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01 Low Grade Astrocytoma

Revised: February 2004

Low grade astrocytomas include pilocytic astrocytomas and fibrillary (or diffuse) astrocytomas. A distinction is crucial as their respective biologic behaviors are markedly divergent. Other low-grade astrocytomas include protoplasmic astrocytomas, granular cell astrocytomas, pleomorphic xanthoastrocytoma, astroblastomas, and dysembryoplastic neuroepithelial tumors.

Fibrillary astrocytomas, in the adult population, are by far the most common type of low-grade astrocytoma. Seizures are the most common mode of presentation. An important feature of these lesions is a high propensity for anaplastic degeneration. These lesions carry a characteristic, but by no means universal, imaging appearance. Typically they appear as low-density/low-signal, non-enhancing lesions with modest mass effect. However, anaplastic tumors can often carry a similar appearance and thus caution must be made in trying to make histologic interpretations based purely on imaging studies. Suffice it to say, tissue diagnosis is generally required for optimal management.

Current management recommendations are very much patient specific. Patient age, neurologic condition, tumor location and size must all be heavily considered before any modality of surgery, radiation or chemotherapy is employed. As a general rule, an attempt at aggressive surgical resection is considered beneficial to outcome, assuming of course minimal associated surgical morbidity. For pilocytic lesions, complete surgical resection is usually considered curative. Recent studies indicate that adjunctive radiation therapy appears to carry equal benefit whether performed early or late. If surgical resection can not be done with safety, the role of radiation therapy must then be carefully considered against its potential side-effects in patients expected to carry a relatively longer survival. As such, seizure control with careful serial imaging and clinical examination is often a treatment of choice. Chemotherapy generally has no role in the primary management of low-grade astrocytomas.

Tumor recurrence or latent progression requires a thoughtful re-appraisal of the patient, bearing in mind the frequent degeneration of these tumors into malignancy.

Protoplasmic astrocytomas, granular cell astrocytomas, pleomorphic xanthoastrocytoma, astroblastomas, and dysembryoplastic neuroepithelial tumors generally have rather indolent biologic behaviors. Aggressive surgical resection can be curative for such lesions.

The general outlook of patients with low grade astrocytoma is more favourable than a malignant astrocytoma with median survival between 5-10 years, depending on the type of tumour.