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

Noninvasive techniques such as dermoscopy and reflectant confocal microscopy (RCM) may enhance the diagnosis in some unusual nodules, as illustrated by the present case.

A woman in her 30s reported changes in the last 6 months to an originally asymptomatic nodule on her right thigh. The 2-tone lesion of about 0.5 × 1 cm appeared to be exophytic and well demarcated: half of the lesion appeared whitish, and the other half was black (Figure 1A). Polarized-light dermoscopy (DermLite hybrid; 3Gen) showed the presence of 2 well-defined areas; one of them had a homogeneous yellowish color, the other was irregularly bluish. Within the bluish area, a circular, keratin-filled pore was observed (Figure 1B).

Analysis by RCM, performed with the handheld VivaScope 3000 (Mavig GmbH), showed beyond the pore a keratin-filled duct extending below the epidermis. In addition, just beneath a thinned epidermis, highly reflectant, geometrical, platelike structures with notched corners were revealed (Figure 2A). Histopathologic analysis of the excised nodule demonstrated the presence of a superficial epidermal cyst with squamous epithelial lining containing several cholesterol clefts (Figure 2B). A large area of the lesion was filled by a foreign-body, giant-cell reaction and some red blood cell extravasations.

An epidermal cyst is a common, keratin-filled, epithelial-lined cyst of the skin. It is usually a slow-growing, asymptomatic, dermal or subcutaneous elastic nodule that may be skin colored or yellowish white when located near the skin surface. The cyst may be connected to the surface by a duct, and the clinical identification of the corresponding pore represents a diagnostic clue. Two previous studies have highlighted the usefulness of dermoscopy in identifying the pore, described as a keratin-filled, roughly circular orifice that may be whitish, yellow, brown, or black.^1,2

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.³

A noninvasive technique, RCM is increasingly being used for several dermatologic conditions other than melanocytic tumors.^4,5 Unlike conventional vertical histopathologic sections, it provides 2-dimensional pictures representing horizontal (en face) scans of the skin. Superficial laser depth penetration (250 μm) represents a limitation in the assessment of epidermal cysts, which are generally located deeper in the dermis and the subcutis. 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. The cholesterol clefts represent virtual structures frequently seen in biopsy specimens of dermoid, trichilemmal, and sometimes epidermal cysts, and they correspond to cholesterol crystals that dissolve during the fixation process. In our case, it was possible to detect the cholesterol crystals by RCM thanks to the superficial location of the cyst. Their appearance is similar to that of synovial fluid under polarized microscopy in some rheumatologic conditions.⁶

In conclusion, an epidermal cyst may undergo rupture that causes changes in its clinical presentation such that it shows an irregular bluish color under dermoscopy. To our knowledge, this is the first case report to describe in vivo cholesterol crystals within the cyst.

Corresponding Author: Giuseppe Micali, MD, Dermatology Clinic, University of Catania, AOU Policlinico-Vittorio Emanuele, Via Santa Sofia, 78-95123, Catania, Italy (cldermct@gmail.com).

Published Online: September 9, 2015. doi:10.1001/jamadermatol.2015.2505.

Conflict of Interest Disclosure: None reported.