Purpose Pilocytic astrocytomas (PAs), the most common posterior fossa tumors in children, are characterized by KIAA1549-BRAF fusions and show excellent 5-year survival rates. Pilocytic astrocytoma with gangliocytic differentiation (PA-GD), a recently defined PA variant that includes glial and neuronal elements like a ganglioglioma, may be distinguished from a classic ganglioglioma by molecular, radiological and histopathologic features. This study investigated whether imaging could distinguish between posterior fossa PA-GDs and PAs. Materials and Methods Pre-operative MRIs (± CTs) of 41 children (7mo-15 years, mean 7.3±3.7 years; 58.5% male) with PA-GD (n=7) or PA (n= 34) were evaluated; differences in tumor location, morphology, and minimum rADC between tumor types were compared (Wilcoxon rank sum test, Fisher’s exact test). Histopathology and BRAF fusion / mutation status were reviewed. Associations of progression-free survival (PFS) with diagnosis, imaging features and BRAF status were examined by Cox proportional hazards models. Results PA-GDs appeared similar to PAs, but had lower minimum rADC (mean 1.01±0.17 compared to 2.01±0.38 for PAs; p=0.0005), and were more commonly located within midline structures (p=0.0034). BRAF status was similar for both groups. Non-total resection (hazard ratio 52.64, p=0.0002), PA-GD diagnosis (hazard ratio 4.66, p=0.0104) and midline involvement (hazard ratio 3.32, p=0.0433) were associated with shorter PFS. Conclusion Minimum rADC and tumor location may be useful adjuncts to histopathology in differentiating PA-GD from PA. Shorter PFS in PA-GD is likely due to a propensity for involvement of midline structures and poor resectability.

Background and Purpose The conventional MRI appearance of diffuse intrinsic pontine glioma suggests intralesional histopathological heterogeneity, and various distinct lesion components, including T2-hypointense foci, have been described. Here we report the prevalence, conventional MRI semiology, and advanced MRI features of non-necrotic T2-hyperintense foci within diffuse intrinsic pontine glioma. Materials and Methods Twenty-five patients with diffuse intrinsic pontine glioma were included in this study. MRI studies were performed at 3T by using conventional and advanced MRI sequences. Perfusion (CBV), vascular permeability (ve, Ktrans) and diffusion (ADC) metrics were calculated and used to characterize non-necrotic T2-hyperintense foci in comparison with other lesion components, namely necrotic T2-hyperintense foci, T2-hypointense foci, peritumoral edema, and normal brainstem. Statistical analysis was performed by using Kruskal–Wallis and Wilcoxon rank sum tests. Results Sixteen non-necrotic T2-hyperintense foci were found in 12 tumors. In these foci, ADC values were significantly higher than those in either T2-hypointense foci (P=.002) or normal parenchyma (P=.0002), and relative CBV values were significantly lower than those in either T2-hypointense (P=.0002) or necrotic T2-hyperintense (P=.006) foci. Ktrans values in T2-hyperintense foci were lower than those in T2-hypointense (P=.0005) or necrotic T2-hyperintense (P=.0348) foci. Conclusion Non-necrotic T2-hyperintense foci are common, distinct lesion components within diffuse intrinsic pontine glioma. Advanced MR data suggest low cellularity and an early stage of angioneogenesis with leaky vessels resulting in expansion of the extracellular space. Because of the lack of biopsy validation, the underlying histoarchitectural and pathophysiological changes remain unclear; therefore, these foci may correspond to a poorly understood biological event in tumor evolution.

Purpose/Objective(s): Pediatric sarcomas, accounting for approximately 15-20% of pediatric cancers, provide a unique diagnostic challenge. There is considerable morphologic overlap between entities, increasing the importance of molecular studies in the diagnosis, treatment, and identification of therapeutic targets. While these tumors can often occur in similar locations in the bone, the optimal treatment strategies are quite different between tumor histologies, and consist of multimodal therapies including unique chemotherapy regimens, surgery and/or radiation therapy. We developed and validated a genome-wide DNA methylation based classifier to differentiate between osteosarcoma, Ewing's sarcoma, and synovial sarcoma. Materials/Methods: DNA methylation status of 482,421 CpG sites in 10 Ewing's sarcoma, 11 synovial sarcoma, and 15 osteosarcoma samples were determined using the Illumina HumanMethylation450 array. Unsupervised hierarchical clustering was implemented with Euclidean measure for distance matrix and complete agglomeration method for clustering. We developed a classifier from the 400 most differentially methylated CpG sites within the training set of 36 sarcoma samples using the randomForest package in R. This classifier was validated with data drawn from The Cancer Genome Atlas (TCGA) synovial sarcoma data set, TARGET Osteosarcoma data set, and a recently published series of Ewing's sarcoma tumors. Results: Methylation profiling revealed three distinct patterns, each enriched with a single sarcoma subtype. Within the validation cohorts, all samples from TCGA were accurately classified as synovial sarcoma (10/ 10, sensitivity and specificity 100%), all but one sample from TARGET Osteosarcoma were classified as osteosarcoma (85/86, sensitivity 98%, specificity 100%), and 14/15 Ewing's sarcoma samples classified correctly (sensitivity 93%, specificity 100%). The single misclassified osteosarcoma sample was determined to be a misdiagnosed Ewing's sarcoma based on RNA-Seq data demonstrating high EWRS1 and ETV1 expression. The misclassified Ewing's sarcoma sample may represent a true misclassification. An additional clinical sample from a patient who had previous radiation in the area where a new tumor developed was initially misdiagnosed as synovial sarcoma on histopathology and later accurately recognized as osteosarcoma by the methylation classifier and confirmatory additional immunohistochemical staining. Conclusion: Osteosarcoma, synovial sarcoma, and Ewing's sarcoma have distinct epigenetic profiles. Our validated methylation-based classifier can be used to provide a definitive diagnosis when histological and standard techniques are inconclusive.