Fluorescence-guided resection of metastatic brain tumors using a 5-aminolevulinic acid-induced protoporphyrin IX: pathological study

We performed a pathological study to identify the locus of production of protoporphyrin IX (PPIX) in human metastatic brain tumors. Patients with metastatic brain tumors (n = 11) received 1g of 5-aminolevulinic acid (5-ALA) perorally 2h before undergoing surgery. The target region was exposed to laser light with a peak wavelength of 405 +/- 1nm and an output of 40mW. Tissue samples from the tumor bulk and surrounding areas were examined by histological and fluorescence methods. Of the 11 tumors, 9 manifested PPIX fluorescence in the tumor bulk and peritumoral brain tissue. Our findings indicate that PPIX fluorescence can be observed in peritumoral edematous areas that are free of neoplastic cells, because PPIX produced by neoplastic cells leaks into the surrounding edematous area.