Cysts – Epidermal Inclusion Cysts
Epidermal inclusion cysts (EICs) are one of the most common skin lesions I encounter in my The Woodlands dermatology and Conroe dermatology clinics. EICs arise spontaneously without a known precipitating cause in many cases, but may occur secondary to acne or trauma which places the epidermis into the dermis or subcutaneous tissue. They begin as an outgrowth of the infundibular portion of the hair shaft which forms a silver/white sac lining. As this sac lining is connected to a skin pore, oil and debris fill this sac lining like a balloon gradually getting larger and expanding under the skin rather than extruding the contents out of the pore. Patients may notice a soft mass or swelling under their skin that becomes larger over time. EICs can occur anywhere on the body except the scalp. The scalp can produce a cyst called a Pilar cyst, which is slightly different than an EIC. Cysts are removed surgically by anesthetizing the area around the cyst with a local anesthetic and making an incision into the cyst large enough to extract the entire cyst sac lining and its contents. If the lining is not completely removed, the cyst will recur. Simply, incising and draining the the cyst will not remove the sac lining. Occasionally, the cyst contents rupture out of the sac lining and enter into the dermis or subcutaneous layer of the skin. This causes an intense inflammatory reaction as the cyst material is treated as a foriegn object by the patient’s immune system. The EIC becomes swollen, tender and red and appears infected. Many patients present when their cyst has become inflamed. I typically inject a low dose kenalog (steroid) into the inflammed cyst to calm the inflammatory reaction and place the patient on a two week course of antibiotics prior to excising the cyst, since an inflammed cyst cannot be excised and sutured closed without the risk of dehiscence or infection.