Epidermal Inclusion Cysts and Variants

Epidermal inclusion cysts arise from a plugged follicular opening, resulting in a nodular cyst filled with cheesy malodorous keratin material. These are also commonly and incorrectly called sebaceous cysts but do not in fact contain any sebum. Unfortunately, the ICD code for these cysts is named “sebaceous cyst” so you must know this misnomer for billing purposes. Other names include infundibular cysts, keratinous cysts, and epidermoid cysts. Generally, these present as a compressible but nonfluctuant nodule, which can be diagnosed clinically due to a comedo-like central punctum that can be distinguished at the apex (Figure 12-1). Because the keratin material inside the cyst wall is highly inflammatory, any cyst that has ruptured can spark a vigorous inflammatory response that can be mistaken for cellulitis (Figure 12-2). Even if these do become superinfected, the treatment of choice is incision and drainage to remove the inflammatory and/or infected contents.

FIGURE 12-1 An epidermal inclusion cyst with a central punctum that looks like an open comedone.

(Copyright Richard P. Usatine, MD.)

FIGURE 12-2 Local inflammation around an epidermal inclusion cyst can mimic cellulitis or an abscess. The best treatment is incision and drainage.

(Copyright Richard P. Usatine, MD.)

Pilar cysts (also known as trichilemmal cysts and commonly called wens) are very similar to epidermal inclusion cysts with the exception that the capsule is much thicker and the location generally on the scalp (Figures 12-3 and 12-4). Pilar cysts rarely have a punctum but the thickness of the capsule makes removal somewhat easier. These can also become very large but in most cases they are 5 to 20 mm in size. It is not unusual for the hair to become thinned or actually stop growing over the cyst (Figures 12-3 and 12-4).

FIGURE 12-3 A typical presentation of a pilar cyst (trichilemmal cyst or wen) on the scalp.

(Copyright Richard P. Usatine, MD.)

FIGURE 12-4 A fairly large pilar cyst with hair loss over the cyst. A simple ellipse over the cyst will remove redundant tissue.

(Copyright Richard P. Usatine, MD.)

One variant of the epidermal cyst is the milium cyst. Milia are histologically identical to classic epidermal cysts but only grow to 1 to 2 mm. They are generally located around the eyes and central portion of the face (See Figure 33-20 in Chapter 33, Procedures to Treat Benign Conditions).

Cysts can be located almost anywhere but are common on the trunk, neck, face, and behind the ears. They range in size from millimeters to centimeters. Epidermal inclusion cysts are benign; however, there are rare proliferating epidermal inclusion cysts that can become carcinogenic. Any cyst that does not look 100% typical on excision should be sent to the pathologist. A full differential diagnosis is given in Box 12-1.

FIGURE 12-5 A Bartholin’s duct cyst.

(Copyright Richard P. Usatine, MD.)

FIGURE 12-6 A branchial cleft cyst after removal.

(Courtesy of Frank Miller, MD.)

FIGURE 12-7 A solid cystic hidradenoma.

(Copyright Richard P. Usatine, MD.)

FIGURE 12-8 Hydrocystoma around the eye. It is benign and has a very thin wall that is easy to cut.

(Copyright Richard P. Usatine, MD.)

FIGURE 12-9 A mucinous cystadenoma near the eye.

(Copyright Richard P. Usatine, MD.)

FIGURE 12-11 Pilonidal cyst.

(Copyright Richard P. Usatine, MD.)

FIGURE 12-12 A thyroglossal duct cyst in a young girl. Note how it is midline. These will move up with swallowing.

(Courtesy of Frank Miller, MD.)

Dermoid cysts are far less common. They occur along congenital lines of cleavage (lingually, lateral eyes, behind the ears, and base of the nose) due to sequestration of embryonic cells. Unlike the common cyst, they are usually found in children and teenagers. So, young age is a warning sign for “something different.” Facial cysts in young children need to be approached with caution and may need an imaging study before performing an excision.

The occurrence of multiple true sebaceous cysts at a younger age is termed steatocystoma multiplex, which is a genetically inherited problem. These capsules are extremely thin. Small fluid-filled very thin-walled cysts around the eyes are called hidrocystomas (Figure 12-10).

FIGURE 12-10 Digital mucous (myxoid) cyst on the finger. They are most commonly found distal to the DIP joint.

(Copyright Richard P. Usatine, MD.)

Several techniques for removing epidermal inclusion cysts and pilar cysts are described below. The best approach depends on size, location, and cyst condition. The minimal excision technique is simplest. Other methods include elliptical excision and incision and drainage with iodine crystals. Each offers advantages in select cases. Familiarity with various techniques balances preventing recurrence with maximizing efficiency and cosmetic outcome.

Contraindications for Cyst Removal

• Avoid trying to remove cysts that are actively inflamed (Figure 12-2). Although it can be done successfully, wound healing may be impaired. The keratinaceous material in epidermal inclusion cysts is highly immunogenic and an inflamed cyst should be treated with incision and drainage and allowed to heal before attempting to remove the cyst wall. Antibiotics are rarely helpful. Small lesions can be excised going around the entire area of inflammation.¹

• Make note of the surrounding anatomy and the size/depth of tissue that contains the cyst. Consider deferring or referring lesions that overlie areas such as large vascular networks, special sensory organs, or cosmetically sensitive areas. With experience, these areas may be managed in the office, but this depends on comfort, experience, and support services. Be aware of the spinal accessory nerve when neck lesions are involved because the nerve lies immediately under the skin and can be easily severed, leading to difficulty in abducting the arm (See Figure 11-4 in Chapter 11). Also be careful to not cut the temporal branch of the facial nerve with cysts over the temple (See Figures 11-2 and 11-3 in Chapter 11).

• Diagnosis is usually made on clinical grounds before proceeding with removal. Keep the differential in mind even though the diagnosis may seem certain (Box 12-1). For example, a dermoid cyst on the face can communicate with the cerebrospinal fluid in some circumstances. Consider imaging for a possible dermoid cyst if the cyst has been present on the face since early childhood and is midline (Figure 12-13). When encountering something atypical, send samples to pathology, or confer with a colleague before proceeding.

FIGURE 12-13 A midline dermoid cyst on the face of a young girl.

(Copyright Richard P. Usatine, MD.)

Minimal Excision Technique

The minimal incision technique for removing cysts involves purposefully incising the cyst wall and expressing its contents allowing cyst removal through a smaller incision (linear opening or small punch rather than a larger ellipse that surrounds the cyst).