Superficial Soft Tissue Masses
Epidermal inclusion cyst is a benign lesion derived from the focal proliferation of dermal squamous epithelium. This tumor is also referred to as sebaceous, epidermoid, epidermal, infundibular, or keratin cysts (Kim et al. 2011a). Epidermal inclusion cysts are lined with stratified squamous epithelium and filled with a white, cheesy material, reflecting layers of keratin and cholesterol-rich debris (Hong et al. 2006). The cyst may be a congenital lesion developed from the subcutaneous implantation of keratinizing epithelial cells during embryogenesis. Epidermal inclusion cysts can also be a result of downward growth of epithelial cells after occlusion of the hair follicle and the growth of implanted epithelial elements after trauma or surgery (Hong et al. 2006; Huang et al. 2011; Kim et al. 2011a). Clinically, epidermal inclusion cysts present as slow-growing dermal or subcutaneous cysts. These cysts usually occur in the hair-bearing areas of the body, such as the scalp, face, neck, trunk, and back (Kim et al. 2011a). Moreover, they usually remain asymptomatic unless they become infected or rupture into the adjacent soft tissues.