inclusion in future CNS tumor classifications. In addition, the group endorsed a number of principles-relating to classification categories, approaches to classification, nomenclature, and grading-that the group hopes will also inform the future classification of CNS neoplasms.

Multinodular and vacuolating neuronal tumor associated with focal cortical dysplasia in a child with refractory epilepsy: a case report and brief review of literature

Multinodular and vacuolating neuronal tumor (MVNT) is a rare newly identified benign lesion, firstly included in the World Health Organization classification of tumors of the central nervous system in 2016, whose neoplastic or dysplastic nature remains unclear but with a distinctive cytoarchitectural pattern and radiological features. It is usually discovered as late-onset refractory epilepsy, headache related, or an incidental lesion of adulthood. As it is typically a stable disease, many opt for follow-up, as long as it keeps remaining asymptomatic, leaving surgery for refractory epilepsy, neurological deficits, or intracranial hypertension symptoms. A subtotal or complete resection seems to control seizures and neurological manifestations. We herein present the case of a child with refractory epilepsy related to MVNT and focal cortical dysplasia, a dual pathology case in a less frequent age group and without the typical radiological imaging. We report its radiologic features, histologic description, and management, and we present a brief literature review on MVNT focusing on the pediatric cases reported. MVNT should now be another probable low-grade epilepsy-associated lesion (LEAT) in patients of all ages, with a benign and stable course as it constitutes a curable cause of focal epilepsy. As all the refractory cases, surgery should be indicated after a comprehensive evaluation of a multidisciplinary epilepsy surgery team.

Advanced multiparametric magnetic resonance imaging of multinodular and vacuolating neuronal tumor

BACKGROUND AND PURPOSE

Multinodular and vacuolating neuronal tumor (MVNT) of the cerebrum is a rare brain lesion with suggestive imaging features. The aim of our study was to report the largest series of MVNTs so far and to evaluate the utility of advanced multiparametric magnetic resonance (MR) techniques.

METHODS

This multicenter retrospective study was approved by our institutional research ethics board. From July 2014 to May 2019, two radiologists read in consensus the MR examinations of patients presenting with a lesion suggestive of an MVNT. They analyzed the lesions' MR characteristics on structural images and advanced multiparametric MR imaging.

RESULTS

A total of 64 patients (29 women and 35 men, mean age 44.2 ± 15.1 years) from 25 centers were included. Lesions were all hyperintense on fluid-attenuated inversion recovery and T2-weighted imaging without post-contrast enhancement. The median relative apparent diffusion coefficient on diffusion-weighted imaging was 1.13 [interquartile range (IQR), 0.2]. Perfusion-weighted imaging showed no increase in perfusion, with a relative cerebral blood volume of 1.02 (IQR, 0.05) and a relative cerebral blood flow of 1.01 (IQR, 0.08). MR spectroscopy showed no abnormal peaks. Median follow-up was 2 (IQR, 1.2) years, without any changes in size.

CONCLUSIONS

A comprehensive characterization protocol including advanced multiparametric magnetic resonance imaging sequences showed no imaging patterns suggestive of malignancy in MVNTs. It might be useful to better characterize MVNTs.

Magnetic resonance imaging findings of two cases with multinodular and vacuolating neuronal tumor

Multinodular and vacuolating neuronal tumors (MVNT) are low grade neuronal tumors classified in cerebral tumors based on 2016 WHO central nerve system classification. Previously, MVNTs were probably tumors incidentally determined by imaging methods, but they could not be diagnosed or they were misdiagnosed. Two cases are reported in the present study, for which radiological imaging was carried out for epilepsy in one and for headache in the other. The first case was a twenty seven years old female patient with headache complaint. Brain MRI examination revealed a clustering lesion of multinodular character located in an about 4.0 × 3.5 × 1.5 cm area which had a left precuneal subcortical-juxtacortical location. The other case was a male patient with epilepsy. A clustering lesion of multinodular nature was determined in an area of about 2.0 × 2.0 × 1.5 cm in cortical-subcortical area in corona radiata-convexity plane of right middle frontal girus. No changes in size or nature were determined in follow-up examinations. MVNTs are recently defined tumors, and the characteristic feature for diagnosis of these rare tumor entities could be a subcortical white matter lesion with satellite nodules that manifest itself as T2/FLAIRhyperintensity. Increasing number of case reports and studies in the literature could make the radiological and pathological signs of the condition clearer.

Clinicopathological and molecular analysis of multinodular and vacuolating neuronal tumors of the cerebrum

Multinodular and vacuolating neuronal tumor (MVNT) of the cerebrum is a recently recognized rare neuronal tumor, and its pathogenesis is unclear. We analyzed 7 cases of histologically typical MVNT: 6 were adults (mean age, 43.0 years [range, 23-56 years]) and 1 was a child (age, 10 years). The most common symptoms were seizures (n = 4) and headache (n = 2). The tumors were supratentorial (temporal, 5; frontal lobes, 2) in origin as reported. Vacuolated tumor cells were robustly positive for α-INA and Olig2 and at least partly positive for synaptophysin and MAP2, but negative for Neu-N, nestin and CD34. GFAP and vimentin were expressed in reactive astrocytes but not in tumor cells. Negative results were obtained for p53, IDH-1, BRAF^V600E, H3 K27M, EGFR, Lin28A, and L1CAM. ATRX, BRG1, INI-1, and TMHH were retained. The Ki-67 labeling index was very low (<1%), and pHH3 revealed no mitotic figure. Ultrastructural features of tumor cells were comparable with those of immature neuronal cells, with several intracytoplasmic myelin-like autophagosomes and pericellular vacuolization. No IDH1/IDH2 and BRAF^V600E mutations were found upon direct sequencing. Whole-exome sequencing revealed FGFR2-ZMYND11 gene fusion in 1 case. After gross total resection, all patients were alive without seizures. There was no tumor recurrence during an average period of 68 months (range, 23-101 months). The analysis of 7 typical cases of MVNT suggested that these lesions may be clonal tumors because FGFR2-ZMYND11 fusion was found (1 case).

Multinodular and vacuolating neuronal tumor incidentally discovered in a young man: Conventional and advanced MRI features

Multinodular and Vacuolating Neuronal Tumor (MVNT) has been included in the most recent (2016) World Health Organization Classification of Tumors of the Central Nervous System as unique cytoarchitectural pattern of gangliocytoma. We present a case of a MVNT incidentally discovered in a 22-year old male, who presented with seizures after a head injury. Conventional MRI revealed a left parietal lesion with characteristic tiny, coalescent, well-defined, non-enhancing nodules, located in the juxtacortical white matter with partial involvement of an otherwise normal adjacent cortex and characterized by slight relative increase of the cerebral blood volume (CBV), compared to the contralateral white matter (lesional CBV/contralateral CBV = 1.112) and mild increase of choline and reduction of NAA (lesional choline/creatine ratio =1.36 and choline/NAA ratio=0.77, compared to 0.87 and 0.51, respectively). The patient fully responded to treatment with phenytoin and a follow-up MRI, six months later, showed the lesion without any substantial difference.

New clinicopathological associations and histoprognostic markers in ILAE types of hippocampal sclerosis

Mesial temporal lobe epilepsy with hippocampal sclerosis (MTLE-HS) is a heterogeneous syndrome. Surgery results in seizure freedom for most pharmacoresistant patients, but the epileptic and cognitive prognosis remains variable. The 2013 International League Against Epilepsy (ILAE) histopathological classification of hippocampal sclerosis (HS) has fostered research to understand MTLE-HS heterogeneity. We investigated the associations between histopathological features (ILAE types, hypertrophic CA4 neurons, granule cell layer alterations, CD34 immunopositive cells) and clinical features (presurgical history, postsurgical outcome) in a monocentric series of 247 MTLE-HS patients treated by surgery. NeuN, GFAP and CD34 immunostainings and a double independent pathological examination were performed. 186 samples were type 1, 47 type 2, 7 type 3 and 7 samples were gliosis only but no neuronal loss (noHS). In the type 1, hypertrophic CA4 neurons were associated with a worse postsurgical outcome and granule cell layer duplication was associated with generalized seizures and episodes of status epilepticus. In the type 2, granule cell layer duplication was associated with generalized seizures. CD34+ stellate cells were more frequent in the type 2, type 3 and in noHS. These cells had a Nestin and SOX2 positive, immature neural immunophenotype. Patients with nodules of CD34+ cells had more frequent dysmnesic auras. CD34+ stellate cells in scarce pattern were associated with higher ratio of normal MRI and of stereo-electroencephalographic studies. CD34+ cells were associated with a trend for a better postsurgical outcome. Among CD34+ cases, we proposed a new entity of BRAF V600E positive HS and we described three hippocampal multinodular and vacuolating neuronal tumors. To conclude, our data identified new clinicopathological associations with ILAE types. They showed the prognostic value of CA4 hypertrophic neurons. They highlighted CD34+ stellate cells and BRAF V600E as biomarkers to further decipher MTLE-HS heterogeneity.

Multinodular and vacuolating neuronal tumor: A case report and literature review

Background:

Multinodular and vacuolated neuronal tumor (MVNT) is a benign neuronal tumor that is newly recognized as architectural appearance that may be related to ganglion cell tumors in 2016 World Health Organization Classification of Tumors of the Central Nervous System. Herein, we report a case of MVNT in a 60-year-old man with a thorough literature review.

Case Description:

A 60-year-old male was pointed out the presence of intracerebral neoplasm located in left frontal lobe by a comprehensive medical examination. We suspected dysembryoplastic neuroepithelial tumors and proposed him to wait and see, but he wished to undergo surgery for diagnosis. We performed en bloc resection and pathological findings were consistent with MVNT. He was discharged on the 8^th day after the operation without any complications. He remained stable without recurrence at the 16-month postoperative follow-up.

Conclusions:

Further studies may be helpful to fully understand the radiological and histological findings of MVNT development. As a result, we will be able to prevent the aggressive treatment if we established their major features.

Multinodular and vacuolating neuronal tumors in epilepsy: dysplasia or neoplasia?

Multinodular and vacuolating neuronal tumor (MVNT) is a new pattern of neuronal tumour included in the recently revised WHO 2016 classification of tumors of the CNS. There are 15 reports in the literature to date. They are typically associated with late onset epilepsy and a neoplastic vs. malformative biology has been questioned. We present a series of ten cases and compare their pathological and genetic features to better characterized epilepsy‐associated malformations including focal cortical dysplasia type II (FCDII) and low‐grade epilepsy‐associated tumors (LEAT). Clinical and neuroradiology data were reviewed and a broad immunohistochemistry panel was applied to explore neuronal and glial differentiation, interneuronal populations, mTOR pathway activation and neurodegenerative changes. Next generation sequencing was performed for targeted multi‐gene analysis to identify mutations common to epilepsy lesions including FCDII and LEAT. All of the surgical cases in this series presented with seizures, and were located in the temporal lobe. There was a lack of any progressive changes on serial pre‐operative MRI and a mean age at surgery of 45 years. The vacuolated cells of the lesion expressed mature neuronal markers (neurofilament/SMI32, MAP2, synaptophysin). Prominent labelling of the lesional cells for developmentally regulated proteins (OTX1, TBR1, SOX2, MAP1b, CD34, GFAPδ) and oligodendroglial lineage markers (OLIG2, SMI94) was observed. No mutations were detected in the mTOR pathway genes, BRAF, FGFR1 or MYB. Clinical, pathological and genetic data could indicate that MVNT aligns more with a malformative lesion than a true neoplasm with origin from a progenitor neuro‐glial cell type showing aberrant maturation.

Multinodular and Vacuolating Neuronal Tumor of the Cerebrum: A New "Leave Me Alone" Lesion with a Characteristic Imaging Pattern

Multinodular and vacuolating neuronal tumor of the cerebrum is a recently reported benign, mixed glial neuronal lesion that is included in the 2016 updated World Health Organization classification of brain neoplasms as a unique cytoarchitectural pattern of gangliocytoma. We report 33 cases of presumed multinodular and vacuolating neuronal tumor of the cerebrum that exhibit a remarkably similar pattern of imaging findings consisting of a subcortical cluster of nodular lesions located on the inner surface of an otherwise normal-appearing cortex, principally within the deep cortical ribbon and superficial subcortical white matter, which is hyperintense on FLAIR. Only 4 of our cases are biopsy-proven because most were asymptomatic and incidentally discovered. The remaining were followed for a minimum of 24 months (mean, 3 years) without interval change. We demonstrate that these are benign, nonaggressive lesions that do not require biopsy in asymptomatic patients and behave more like a malformative process than a true neoplasm.

The 2016 WHO Classification of Tumours of the Central Nervous System: The Major Points of Revision

The updated 2016 edition of the World Health Organization (WHO) Classification of Tumours of the Central Nervous System (CNS) uses molecular parameters and the histology to define the main tumor categories for the first time. This represents a shift from the traditional principle of using neuropathological diagnoses, which are primarily based on the microscopic features, to using molecularly-oriented diagnoses. Major restructuring was made with regard to diffuse gliomas, medulloblastomas and other embryonal tumors. New entities that are defined by both the histological and molecular features include glioblastoma, isocitrate dehydrogenase (IDH)-wildtype and glioblastoma, IDH-mutant; diffuse midline glioma, H3 K27M-mutant; RELA fusion-positive ependymoma; medulloblastoma, wingless (WNT)-activated and medulloblastoma, sonic hedgehog (SHH)-activated; and embryonal tumor with multilayered rosettes, C19MC-altered. In addition, some entities that are no longer diagnostically relevant—such as CNS-primitive neuroectodermal tumor—have been deleted from this updated edition. The WHO2016 certainly facilitates clinical and basic research to improve the diagnosis of brain tumors and patient care.

Low-grade epilepsy-associated neuroepithelial tumours - the 2016 WHO classification

Rapid developments in molecular genetic technology and research have swiftly advanced our understanding of neuro-oncology. As a consequence, the WHO invited their expert panels to revise the current classification system of brain tumours and to introduce, for the first time, a molecular genetic approach for selected tumour entities, thus setting a new gold standard in histopathology. The revised 5th edition of the 'blue book' was released in May 2016 and will have a major impact in stratifying diagnosis and treatment. However, low-grade neuroepithelial tumours that present with early-onset focal epilepsy and are mostly seen in children and young adults (previously designated as long-term epilepsy-associated neuroepithelial tumours, LEAT) lack such innovative clinicopathological and molecular genetic tools. The Neuropathology Task Force of the International League against Epilepsy will critically discuss this issue, and will offer perspectives on how to decipher and validate clinically meaningful LEAT entities using the current WHO approach that integrates clinicopathological and genetic classification systems.