Introduction. Visual confirmation of suspicious changes in the urinary tract mucosa is the cornerstone in the diagnosis of urothelial cancer. However, with bladder tumors, it is impossible to obtain histopathological data during cystoscopy both in white light and in photodynamic and narrow-spectrum modes, as well as with computerized chromoendoscopy. Confocal laser endomicroscopy (probe-based confocal laser endomicroscopy – pCLE) is an optical imaging technique that provides high-resolution in vivo imaging and real-time evaluation of urothelial lesions.
Aim. To assess the diagnostic capabilities of pCLE in papillary bladder tumors and compare its results with standard pathomorphological study.
Materials and methods. A total of 38 patients (27 men, 11 women, aged 41–82 years) with primary bladder tumors diagnosed on the imaging methods were included in the study. For the diagnosis and treatment, all patients underwent transurethral resection (TUR) of the bladder. When a standard white light cystoscopy with assessment of the entire urothelium, 10% sodium fluorescein was administrated intravenously as a contrast dye. pCLE was performed with CystoFlexTMUHD 2.6 mm (7.8 Fr) probe, which was passed through the 26 Fr resectoscope using a telescope bridge to visualize normal and pathological urothelial lesions. A laser with a wavelength of 488 nm and a speed of 8 to 12 frames per second allowed to obtain an endomicroscopic image. These images were compared with standard histopathological analysis using hematoxylin-eosin (H&E) staining of tumor fragments removed during TUR of the bladder.
Results. Based on real-time pCLE, 23 patients had a diagnosis of low-grade urothelial carcinoma, while in 12 patients the endomicroscopic picture corresponded to high-grade urothelial carcinoma, 2 patients had typical changes for inflammatory process and 1 case of carcinoma in situ was suspected, which was confirmed by histopathological study. Endomicroscopic images demonstrated clear differences between normal bladder mucosa and high- and low-grade tumors. In the normal urothelium, the larger umbrella cells are located most superficially, followed by smaller intermediate cells, as well as the lamina propria with blood vessels network. In contrast, low-grade urothelial carcinoma is characterized by denser, normal-shaped small cells located superficially than a central fibrovascular core. High-grade urothelial carcinoma exhibits markedly irregular cell architecture and cellular pleomorphism.
Conclusion. pCLE is a promising new method for in-vivo diagnosing of bladder cancer. Our results show its potential for endoscopic determination of the histological characteristics of bladder tumors and the ability to differentiate between benign and malignant processes, as well as the histological grade of tumor cells.

Keywords: urinary bladder neoplasms, confocal laser endomicroscopy, cystoscopy, transurethral resection of the bladder