Chapter 14 - Extent of Resection for High- and Low-Grade Gliomas

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Glioma surgery aims to maximize tumor resection while minimizing the risk of functional decline. The natural history of gliomas is progressive growth with malignant transformation and recurrence; therefore, the role of surgical resection in the natural history of gliomas has been extensively studied in the last three decades although there is still a need for randomized and prospective trials. In this chapter, we present the available data for extent of resection (EOR) for both high-grade glioma (HGG) and low-grade glioma (LGG). The current mainstay for treatment of HGGs is maximal resection followed by radiation therapy with concurrent or adjuvant chemotherapy. There is clear evidence that maximal EOR helps improve both survival rates and clinical factors such as seizure control, steroid burden, and quality of life, although careful balance between EOR and new postoperative deficits is essential. EOR in LGGs is still a very controversial topic since LGGs have been traditionally considered indolent and slow growing tumors. However, the analyses of molecular markers and the malignant transformation of LGGs are gaining importance. Some studies confirm that those LGGs managed with biopsy or subtotal resection and conservative management have a higher risk of malignant transformation compared with those treated with more extensive tumor removal. As we collect long-term survival data and analyze the impact of resection over decades, the evidence points toward an important benefit in maximal resection for LGGs. Finally, studies on EOR are biased by the patient selection criteria, the quantitative methods used to calculate the amount of resection, and the lack of a truly homogeneous patient treatment. Fortunately, technology and clinical knowledge are constantly evolving to improve both the safety of increased EOR and the opportunities to obtain higher quality data available to our patients and the neurosurgical community.