5-ALA fluorescence-guided surgery is an intraoperative technique that takes advantage of tumor cells accumulating a fluorescent compound to make the location of the tumor more readily apparent. It is primarily used in the resection of high-grade gliomas (e.g. glioblastoma, grade 3 or 4 astrocytomas) although it is also possible to use it in lower grade tumors 1,2.
The use of fluorescence-guided surgery has been shown to increase the amount of tumor resected and increase the percentage of patients achieving gross macroscopic resection 1,2.
Pharmacology
5-aminolevulinic acid (5-ALA) is given orally as a tablet (commercially known as Gliolan®), penetrates the blood brain barrier and is disproportionately absorbed by tumor cells. The amount absorbed is multifactorial, including a paucity of ferrochelatase, increased local permeability of the blood-brain barrier, tumor cell proliferative activity and neovascularity 1,2.
Once inside the cell 5-ALA is converted to protoporphyrin IX (PpIX) which has the useful property of fluorescing red/pink when exposed to 405 nm blue light 1,2.
Intraoperative use
Fluorescence can be identified intraoperatively by bathing the operative field in blue light of the appropriate wavelength. This can be achieved with the use of an appropriate operating microscope or with a small field of view probe 2.
Solid areas of abnormal tissue fluoresce red, whereas areas in which tumor cells are fewer and infiltrating into the adjacent normal brain will appear pink 1.
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