Astrocytoma

Encyclopedia : A : AS : AST : 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, 3, and 4 astrocytomas, see respective article headings:

Contents

1 Pathogenesis

1.1 Grading

2 Symptoms
3 Diagnosis
4 Treatment
5 See also

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