Confocal Laser Endomicroscopy in glial tumors – a histomorphological analysis

Objective: Extent of resection and neurological outcome are important prognostic markers for overall survival. Confocal laser endomicroscopy is a tool to examine tissue without the need for fixation or staining. This study aims to analyze gliomas in confocal laser endomicroscopy identify reliable diagnostic criteria for glial matter and glial tumors. Material and methods: One-hundred-and-five glioma specimens were analyzed using a 670nm confocal laser endomicroscope, then processed to hematoxylin-eosin-stained frozen sections. All confocal images and frozen sections were evaluated for the following criteria: presence of tumor; cellularity, nuclear pleomorphism, changes of the extracellular glial matrix, microvascular proliferation, necrosis and mitotic activity. Recurring characteristics were identified. Accuracy, sensitivity, specificity and positive and negative predictive values were assessed for each feature. Results: All 125 specimens could be processed and successfully analyzed via confocal laser endomicroscopy. We found diagnostic criteria to identify white and grey matter and analyze cellularity, nuclear pleomorphism, changes of the glial matrix, vascularization and necrosis in glial tumors. An accuracy of > 90.0% was reached for grey matter, cellularity and necrosis, > 80.0% for white matter and nuclear pleomorphism and > 70.0% for microsvascular proliferation and changes of the glial matrix. Mitotic activity could not be identified. Conclusion: Autofluorescence-based confocal laser endomicroscopy provides reliable information on tissue microstructure in glial tissue without further processing. The use of those diagnostic criteria to differentiate between glial tumor tissue and surrounding brain tissue as well as high grade versus low grade and astroglial versus oligodendroglial tumors was assessed in a follow-up study.