The most common type of primary brain tumor, glioma, actually comprises a spectrum of tumor types and behavior.

Astrocytoma

The most common subtype is astrocytoma. This category is further separated into three groups. These groups are termed low grade astrocytoma (WHO grade II/IV), Anaplastic astrocytoma (WHO grade III/IV), and Glioblastoma Multiforme or GBM (WHO grade IV/IV). Although all these types are to some degree malignant, lower grade lesions typically behave much less aggressively than those of higher grade.

Oligodendroglioma

A second common subtype is oligodendroglioma. These tumors are also graded with respect to characteristics associated with malignancy and aggressive behavior. As a general rule, however, they often behave in a less aggressive fashion than astrocytomas. Many primary brain tumors, however, will not fit within one of these categories. Microscopic examination of the tissue specimen may reveal cellular characteristics typical of multiple cell lines. These tumors will be termed mixed gliomas. They may also be assigned a grade in attempt to predict and characterize likely behavior and guide treatment.

Although a suspected asymptomatic low grade glioma may be observed under certain circumstances, most gliomas will require surgical resection (removal) if possible. Following surgery, further treatment will be dictated by the type of tumor and in some cases, extent of resection. Many will require radiation and/or chemotherapy. Regardless of the tumor subtype and grade, all of these tumors have the potential for recurrence and follow-up MRI scans will be necessary for long-term surveillance.

MRI before removal of a low-grade glioma

Pilocytic Astrocytoma

As opposed to most gliomas, pilocytic astrocytomas (WHO grade I/IV) are potentially curable with complete surgical removal. They are more common in children and young adults. They may occur anywhere within the brain, but are commonly found in the cerebellum, brainstem, and deep brain structures such as the thalamus. Surgery for lesions in these locations is often very complicated, but may provide great benefit, given the nature of these tumors. With complete resection of the tumor, pilocytic astrocytomas may not require any further treatment.

Ependymoma

MRI after removal of a low-grade glioma

Another type of primary brain tumor, ependymomas, may occur at any location along the brain and spinal cord. Most, however, are found in a region at the base of the brain known as the posterior fossa. The most common presenting symptoms are headache, nausea and vomiting, and difficulty with balance. Ependymomas are one of the more common types of brain tumors in children. Patients with this type of tumor should usually undergo surgical resection of the tumor. Follow-up treatment will depend on whether or not the entire tumor is resected. This type of tumor is at risk to metastasize (spread) within the central nervous system.