Tumor Classification

Astrocytomas: (3,5)

Pilocytic astrocytomas (Grade I) primarily affect children and tend to be treated effectively by surgical resection. They appear more commonly in the posterior fossa and are often associated with cyst formation, contributing to mass effect. Although complete resection usually affords longtime survival, frequent postoperative radiological imaging with MRI should be assessed for any evidence of recurrence.

Diffuse type astrocytomas are classified as Grade II and generally occur in adulthood (mean age 35). These tumors are slower growing tumors, but they may have an inherent tendency to progress to anaplastic astrocytoma and eventually to glioblastoma. Most diffuse astrocytomas develop in the cerebral cortex with a predilection for the frontal and temporal lobes. The brain stem and spinal cord are the next most frequently affected sites, while the cerebellum is a distinctly uncommon site for the development of diffuse astrocytomas.12 These tumors are differentiated from other types by their moderate cellularity and level of infiltration.

Anaplastic Astrocytomas are Grade III and tend to arise in the same locations as diffuse astrocytomas, with a preference for the cerebral hemispheres. These tumors have an aggressive tendency to infiltrate through neighboring tissues and are often diagnosed when they have become large and are causing mass effect on eloquent structures. These tumors tend to occur later in adulthood, around 50 years of age.

Glioblastoma multiformes (GBMs) are Grade IV and usually affect adults later in life, i.e., after the fifth decade. These tumors are rapidly growing and aggressive, such that the prognosis for patients with glioblastoma remains approximately 1 year despite aggressive surgical resection, radio- and chemotherapy. GBMs are also highly heterogeneous in gross and microscopic appearance. Macroscopic multifocality is not uncommon in glioblastomas, particularly at autopsy. This histiological finding almost always represents spread of a single tumor rather than true multiple primary gliomas. Spread in this fashion along white matter tracts may be prominent.

Oligodendrogliomas:3,5,6

Oligodendrogliomas represent 30% of all adult gliomas. Oligodendrogliomas infiltrate the gray and white matter in a diffuse manner, similar to diffuse astrocytomas, although these tumors are usually more solid and more demarcated. These tumors can be either low or high-grade as determined by their mixed anatomic structure, although there fails to be a uniform agreement on distinguishing between the classes. Generally, the lower grade oligodendrogliomas tend to have well defined macroscopic margins with the adjacent brain and grow at a slower rate than the more aggressive infiltrative anaplastic oligodendrogliomas. These tumors are a subset of gliomas that seem to evolve from low grade well-differentiated oligodendrogliomas. Salient features of this class of tumor include: necrosis, microvascular hyperplasia, and brisk mitoic activity along with significantly more aggressive clinical manifestations. A unique characteristic of these tumors is that a subtype are among the most chemosensitive of all the solid brain malignancies. Oligodendrogliomas which have a 1p- phenotype respond extremely well to specific chemotherapy.

Mixed gliomas typically are comprised of oligoastrocytomas. The histogenesis of oligoastrocytomas remains controversial, with some data arguing similarity of oligoastrocytomas to astrocytic tumors, and other data suggesting closer relationships with oligodendroglial neoplasms. The classification is mainly determined on the basis of molecular markers. However, in some cases the presence of particular cellular pathology may blur these distinctions with those of anaplastic oligodendrogliomas.

Ependymal gliomas:

Ependymal gliomas are commonly divided into classic ependymomas (Grade II) and anaplastic ependymomas (Grade III), with two important benign (i.e., Grade II) subtypes being subependymoma and myxopapillary ependymoma. Intracranial ependymomas and subependymomas often grow as intraventricular masses, most characteristically from the floor of the fourth ventricle. These tumors do not infiltrate normal central nervous system tissue as extensively as astrocytomas and may be cured by surgical resection alone.

Spinal Ependymomas:

Spinal ependymomas, alternatively, grow within the parenchyma of the spinal cord, forming well defined, often elongated masses. In the cauda equina, the myxopapillary subtype usually presents as a sausage-shaped, apparently encapsulated growth. Many patients present with lower extremity weakness or bowel/bladder complaints. Radiation therapy may be recommended to prevent regrowth. Chemotherapy may also be given, especially if the tumor is an ependymoblastoma (high grade).