Background: The diagnosis of flat pigmented lesions on the face is challenging because of the morphologic overlap of biologically different lesions and the unknown significance of dermatoscopic patterns.
Objective: To better characterize dermatoscopic patterns of various types of flat pigmented facial lesions and to analyse their significance by calculating their relative risks and diagnostic values.
Methods: We prospectively analysed dermatoscopic images of 240 flat pigmented facial skin lesions collected consecutively from 195 patients (41.5% females, mean age: 61 ± 14 years) between 2007 and March 2012 in a primary skin cancer practice situated in Queensland, Australia.
Results: Histopathologically 114 (47.5%) lesions were malignant (24 lentigo maligna, 21 basal cell carcinomas and 69 pigmented actinic keratoses). Compared with all other patterns the positive predictive value for lentigo maligna was highest for a pattern of circles (31.3%, 95% CI: 11.1-58.6%). A pattern of clods was associated with basal cell carcinoma. If grey structures were present the relative risk for malignancy was 2.2 (95%CI: 1.4-3.4). The best clues to differentiate pigmented actinic keratosis from other lesions were the presence of scale (positive predictive value: 72.2%, specificity: 94.2%), white circles (positive predictive value: 68.8%, specificity: 94.2%) and a sharply demarcated border (positive predictive value: 44.2%, specificity: 86.0%).
Conclusions: In flat lesions a pattern of circles bears the highest risk for facial melanoma but other patterns do not exclude it. Scale, white circles and a sharply demarcated border are clues to pigmented actinic keratoses. The presence of grey colour is a clue to malignancy regardless of pattern.