Determination of optical properties of human brain tumor tissues from 350 to 1000 nm to investigate the cause of false negatives in fluorescence-guided resection with 5-aminolevulinic acid.

The optical properties of human brain tumor tissues, including glioblastoma, meningioma, oligodendroglioma, and metastasis, that were classified into "strong," "vague," and "unobservable" fluorescence by a neurosurgeon were measured and compared. The optical properties of the tissues were measured with a double integrating sphere and the inverse Monte Carlo technique from 350 to 1000 nm. Using reasons of ex-vivo measurement, the optical properties at around 420 nm were potentially affected by the hemoglobin content in tissues. Significant differences were not observed between the optical properties of the glioblastoma regions with "strong" and "unobservable" fluorescence. Sections of human brain tumor tissue with "strong" and "unobservable" fluorescence were stained with hematoxylin and eosin. The cell densities [mean ± standard deviation (S.D.)] in regions with "strong" and "unobservable" fluorescence were 31  ±  9  ×  102  per mm2 and 12  ±  4  ×  102  per mm2, respectively, which is a statistically significant difference. The higher fluorescence intensity is associated with higher cell density. The difference in cell density modified the scattering coefficient yet it does not lead to significant differences in the reduced scattering coefficient and thus does not affect the propagation of the diffuse fluorescent light. Hence, the false negatives, which mean a brain tumor only shows "unobservable" fluorescence and is hence classified incorrectly as nontumor, in using 5-ALA for detection of human glioblastoma do not result from the differences in optical properties of human brain glioblastoma tissues. Our results suggest that the primary cause of false negatives may be a lack of PpIX or a low accumulation of PpIX.