Intraoperative 5-aminolevulinic
acid (5-ALA)-induced fluorescence guidance for resection of malignant
brain tumors was correlated with histological examination to investigate false positive findings in 42 patients with
malignant glioma and six patients with metastatic
brain tumor. Patients received a single 1 g oral dose of 5-ALA 2 hours before surgery. The
tumor site was illuminated with a
laser with a peak wavelength of 405 +/- 1 nm and output of 40 mW. Samples with strong fluorescence were obtained from the
tumor bulk and samples with weak fluorescence from the
tumor cavity. Fluorescence was observed in 36 of the 42
malignant gliomas and four of the six metastatic
brain tumors. No
tumor cells were found in fluorescent samples from six of the 36
malignant gliomas and all four metastatic
brain tumors. Five of the six
malignant gliomas were recurrent cases. Fluorescence was found in areas of peritumoral
edema or inflammatory cell and reactive astrocyte infiltration. Intraoperative 5-ALA-induced fluorescence guidance is useful for the resection of initial
malignant glioma since false positive results are rare, but only non-eloquent weak positive areas should be resected. In contrast, all weak positive areas of recurrent
malignant gliomas must be resected. Weak positive areas of the peritumoral
edema surrounding metastatic
brain tumors should be removed carefully as false positive results are common.