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Astrocytomas are primary intracranial tumors derived from astrocytes cells of the brain. They may arise in the cerebral hemispheres, in the posterior fossa, in the optic nerve, and rarely, the spinal cord. The WHO has given a four point scale depending on the histologic grade of the tumor (see below). This article focuses on the well-differentiated (Grade 2) astrocytoma. For grade 1, 3, and 4 astrocytomas, see respective article headings:
Pathogenesis
The well-differentiated astrocytomas constitutes about 25 to 30% of cerebral gliomas. It has a predilection for the cerebrum, cerebellum, hypothalamus, optic nerve and chiasm, and pons. Although astrocytomas has many different histological characteristics, the most common is the well-differentiated fibrillary astrocytomas. These tumors contain the glial fibrillary acidic protein (GFAP), which is a useful diagnostic marker in a tissue biopsy.
Grading
Astrocytomas have great variation in their presentation. The World Health Organization acknowledges the following grading system for astrocytomas:- Grade 1 — pilocytic astrocytoma - primarily pediatric tumor, with median age of diagnosis at 12
- Grade 2 — diffuse astrocytoma
- Grade 3 — anaplastic (malignant) astrocytoma
- Grade 4 — glioblastoma multiforme (most common)
In addition to these four tumor grades, astrocytomas may combine with oligodendrocytes to produce oligoastrocytoma. Unique astrocytoma variants have also been known to exist.
Symptoms
In almost half of the cases, the first symptom of an astrocytoma is the onset of a focal or generalized seizure. Between 60 to 75% of patients will have recurrent seizures in the course of their illness. Headache and signs of increased intracranial pressure (headache, vomiting) usually present late in the disease.
In children, the tumor is usually located in the cerebellum and will present with some combination of gait instability, unilateral ataxia, and signs of increased intracranial pressure (headache, vomiting).
Diagnosis
A Computed Tomography (CT) or Magnetic Resonance Imaging (MRI) scan is necessary to characterize the anatomy of this tumor (size, location, consistency). CT will usually show distortion of third and lateral ventricles with displacement of anterior and middle cerebral arteries.
Histologic diagnosis with tissue biopsy will normally reveal an infiltrative character suggestive of the slow growing nature of the tumor. The tumor may be cavitating, pseudocyst-forming, or noncavitating. Appearance is usually white-gray, firm, and almost indistinguishable from normal white matter.
Treatment
Resection of the tumor will generally allow functional survival for many years. In recent reports, the 5 year survival has been over 90% with well resected tumors. These tumors will eventually undergo malignant transformation, and addition of radiation therapy or chemotherapy will be necessary. Astrocytomas often recur even after treatment and are usually treated similarly as the initial tumor, with sometimes more aggressive chemotherapy or radiation therapy.
See also
"Astrocytoma"