Gliomas represent a type of primary brain tumors that accounts for almost 30% of all primary brain tumors, 80% of all malignant ones, and are responsible for the majority of deaths from primary brain tumors. The term "glioma" refers to tumors that have histologic features similar to normal glial cells (i.e. astrocytes, oligodendrocytes, oligoastrocytes and ependymal cells). For each of these types of gliomas, there are neoplasms that span a broad spectrum of biological aggressiveness.
Slower growing lesions, corresponding to World Health Organization (WHO) grades I and II, have been commonly referred to as “low-grade gliomas” and tend to have more circumscribed growth, while the more rapidly progressive tumors (WHO grades III and IV) are referred to as “high-grade gliomas”.
Low grade gliomas are comprised of:
- WHO grade I gliomas: slow growing and usually well-defined.
- WHO grade II gliomas: slow growing but often show brain-invasive growth that precludes complete resection.
High grade gliomas include:
- WHO grade III gliomas: rapidly growing high-grade tumours characterized by histological features of anaplasia.
- WHO grade IV: reserved for glioblastomas, the most malignant form of glioma which are mitotically active, necrosis-prone neoplasms often associated with a fatal outcome.