Intraoperative confocal microscopy in the visualization of 5-aminolevulinic acid fluorescence in low-grade gliomas

Clinical article

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Greater extent of resection (EOR) for patients with low-grade glioma (LGG) corresponds with improved clinical outcome, yet remains a central challenge to the neurosurgical oncologist. Although 5-aminolevulinic acid (5-ALA)–induced tumor fluorescence is a strategy that can improve EOR in gliomas, only glioblastomas routinely fluoresce following 5-ALA administration. Intraoperative confocal microscopy adapts conventional confocal technology to a handheld probe that provides real-time fluorescent imaging at up to 1000× magnification. The authors report a combined approach in which intraoperative confocal microscopy is used to visualize 5-ALA tumor fluorescence in LGGs during the course of microsurgical resection.


Following 5-ALA administration, patients with newly diagnosed LGG underwent microsurgical resection. Intraoperative confocal microscopy was conducted at the following points: 1) initial encounter with the tumor; 2) the midpoint of tumor resection; and 3) the presumed brain-tumor interface. Histopathological analysis of these sites correlated tumor infiltration with intraoperative cellular tumor fluorescence.


Ten consecutive patients with WHO Grades I and II gliomas underwent microsurgical resection with 5-ALA and intraoperative confocal microscopy. Macroscopic tumor fluorescence was not evident in any patient. However, in each case, intraoperative confocal microscopy identified tumor fluorescence at a cellular level, a finding that corresponded to tumor infiltration on matched histological analyses.


Intraoperative confocal microscopy can visualize cellular 5-ALA–induced tumor fluorescence within LGGs and at the brain-tumor interface. To assess the clinical value of 5-ALA for high-grade gliomas in conjunction with neuronavigation, and for LGGs in combination with intraoperative confocal microscopy and neuronavigation, a Phase IIIa randomized placebo-controlled trial (BALANCE) is underway at the authors' institution.

Abbreviations used in this paper: 5-ALA = 5-aminolevulinic acid; BALANCE = Barrow ALA Intraoperative Confocal Evaluation; BNI = Barrow Neurological Institute; EOR = extent of resection; GTR = gross-total resection; HGG = high-grade glioma; LGG = low-grade glioma; NIHSS = National Institutes of Health Stroke Scale; ROI = region of interest.

Article Information

Address correspondence to: Nader Sanai, M.D., Division of Neurosurgical Oncology, Barrow Brain Tumor Research Center, Barrow Neurological Institute, 2910 North Third Avenue, Phoenix, Arizona 85013. email:

Please include this information when citing this paper: published online July 15, 2011; DOI: 10.3171/2011.6.JNS11252.

© AANS, except where prohibited by US copyright law.



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    Microscopic 5-ALA tumor fluorescence detected in a WHO Grade II glioma by using intraoperative confocal microscopy. A: Axial MR image obtained in a 21-year-old man in whom a right frontal LGG was detected incidentally following a motor vehicle accident. B: Intraoperative view; the handheld confocal microscope was used in the absence of macroscopic 5-ALA tumor fluorescence. C: Intraoperative neuronavigation studies confirming localization of the confocal imaging within the tumor mass. D: Multiple fluorescent cells were observed within this region, corresponding to 5-ALA metabolism. E: Postoperative axial FLAIR MR imaging study confirming a 98% volumetric EOR.

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    Identification of LGG tumor margins by using confocal microscopy and 5-ALA tumor fluorescence. A: Axial MR image obtained in a 39-year-old woman with a right parietal WHO Grade II glioma who underwent routine microsurgical resection. B: Intraoperative neuronavigation studies identifying a resection cavity margin as radiographically free of tumor. C: Results of intraoperative confocal microscopy at this site were negative, suggesting an absence of infiltrating LGG. D: Histological analysis of this same region, with an H & E–stained section confirming the absence of tumor. Original magnification × 40. E: Intraoperative neuronavigation studies identifying the presumed margin of the brain-tumor interface. F: Macroscopic 5-ALA tumor fluorescence was not evident, and a region of the cavity wall (box) was analyzed using intraoperative confocal microscopy. G: Image of the same region revealing evidence of persistent fluorescent tumor infiltration. H: Corresponding histopathological analysis of this ROI, with an H & E–stained section confirming the presence of infiltrating tumor, including cells with nuclear atypia (arrows). Original magnification × 40. I: Postoperative axial FLAIR MR imaging study confirming a 99% volumetric EOR.

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    Intraoperative confocal microscopy visualization of 5-ALA cellular fluorescence in a transforming WHO Grade II/III oligodendroglioma. A: Axial MR image obtained in a 37-year-old woman who presented with new-onset seizures and a nonenhancing right supplementary motor area mass. B: During microsurgical resection, intraoperative neuronavigation confirmed localization of the confocal imaging within the tumor mass. C: Macroscopic 5-ALA tumor fluorescence was not evident, and a region of the tumor (box) was analyzed using intraoperative confocal microscopy. D: Image of the same region revealing 5-ALA–induced tumor fluorescence. E: Correlative analysis of this site with an H & E–stained section identifying it as a focal region of WHO Grade III histological characteristics, as evidenced by the presence of microvascular proliferation (arrows). Original magnification × 40. F: Within this same region, atypical mitotic figures (arrow) were also encountered on an H & E–stained section. Original magnification × 80. G: Postoperative axial FLAIR MR imaging study confirming a 100% volumetric EOR.



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