5.2.2.2　Pigmented nevi and melanomas

So far，only few studies have investigated OCT imaging of pigmented nevi and melanomas.The reason is that melanin is a strong scatterer of light；images of pigmented lesions like melanomas and nevi have been proven more difficult to obtain by techniques based on the penetration of light.Conventional OCT with an imaging resolution of 5-7 mm cannot visualize cellular features and therefore the image analysis of melanocytic lesions must rely on distinct morphological changes in the tissue.In benign nevi，an intact DEJ and acantholysis is often seen in OCT images.In comparison，melanoma often shows marked architectural disarray and rarely displays a clear dermoepidermal border because of the infiltrative tumor growth.The most characteristic feature seen in melanoma with conventional OCT is large，vertical，and icicle-shaped structures that are not observed in the benign nevi；however，despite this finding，conventional OCT cannot demonstrate enough clear-cut differences between malignant and benign pigmented lesions to be used as a diagnostic tool for melanoma.

Compared with conventional OCT，HD-OCT has a high enough resolution to image the tissue on a cellular level but with a limited penetration depth complementary to that of RCM.The high resolution of HD-OCT allows detailed imaging of pathological changes in melanocytic lesions，and studies have suggested that HD-OCT can provide morphological imaging that can discriminate architectural patterns and cytological features of pigmented lesions and cells in the epidermis and superficial dermis.With regard to diagnostic accuracy of HD-OCT in melanoma，a recent multicenter study employing one blinded investigator assessed the diagnostic performance of HD-OCT in the differentiation of benign melanocytic skin lesions and melanoma.The study included 93 histopathologically proven melanocytic skin lesions，of which 27 were melanoma.The sensitivity of HD-OCT was found to be 74.1％and the specificity was 92.4％.The positive predictive value was 80％and the negative predictive value was 89.7％.The performance of HD-OCT was dependent on tumor thickness and the presence of borderline lesions，indicated by high false negative rates in very thin melanomas and high false positive rates in dysplastic nevi.In conclusion，the performance in diagnosing melanoma by OCT is still inferior to other competing techniques such as RCM，although recent studies have provided some encouragement.To optimize early diagnosis of melanoma，OCT may develop into a valuable adjunct tool；however，further technical development and more extensive studies of OCT are required before this can be achieved.(https://www.daowen.com)