DNA methylation-based classification of glioneuronal tumours synergises with histology and radiology to refine accurate molecular stratification.

AIMS: Glioneuronal tumours (GNTs) are poorly distinguished by their histology and lack robust diagnostic indicators. Previously, we showed that common GNTs comprise two molecularly distinct groups, correlating poorly with histology. To refine diagnosis, we constructed a methylation-based model for GNT classification, subsequently evaluating standards for molecular stratification by methylation, histology and radiology. METHODS: We comprehensively analysed methylation, radiology and histology for 83 GNT samples: a training cohort of 49, previously classified into molecularly defined groups by genomic profiles, plus a validation cohort of 34. We identified histological and radiological correlates to molecular classification and constructed a methylation-based support vector machine (SVM) model for prediction. Subsequently, we contrasted methylation, radiological and histological classifications in validation GNTs. RESULTS: By methylation clustering, all training and 23/34 validation GNTs segregated into two groups, the remaining 11 clustering alongside control cortex. Histological review identified prominent astrocytic/oligodendrocyte-like components, dysplastic neurons and a specific glioneuronal element as discriminators between groups. However, these were present in only a subset of tumours. Radiological review identified location, margin definition, enhancement and T2 FLAIR-rim sign as discriminators. When validation GNTs were classified by SVM, 22/23 classified correctly, comparing favourably against histology and radiology that resolved 17/22 and 15/21, respectively, where data were available for comparison. CONCLUSIONS: Diagnostic criteria inadequately reflect glioneuronal tumour biology, leaving a proportion unresolvable. In the largest cohort of molecularly defined glioneuronal tumours, we develop molecular, histological and radiological approaches for biologically meaningful classification and demonstrate almost all cases are resolvable, emphasising the importance of an integrated diagnostic approach.

Pediatric spinal pilocytic astrocytomas form a distinct epigenetic subclass from pilocytic astrocytomas of other locations and diffuse leptomeningeal glioneuronal tumours.

Pediatric spinal low-grade glioma (LGG) and glioneuronal tumours are rare, accounting for less 2.8-5.2% of pediatric LGG. New tumour types frequently found in spinal location such as diffuse leptomeningeal glioneuronal tumours (DLGNT) have been added to the World Health Organization (WHO) classification of tumours of the central nervous system since 2016, but their distinction from others gliomas and particularly from pilocytic astrocytoma (PA) are poorly defined. Most large studies on this subject were published before the era of the molecular diagnosis and did not address the differential diagnosis between PAs and DLGNTs in this peculiar location. Our study retrospectively examined a cohort of 28 children with LGGs and glioneuronal intramedullary tumours using detailed radiological, clinico-pathological and molecular analysis. 25% of spinal PAs were reclassified as DLGNTs. PA and DLGNT are nearly indistinguishable in histopathology or neuroradiology. 83% of spinal DLGNTs presented first without leptomeningeal contrast enhancement. Unsupervised t-distributed stochastic neighbor embedding (t-SNE) analysis of DNA methylation profiles showed that spinal PAs formed a unique methylation cluster distinct from reference midline and posterior fossa PAs, whereas spinal DLGNTs clustered with reference DLGNT cohort. FGFR1 alterations were found in 36% of spinal tumours and were restricted to PAs. Spinal PAs affected significantly younger patients (median age 2 years old) than DLGNTs (median age 8.2 years old). Progression-free survival was similar among the two groups. In this location, histopathology and radiology are of limited interest, but molecular data (methyloma, 1p and FGFR1 status) represent important tools differentiating these two mitogen-activated protein kinase (MAPK) altered tumour types, PA and DLGNT. Thus, these molecular alterations should systematically be explored in this type of tumour in a spinal location.

Atypical clinical presentation mimicking stroke in an adult patient caused by a rare diffuse leptomeningeal glioneuronal tumour.

A diffuse leptomeningeal glioneuronal tumours (DLGNT) are very rare tumours of the central nervous system, typically characterized by enhancement of subarachnoid space with cystic lesions, diffuse leptomeningeal infiltration, and no primary mass. We report an atypical clinical presentation of DLGNT. A 48-year-old male was admitted to hospital with symptoms of ischaemic stroke. Magnetic resonance imaging of the head revealed contrast enhancement of the meninges and other parts of the brain. A stereotactic frame biopsy was performed on the patient, which revealed the DLGNT. Diffuse leptomeningeal glioneuronal tumours are mostly seen in individuals less than 18 years old and are characterized by slow growth and low-grade histological appearance. Diffuse leptomeningeal glioneuronal tumours can be aggressive in adults.

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.

A case series of Diffuse Glioneuronal Tumours with Oligodendroglioma-like features and Nuclear Clusters (DGONC).

In this study, we report three paediatric cases of Diffuse Glioneuronal Tumours with Oligodendroglioma-like features and Nuclear Clusters (DGONC).

Operative Procedure in a Suprasellar Paediatric Lesion of the Optic Chiasm with Hydrocephalus Caused by a Papillary Glioneuronal Tumour.

INTRODUCTION: Paediatric tumours in the sellar and parasellar regions present clinical and surgical challenges due to anatomical position and behaviour. We illustrate a rare case which caused obstructive hydrocephalus. CASE PRESENTATION: The study included a 14-year-old girl with a glioneuronal tumour (40 mm) originating from the optic chiasm, obliterating the aqueduct, with consequent triventricular hydrocephalus. The patient underwent extended endoscopic endonasal surgery and repair of the skull-base deficiency using a multi-layer technique with fascia lata. The 12-month follow-up showed no complications or recurrences, with recovery in visual acuity. CONCLUSION: The immediate placement of external ventricular drainage, in combination with an extended trans-sphenoidal approach, is a safe and feasible option to treat suprasellar paediatric lesions with hydrocephalus.

Papillary glioneuronal tumor: a case report of the cerebral aqueduct and review of literature.

Papillary glioneuronal tumour is an entity described as grade I neuronal-glial tumour by the World Health Organization. Headaches, seizures, vomiting, language or visual disturbances, and hemiparesis are the most common clinical findings. This tumour typically presents as cystic with enhancing mural nodule in the cerebral hemisphere. In this paper, we reported a case of a papillary glioneuronal tumour in a young adult whose magnetic resonance imaging revealed a solid tumour in the cerebral aqueduct. The tumour was totally resected surgically 13 years ago. The histological and immunohistochemical examination determined the diagnosis. No further therapy was necessary. Currently, the patient presents no neurologic signs or symptoms and there is no radiologic evidence of tumour relapse. The case of papillary glioneuronal tumour reported here displayed unusual location and radiologic features. The long duration of follow-up of this case with no tumour relapse enhances that the preferred management for this type of tumour is its total surgical resection.

Diffuse glioneuronal tumour with oligodendroglioma-like features and nuclear clusters (DGONC) - a molecularly defined glioneuronal CNS tumour class displaying recurrent monosomy 14.

AIMS: DNA methylation-based central nervous system (CNS) tumour classification has identified numerous molecularly distinct tumour types, and clinically relevant subgroups among known CNS tumour entities that were previously thought to represent homogeneous diseases. Our study aimed at characterizing a novel, molecularly defined variant of glioneuronal CNS tumour. PATIENTS AND METHODS: DNA methylation profiling was performed using the Infinium MethylationEPIC or 450 k BeadChip arrays (Illumina) and analysed using the 'conumee' package in R computing environment. Additional gene panel sequencing was also performed. Tumour samples were collected at the German Cancer Research Centre (DKFZ) and provided by multinational collaborators. Histological sections were also collected and independently reviewed. RESULTS: Genome-wide DNA methylation data from >25 000 CNS tumours were screened for clusters separated from established DNA methylation classes, revealing a novel group comprising 31 tumours, mainly found in paediatric patients. This DNA methylation-defined variant of low-grade CNS tumours with glioneuronal differentiation displays recurrent monosomy 14, nuclear clusters within a morphology that is otherwise reminiscent of oligodendroglioma and other established entities with clear cell histology, and a lack of genetic alterations commonly observed in other (paediatric) glioneuronal entities. CONCLUSIONS: DNA methylation-based tumour classification is an objective method of assessing tumour origins, which may aid in diagnosis, especially for atypical cases. With increasing sample size, methylation analysis allows for the identification of rare, putative new tumour entities, which are currently not recognized by the WHO classification. Our study revealed the existence of a DNA methylation-defined class of low-grade glioneuronal tumours with recurrent monosomy 14, oligodendroglioma-like features and nuclear clusters.

Diffuse leptomeningeal glioneuronal tumour (DLGNT) with hydrocephalus as an initial symptom: a case-based update.

PURPOSE: Diffuse leptomeningeal glioneuronal tumour (DLGNT) is a rare disease classified in 2016. There are different views of the clinical, pathologic and neuroradiologic characteristics of DLGNT due to the minor studies on this disease. METHODS: We describe a case of a 12-year-old boy who initially presented intermittent headache, vomiting and communicating hydrocephalus. A literature review is also presented summarizing the clinical characteristics and treatments of DLGNT. RESULTS: In our case, a ventriculoperitoneal shunt was applied to reduce intracranial pressure caused by communicating hydrocephalus. T1-weighted contrast-enhanced magnetic resonance imaging (MRI) showed linear enhancement, and microscopy showed tumour-like spindle cells. The diagnosis of DLGNT was confirmed, and temozolomide was administered. The clinical characteristics were similar in the reported cases, while the treatments showed differences. CONCLUSION: Ventriculoperitoneal shunts are effective for patients with hydrocephalus-related intracranial hypertension. Chemotherapy including temozolomide has shown varying outcomes, and further studies are expected.

A germline variant of TP53 in paediatric diffuse leptomeningeal glioneuronal tumour.

PURPOSE: Diffuse leptomeningeal glioneuronal tumour (DLGNT) is an extremely rare tumour involving the neuroaxis. At present, its exact pathogenesis and associated factors remain incompletely characterised. Recent molecular investigations in a small cohort have offered some insights into this disease. However, the role of germline findings has not yet been fully explored in affected patients. The authors present a case of DLGNT, focusing on the clinical and molecular features with reference to current disease knowledge. METHODS: A 4-year-old male presented with raised intracranial pressure symptoms secondary to extensive leptomeningeal disease of the brain and spine. Preliminary impression was that of an inflammatory lesion. RESULTS: A lumbar biopsy of the lesion confirmed DLGNT on routine diagnostic examination. Further molecular analysis of his tumour and blood demonstrated a previously unreported TP53 exon 5 (c.147V > I) germline variant. Based on the latest DLGNT molecular subtyping classification, his tumour falls into the group with better clinical outcome. However, his germline findings may add an extra layer of uncertainty to his overall prognosis. CONCLUSION: Given that much remains unknown in many rare paediatric tumours at this stage, isolated findings found in an individual may be of significance. Supplementary genetic information, together with tumour molecular analysis, add to our current understanding of this uncommon disease. This case highlights the benefit of combined clinical and molecular efforts, including germline testing, especially for children affected by such challenging neoplasms.

Review: Molecular characteristics of long-term epilepsy-associated tumours (LEATs) and mechanisms for tumour-related epilepsy (TRE).

Brain tumours are the second most common cause of seizures identified in epilepsy surgical series. While any tumour involving the brain has the potential to cause seizures, specific subtypes are more frequently associated with epilepsy. Tumour-related epilepsy (TRE) has a profound impact on patients with brain tumours and these seizures are often refractory to anti-epileptic treatments, resulting in long-term disability and patient morbidity. Despite the drastic impact of epilepsy-associated tumours on patients, they have not traditionally enjoyed as much attention as more malignant neoplasms. However, recently a number of developments have been achieved towards further understanding of the molecular and developmental backgrounds of specific epilepsy-associated tumours. In addition, the past decade has seen an expansion in the literature on the pathophysiology of TRE. In this review, we aim to summarize the mechanisms by which tumours may cause seizures and detail recent data regarding the pathogenesis of specific developmental epilepsy-associated tumours.

Comprehensive molecular characterisation of epilepsy-associated glioneuronal tumours.

Glioneuronal tumours are an important cause of treatment-resistant epilepsy. Subtypes of tumour are often poorly discriminated by histological features and may be difficult to diagnose due to a lack of robust diagnostic tools. This is illustrated by marked variability in the reported frequencies across different epilepsy surgical series. To address this, we used DNA methylation arrays and RNA sequencing to assay the methylation and expression profiles within a large cohort of glioneuronal tumours. By adopting a class discovery approach, we were able to identify two distinct groups of glioneuronal tumour, which only partially corresponded to the existing histological classification. Furthermore, by additional molecular analyses, we were able to identify pathogenic mutations in BRAF and FGFR1, specific to each group, in a high proportion of cases. Finally, by interrogating our expression data, we were able to show that each molecular group possessed expression phenotypes suggesting different cellular differentiation: astrocytic in one group and oligodendroglial in the second. Informed by this, we were able to identify CCND1, CSPG4, and PDGFRA as immunohistochemical targets which could distinguish between molecular groups. Our data suggest that the current histological classification of glioneuronal tumours does not adequately represent their underlying biology. Instead, we show that there are two molecular groups within glioneuronal tumours. The first of these displays astrocytic differentiation and is driven by BRAF mutations, while the second displays oligodendroglial differentiation and is driven by FGFR1 mutations.

Rosette-forming glioneuronal tumour of the fourth ventricle. Not always a foreseeable development.

AIM OF THE STUDY: Rosette-forming glioneuronal tumour (RGNT) of the fourth ventricle is an uncommon tumour. The management is not consensual. Most of the published cases show stable outcome with and without gross total resection and are regarded as having a relatively indolent behaviour. MATERIAL AND METHODS: We present a 32-year-old man with a tumour in the fourth ventricle. He underwent midline suboccipital craniectomy with gross total removal. RESULTS: The histopathological diagnosis was RGNT grade I. Four years later he presented a radiological progression and received stereotactic radiosurgery. At the last follow-up seven years after surgery, the MRI showed no recurrence. CONCLUSIONS: RGNT should be considered in the differential diagnosis of a posterior fossa tumour and has to be differentiated from other lesions for its indolent course and favourable prognosis. Surgical procedures should be carefully performed to avoid serious surgical morbidities. Stereotactic radiosurgery treatment appears to be a useful treatment in recurrence episodes.

Imaging features of rosette-forming glioneuronal tumours (RGNTs): A Series of seven cases.

OBJECTIVE: Rosette-forming glioneuronal tumours (RGNTs) are a recently described, rare, distinct nosological entity of the glioneuronal family. We describe imaging findings (CT and MRI) in seven patients with RGNTs. MATERIALS AND METHODS: This retrospective study includes seven RGNT patients (4 male, 3 female; age range: 7-42 years; mean age: 25 years) diagnosed and treated at our institute. MR studies were performed on 3 T and 1.5-T clinical MR systems. All patients were reviewed by two experienced neuroradiologists and imaging findings were tabulated. RESULTS: Five tumours were located in the posterior fossa, and two were in the pineal region. One of the tumours demonstrated multiple satellite lesions, which involved the midbrain, pons, medulla as well as the cervical cord. Tumours located in the pineal region compressed the 3rd ventricle/aqueduct and extended below the tentorium cerebelli. All the tumours demonstrated enhancement, and susceptibility was evident in six of the seven patients. CSF dissemination was present in two patients. CONCLUSION: RGNTs are usually solid-cystic tumours and frequently demonstrate peripheral/heterogeneous enhancement upon post-contrast study. Haemorrhage is a common feature which may not be evident on CT. Cerebrospinal fluid (CSF) dissemination is a feature and appropriate imaging should be performed whenever an RGNT is suspected. KEY POINTS: CT and MRI findings of seven RGNT cases were retrospectively reviewed. RGNTs are predominantly posterior fossa tumours. RGNTs are typically T1 hypointense and T2 hyperintense. Haemorrhage and peripheral/heterogeneous enhancement are common features of RGNTs. CSF dissemination is a feature of RGNTs and requires appropriate imaging.

One case of myxoid glioneuronal tumour in the left frontal lobe.

Myxoid glioneuronal tumour (MGNT), previously described as dysembryoplastic neuroepithelial tumour of the septum pellucidum, was classified as a new tumour type in the fifth edition of the WHO Central Nervous System Tumor Classification of 2021. This classification was based on its anatomical location, imaging features, and genetic characteristics. MGNTs are clinically rare and prone to misdiagnosis. In this report, we present a case of MGNT in the left frontal lobe, which was confirmed through surgical pathology.

Enrichment of oligodendrocyte precursor phenotypes in subsets of low-grade glioneuronal tumours.

Current histological classification of low-grade glioneuronal tumours does not adequately represent their underlying biology. The neural lineage(s) and differentiation stage(s) involved and the cell state(s) affected by the recurrent genomic alterations are unclear. Here, we describe dysregulated oligodendrocyte lineage developmental programmes in three low-grade glioneuronal tumour subtypes. Ten dysembryoplastic neuroepithelial tumours, four myxoid glioneuronal tumours and five rosette-forming glioneuronal tumours were collected. Besides a comprehensive characterization of clinical features, known diagnostic markers and genomic alterations, we used comprehensive immunohistochemical stainings to characterize activation of rat sarcoma/mitogen-activated protein kinase pathway, involvement of neuronal component, resemblance to glial lineages and differentiation blockage along the stages of oligodendrocyte lineage. The findings were further complemented by gene set enrichment analysis with transcriptome data of dysembryoplastic neuroepithelial tumours from the literature. Dysembryoplastic neuroepithelial tumours, myxoid glioneuronal tumours and rosette-forming glioneuronal tumours occur at different ages, with symptoms closely related to tumour location. Dysembryoplastic neuroepithelial tumours and myxoid glioneuronal tumours contain oligodendrocyte-like cells and neuronal component. Rosette-forming glioneuronal tumours contained regions of rosette-forming neurocytic and astrocytic features. Scattered neurons, identified by neuronal nuclei antigen and microtubule-associated protein-2 staining, were consistently observed in all dysembryoplastic neuroepithelial tumours and myxoid glioneuronal tumours examined, but only in one rosette-forming glioneuronal tumour. Pervasive neurofilament-positive axons were observed only in dysembryoplastic neuroepithelial tumour and myxoid glioneuronal tumour samples. Alterations in B-Raf proto-oncogene, serine/threonine kinase, fibroblast growth factor receptor 1, fibroblast growth factor receptor 3 and platelet-derived growth factor receptor alpha occurred in a mutually exclusive manner, coinciding with strong staining of phospho-p44/42 mitogen-activated protein kinase and low apoptotic signal. All dysembryoplastic neuroepithelial tumours, myxoid glioneuronal tumours and the neurocytic regions of rosette-forming glioneuronal tumours showed strong expression of neuron-glia antigen 2, platelet-derived growth factor receptor alpha (markers of oligodendrocyte precursor cells) and neurite outgrowth inhibitor-A (a marker of developing oligodendrocytes), but lacked the expression of oligodendrocyte markers ectonucleotide pyrophosphatase/phosphodiesterase family member 6 and myelin basic protein. Notably, transcriptomes of dysembryoplastic neuroepithelial tumours were enriched in oligodendrocyte precursor cell signature, but not in signatures of neural stem cells, myelinating oligodendrocytes and astrocytes. Dysembryoplastic neuroepithelial tumour, myxoid glioneuronal tumour and rosette-forming glioneuronal tumour resemble oligodendrocyte precursor cells, and their enrichment of oligodendrocyte precursor cell phenotypes is closely associated with the recurrent mutations in rat sarcoma/mitogen-activated protein kinase pathway.

Application of multiplex ligation-dependent probe amplification (MLPA) and low pass whole genome sequencing (LP-WGS) to the classification / characterisation of low grade glioneuronal tumours.

AIMS: Glioneuronal tumours, although rare, are an important cause of treatment-resistant epilepsy. Differential diagnosis of glioneuronal tumour subtypes is complicated by their variable histological appearance and the lack of pathognomonic histological or molecular biomarkers. In this study we have applied techniques available in a diagnostic laboratory setting to characterise molecular and cytogenetic abnormalities in a single institution cohort of glioneuronal tumours. METHODS: A cohort of 29 glioneuronal tumours that included 21 gangliogliomas and 5 dysembryoplastic neuroepithelial tumours (DNETs) was analysed using low pass whole genome sequencing (WGS) and 2 multiplex ligation-dependent probe amplification (MLPA) central nervous system (CNS) tumour probesets. RESULTS: Low pass WGS identified chromosomal or subchromosomal alterations in 15 specimens. The most common chromosomal alterations were gains of chromosome 7 (n = 8) and chromosome 16 (n = 3). The BRAFV600E mutation was detected by MLPA in 9/21 (42.9%) gangliogliomas and 2/2 pleomorphic xanthoastrocytomas (PXAs). Chromosome 7 gains detected by WGS were reflected in MLPAs by overall gains of chromosome 7 gene probes, including those for BRAF, KIAA1549 and EGFR, while an internal BRAF/MKRN1 duplication was detected in a single ganglioglioma. Homozygous CDKN2A/B loss was detected by MLPA in 3 gangliogliomas, with p16 immunohistochemistry supporting these results. CONCLUSIONS: The combination of low pass WGS and MLPA identifies multiple, diverse genetic and chromosomal alterations in glioneuronal tumours, irrespective of histological tumour grade.

Diffuse Leptomeningeal Glioneuronal Tumour with 9-Year Follow-Up: Case Report and Review of the Literature.

In 2016, the World Health Organisation Classification (WHO) of Tumours was updated with diffuse leptomeningeal glioneuronal tumour (DLGNT) as a provisional unit of mixed neuronal and glial tumours. Here, we report a DLGNT that has been re-diagnosed with the updated WHO classification, with clinical features, imaging, and histopathological findings and a 9-year follow-up. A 16-year-old girl presented with headache, vomiting, and vertigo. Magnetic resonance imaging (MRI) demonstrated a hyperintense mass with heterogenous enhancement in the right cerebellopontine angle and internal auditory canal. No leptomeningeal involvement was seen. The histological examination revealed neoplastic tissue of moderate cellularity formed mostly by oligodendrocyte-like cells. Follow-up MRI scans demonstrated cystic lesions in the subarachnoid spaces in the brain with vivid leptomeningeal enhancement. Later spread of the tumour was found in the spinal canal. On demand biopsy samples were re-examined, and pathological diagnosis was identified as DLGNT. In contrast to most reported DLGNTs, the tumour described in this manuscript did not present with diffuse leptomeningeal spread, but later presented with leptomeningeal involvement in the brain and spinal cord. Our case expands the spectrum of radiological features, provides a long-term clinical and radiological follow-up, and highlights the major role of molecular genetic testing in unusual cases.

Diffuse leptomeningeal glioneuronal tumour (DLGNT) in children: the emerging role of genomic analysis.

Diffuse leptomeningeal glioneuronal tumours (DLGNT) represent rare enigmatic CNS tumours of childhood. Most patients with this disease share common radiological and histopathological features but the clinical course of this disease is variable. A radiological hallmark of this disease is widespread leptomeningeal enhancement that may involve the entire neuroaxis with predilection for the posterior fossa and spine. The classic pathologic features include low- to moderate-density cellular lesions with OLIG2 expression and evidence of 'oligodendroglioma-like' appearance. The MAPK/ERK signaling pathway has recently been reported as a potential driver of tumourigenesis in up to 80% of DLGNT with KIAA1549:BRAF fusions being the most common event seen. Until now, limited analysis of the biological drivers of tumourigenesis has been undertaken via targeted profiling, chromosomal analysis and immunohistochemistry. Our study represents the first examples of comprehensive genomic sequencing in DLGNT and shows that it is not only feasible but crucial to our understanding of this rare disease. Moreover, we demonstrate that DLGNT may be more genomically complex than single-event MAPK/ERK signaling pathway tumours.