2016 Updates to the WHO Brain Tumor Classification System: What the Radiologist Needs to Know

Abstract

Radiologists play a key role in brain tumor diagnosis and management and must stay abreast of developments in the field to advance patient care and communicate with other health care providers. In 2016, the World Health Organization (WHO) released an update to its brain tumor classification system that included numerous significant changes. Several previously recognized brain tumor diagnoses, such as oligoastrocytoma, primitive neuroectodermal tumor, and gliomatosis cerebri, were redefined or eliminated altogether. Conversely, multiple new entities were recognized, including diffuse leptomeningeal glioneuronal tumor and multinodular and vacuolating tumor of the cerebrum. The glioma category has been significantly reorganized, with several infiltrating gliomas in children and adults now defined by genetic features for the first time. These changes were driven by increased understanding of important genetic factors that directly impact tumorigenesis and influence patient care. The increased emphasis on genetic factors in brain tumor diagnosis has important implications for radiology, as we now have tools that allow us to evaluate some of these alterations directly, such as the identification of 2-hydroxyglutarate within infiltrating gliomas harboring mutations in the genes for the isocitrate dehydrogenases. For other tumors, such as medulloblastoma, imaging can demonstrate characteristic patterns that correlate with particular disease subtypes. The purpose of this article is to review the changes to the WHO brain tumor classification system that are most pertinent to radiologists. RSNA, 2017.

Imaging of skull vault tumors in adults

“…Hemangiopericytoma (or solitary fibrous tumor) is an uncommon, highly vascular, dural-based tumor that affects adults, accounting for less than 1% of all CNS tumors with a median age of 40-60 years with a slight male predilection. There are different grades of malignancy and prognosis [49,50]. Hemangiopericytoma and solitary fibrous tumor were previously considered two separate entities but have been combined as one single On imaging, it presents as an extra-axial, avidly enhancing mass, with flow voids and possible "dural tail."…”

Cerebral Neoplasms

“…Gliomas in children have been known to behave differently than those seen in the adult population. This is related to the fact that mutations seen commonly in gliomas in adults including IDH mutation and 1p/19q-codeletion occur only uncommonly in children [27]. In fact, the two common mutation types commonly seen in children, include BRAF mutation and histone H3-K27 m-mutation.…”

“…Hence, these two previously distinct tumors are now combined as SFT/HPC tumor. Of these, the SFT/HPC Grade I is a slowly growing tumor with excellent prognosis, while SFT/HPC Grade II and III have a slightly poor prognosis, carry a high risk to recur following resection, and are associated with metastasis [27].…”

Diffuse Astrocytoma and Oligodendroglioma: An Integrated Diagnosis and Management

“…This approach separates between the astrocytomas with a circumscribed growth pattern, no IDH mutation, and with BRAF mutation (pilocytic astrocytoma, pleomorphic xantoastrocytoma, and subependymal giant cell astrocytoma), on the one hand, and the diffuse astrocytic and oligodendroglial tumors, on the other. According to the new classification, the diffuse astrocytic and oligodendroglial tumors are nosologically closer than the diffuse astrocytoma and the pilocytic astrocytoma [9].…”