Gliomas

[Mark Zuckerberg]

Gliomas are primary tumors that originate in brain parenchyma. Symptoms and diagnosis are similar to those of other brain tumors. Treatment involves surgical excision, radiation therapy, and, for some tumors, chemotherapy. Excision rarely cures.
Gliomas include

Astrocytomas
Oligodendrogliomas
Glioblastoma multiforme
Ependymomas

Many gliomas infiltrate brain tissue diffusely and irregularly.
Astrocytomas are the most common gliomas. They are classified histologically and, in some cases, based on the presence of specific genetic markers, according to the WHO classification (1).
In ascending order of malignancy, astrocytomas are classified as

Grade I: Pilocytic astrocytomas
Grade II: Low-grade astrocytomas
Grade III: Anaplastic astrocytomas (and anaplastic oligoastrocytomas)
Grade IV: Glioblastomas and diffuse midline gliomas

Pilocytic, low-grade, or anaplastic astrocytomas tend to develop in younger patients and can later evolve into glioblastomas (called secondary glioblastomas). Glioblastomas can also develop de novo (called primary glioblastomas), usually in middle-aged or elderly people. Glioblastomas contain chromosomally heterogeneous cells. Both primary and secondary glioblastomas have distinct genetic characteristics, which can change as the tumors evolve. Secondary glioblastomas typically have the IDH1 mutation.
Some astrocytomas contain oligodendroglioma cells; patients with these tumors (called oligoastrocytomas) usually have a better prognosis than those with pure astrocytomas.
Oligodendrogliomas (WHO grade II) are among the most slow-growing gliomas. They are most common in the forebrain, particularly the frontal lobes. Oligodendrogliomas are typically characterized by deletion of the p arm of chromosome 1 (1p deletion), deletion of the q arm of chromosome 19 (19q deletion), or both. These deletions are diagnostic for oligodendroglial tumors, predict longer survival, and predict a better response to radiation therapy and chemotherapy. Like astrocytomas, oligodendrogliomas can evolve into more aggressive forms, such as anaplastic oligodendrogliomas (WHO grade III), which are managed accordingly.
Diffuse midline gliomas are high-grade (WHO grade III to IV) astrocytic tumors that primarily affect children. These tumors include diffuse intrinsic pontine gliomas, which are aggressive and typically lethal tumors that infiltrate the brain stem with rostral extension into the hypothalamus and thalamus and that infiltrate the medulla and spinal cord inferiorly. Children with neurofibromatosis type 1 are at an increased risk of developing these tumors.
Ependymomas are uncommon in adults. They are classified as

Grade I: Subependymoma
Grade II: Ependymoma
Grade III: Anaplastic ependymoma
Grade IV: Ependymoblastoma (which are rare and occur primarily in infants)

All ependymomas typically arise from the ventricular wall and hence may arise in the brain, brain stem, or spinal cord. Ependymomas of the 4th ventricle in particular can manifest with obstructive hydrocephalus.
Symptoms and signs of gliomas vary by location (see Table: Common Localizing Manifestations of Primary Brain Tumors#160;). Diagnosis is the same as that of other brain tumors: MRI followed by biopsy.