gms | German Medical Science

Objective: The use of 5-aminolevulinic acid (5-ALA) fluorescence to delineate tumors tissue is an established technique for primary malignant brain tumors, less so for metastatic brain disease. Critics argue that visibility of tumor cells at resection margins may elude microscopic visualization. Therefore, a specific 5-ALA endoscope was developed with the aim of 1) improving exposure of the deep surgical site to photons with the exciting wavelength emitted by the optic apparatus and 2) improving the restricted penetration depth of 5-ALA-induced fluorescence. We assessed the utility of endoscopic 5-ALA-assisted resection of brain metastases

Methods: A standard dose of 5-ALA 20 mg/kg was administered to 26 patients with suspected brain metastases 4 hours before surgery. After microsurgical tumor resection a microscope and the 5-ALA fluorescence-enabled endoscope were used to examine tumor margins. We quantified fluorescence into 3 grades (0=none, 1=weak and 2=strong). Endoscopic visualization was employed in cases of no or weak microscopic fluorescence. If possible, 5-ALA positive margins were resected and evaluated by histologic examination.

Results: In 26 patients histological specimens were obtained from the margin of the microsurgical resection cavity. Average age was 66 ± 18. Sixteen patients were male (61.5%). Non-small cell lung cancer accounted for 9 cases (34.6%). In 22/26 patients (85%) fluorescence-guided endoscopic visualization identified 5-ALA-positive tissue not previously deemed strongly fluorescent using the conventional fluorescence-microscope. No fluorescence was found neither with the microscope nor the endoscope in 4/26 cases (15%). In 7 cases with no fluorescence under microscopic examination the endoscope revealed positive fluorescence (27%). In 15/26 cases (58%), weak fluorescence under the microscope translated into strong fluorescence upon endoscopic reappraisal. After correlation with the histopathological findings the 5-ALA endoscope allowed identification of peri-metastatic infiltration with a 95.5% sensitivity and 75% specificity.

Conclusion: Fluorescence-guided endoscopic visualization might help to overcome technical limitations of the conventional microscopic exposure of 5-ALA-positive metastatic tissue.