Glioma
The Common Vein Copyright 2010
Definition
Glioma – low grade/anaplastic glioma
Gliomas are tumors that arise from glial cells,. The most common type of glioma is an astrocytoma which is then further subdivided into infiltrating and non-infiltrating. Among the infiltrating, there is a spectrum of histologic changes which correlates well with clinical outcome. These infiltrating astrocytomas span a spectrum from diffuse (or low grade) astrocytoma to anaplastic astrocytoma through glioblastoma, which is discussed in another section.
Pathologically, diffuse astrocytomas are characterized by a poorly defined mass which expands and distorts involved brain parenchyma. Microscopically, diffuse astrocytomas demonstrate increased cellularity, variable nuclear pleomorphism, and a mesh of GFAP-positive astrocytic processes with a characteristic fibrillary appearance. As with many other tumors, the neoplastic cells infiltrate into adjacent normal brain, often leading to underestimation of true tumor involvement at gross pathology or on imaging. Anaplastic astrocytomas are slightly more aggressive with pathologic features of increased nuclear pleomorphism and presence of mitotic figures compared to the low grade astrocytoma.
Specific predisposing factors are unknown at this point. Patients can present at any age but are commonly between 40-50 years old.
As with most brain tumors, symptoms depend on the location of the mass. Seizure or signs of increased intracranial pressure are common as are focal neurologic deficits or personality changes.
These tumors commonly demonstrate malignant degeneration to a more aggressive form. Diffuse astrocytomas will degenerate into anaplastic astrocytomas. Ananplastic astrocytomas degenerate into glioblastomas. The prognosis subsequently worsens.
Astrocytomas can be imaged by CT however MRI is more sensitive. Typical imaging characteristics of these astrocytomas include a focal region of white matter hypodensity on CT with associated expansion. These tumors have a predilection for the frontal and temporal lobes. MRI demonstrates a focal area of T2 hyperintensity. Although the imaging may suggest a well circumscribed mass, it is well established that these infiltrating tumors extend beyond the border of the abnormality on imaging. Diffuse astrocytomas generally do not demonstrate enhancement after contrast. Most anaplastic astrocytomas do not enhance either however, some may demonstrate homogeneous or regions of patchy enhancement. Peripheral enhancement however should raise the suspicion for the more aggressive glioblastoma.
Treatment options for diffuse and anaplastic astrocytomas include resection and radiation with or without chemotherapy. Prognosis for these patients, however is guarded with median survival of 6-10 years for diffuse and 2-3 years for anaplastic astrocytomas.
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