Fluorescence Guidance and Intraoperative Adjuvants to Maximize Extent of Resection

Abstract

Safely maximizing extent of resection has become the central goal in glioma surgery. Especially in eloquent cortex, the goal of maximal resection is balanced with neurological risk. As new technologies emerge in the field of neurosurgery, the standards for maximal safe resection have been elevated. Fluorescence-guided surgery, intraoperative magnetic resonance imaging, and microscopic imaging methods are among the most well-validated tools available to enhance the level of accuracy and safety in glioma surgery. Each technology uses a different characteristic of glioma tissue to identify and differentiate tumor tissue from normal brain and is most effective in the context of anatomic, connectomic, and neurophysiologic context. While each tool is able to enhance resection, multiple modalities are often used in conjunction to achieve maximal safe resection. This paper reviews the mechanism and utility of the major adjuncts available for use in glioma surgery, especially in tumors within eloquent areas, and puts forth the foundation for a unified approach to how leverage currently available technology to ensure maximal safe resection.

Keywords: 5-aminolevulinic acid (5-ALA); Fluorescence-guided surgery (FGS); Raman microscopy; intraoperative MRI (iMRI).

FIGURE 1.

The use of iMRI in the resection of an anaplastic ependymoma of the fourth ventricle: The preoperative image A demonstrates a contrast-enhancing mass in the fourth ventricle. After GTR is achieved, an MRI is obtained intraoperatively revealing residual-enhancing tissue within the fourth ventricle B. Based on the intraoperative image, further resection is carried out until all enhancing tissue is removed from the fourth ventricle C.

FIGURE 2.

The use of SRH to evaluate the cellularity of glioma margins. A patient with a left frontal pole glioma underwent the MRI shown here and was taken to the OR. 3 × 3 mm biopsies were removed and evaluated in minutes at the bedside with SRH. Tissue taken from the core (*) reveals a hypercellular infiltrating glioma intermixed with axons, which appear as linear “white” elements. All visible and MRI detectable tumor was removed. Sampling of the deep margin (▽) revealed hypercellular white matter and suggested that further resection was required to fully resect all infiltrated tissue in this area. Sampling of the superior margin () revealed mildly gliotic cortex with normal cellularity without evidence of tumor infiltration. No additional resection was required or carried out at the superior margin.

FIGURE 3.

SRH, 5-ALA fluorescence microscopy, and iMRI were all used as intraoperative adjuvants during the resection of a suspected HGG to ensure maximal safe resection in a 46-yr-old woman.