Low-grade hemispheric gliomas in adults: a critical review of extent of resection as a factor influencing outcome

Object. The goal of this study was to perform a critical review of literatu re pertinent to low-grade gliomas of the cerebral hemisphere in adults and, on the basis of this review, to evaluate systematically the prognostic eff ect of extent of resection on survival and to determine if treatment-relate d guidelines could be established for patients in whom these tumors have be en newly diagnosed. Quality of evidence for current treatment options, guid elines, and standards as well as methodological limitations were evaluated. Methods. Several prognostic factors thought to affect outcome in patients w ith low-grade gliomas include the patient's age and neurological status, tu mor volume and histological characteristics, and treatment-related variable s such as timing of surgical intervention, extent of resection, postoperati ve tumor volume, and radiation therapy. Patient age and the histological ch aracteristics of the lesion are generally accepted prognostic factors. Amon g treatment-related factors, timing and extent of resection are controversi al because of the lack of randomized controlled trials addressing these iss ues and the difficulty in obtaining information from available studies that have methodological limitations. All English-language studies on low-grade gliomas published between January 1970 and April 2000 were reviewed. Thirty studies that included statistica l analyses were further evaluated with regard to the prognostic effect of e xtent of resection. Of these 30 studies, those that included pediatric pati ents, unless adults were analyzed separately, were excluded from further st udy because of the favorable outcome associated with the pediatric age grou p. Also excluded were studies including pilocytic and gemistocytic astrocyt omas, because the natural histories of these histological subtypes are sign ificantly different from that of low-grade gliomas. Series in which there w ere small numbers of patients (< 75) were also excluded. Results for oligod endrogliomas are reported separately. Currently, for patients with low-grade glial tumors located in the cerebral hemisphere, the only management standard based on high-quality evidence is tissue diagnosis. All other treatment methods are practice options support ed by evidence that is inconclusive or conflicting. The majority of publish ed series that the authors identified had design-related limitations includ ing a small study size, a small number of events (that is, deaths for survi val studies), inclusion of pediatric patients, and/or inclusion of various histological types of tumors with different natural histories. Of the 30 se ries addressing the issue of timing and extent of surgery, almost all had a dditional design limitations. Methods used to determine the extent of resec tion were subjective and qualitative in almost all studies. Only five of th e 30 series met the authors' criteria, and these studies are discussed in d etail. Conclusions. Management of low-grade gliomas is controversial and practice parameters are ill defined. This is caused by limited knowledge regarding t he natural history of these tumors and the lack of high-quality evidence su pporting various treatment options. Although a prospective randomized study seems unlikely, both retrospective matched studies and prospective observa tional trials will improve the clinician's ability to understand the import ance of various prognostic factors.