A Rare Presentation of a Giant Epidermoid Inclusion Cyst Mimicking Malignancy

Epidermoid inclusion cysts, infundibular cysts, and retention cysts are dense, well-encapsulated benign soft tissue lesions that develop after a portion of the epidermis has become implanted in the dermis on a follicular surface such as the scalp, face, or trunk. However, on acral surfaces such as the palms and soles, these cysts present <10% of the time. Typically, these lesions will not progress to sizes >5 cm. However, a rare subtype of epidermal cysts known as giant epidermal cysts tends to be much larger. Unlike epidermal inclusion cysts, giant cysts lack a central punctum, present on areas of thick skin lacking hair follicles, and affect an older patient population. Because of their large size and unique characteristics, few cases of giant epidermal cysts localized to the foot have been reported. We present a case report of a 57-year-old male with a rapidly growing, large, ulcerated, atypical epidermal inclusion cyst that had developed on the medial aspect of his hallux with underlying osseous changes. In this particular case, the location, overlying skin changes, and rapid growth of the lesion raised suspicion for malignancy. In the present report, we discuss the unusual features of this particular cyst and the etiologies, treatment course, and short-term outcomes regarding this unique tumor. (C) 2017 by the American College of Foot and Ankle Surgeons. All rights reserved.