Visualization of 5-Aminolevulinic Acid Flourescence in Low Grade Gliomas

Keywords: glioma, Imaging, astrocytoma, brain tumor, resection

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     Greater extent of resection (EOR) for low-grade glioma (LGG) patients corresponds with improved clinical outcome, yet remains a challenge to the neurosurgical oncologist. Although 5-aminolevulinic acid (5-ALA)-induced tumor fluorescence improves glioma extent of resection, only glioblastomas routinely fluoresce with 5-ALA. Intraoperative confocal microscopy adapts confocal technology to a handheld probe, providing real-time cellular fluorescent imaging at 1000-fold magnification.
     We report the first combined approach using intraoperative confocal microscopy to visualize 5-ALA fluorescence in LGG during microsurgical resection.
     Following 5-ALA administration, 10 newly-diagnosed LGG patients underwent microsurgical resection.
     Confocal microscopy was conducted at initial tumor encounter, midpoint of tumor resection, and presumed brain-tumor interface. Correlative histopathological analysis of these sites was performed. Routine pre- and postoperative clinical data, including neurological deficits and volumetric EOR, were quantified.
     Ten consecutive patients with WHO grades I and II gliomas underwent microsurgical resection using 5-ALA and intraoperative confocal microscopy. Macroscopic tumor fluorescence was not evident in any patient. However, in all cases, intraoperative confocal microscopy identified tumor fluorescence at a cellular level, a finding that corresponded to tumor infiltration on matched histological analyses. In 3 patients (30%), the presence of infiltrating tumors at the margins did not correspond with neuronavigational MR imaging and led to additional tumor resection.
     This is a retrospective study.
     Intraoperative confocal microscopy can routinely visualize cellular 5-ALA-induced tumor fluorescence within LGG and at the brain-tumor interface.
     This combination of technologies enables a quick optical biopsy at the margins of resection, enabling verification of neuronavigational imaging and a real-time, in vivo assessment of microscopic residual.


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