Glioma

Glioma is a collective term for primary brain tumors arising from the brain's glial cells — the supportive cells of the central nervous system that include astrocytes, oligodendrocytes, and ependymal cells. Gliomas are the most common type of malignant primary brain tumor in adults. They occur across a wide spectrum of biological aggressiveness, from slow-growing, low-grade tumors that may be managed conservatively for years, to glioblastoma — the most aggressive form — which carries a poor prognosis despite aggressive treatment.

The major types of glioma in adults are astrocytoma, oligodendroglioma, and glioblastoma. 

Astrocytomas arise from astrocytes and range from grade 1 (pilocytic astrocytoma, typically affecting children and young adults, with excellent prognosis) through grade 2 and 3 diffuse astrocytomas to grade 4 glioblastoma, which may arise de novo (primary glioblastoma) or from malignant transformation of a lower-grade precursor (secondary glioblastoma).

Oligodendrogliomas, which carry a mutation in the IDH gene along with codeletion of chromosomal arms 1p and 19q, tend to have a better prognosis than astrocytomas of the same grade. 

Glioblastoma is the most common and most aggressive adult glioma; histologically characterized by necrosis and microvascular proliferation, it carries a uniformly poor prognosis with available therapies.

Glioma symptoms depend on the tumor's location, size, rate of growth, and effect on surrounding brain tissue. Common presenting symptoms include:

• Headache — often worse in the morning or when lying down, caused by increased intracranial pressure.
• Seizures — a common presenting symptom, particularly with lower-grade, cortically located tumors.
• Cognitive and personality changes — memory difficulties, altered judgment, or behavioral shifts, particularly with frontal lobe tumors.
• Focal neurological deficits — weakness, numbness, speech difficulty, or visual field loss, depending on the brain region involved.
• Nausea and vomiting — associated with elevated intracranial pressure.

Lower-grade gliomas may grow silently for years and be discovered incidentally on imaging. Higher-grade gliomas tend to produce more rapid symptom onset over weeks to months.

The precise causes of sporadic glioma remain poorly understood. Ionizing radiation to the brain is the only well-established environmental risk factor: individuals who received therapeutic cranial irradiation in childhood have a significantly elevated lifetime risk of developing a glioma. No convincing evidence supports a causal role for common exposures such as mobile phone use, power lines, or head trauma, despite extensive investigation.

Prior therapeutic radiation to the brain or skull is the most clearly established modifiable risk factor. Hereditary cancer syndromes, including neurofibromatosis type 1, Li-Fraumeni syndrome, Lynch syndrome, Turcot syndrome, and certain rare familial glioma conditions, confer an elevated lifetime risk of glioma development. Individuals with a first-degree relative with glioma also have a modestly elevated risk, though most cases are sporadic. These genetic syndromes account for only a small fraction of the total glioma burden.