In vivo characterization of pancreatic cystic lesions by needle-based confocal laser endomicroscopy (nCLE): proposition of a comprehensive nCLE classification confirmed by an external retrospective evaluation

Background and aims The differential diagnosis of solitary pancreatic cystic lesions is sometimes difficult. Needle-based confocal laser endomicroscopy (nCLE) performed during endoscopic ultrasound-fine-needle aspiration (EUS-FNA) enables real-time imaging of the internal structure of such cysts. Criteria have already been described for serous cystadenoma and intraductal papillary mucinous neoplasm (IPMN). The aims of the study were to determine new nCLE criteria for the diagnosis of pancreatic cystic lesions, to propose a comprehensive nCLE classification for the characterization of those lesions, and to carry out a first external retrospective validation. Methods Thirty-three patients with a lone pancreatic cystic lesion were included (CONTACT 1 study). EUS-FNA was combined with nCLE. Diagnosis was based on either pathology result (Group 1, n = 20) or an adjudication committee consensus (Group 2, n = 13). Six investigators, unblinded, studied cases from Group 1 and identified nCLE criteria for mucinous cystic neoplasm (MCN), pseudocyst (PC), and cystic neuroendocrine neoplasm (NEN). Four external reviewers assessed, blinded, the yield and interobserver agreement for the newly identified (MCN, PC) and previously described (IPMN, SC) criteria in a subset of 31 cases. Results New nCLE criteria were described for MCN (thick gray line), PC (field of bright particles), and cystic NEN (black neoplastic cells clusters with white fibrous areas). These criteria correlated with the histological features of the corresponding lesions. In the retrospective validation, a conclusive nCLE result was obtained for 74 % of the cases (87 % "true'' and 13 % "false'' with respect to the final diagnosis). On this limited case series, the nCLE criteria showed a trend for high diagnostic specificity ([ 90 % for mucinous cysts, 100 % for non-mucinous cysts). Conclusions Based on this newly completed atlas of interpretation criteria, nCLE could facilitate the diagnosis of pancreatic cystic lesion types.