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The World Health Organization (WHO) classification of central nervous system (CNS) tumors was revised in 2016 with a basis on the integrated diagnosis of molecular genetics. We herein provide the guidelines for using molecular genetic tests in routine pathological practice for an accurate diagnosis and appropriate management. While astrocytomas and IDH-mutant (secondary) glioblastomas are characterized by the mutational status of IDH, TP53, and ATRX, oligodendrogliomas have a 1p/19q codeletion and mutations in IDH, CIC, FUBP1, and the promoter region of telomerase reverse transcriptase (TERTp). IDH-wildtype (primary) glioblastomas typically lack mutations in IDH, but are characterized by copy number variations of EGFR, PTEN, CDKN2A/B, PDGFRA, and NF1 as well as mutations of TERTp. High-grade pediatric gliomas differ from those of adult gliomas, consisting of mutations in H3F3A, ATRX, and DAXX, but not in IDH genes. In contrast, well-circumscribed low-grade neuroepithelial tumors in children, such as pilocytic astrocytoma, pleomorphic xanthoastrocytoma, and ganglioglioma, often have mutations or activating rearrangements in the BRAF, FGFR1, and MYB genes. Other CNS tumors, such as ependymomas, neuronal and glioneuronal tumors, embryonal tumors, meningothelial, and other mesenchymal tumors have important genetic alterations, many of which are diagnostic, prognostic, and predictive markers and therapeutic targets. Therefore, the neuropathological evaluation of brain tumors is increasingly dependent on molecular genetic tests for proper classification, prediction of biological behavior and patient management. Identifying these gene abnormalities requires cost-effective and high-throughput testing, such as next-generation sequencing. Overall, this paper reviews the global guidelines and diagnostic algorithms for molecular genetic testing of brain tumors.

Brain tumors are the second most common form of cancer in the pediatric age group. Surgical treatment is the mainstay of therapy for many brain tumors and is usually the first treatment given to children with brain tumors. Pediatric brain tumors differ from those of adults in many aspects: histological diagnosis, immaturity of the pediatric central nervous system, and the vulnerability of children to blood loss during the operation. The completeness of surgery is strongly associated with the prognosis of afflicted children, whereas surgical morbidities can be life-time deficits and handicaps for the children. Therefore, practicing pediatric neurosurgeons should combine a thorough knowledge on neuroanatomy and pathophysiology with state-of-theart surgical skills and experience to obtain the best results. They should also take time for reflecting on the difficulties encountered and complications arising during operations. [ABSTRACT FROM AUTHOR]

Ependymoma is the third most common pediatric primary brain tumor. Ependymomas are categorized according to their locations and genetic abnormalities, and these two parameters are important prognostic factors for patient outcome. For supratentorial (ST) ependymomas, RELA fusion-positive ependymomas show a more aggressive behavior than YAP1 fusion-positive ependymomas. Extracranial metastases of intra-axial neuroepithelial tumors are extremely rare. In this paper, we report a case of aggressive anaplastic ependymoma arising in the right frontoparietal lobe, which had genetically 1q25 gain, CDKN2A homozygous deletion, and L1CAM overexpression. The patient was a 10-year-old boy who underwent four times of tumor removal and seven times of gamma knife surgery. Metastatic loci were scalp and temporalis muscle overlying primary operation site, lung, liver, buttock, bone, and mediastinal lymph nodes. He had the malignancy for 10 years and died. This tumor is a representative case of RELA fusion-positive ST ependymoma, showing aggressive behavior.