Endoscopic 5ALA-induced Fluorescence Guided Intraparenchymal Brain Tumour Resection – Can the Endoscope Detect More Fluorescence than the Microscope?

Objectives Using a laboratory-based optical setup we show that 5ALA fluorescence is better detected using the endoscope than the microscope. Furthermore, we present our case series of fully-endoscopic 5ALA guided resection of intraparenchymal tumors. Methods A Zeiss Pentero® microscope was compared to the Karl Storz Hopkins® endoscope. The spectra and intensity of each blue light source were measured. Quantitative fluorescence detection thresholds were measured using a spectrometer. Subjective fluorescence detection thresholds were measured by 6 blinded neuro-oncology surgeons. Clinical data were prospectively collected for all consecutive cases of fully-endoscopic 5ALA guided resection of intraparenchymal tumors between 2012-2023. Results The intensity of blue light on the sample was greater for the endoscope than the microscope at working distances below 20mm. The quantitative fluorescence detection thresholds were lower for the endoscope than the microscope at both 30/10mm working distances. Fluorescence detection threshold was 0.65-0.80% relative DCM concentration (3.20x10-7 to 3.94x10-7mol/dm-3) for the microscope, 0.40-0.55 % relative concentrations (1.97x10-7 to 2.71x10-7mol/dm-3) for the endoscope at 30mm and 0.15-0.30% relative concentrations (7.40x10-8 to 1.48x10-7mol/dm-3) for the endoscope at 10mm.49 5ALA endoscope-assisted brain tumor resections were carried out on 45 patients (mean age=41, male=28). Greater than 95% resection was achieved in 80% of cases and gross total resection (GTR) in 42%. GTR was achieved in 100% of tumors in non-eloquent locations. There was 1 new neurological deficit. Conclusion The endoscope provides enhanced visualization/detection of 5ALA-induced fluorescence compared to the microscope. 5ALA endoscopic-assisted resection of intraparenchymal tumors is safe and feasible.