Definition

Atheroma cyst is the most common cutaneous cyst. Atheroma cyst has other names, such as:

• Epidermoid cyst
• Epidermal cyst
• Epidermal inclusion cyst
• Infundibular cyst
• Keratin cyst
• Sebaceous cyst

The term sebaceous cyst is a misnomer because the cyst originates from sebaceous glands that produce sebum to lubricate the hair and skin. Meanwhile, atheroma cysts do not involve sebaceous glands or contain oil or sebum. Sebaceous cysts are less common than atheroma cysts.

Causes

The skin's surface (epidermis) comprises a thin layer of cells that protect the skin. This layer will regularly shed. Most atheroma cysts form when these cells move further into the skin and multiply rather than shedding. Sometimes cysts can also form due to irritation or injury to the skin or the superficial part of the hair follicle.

The epidermal cells will form the cyst wall and produce keratin protein to the inferior part of the cyst. Keratin is a thick, yellowish substance that sometimes oozes out of the cyst. This abnormal cell growth may be caused by damage or blockage of the pilosebaceous structure (the structure of hair follicles and sebaceous glands). On hairless areas of the body such as the palms of the hands or soles of the feet, atheroma cysts may also form due to injury.

Risk factor

Almost everyone can have one or more atheroma cysts. However, atheroma cysts are most common in adults, especially in young adults to middle age (30 to 40 years) and are rarely found before puberty. They are twice as common in men as in women.

Several genetic disorders can increase the risk of developing multiple atheroma cysts, namely:

• Gardner syndrome (familial adenomatous polyposis)
• Pachyonychia congenital type 2
• Gorlin syndrome (basal cell nevus syndrome)

In these syndromes, epidermoid cysts usually appear before puberty with an unusual number of cysts and locations in the body.

Recent studies have shown that exposure to ultraviolet light and infection by human papillomavirus (HPV) can trigger the development of atheroma cysts.

Symptoms

The following are the symptoms of atheroma cysts:

• A solid, flesh-colored or yellowish, round-shaped papule or nodule fixed to the surface of the skin but usually mobile in the deeper part
• 1-3 cm in diameter
• Has a blackhead-like point at the apex of its center as a small channel. When the cyst is squeezed, the spot may ooze a smelly and cheese-like discharge.

Atheroma cysts are commonly found on the torso (e.g., chest and shoulders), neck and face, but can occur in any body area. They can also be found on the skin of the testicles and genital area, fingers, and even on the mucous membranes in the mouth. Cysts growing on the fingertips may interfere with nail growth.

Atheroma cysts can be one or more in number and usually cause no symptoms unless they rupture. When they rupture, the contents of the cyst ooze off into the surrounding tissue, causing inflammation. This inflammation is characterized by redness, swelling and pain in the infected or inflamed area of the cyst.

Diagnosis

Doctors usually diagnose an atheroma cyst from anamnesis by asking about your symptoms and inspecting the cyst on your body. The doctor may also take a cyst sample by scraping the skin cells and examining it under a microscope. There is usually no need for other tests such as ultrasound (USG) or biopsy.

Management

Atheroma cysts are usually benign, grow slowly over many years, and rarely become malignant. Small cysts and uncomplicated ones mostly cause no symptoms, require no treatment and will resolve on their own. However, if they are bothersome for cosmetic reasons, the most effective treatment is complete surgical excision to remove the cyst with an intact cyst wall. Complete removal of the cyst lining may reduce the recurrence rate. However, this can be difficult with ruptured cysts. In ruptured cysts, the remnants of the cyst lining must be removed to prevent recurrence.

After the cyst is removed, it is usually sent to the laboratory for examination under a microscope. This is done because atheroma cysts have a risk of becoming malignant and to rule out other possible diagnoses.

In infected cysts, initial antibiotics will be given before incision and drainage of pus. If there is inflammation around the cyst, steroids such as triamcinolone may be injected to reduce inflammation.

After the surgery, you are advised to avoid contact sports that can cause injury and other strenuous activities. The sutures may be removed within 7-10 days.

Complications

Potential complications that can occur with atheroma cysts are:

• Atheroma cysts may become inflamed, causing the area to be painful and swollen even if not infected. These inflamed cysts are difficult to remove. Doctors will usually delay the removal of the cyst until the inflammation subsides.
• Cyst rupture. A ruptured cyst will ooze off its contents to the skin and cause swelling, redness and pain. Cyst rupture may result from injury.
• Infection. A cyst may become infected and painful, forming an abscess (collection of pus). The bacteria that most commonly cause cyst infections are Staphylococcus aureus, Escherichia coli and group A Streptococcus.
• Recurrence. If the cyst ruptures and its capsule or lining is not completely removed, it may return.
• Potential to become malignant. Although atheroma cysts are benign, there are still possibilities of them becoming malignant (rarely happens). As many as 1% of atheroma cysts are known to turn into skin cancer in the form of squamous cell carcinoma or basal cell carcinoma. Squamous cell carcinoma is the most common skin cancer compared to basal cell carcinoma, accounting for 70% of all atheroma cysts that become malignant.

In addition, cyst removal procedures may result in bleeding, bacterial infection and scarring.

Prevention

You cannot prevent atheroma cysts from developing. However, you can prevent scarring and infection by:

• Not squeezing the cyst or trying to remove the contents of the cyst
• Compressing the cyst area with a warm wet cloth to aid spontaneous drainage of the cyst and cyst healing

When to see a doctor?

Most atheroma cysts do not cause any problems and do not require treatment. You are advised to consult your doctor if you experience any of the following conditions:

• A cyst that enlarges rapidly
• A cyst that ruptures or becomes painful
• Infected cyst 
• The cyst causing cosmetic problems
• A cyst that grows in an unusual area in the body, such as on the fingers or toes

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