Cysts are benign nodules located underneath the skin that form when the skin cells from the epidermis do not shed appropriately. These cells along with keratin buildup become trapped underneath the top layer of skin. Keratin is a protein that makes up the hair and nails. A “sac” or cyst wall then forms and encapsulates the skin cells. Cysts may continue to enlarge over time and can occasionally become red, painful and inflamed.
Epidermal cysts are formed from the uppermost portion of the hair follicle known as the infundibulum. They have a predilection for the extremities. The cyst can form for various reasons. Common causes include trauma to the skin or inappropriate shedding of skin cells causing them to be trapped underneath the skin. An epidermal cyst may stay stable for years and be asymptomatic. Occasionally, the cyst grows, ruptures, or becomes inflamed and causes pain. This is often dependent on body location. Some patients state they are in pain when they sit down or rest their back on the chair. A small black dot is commonly seen on the surface of the epidermal cyst, this is called the punctum. This punctum is the opening of the cyst and turns black due to oxidation.
Treatment: Epidermal cysts that are inflamed or irritated can be treated with a steroid injection right underneath the skin to help reduce local inflammation and shrink the size of the cyst. If the cyst becomes markedly inflamed, painful and fluctuant an incision and drainage may be recommended. After this in-office procedure, the cyst will continue to drain from the small opening in the skin for about a week. Cysts are packed with a sterile gauze dressing that is to be removed two days later. Patients may be placed on a course of oral antibiotics to further help reduce inflammation. Draining the cyst offers initial relief but does not remove the cyst completely. The remaining cyst sac will likely refill over time and continue to cause pain for the patient. Excision of the entire cyst with the sac is the preferred treatment for symptomatic cysts. This includes numbing the surrounding area and making a small incision to remove the entire cyst. Cysts that are inflamed are often not excised until the inflammation subsides. This allows for a smaller scar and decreases the risk of recurrence in the future.
Pilar cysts, often referred to as trichilemmal cysts, are common cysts found on the scalp. These cysts are formed from the hair follicle when dead skin cells become trapped under the skin. This cyst sac is thicker than epidermal cysts and is less likely to become inflamed and rupture. There is no black central punctum located on pilar cysts. They are benign and do not require treatment unless they are symptomatic. Given their common location on the scalp, these may become painful for patients when brushing their hair or laying down with pressure on the cyst. There is a genetic predisposition for the formation of these cysts which exhibit an autosomal dominant pattern of inheritance.
Treatment: The treatment for symptomatic pilar cysts is local excision with suture placement. These cysts are easier to remove than epidermal cysts as they often protrude from the excision site with the sac fully intact.