Astrocytoma

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. This article focuses on the well-differentiated (Grade 2) astrocytoma. For grade 1 and 4 astrocytomas.

Pathogenesis

 Well-differentiated astrocytomas constitute about 25 to 30% of cerebral gliomas. They have a predilection for the cerebrum, cerebellum, hypothalamus, pons, and optic nerve and chiasm. Although astrocytomas have many different histological characteristics, the most common type is the well-differentiated fibrillary astrocytoma. These tumors express glial fibrillary acidic protein (GFAP), which possibly functions as a tumor supressor, and 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 at diagnosis of 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 course.

 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).

 Children with astrocytoma usually have decreased memory, attention, and motor abilities, but unaffected intelligence, language, and academic skills. When metastasis occurs, it can spread via the lymphatic system, causing death even when the primary tumor is well controlled.

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. In some rare cases, the tumor creates two or more cell types, and treatment may kill one cell type while allowing the other to become more aggressive and immune to future treatments.