gms | German Medical Science

Objective: Today, microscopic fluorescence-guided (FG) resection is routine in brain tumor surgery. It has been shown, that the percentage of complete tumor removal can be increased from 36 to 65% by MFG resection, offering a survival benefit for the patient. Possible reasons for incomplete tumor resection despite the intake of 5-aminolevulinic acid (ALA) might be eloquence of tumor-infiltrated brain tissue, wrong interpretation of fading fluorescence or overseen fluorescent tumor tissue by a lacking line of sight between tumor tissue and microscope. Aim of this study was to evaluate if an endoscope being capable of inducing fluorescence and visualizing hidden areas in the tumor cavity might overcome some of the limitations of microscopic FG resection.

Method: During microscopic FG resection of either a glioblastoma (n=10) or an infiltrating metastasis (n=5) in a non-eloquent brain area a prototype endoscope with a white and a blue light source was used at least twice:

1.

To assure a comparability of the microscopic and the endoscopic visualization of ALA-fluorescence, tumor tissue with clear fluorescence under the microscope was harvested and investigated under the endoscope.

2.

After microscopic resection with removal of all fluorescent tissue, the resection cavity was endoscopically scanned for overseen fluorescent tissue.

Results: The ex vivo investigation of the harvested tumor tissue proved in all cases, that, irrespective of the histology, the endoscope allows visualization of fluorescent tumor tissue as good as the microscope. The endoscopic scanning of the resection cavity after microscopic FG resection allowed detecting remaining fluorescent tissue in 3 of the 15 patients (20%). In 2 cases of fading fluorescence under the microscope, the endoscope allowed a clearer differentiation between fluorescent and non-fluorescent tissue.

Conclusions: ALA-uptake in tumor tissue can be visualized as good by the endoscope as by the microscope. The endoscope allows detecting fluorescent tumor tissue overseen by the microscope. One might assume that the 20% detection rate will increase if the endoscope is used in the subset of patients with deep seated or ventricular tumors. By bringing the light source closer to the tissue and enhancing the fluorescence, the endoscope might be helpful in the indistinct tumor cases of fading fluorescence under the microscope.