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 (see below). This article focuses on the well-differentiated (Grade 2) astrocytoma. For grade 1 and 4 astrocytomas, see respective article headings:

Main articles: pilocytic astrocytoma and glioblastoma multiforme

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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 suppressor^[1], and is a useful diagnostic marker in a tissue biopsy. ^[2]

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 vision deterioration (which is typically uncorrectable by glasses), 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. ^[3] When metastasis occurs, it can spread via the lymphatic system, causing death even when the primary tumor is well controlled.^[4]

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.

References

1. ^ M Toda et al (1994). "Cell growth suppression of astrocytoma C6 cells by glial fibrillary acidic protein cDNA transfection". Journal of Neurochemistry 63 (5): 1975-1978. PMID 7931355.
2. ^ JHN Deck et al (1978). "The role of glial fibrillary acidic protein in the diagnosis of central nervous system tumors". Acta Neuropathologica 42 (3): 183-190. Springer Berlin / Heidelberg. doi:10.1007/BF00690355.
3. ^ JL Ater et al (1996). "Correlation of medical and neurosurgical events with neuropsychological status in children at diagnosis of astrocytoma: utilization of a neurological severity score". Journal of Child Neurology 11 (6): 462-469. PMID 9120225.
4. ^ JM Dewar, PJ Dady and V Balakrishnan (1985). "Metastatic astrocytoma". Australian and New Zealand Journal of Medicine 15 (6): 745-747. PMID 3010926.

See also

• glioma
• brain tumor
• pilocytic astrocytoma
• glioblastoma multiforme
• intracranial pressure
• Histopathologic video of low grade astrocytoma