WHO-Klassifikation der Hirntumoren 2016: radiologisch relevante Neuerungen

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.

Im Jahr 2016 hat die WHO ihr primäres Klassifikationsschema für Hirntumoren revidiert und dabei erstmals genetische Informationen in das Schema aufgenommen. Dieser Artikel gibt einen Überblick über die wichtigsten Änderungen des Klassifikationssystems. Dabei wird besonders auf diejenigen Änderungen eingegangen, die für Radiologen die größte Relevanz besitzen.

Kernaussagen

• In der Neufassung des WHO-Klassifikationssystems für ZNS-Tumoren des Jahres 2016 werden einige Tumoren durch die Kombination von mikroskopisch-morphologischen und molekularen sowie genetischen Faktoren definiert. Hingegen werden andere Tumoren nach wie vor rein anhand ihrer Morphologie charakterisiert.

• Mehrere bis dahin anerkannte Hirntumordiagnosen – so z. B. das Oligoastrozytom, primitive neuroektodermale Tumoren und die Gliomatosis cerebri – wurden entweder neu definiert oder vollständig gestrichen. Im Gegenzug wurden verschiedene neue Tumorentitäten eingeführt, darunter der diffuse leptomeningeal-glioneuronale Tumor und der multinoduläre und vakuolisierte Tumor des Zerebrums.

• In der WHO-Revision von 2016 gilt nun die IDH-Mutation als definitorisch für infiltrierende Gliome bei Erwachsenen. Dabei wird dieser Tumortyp durch die Kodeletion 1p/19q weiter charakterisiert. Beim Oligodendrogliom handelt es sich um ein infiltrierendes Gliom, das sowohl die IDH-Mutation als auch die Kodeletion 1p/19q (die bei Fehlen der IDH-Mutation nicht auftritt) aufweist. Das Astrozytom hingegen ist ein infiltrierendes Gliom, das nach dem neuen Klassifikationssystem entsprechend dem Vorliegen der IDH-Mutation weiter unterteilt wird und niemals eine Kodeletion 1p/19q aufweist. Obwohl IDH-Mutanten an sich keine klare radiologische Signatur besitzen, lässt sich 2HG in der MRS nachweisen.

• Aufgrund ihrer gemeinsamen genetischen Merkmale wurden SFT und HPZ unter dem Terminus „SFT/HPZ“ zusammengefasst. Diese lassen sich dem WHO-Grad I, II oder III zuordnen.

• Hinsichtlich der Lokalisation von einzelnen Tumorsubtypen des Medulloblastoms wurden Trends beobachtet, darunter WNT-aktivierte Tumoren mit zentraler Lokalisation im Bereich von Kleinhirnstiel oder Kleinhirnbrückenwinkel, SHH-aktivierte Tumoren innerhalb der rostralen Kleinhirnhälfte sowie Tumoren der Gruppe 3 und 4 im Bereich der Mittellinie. Allerdings handelt es sich dabei eher um Verallgemeinerungen oder Trends als um Gesetzmäßigkeiten.

Schlüsselwörter

WHO-Klassifikation 2016 - Hirntumoren - Genetik - Bildgebung

Keywords

WHO classification system 2016 - brain tumors - genetic features - radiology

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