High resolution diagnosis of common nevi by multiphoton laser tomography and fluorescence lifetime imaging

Background Multiphoton Laser Tomography (MPT) has developed as a non-invasive tool that allows real-time observation of the skin with subcellular resolution. MPT is readily combined with time resolved detectors to achieve fluorescence lifetime imaging (FLIM). The aim of our study was to identify morphologic MPT/FLIM descriptors of melanocytic nevi, referring to cellular and architectural features. Methods In the preliminary study, MPT/FLIM images referring to 16 ex vivo nevi were simultaneously evaluated by 3 observers for the identification of morphologic descriptors characteristic of melanocytic nevi. Proposed descriptors were discussed and the parameters referring to epidermal keratinocytes, epidermal melanocytes, dermo-epidermal junction, papillary dermis and overall architecture were selected. In the main study, the presence/absence of the specified criteria were blindly evaluated on a test set, comprising 102 ex vivo samples (51 melanocytic nevi, 51 miscellaneous skin lesions) by 2 observers. Results Twelve descriptors were identified: short-lifetime cells in the stratum corneum, melanin-containing keratinocytes, dendritic cells, small short-lifetime cells in the upper and lower layers, edged papillae, non-edged papillae, junctional nests of short-lifetime cells, dermal cell clusters, short-lifetime cells in the papilla, monomorphic and regular histoarchitecture, architectural disarray. Conclusion Identified descriptors for benign melanocytic lesions proved sensitive and specific, enabling the differentiation between melanocytic nevi and non-melanocytic lesions.