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We report the neuropathology of two pediatric brain biopsy cases associated with serum anti-myelin oligodendrocyte glycoprotein (MOG) positivity. Descriptions of anti-MOG associated neuropathology are limited, with initial reports describing various patterns of inflammatory demyelination. Our first patient presented with confusion, speech abnormalities and personality changes following a treated strep throat infection. Our second patient had a past medical history of neurofibromatosis type 1 (NF1) and presented with hypersomnolence and focal neurological deficits. MRI abnormalities included diffuse scattered T2 FLAIR hyperintensities +/- enhancement. CSF was positive for anti-MOG antibodies in both cases, while one case exhibited additional anti-NMDA-R antibodies. Brain biopsies revealed vasocentric mononuclear inflammation featuring a predominance of lymphocytes that included intramural forms, as well as diffuse microglial activation, but no evidence of microglial nodules or microorganisms. One case demonstrated mild perivascular demyelination. The prevailing pattern in both cases was suggestive of “small vessel childhood primary angiitis of the central nervous system” (SVcPACNS). Our results parallel recent reports of anti-MOG neuropathology describing small vessel vasculitis, contrary to initial and subsequent reports that describe “encephalitis”. The foregoing suggests that the neuropathology associated with serum anti-MOG positivity may be broader than first appreciated. Moreover, this pattern of vasculitis might have implications for the natural history of this nascent disorder.Learning ObjectivesDefine anti-MOG encephalitis.Recognize the pathologic spectrum of reported cases of anti-MOG encephalitis.Contrast the pathologic features of pediatric and adult CNS vasculitis.Describe the histologic overlap of vasculitis and encephalitis.

Alexander Disease (AD) is a rare and ultimately lethal leukodystrophy, typically presenting in infants who exhibit developmental delay, macrocephaly, seizures, spasticity and quadriparesis. Classic infantile forms are generally due to sporadic mutations in GFAP that result in the massive deposition of intra-astrocytic Rosenthal fibres, particularly in the frontal white matter. However, phenotypic manifestations are broad and include both juvenile and adult forms that often display infratentorial pathology and a paucity of leukodystrophic features. We describe the unique case of an 8.5 year old female who presented with an 8 month history of progressively worsening vomiting and cachexia, whose extensive multidisciplinary systemic workup, including GI biopsies, proved negative. Neuroimaging ultimately revealed bilaterally symmetric and anterior predominant supratentorial signal alterations in the white matter plus a 1.7 x 1.2 x 0.7 mm right dorsal medullary mass. Biopsy of this presumed low-grade glioma revealed features in keeping with AD, which was later confirmed on whole exome sequencing. The proband exhibited a pathogenic p.Arg239Cys heterozygous missense mutation in GFAP, which was apparently inherited from her asymptomatic mother (1% mosaicism in the mother’s blood). Germline mosaic inheritance patterns of young-onset AD, particularly those presenting with a tumor-like mass of the brainstem, are scarcely reported in the literature and serve to expand the clinicopathologic spectrum of AD.LEARNING OBJECTIVESThis presentation with enable the learner to: 1.Recognize an uncommon clinical presentation of AD.2.Describe the underlying genetics of AD, including a rare familial juvenile onset form featuring germline mosaicism.

We describe the case of an 11-month-old girl with a rare cerebellar glioblastoma driven by a NACC2-NTRK2 (Nucleus Accumbens Associated Protein 2-Neurotrophic Receptor Tyrosine Kinase 2) fusion. Initial workup of our case demonstrated homozygous CDKN2A deletion, but immunohistochemistry for other driver mutations, including IDH1 R132H, BRAF V600E, and H3F3A K27M were negative, and ATRX was retained. Tissue was subsequently submitted for personalized oncogenomic analysis, including whole genome and whole transcriptome sequencing, which demonstrated an activating NTRK2 fusion, as well as high PD-L1 expression, which was subsequently confirmed by immunohistochemistry. Furthermore, H3 and IDH demonstrated wildtype status. These findings suggested the possibility of treatment with either NTRK- or immune checkpoint- inhibitors through active clinical trials. Ultimately, the family pursued standard treatment that involved Head Start III chemotherapy and proton radiotherapy. Notably, at most recent follow upapproximately two years from initial diagnosis, the patient is in disease remission and thriving, suggesting favorable biology despite histologic malignancy. This case illustrates the value of personalized oncogenomics, as the molecular profiling revealed two actionable changes that would not have been apparent through routine diagnostics. NTRK fusions are known oncogenic drivers in a range of cancer types, but this is the first report of a NACC2-NTRK2 fusion in a glioblastoma.LEARNING OBJECTIVESThis presentation will enable the learner to:1.Explore the current molecular landscape of pediatric high grade gliomas2.Recognize the value of personalized oncogenomic analysis, particularly in rare and/or aggressive tumors3.Discuss the current status of NTRK inhibitor clinical trials

An immunosuppressed 11-year-old with relapsed T-cell leukemia presented with subacute onset fever, headache and a “heavy” right hand. Neurologic examination revealed right-sided hemiparesis and hypesthesia. Magnetic resonance imaging (MRI) 24 hours after symptom onset disclosed lesions involving the right cerebellar hemisphere, left putamen, and cortex in the right frontal lobe and left frontoparietal region (Figure 1). The lesions were gyriform, T1 hypointense, non-enhancing, and T2 hyperintense, with blooming of the larger lesions on the gradient echo sequence consistent with hemorrhage. Interestingly, on fluid attenuation inversion recovery (FLAIR) imaging, the lesions were predominantly isointense with only a small peripheral rim of increased signal. The lesions demonstrated increased signal on the diffusion weighted sequences (DWI) and decreased signal on the apparent diffusion coefficient (ADC) map in keeping with restricted diffusion. There was minimal edema and mass effect. Cerebrospinal fluid (CSF) showed normal glucose, protein, red and white blood cell counts. Flow cytometry did not reveal leukemic cells. There was no serum or CSF evidence of acid-fast bacilli, toxoplasma, enterovirus or herpes simplex virus. Echocardiogram was normal. Biopsy of a lung infiltrate was non-diagnostic. The clinical course fluctuated, with worsening hemiparesis, expressive language difficulties and depressed level of consciousness, which responded only temporarily to corticosteroids. The lesions progressed in size despite maximal empiric broad-spectrum antimicrobial treatment against bacteria, viruses, fungi and toxoplasma. Repeat MRI one week after onset showed enlargement of the lesions. They were hyperintense on T1 sequences and without clear contrast-enhancement. They continued to show restricted diffusion. MRI 17 days after symptom onset again showed lesion growth. There was ring enhancement and significant vasogenic edema with mass effect (Figure 2). The lesions no longer showed restricted diffusion. Due to disease progression despite maximal therapy, the brain lesions were not biopsied and the child was transferred to the palliative care service. He died at home six weeks after symptom onset. Postmortem brain examination showed multifocal chronic fungal abscesses in the frontal lobes, left putamen and right cerebellum. Central coagulative necrosis harboured thrombosed blood vessels bearing fungal angioinvasion. Though morphologically suggestive of Aspergillus, the hyphae were degenerate, precluding definitive identification (Figure 3). Abscess capsules were well-formed and contained multinucleated giant cells and focal granulomata (Figure 4). Adjacent parenchyma was gliotic and focally degenerate, suggesting chronic edema. Leukemic infiltrates were not present. We report a case of multifocal fungal cerebritis with MRI showing restricted diffusion. At the time of presentation, the

IntroductionIn 2007, Ellison et al coined the term “biphasic” medulloblastoma (B-MB) to characterize histology that mimicked the desmoplastic nodular (DN) variant on routine staining, but which lacked internodular reticulin deposition. Via interphase FISH, and utilizing markers for 9q22 and chromosome 17 alterations (ie, -17p and i17q), Ellison et al. suggested that B-MB and DN-MB were genetically different.MethodsWe performed a clinicopathologic review of MBs treated at BCCH from 1986-2011. Using nanoString’s n Counter Analysis System (nCAS), each tumor was molecularly subtyped (ie, WNT, SHH, group 3 or group 4). All original glass slides were reviewed to determine WHO histologic subtype [ie, classic, large cell anaplastic (LCA), DN, MB with extensive nodularity (MBEN)]. Tumors were also evaluated for nodularity (scattered vs. frequent) and advanced neuronal differentiation. Reticulin staining was assessed on all cases.Results20 B-MB were identified; by WHO definition, most of these resided within the classic category (N=19), while one was LCA. 13 of 20 B-MB displayed ‘scattered” nodules; by molecular subtype, these included eight group 4, four group 3 and one WNT tumors. Seven of the 20 B-MB exhibited “frequent” nodules; by molecular subtype, these included six group 4 and one group 3 tumors. Statistical analysis confirmed this non random distribution of B-MB across molecular subtypes.ConclusionOur data confirm the work of Ellison et al. that suggested B-MB is genetically different than DN-MB. In particular, B-MB resides in the non-WNT/SHH molecular category, but especially amongst group 4 when nodularity is “frequent”.

Cerebral hyaline astrocytic inclusions (HAI) have been observed in a subset of patients with epilepsy, structural brain anomalies, and developmental delay. We present a case of a 2.5-year-old male with epilepsy and global developmental delay. Chromosomal microarray detected a copy loss at 22q13 that resulted in a partial deletion of SHANK3 gene. The EEGs revealed seizure activity arising from left frontal central region. Invasive video electrocorticography captured clusters of epileptic spasms, all originating from left antero-lateral frontal lobe rostral to the motor cortex. We utilized routine histology to identify the inclusions and mapped their distribution in the resected portion of the cortex against electrocorticographic data. Histologic analysis revealed the presence of HAI in the posterio-medial portion of the resected cortex, which corresponded to the site of seizure generalization. HAI were present at the resection margin. Immunohistochemistry was largely non-contributory. HAI is a rare but emerging entity that is associated with epilepsy. To our knowledge, the distribution of inclusions in HAI has never been mapped to electrophysiologic data. In our case, seizure generalization correlated with the inclusions distribution. This suggests that the inclusions may: 1) play a role in epileptogenesis; or, 2) be a biomarker of disease distribution. Finally, the presence of the HAI at the resection margin may foreshadow future seizure activity in this patient.