Revised: June 2014
Low grade astrocytomas include pilocytic astrocytomas and fibrillary (or diffuse) astrocytomas. A distinction is crucial as their respective biologic behaviours are markedly divergent. Other low-grade astrocytomas include protoplasmic astrocytomas, granular cell astrocytomas, pleomorphic xanthoastrocytoma, astroblastomas, and dysembryoplastic neuroepithelial tumours (1).
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 tumours 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, tumour location and size must all be heavily considered before any modality of surgery, radiation or chemotherapy is employed. As a general rule, an early attempt at aggressive surgical resection is considered beneficial to outcome, assuming of course minimal associated surgical morbidity (2). For pilocytic lesions, complete surgical resection is usually considered curative. Recent studies indicate in high risk low grade gliomas (age >40, or incomplete resection) a combination of radiotherapy with adjuvant PCV chemotherapy carries an improved prognosis (3).Currently a watchful waiting approach can be recommended for younger patients with gross total resection, but it may be that these patients would also benefit from combined modality therapy.
Tumour recurrence or latent progression requires a thoughtful re-appraisal of the patient, bearing in mind the frequent degeneration of these tumours into malignancy. Re-resection, palliative chemotherapy and occasionally re-irradiation remain possible interventions for these patients.
Protoplasmic astrocytomas, granular cell astrocytomas, pleomorphic xanthoastrocytoma, astroblastomas, and dysembryoplastic neuroepithelial tumours generally have rather indolent biologic behaviours. 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.
References:
Louis DN, Ohgaki H, Wiestler OD, Cavenee WK (eds.). World Health Organization Histological Classification of Tumours of the Central Nervous System. Lyon: International Agency for Research on Cancer, 2007
Jakola AS, Myrmel KS, Kloster R, et al. Comparison of a strategy favoring early surgical resection vs a strategy favoring watchful waiting in low-grade gliomas. Journal of the American Medical Association. 2012; 08(18):1881-1888.
Buckner JC, Pugh SL, Shaw EG, et al. Phase III study of radiation therapy with or without procarbazine, CCNU and vincristine (PCV) in low grade glioma: RTOG 9802 with Alliance, ECOG and SWOG. J Clin Oncol 2014. 32:5s, abstr 2000.
