E-cadherin expression and gene expression profiles in corticotroph pituitary neuroendocrine tumor subtypes.

Corticotroph adenomas/pituitary neuroendocrine tumors (PitNETs) are associated with significant morbidity and mortality. Predictors of tumor behavior have not shown high prognostic accuracy. For somatotroph adenomas/PitNETs, E-cadherin expression correlates strongly with prognosis. E-cadherin expression has not been investigated in other PitNETs. A retrospective chart review of adults with corticotroph adenomas/PitNETs was conducted to assess correlation between E-cadherin expression and tumor characteristics. In addition, gene expression microarray was performed in subset of tumors (n = 16). Seventy-seven patients were identified; 71% were female, with median age of cohort 45.2 years. Seventy-five percent had macroadenomas, of which 22% were hormonally active. Ninety-five percent of microadenomas were hormonally active. Adrenocorticotropic hormone granulation pattern by IHC identified 63% as densely granulated (DG) and 34% as sparsely granulated (SG). All microadenomas were DG (p < .001); 50% of macroadenomas were DG associated with increased tumor invasion compared to SG. E-cadherin IHC was positive in 80%, diminished in 17%, and absent in 20% and did not correlate with corticotroph PitNETs subtype, size, or prognosis. In contrast to the distinct transcriptomes of corticotroph PitNETs and normal pituitaries, a comparison of clinically active and silent corticotroph PitNETs demonstrated similar molecular signatures indicating their common origin, but with unique differences related to their secretory status.

Histological and neuroimaging comparison of SMART syndrome versus focal neuronal gigantism.

Two of the rarest radiation-induced adverse effects are focal neuronal gigantism (FNG) and SMART syndrome (stroke-like migraine attacks after radiation therapy). Both conditions develop years, and sometimes decades, after receipt of therapeutic radiation to the brain. To date, there are only 3 previously reported cases of FNG, all of which describe cortical thickening, enlarged "hypertrophic" neurons, and neuronal cytological changes. No detailed studies exist of histological features of SMART or the comparison between FNG and SMART. In this study, we contrast histological and neuroimaging features of 3 FNG vs. 4 SMART cases, the latter diagnosed by a neuroradiologist, neurooncologist, and/or neurosurgeon. We confirm the cortical thickening, dyslamination, neuronal cytomegaly, and gliosis in FNG vs. cortical architectural preservation and normal neuronal cytology in SMART, although both showed gliosis, scattered neurons with cytoplasmic accumulation of tau and neurofibrillary protein and variable co-existence of other radiation-induced lesions. Both conditions lacked significant inflammation or consistent small vessel hyalinization throughout the entire resection specimen. The absence of pathognomonic histologic alterations in SMART cases suggests underlying vascular dysregulation. Despite differing histology, some overlap may exist in neuroimaging features. Molecular assessment conducted in 2 cases of FNG was negative for significant alterations including in the MAPK pathway.

Leptomeningeal metastases and dural spread in adult high-grade astrocytomas.

Leptomeningeal (LM) metastases or dural spread by adult high-grade astrocytomas are problematic; it is unclear which tumor types are predisposed to spread and at what time intervals from original diagnosis. We reviewed our recent experience with these tumor types with LM or dural spread, all of which had assessments that allowed CNS World Health Organization, 5th Edition classification. Following a database search, 2018-present, 10 patients were identified: 4 glioblastomas, IDH-wildtype, WHO grade 4; 4 astrocytomas, IDH-mutant, WHO grade 4; 1 high-grade astrocytoma with piloid features (HGAP) proven by DNA methylation, and 1 high-grade astrocytic tumor that fell closest to the HGAP category by DNA methylation. Most had LM dissemination; 2 had dural spread. Intervals from initial tumor diagnosis to LM spread for 4 astrocytomas, IDH-mutant were 1, 6, 7, and 14 years. Two glioblastomas, IDH-wildtype had dural spread at the time of diagnosis; 1 had a 6-year interval to metastasis; and 1 had a 3-month interval to LM spread. The definite HGAP showed an interval of 7 years to metastasis and the possible HGAP had LM spread recognized at the time of initial diagnosis. All adult high-grade astrocytic tumor types are capable of LM or dural spread, including HGAP.

Some CNS sarcomas seen: A 22-year series.

AIMS: Central nervous system (CNS) and spine are seldom impacted by primary or metastatic sarcomas. We reviewed our 22-year experience with metastatic versus primary mesenchymal sarcomas in adults versus pediatric patients, additionally asking how many might today undergo nomenclature changes using CNS World Health Organization, 5th edition criteria. MATERIALS AND METHODS: Case identification via text word search of pathology databases from our adult and pediatric referral hospitals, 2000 to August 2022, with exclusion of peripheral nervous system and primary chondro-osseous and notochordal tumors. Demographic, immunohistochemical, fluorescence in situ hybridization (FISH), and fusion results performed at the time of original diagnosis were acquired from reports. RESULTS: 57 cases were identified, with a 16 : 15 primary and 19 : 7 metastatic ratio in adult versus pediatric patients. Ewing sarcoma was the most frequent type (n = 18, 7 adult, 11 pediatric), with a rare primary PEComa, 2 alveolar soft part sarcomas, and metastatic angiosarcoma in the cohort. Only 3 cases, an intracranial sarcoma, DICER-1 mutant formerly diagnosed as rhabdomyosarcoma, an intracranial mesenchymal tumor, FET::CREB fusion-positive formerly diagnosed as angiomatoid fibrous histiocytoma, and a CIC-rearranged sarcoma required nomenclature updating by CNS WHO5 criteria. CONCLUSIONS: Few primary or metastatic, adult or pediatric, CNS/spinal sarcomas required nomenclature updates; almost all had been satisfactorily classified at the time of diagnosis, using immunohistochemistry, FISH, or fusion results.

Childhood Small-Vessel Primary Angiitis of the Central Nervous System: Overlap With MOG-Associated Disease.

BACKGROUND: Childhood (c) primary angiitis of the central nervous system (PACNS) is a rare condition that most often affects small vessels (SV), is nearly exclusively lymphocytic, and devoid of vessel necrosis. Diagnosis of cSV-PACNS is challenging. We noted possible histological overlap of cSV-PACNS with myelin oligodendrocyte glycoprotein disease (MOGAD) on biopsy, prompting a 10-year retrospective review of our experience. MATERIALS AND METHODS: Database-search for brain biopsy cases, age <18 years, performed for an acquired neurological deficit with suspicion of vasculitis, with histological evidence of lymphocytic small-vessel inflammation. RESULTS: We identified 7 patients; 2/7 were serum-positive for anti-MOG antibodies and 1/7 for anti-NMDA antibodies. The remaining 4/7 proved to be idiopathic lymphocytic vasculitis/cSV-PACNS. All 7 showed overlapping features of lymphocytes permeating parenchymal SV walls, vessel wall distortion without fibrinoid necrosis, and absence of microglial clusters or intravascular thrombi. Tissue infarction was confined to a single case of idiopathic lymphocytic vasculitis. Although demyelination was diligently sought, only subtle demyelination was identified in the 2 MOGAD cases and absent in the remainder. CONCLUSION: There is considerable histological overlap between cSV-PACNS and at least some cases of MOGAD or anti-NMDA-encephalitis; at diagnosis, the differential should include cSV-PACNS but correct classification requires post-biopsy serological testing.

Cerebral amyloidomas: Perspective on unusual morphological features.

AIMS: Cerebral amyloidomas (CAs) are mass-producing congophilic lesions most commonly due to λ light chain deposits, contrasting them with light chain deposition disease (LCDD) which has non-polarizable, often κ light chain deposition. MATERIALS AND METHODS: Although usual histological features are well known, we detail 3 recent CAs with unusual morphological findings and review the literature specifically for these features. RESULTS: Two women, aged 56 and 58 years, had right cerebral white matter CAs. The biopsy of case 1 disclosed congophilic polarizable deposits with prominent dystrophic mineralization as well as scant plasma cells. Case 2 had a CA with significant multinucleated giant cell reaction to the amyloid and additionally contained an area suspicious for marginal zone B-cell lymphoma. Case 3 was a clinically unsuspected CA identified at autopsy in a 75-year-old woman that manifested as several contiguous left frontal lobe white matter erythematous, hyperemic lesions; microscopy showed nodular and concentric amyloid deposits and thick perivascular cuffs of plasma cells. Mass spectrometry proved λ light and α heavy chain amyloid deposits in all 3 cases. CONCLUSION: These 3 CA cases illustrate several unusual gross and microscopic features that are discussed in context with the literature.

Intracranial mesenchymal tumors with FET-CREB fusion are composed of at least two epigenetic subgroups distinct from meningioma and extracranial sarcomas.

'Intracranial mesenchymal tumor, FET-CREB fusion-positive' occurs primarily in children and young adults and has previously been termed intracranial angiomatoid fibrous histiocytoma (AFH) or intracranial myxoid mesenchymal tumor (IMMT). Here we performed genome-wide DNA methylation array profiling of 20 primary intracranial mesenchymal tumors with FET-CREB fusion to further study their ontology. These tumors resolved into two distinct epigenetic subgroups that were both divergent from all other analyzed intracranial neoplasms and soft tissue sarcomas, including meningioma, clear cell sarcoma of soft tissue (CCS), and AFH of extracranial soft tissue. The first subgroup (Group A, 16 tumors) clustered nearest to but independent of solitary fibrous tumor and AFH of extracranial soft tissue, whereas the second epigenetic subgroup (Group B, 4 tumors) clustered nearest to but independent of CCS and also lacked expression of melanocytic markers (HMB45, Melan A, or MITF) characteristic of CCS. Group A tumors most often occurred in adolescence or early adulthood, arose throughout the neuroaxis, and contained mostly EWSR1-ATF1 and EWSR1-CREB1 fusions. Group B tumors arose most often in early childhood, were located along the cerebral convexities or spinal cord, and demonstrated an enrichment for tumors with CREM as the fusion partner (either EWSR1-CREM or FUS-CREM). Group A tumors more often demonstrated stellate/spindle cell morphology and hemangioma-like vasculature, whereas Group B tumors more often demonstrated round cell or epithelioid/rhabdoid morphology without hemangioma-like vasculature, although robust comparison of these clinical and histologic features requires future study. Patients with Group B tumors had inferior progression-free survival relative to Group A tumors (median 4.5 vs. 49 months, p = 0.001). Together, these findings confirm that intracranial AFH-like neoplasms and IMMT represent histologic variants of a single tumor type ('intracranial mesenchymal tumor, FET-CREB fusion-positive') that is distinct from meningioma and extracranial sarcomas. Additionally, epigenomic evaluation may provide important prognostic subtyping for this unique tumor entity.

Genetic and epigenetic characterization of posterior pituitary tumors.

Pituicytoma (PITUI), granular cell tumor (GCT), and spindle cell oncocytoma (SCO) are rare tumors of the posterior pituitary. Histologically, they may be challenging to distinguish and have been proposed to represent a histological spectrum of a single entity. We performed targeted next-generation sequencing, DNA methylation profiling, and copy number analysis on 47 tumors (14 PITUI; 12 GCT; 21 SCO) to investigate molecular features and explore possibilities of clinically meaningful tumor subclassification. We detected two main epigenomic subgroups by unsupervised clustering of DNA methylation data, though the overall methylation differences were subtle. The largest group (n = 23) contained most PITUIs and a subset of SCOs and was enriched for pathogenic mutations within genes in the MAPK/PI3K pathways (12/17 [71%] of sequenced tumors: FGFR1 (3), HRAS (3), BRAF (2), NF1 (2), CBL (1), MAP2K2 (1), PTEN (1)) and two with accompanying TERT promoter mutation. The second group (n = 16) contained most GCTs and a subset of SCOs, all of which mostly lacked identifiable genetic drivers. Outcome analysis demonstrated that the presence of chromosomal imbalances was significantly associated with reduced progression-free survival especially within the combined PITUI and SCO group (p = 0.031). In summary, we observed only subtle DNA methylation differences between posterior pituitary tumors, indicating that these tumors may be best classified as subtypes of a single entity. Nevertheless, our data indicate differences in mutation patterns and clinical outcome. For a clinically meaningful subclassification, we propose a combined histo-molecular approach into three subtypes: one subtype is defined by granular cell histology, scarcity of identifiable oncogenic mutations, and favorable outcome. The other two subtypes have either SCO or PITUI histology but are segregated by chromosomal copy number profile into a favorable group (no copy number changes) and a less favorable group (copy number imbalances present). Both of the latter groups have recurrent MAPK/PI3K genetic alterations that represent potential therapeutic targets.

Morphological diversity in H3G34-mutant high-grade gliomas: Ganglionic and epithelioid features.

Although increasing numbers of central nervous system (CNS) tumors with stereotypic morphological, molecular, and/or site-specific features have been recently reported, morphological diversity is often recognized within a tumor category as more cases are encountered. Such was the case with diffuse midline gliomas, H3K27M-mutant. Therefore, it is not surprising that two cases of H3G34-mutant. CNS tumors with advanced ganglionic differentiation were recently published, especially given the posited role of this mutation in neuronal differentiation. We have encountered, in a 17-year-old female, a third example with advanced neoplastic ganglion cell differentiation that mimicked anaplastic ganglioglioma, with the ganglionic elements further confirmed as neoplastic by H3G34 immunohistochemistry (IHC). We therefore sought to review our experience with H3G34-mutant tumors, assessing for morphological diversity, supplemented by IHC. Six cases (ages 17 - 33 years), all confirmed on mutational analyses, were identified that were further negative for BRAFV600E or other major oncogenic mutations/fusions. The index anaplastic ganglioglioma-like case manifested multifocal large dysmorphic ganglion cells IHC+ for synaptophysin, chromogranin, and neurofilament, but no CD34 immunopositivity. A tumor from a 33-year-old male contained rare neuronal-like cells, with subtler enlargement, that were synaptophysin and neurofilament protein IHC+ and exceeded the size expected in "primitive neuroectodermal like (PNET)" tumors. A third example with morphological diversity was a glioblastoma with prominent epithelioid cells. We conclude that a spectrum of morphological differentiation does occur beyond the well-known glioblastoma or PNET-like morphology in H3G34-mutant tumors, adding to the literature one more example with advanced ganglionic differentiation and one with epithelioid features.

Intracranial mesenchymal tumor with FET-CREB fusion-A unifying diagnosis for the spectrum of intracranial myxoid mesenchymal tumors and angiomatoid fibrous histiocytoma-like neoplasms.

Intracranial mesenchymal tumors with FET-CREB fusions are a recently described group of neoplasms in children and young adults characterized by fusion of a FET family gene (usually EWSR1, but rarely FUS) to a CREB family transcription factor (ATF1, CREB1, or CREM), and have been variously termed intracranial angiomatoid fibrous histiocytoma or intracranial myxoid mesenchymal tumor. The clinical outcomes, histologic features, and genomic landscape are not well defined. Here, we studied 20 patients with intracranial mesenchymal tumors proven to harbor FET-CREB fusion by next-generation sequencing (NGS). The 16 female and four male patients had a median age of 14 years (range 4-70). Tumors were uniformly extra-axial or intraventricular and located at the cerebral convexities (n = 7), falx (2), lateral ventricles (4), tentorium (2), cerebellopontine angle (4), and spinal cord (1). NGS demonstrated that eight tumors harbored EWSR1-ATF1 fusion, seven had EWSR1-CREB1, four had EWSR1-CREM, and one had FUS-CREM. Tumors were uniformly well circumscribed and typically contrast enhancing with solid and cystic growth. Tumors with EWSR1-CREB1 fusions more often featured stellate/spindle cell morphology, mucin-rich stroma, and hemangioma-like vasculature compared to tumors with EWSR1-ATF1 fusions that most often featured sheets of epithelioid cells with mucin-poor collagenous stroma. These tumors demonstrated polyphenotypic immunoprofiles with frequent positivity for desmin, EMA, CD99, MUC4, and synaptophysin, but absence of SSTR2A, myogenin, and HMB45 expression. There was a propensity for local recurrence with a median progression-free survival of 12 months and a median overall survival of greater than 60 months, with three patients succumbing to disease (all with EWSR1-ATF1 fusions). In combination with prior case series, this study provides further insight into intracranial mesenchymal tumors with FET-CREB fusion, which represent a distinct group of CNS tumors encompassing both intracranial myxoid mesenchymal tumor and angiomatoid fibrous histiocytoma-like neoplasms.

Comprehensive analysis of diverse low-grade neuroepithelial tumors with FGFR1 alterations reveals a distinct molecular signature of rosette-forming glioneuronal tumor.

The FGFR1 gene encoding fibroblast growth factor receptor 1 has emerged as a frequently altered oncogene in the pathogenesis of multiple low-grade neuroepithelial tumor (LGNET) subtypes including pilocytic astrocytoma, dysembryoplastic neuroepithelial tumor (DNT), rosette-forming glioneuronal tumor (RGNT), and extraventricular neurocytoma (EVN). These activating FGFR1 alterations in LGNET can include tandem duplication of the exons encoding the intracellular tyrosine kinase domain, in-frame gene fusions most often with TACC1 as the partner, or hotspot missense mutations within the tyrosine kinase domain (either at p.N546 or p.K656). However, the specificity of these different FGFR1 events for the various LGNET subtypes and accompanying genetic alterations are not well defined. Here we performed comprehensive genomic and epigenomic characterization on a diverse cohort of 30 LGNET with FGFR1 alterations. We identified that RGNT harbors a distinct epigenetic signature compared to other LGNET with FGFR1 alterations, and is uniquely characterized by FGFR1 kinase domain hotspot missense mutations in combination with either PIK3CA or PIK3R1 mutation, often with accompanying NF1 or PTPN11 mutation. In contrast, EVN harbors its own distinct epigenetic signature and is characterized by FGFR1-TACC1 fusion as the solitary pathogenic alteration. Additionally, DNT and pilocytic astrocytoma are characterized by either kinase domain tandem duplication or hotspot missense mutations, occasionally with accompanying NF1 or PTPN11 mutation, but lacking the accompanying PIK3CA or PIK3R1 mutation that characterizes RGNT. The glial component of LGNET with FGFR1 alterations typically has a predominantly oligodendroglial morphology, and many of the pilocytic astrocytomas with FGFR1 alterations lack the biphasic pattern, piloid processes, and Rosenthal fibers that characterize pilocytic astrocytomas with BRAF mutation or fusion. Together, this analysis improves the classification and histopathologic stratification of LGNET with FGFR1 alterations.

Reliability of fluorescein-assisted stereotactic brain biopsies in predicting conclusive tissue diagnosis.

BACKGROUND: The purpose of this study was to assess the reliability of fluorescein sodium in predicting conclusive tissue diagnosis in stereotactic brain biopsies and to characterize features of contrast-enhancing and non-enhancing MRI lesions associated with fluorescence. METHODS: A total of 19 patients were studied, 14 of which had contrast-enhancing and 5 of which had non-enhancing lesions on preoperative T1 post-gadolinium MRI scan. All patients received 3 mg/kg fluorescein sodium during anesthesia induction. Biopsy specimens were photographed under the operating microscope, using the Yellow560 module, prior to histopathological analysis. Two observers blinded to the MRI scans and histopathological results categorized the photographs retrospectively as "fluorescent" or "not fluorescent." Inter-rater agreement was assessed using Cohen's kappa coefficient. Sensitivity, specificity, and positive predictive value of fluorescence reliability were calculated for MRI contrast-enhancing lesions and confirmed location-concordance of tumor pathology based on rater's fluorescence status assessment. Results were correlated finally with final results on permanent sections. RESULTS: Strength of inter-rater fluorescence status agreement was found to be "substantial" (kappa = 0.771). Sensitivity, specificity, and positive predictive value for "fluorescent" and "not fluorescent" specimen in comparison with MRI contrast-enhancing lesions were 97%, 40%, and 82%, respectively. Sensitivity, specificity, and positive predictive value for confirmed tumor pathology were 100%, 63%, and 91%, respectively. Permanent pathology revealed high-grade glioma n = 5, low-grade glioma n = 3, lymphoma n = 5, pineal tumor n = 2, hamartoma n = 1, and nonspecific hypercellularity n = 3. CONCLUSIONS: Fluorescein-assisted stereotactic brain biopsies demonstrated a high likelihood to manifest fluorescence in contrast-enhancing MRI lesions, while adequately predicting conclusive tumor pathology.

Distinguishing Encephaloclastic Lesions Resulting From Primary or Secondary Pyruvate Dehydrogenase Deficiency From Other Neonatal or Infantile Cavitary Brain Lesions.

The central nervous system (CNS) is a highly complex and energy-dependent organ that is subject to a wide variety of metabolic, hypoxic-ischemic, and infectious insults that result in cystic changes. Diagnosis of metabolic defects causing extensive cystic changes is particularly challenging for the pediatric pathologist, due to the rarity of these conditions. Pyruvate dehydrogenase (PDH) deficiency is one of the most common etiologies of congenital lactic acidosis, caused by mutations in subunits of the large mitochondrial matrix complex, and characterized by periventricular cysts, although few detailed reports focusing on neuropathologic findings exist. In addition, rare defects in other mitochondrial enzymes such as short-chain enoyl-CoA hydratase (SCEH, encoded by ECHS1 gene) can cause secondary PDH deficiency and present with neonatal lactic acidosis, but neuropathological findings have never been reported. Nonmetabolic conditions can also produce CNS cystic lesions, primarily in newborns. The pathologist must therefore distinguish between these etiologically disparate conditions which can produce CNS cavitary lesions. Here, we compare and contrast the gross and microscopic findings of cysts associated with cases of PDH and SCEH deficiencies with other neonatal cystic brain diseases including periventricular leukomalacia, neonatal Alexander disease, Canavan disease, and a case of cysts associated with a vascular abnormality. Our studies show that PDH and SCEH deficiencies are not grossly or histologically distinguishable from each other and both are associated with smooth-walled cysts largely limited to the telencephalic germinal matrix. Both show an absence of prominent hemosiderin deposits, Rosenthal fibers, vacuolization of the white matter, and gliosis or axonal damage in the surrounding parenchyma. These features can help distinguish PDH/SCEH deficiency from other pediatric/neonatal cystic CNS disorders, especially those produced by hypoxic ischemic conditions. Cysts, usually bilateral, confined to the telencephalic germinal matrix should elicit metabolic and genetic testing to appropriately diagnose PDH and SCEH and distinguish them from each other.

Cystic sellar salivary gland-like lesions.

INTRODUCTION: Cystic sellar salivary gland-like lesions (CSSLs) are exceedingly rare, with fewer than a dozen case reports. They contain amorphous colloid identical to Rathke cleft cyst contents, but the cyst wall additionally shows cohesive aggregates of benign salivary glands. We report three new examples. MATERIALS AND METHODS: Two cases were seen at University of Colorado Denver and one at Memorial Sloan Kettering (MSK). Molecular testing was attempted on two of three. RESULTS: Case 1 is a 20-year-old female who presented with panhypopituitarism and was found to have a suprasellar mass that proved to be a CSSL. She received no postoperative adjuvant therapy, but recurrence of headaches and blurred vision 2 years later prompted return to medical attention. A much smaller local cyst recurrence was now accompanied by a thickened, bulbous infundibular stalk. Second resection yielded a gliotic infundibular stalk and amorphous mucin, but no residual salivary-like glands. She is without further recurrence on 6-year follow-up. Case 2 is a 29-year-old female with headache; while seen initially at a tertiary care center, diagnosis was only made after consultation at MSK. Case 3 is 68-year-old female who had originally presented with apoplexy to an outside hospital 7 years prior to surgery and diagnosis. Molecular testing was uninformative on case 1 and negative for mutations or fusions on case 3. CONCLUSION: Few pathologists or neuropathologists have encountered CSSLs in their practices; case 1 produced recurrence and significant infundibular stalk damage, and case 3 originally manifested apoplexy, features not previously reported.

How frequent is double pathology in Rasmussen encephalitis?

Rasmussen encephalitis (RE) is an uncommon, medically refractory cause of seizures that usually presents in childhood or adolescence resulting in unilateral hemispheric atrophy in most cases. The purported immune-mediated cause of the disease is supported by the characteristic histopathologic features of diffuse perivascular and intraparenchymal T-cell-predominant infiltrates, microglial activation with microglial nodules, and neuronophagia. A small number of reports have emerged, however, suggesting that double pathology (such as focal cortical dysplasia (FCD) or hippocampal sclerosis) may be present. We asked how often double pathology could be demonstrated in RE. A 15-year retrospective review of all RE cases seen at our pediatric tertiary care hospital yielded 11 patients, many of which had some degree of double pathology. The most diagnostically incontrovertible examples showed leptomeningeal neuronal heterotopia (n = 1) or leptomeningeal melanocytic nevus (n = 1). Another coexistent feature was neuronal gigantism unassociated with hemimegaloencephaly, particularly prominent in layer II (n = 2). Three additional cases showed dysmorphic neurons in the hippocampus (n = 2) and dentate granule cell layer dispersion/bilamination (n = 1). Finally, 2 cases had exaggerated radial arrangement of neurons FCD type Ia-like changes) (n = 2), a condition known to have interobserver discordance. In summary, 7/11 of our RE cases showed prominent additional pathologies, 6 of which demonstrated disproportionately more severe inflammation, neuronophagia, or microglial activation in regions of double pathology. Our collection of cases shows that a majority of RE cases show double pathology. Although some of these cases can be reactive, the presence of maldevelopment in a subset raises the possibility of a causal relationship with RE.
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Clinicopathologic and molecular features of intracranial desmoplastic small round cell tumors.

Desmoplastic small round cell tumors (DSRCTs) are highly aggressive sarcomas that most commonly occur intra-abdominally, and are defined by EWSR1-WT1 gene fusion. Intracranial DSRCTs are exceptionally rare with only seven previously reported fusion-positive cases. Herein, we evaluate the clinical, morphologic, immunohistochemical and molecular features of five additional examples. All patients were male (age range 6-25 years; median 11 years), with four tumors located supratentorially and one within the posterior fossa. The histologic features were highly variable including small cell, embryonal, clear cell, rhabdoid, anaplastic and glioma-like appearances. A prominent desmoplastic stroma was seen in only two cases. The mitotic index ranged from <1 to 12/10 HPF (median 5). While all tumors showed strong desmin positivity, epithelial markers such as EMA, CAM 5.2 and other keratins were strongly positive in only one, focally positive in two and negative in two cases. EWSR1-WT1 gene fusion was present in all cases, with accompanying mutations in the TERT promoter or STAG2 gene in individual cases. Given the significant histologic diversity, in the absence of genetic evaluation these cases could easily be misinterpreted as other entities. Desmin immunostaining is a useful initial screening method for consideration of a DSRCT diagnosis, prompting confirmatory molecular testing. Demonstrating the presence of an EWSR1-WT1 fusion provides a definitive diagnosis of DSRCT. Genome-wide methylation profiles of intracranial DSRCTs matched those of extracranial DSRCTs. Thus, despite the occasionally unusual histologic features and immunoprofile, intracranial DSRCTs likely represent a similar, if not the same, entity as their soft tissue counterpart based on the shared fusion and methylation profiles.