Fluorescein-stained confocal laser endomicroscopy versus conventional frozen section for intraoperative histopathological assessment of intracranial tumors

BACKGROUND

The aim of this clinical trial was to compare Fluorescein-stained intraoperative confocal laser endomicroscopy (CLE) of intracranial lesions and evaluation by a neuropathologist with routine intraoperative frozen section (FS) assessment by neuropathology.

METHODS

In this phase II noninferiority, prospective, multicenter, nonrandomized, off-label clinical trial (EudraCT: 2019-004512-58), patients above the age of 18 years with any intracranial lesion scheduled for elective resection were included. The diagnostic accuracies of both CLE and FS referenced with the final histopathological diagnosis were statistically compared in a noninferiority analysis, representing the primary endpoint. Secondary endpoints included the safety of the technique and time expedited for CLE and FS.

RESULTS

A total of 210 patients were included by 3 participating sites between November 2020 and June 2022. Most common entities were high-grade gliomas (37.9%), metastases (24.1%), and meningiomas (22.7%). A total of 6 serious adverse events in 4 (2%) patients were recorded. For the primary endpoint, the diagnostic accuracy for CLE was inferior with 0.87 versus 0.91 for FS, resulting in a difference of 0.04 (95% confidence interval -0.10; 0.02; P = .367). The median time expedited until intraoperative diagnosis was 3 minutes for CLE and 27 minutes for FS, with a mean difference of 27.5 minutes (standard deviation 14.5; P < .001).

CONCLUSIONS

CLE allowed for a safe and time-effective intraoperative histological diagnosis with a diagnostic accuracy of 87% across all intracranial entities included. The technique achieved histological assessments in real time with a 10-fold reduction of processing time compared to FS, which may invariably impact surgical strategy on the fly.

P05.01.B Distribution of the staining agent sodium-fluorescein in cerebral neoplasia - a comparison between intraoperative confocal laser endomicroscopy and in vitro fluorescence microscopy

Background

While conventional frozen sections and other ex vivo microscopy always come along with artefacts, in vivo confocal laser endomicroscopy (CLE) offers less invasive, less manipulated imaging of living tissues. Understanding the distribution of the staining agent sodium-fluorescein (NaFl) plays a key role in establishing in vivo CLE as a new opportunity for real-time transmitted, in vivo imaging.

By comparing the distribution of NaFl in in vivo and ex vivo CLE to conventional fluorescence microscopy of NaFl incubated tumor cell cultures we gain a better understanding of the staining mechanism.

Material and Methods

Sodium-fluorescein is the water-soluble sodium salt of fluorescein and is used as a fluorescent tracer in neurosurgery. The staining agent was applied intravenously at the beginning of the surgical procedure. In vivo CLE of the lesion was performed 30 to 50 minutes later and compared to ex vivo CLE imaging and conventional fluorescence microscopy. In addition, different tumor cell lines derived from malignant gliomas and carcinomas, respectively, were incubated with NaFl in vitro and the uptake of the fluorescent dye was monitored over time.

Results

From initial results, the intraoperative images showed specific fluorescein distribution depending on the architecture of the tumor entity. In most cases, glial tumors demonstrated higher accumulation of the staining agent in the extracellular tumor matrix, whereas the cells of carcinoma metastases appeared to take up NaFl intracellularly. These results were corroborated by NaFl uptake in cell culture experiments.

Compared to ex vivo CLE, in vivo imaging offered a faster assessment of the tissue, brighter images and higher staining levels. Due to movement artefacts and the narrow intraoperative imaging time frame, in vivo CLE images were sometimes impaired by lower image quality.

Conclusion

The specific distribution of the fluorescent agent NaFl allowed for a discrimination between the different neoplastic entities. Images from in vivo and ex vivo confocal laser endomicroscopy showed NaFl uptake in concordance with the results of NaFl incubated cell cultures.

Intraoperative, in vivo confocal laser endomicroscopy shows promising first results in the understanding of brain tumor histomorphology in situ. Being faster and less manipulated by artefacts than ex vivo investigations, it opens up wider opportunities for research and intraoperative diagnostics.