Abstract: 【Abstract】 Objective To investigate the imaging characteristics of clear cell acanthoma （CCA） by dermoscopy and reflectance confocal microscopy （RCM）. Methods A retrospective analysis was conducted on 12 patients diagnosed with CCA through histopathological examination at the Department of Dermatology, Wuhan No.1 Hospital, from 2020 to 2024. Dermoscopic and RCM features of these cases were summarized. Results Among the 12 CCA patients, 3 were males and 9 were females, and they were aged 50.08 ± 10.43 years. Clinically, CCA lesions were typically presented as red or brown papules or nodules with well-defined borders, ranging in diameter from 3 mm to 2 cm. Histopathological examination showed that the tumor manifested as psoriasiform or papillary hyperplasia with a thickened spinous layer and a distinct boundary surrounded by the normal skin; proliferating cells were larger with lightly stained cytoplasm; neutrophil infiltration was observed in the epidermis, and vascular dilation was observed in the dermal papillae and superficial dermis; periodic acid-Schiff staining revealed abundant glycogen in the cells. In 10 patients examined by dermoscopy, dotted, globular, or glomerular vessels were arranged in a beaded pattern in all the 10 patients, and collar-like scales were seen at the edges of the lesions in 6 patients. In 6 patients examined by RCM, RCM images all revealed epidermal hyperplasia, thickened spinous layers, large keratinocytes with enlarged nuclei and abundant cytoplasm that blended in with the intercellular demarcations, disordered honeycomb structure of the epidermis, and dilation and up-thrust of blood vessels in the dermal papillae and superficial dermis; segmented cell infiltration was observed in the epidermis of 4 patients. As measured, the longest diameters of cells in the upper part of the CCA spinous layer ranged from 30.25 μm to 35.13 μm; the longest diameters of spinous layer cells at the CCA follicles （19.39 ± 2.93 μm） were significantly lower than those of the surrounding spinous layer cells （30.95 ± 5.66 μm, t = 5.73, P < 0.001）. Conclusions CCA presents a distinctive vascular pattern on dermoscopy, and the majority of histological features can be visualized by RCM. Dermoscopy and RCM can be relatively reliable auxiliary diagnostic methods for CCA.

Key words: Acanthoma, Clear cell acanthoma, Dermoscopy, Reflectance confocal microscopy