DISCUSSION
The correct diagnosis is epidermal inclusion cyst (EIC). The cyst was most likely caused by implantation of epidermal elements by the large-caliber needle used to harvest the patient's blood. Lipomas are benign tumors of adipose origin and often appear in such locations, but lipomas have a firmer, more rubbery feel than cysts. Malignancies, such as liposarcoma, are rightly considered but unlikely given the history of such slow growth, the soft consistency noted on palpation, and the symmetrical shape. Ganglion cysts are quite unusual in this area because they arise from shallow tendon sheaths that are more commonly encountered in the relatively thin skin of the wrist. Ganglion cysts are also much firmer on palpation than other types of cysts.
Comment True EICs are almost
certainly of follicular infundibulum (hair-shaft tissue) origin because they have the same cellular composition. Trauma of any kind, including puncture wounds, can result in implantation of these cells in the dermis, most commonly on the extremities, especially the hands. The cells eventuate in sacs with an organized wall and cheesy, often odoriferous, contents.
EIC is a relatively unusual type of cyst that is generically known as an epidermoid cyst. These cysts originate from a proliferation of epidermal cells in a circumscribed space in the dermis and are extremely prevalent. Heredity, human papillomavirus, and UV exposure are possible triggers. Malignant transformation is possible; therefore, surgically removed cysts should be evaluated by pathology, as was eventually done in this case. JAAPA
Joe Monroe practices at the Dawkins Dermatology Clinic, Oklahoma City, and is the department editor for Dermatology Digest. The author has indicated no relationships to disclose relating to the content of this article.