An Unusual 2-Tone Epidermal Cyst: Dermoscopy, Confocal Microscopy, and Histopathologic Correlations

An epidermal cyst is a common, keratin-filled, epithelial-lined cyst of the skin. The cyst may be connected to the surface by a duct, and the clinical identification of the corresponding pore represents a diagnostic clue. In our case, dermoscopy of the nodule revealed the presence of the pore along with 2 sharply demarcated areas, each showing a different color. Histopathologic analysis showed an epidermal cyst corresponding to the yellowish area along with a foreign-body giant-cell reaction and red blood cell extravasations, likely the result of the cyst rupture, responsible for the bluish color. In our case, RCM allowed us to identify not only the pore but also the duct underneath, which appeared as a keratin-filled roundish canal penetrating down into the epidermis. Also, RCM highlighted several unusual, geometrical, highly reflectant structures located underneath a thinned epidermis, likely related to empty needle-shaped cholesterol clefts, as observed by histopathologic analysis.