A cyst is a pathological cavity filled with fluid, semifluid or gaseous contents and which is not created by the accumulation of pus. Most of the cysts are lined by epithelium but not all. Cysts that are lined by epithelium are known as “true cysts,” whereas cysts not lined by epithelium are known as “pseudocyst.” An epidermal inclusion cyst is a type of cutaneous cyst, and it is the most common of all types of cutaneous cysts.

The other names by which epidermal inclusion cysts are denoted are:

Epidermoid cyst.
Epidermal cyst.
Infundibular cyst.
Keratin cyst.

Sometimes referred to as sebaceous cyst; however, it is a misnomer as it does not involve any sebaceous gland. Epidermal inclusion cysts are mostly benign (non-cancerous). However, in a rare scenario, it may transform into malignancy. Malignant cases account for just about one percent of the cases.

How Does Epidermal Inclusion Cyst Look Like?

As it is a cutaneous cyst, an epidermal inclusion cyst is seen beneath the skin. Their characteristic appearance is dome-shaped lumps which are slowly enlarging, painless, mobile, and fluctuant, often seen along with a punctum (a minute point from which surrounding tissues differ in color and appearance). Epidermal inclusion cyst deep inside the skin communicates with the outer skin through a keratin-filled orifice. Through this orifice, a malodorous yellowish cheese-like material is discharged. Their size may range from a few millimeters to centimeters. Its contents include degraded keratin and lipid materials.

Where Does Epidermal Inclusion Cyst Occur?

Epidermal inclusion cysts are the most common cutaneous cysts and occur most commonly in the face, neck, scalp, back, chest, arms, legs, and genitalia. They originate from the follicular infundibulum (upper portion of the follicle).

What Causes Epidermal Inclusion Cysts?

Epidermal inclusion cysts occur mostly randomly. They do not have any genetic linkage; however, certain genetic conditions are seen in association with the development of epidermoid inclusion cyst. These include:

Gardner syndrome (a type of familial adenomatous polyposis).
Gorlin syndrome (an inherited disorder that affects many organs and tissues of the body).
Favre-Racouchot syndrome (a disorder that consists of open and closed comedones in actinically damaged skin).

Chronically damaged skin due to sunlight exposure in old-aged people have a higher incidence of developing epidermal inclusion cysts. Certain medications are related in association with the development of epidermal inclusion cysts. That includes,

BRAF inhibitors.
Imiquimod.
Cyclosporine.

Epidermoid inclusion cysts originate from the follicular infundibulum, and any disruption to the follicular infundibulum may result in cyst development. They can also occur due to implantation of the epithelium into the skin below by any penetrating injury or trauma.

Who Is Most Commonly Affected by the Epidermal Inclusion Cyst?

They most commonly occur in the third and fourth decades of life. Male predilection is seen as compared to females (ratio 2:1). They are rarely seen before puberty.

What Are the Symptoms of Epidermal Inclusion Cyst?

The symptoms include a dome-shaped lump that is mobile, fluctuant, and painless. In some cases, the lump may become painful as it gets infected and inflamed. The skin becomes red over the affected area. The condition is usually benign, but very rarely, it may transform into a malignant condition.

How to Diagnose Epidermal Inclusion Cyst?

A simple clinical examination could provide a valuable diagnosis. In certain cases, your doctor might suggest some other tests to rule out other findings. These include,

Punch Biopsy: A small amount of tissue is removed from the affected area and examined by the pathologist. It helps in ruling out any cancer associated with the cysts and gives a definitive diagnosis of the condition.

Ultrasound: Ultrasound helps in determining the cystic contents. They appear as a round or oval-shaped and well-circumscribed mass which is seen in the subcutaneous tissue.

Computed Tomography (CT) Scan: CT scan gives a detailed view of the cyst and helps the surgeon in treatment planning for the cyst removal.

MRI (Magnetic Resonance Imaging): MRI is very useful in delineating whether the cyst is benign or malignant.

How Is Epidermal Inclusion Cyst Treated?

In most cases, epidermal inclusion is left untreated as the condition is harmless and painless. The inflamed and uninfected cysts resolve spontaneously without treatment. But close monitoring of the condition is necessary as rarely the cyst may become painful and inflamed. It does not always transform into a malignant condition. Some of the different ways to treat the inflamed, painful conditions include:

To reduce swelling, your doctor might suggest injecting steroid medication over the affected area.
Incision and drainage are done to drain out the yellowish cheesy material discharging through the cyst via skin orifice. Drainage of cyst avoids the chance of getting further infection over the affected area.
Surgical excision helps in the complete removal of the cyst. Your doctor will give local anesthesia to numb the affected area surrounding the cyst before surgical removal.

What Are the Complications Seen in Epidermal Inclusion Cyst?

Some of the potential complications seen in epidermal inclusion cysts are,

Inflammation: The cyst may appear swollen and tender even if there is no infection of the cyst. Your doctor will suggest some anti-inflammatory medication before surgical removal of the cyst.

Rupture of Cyst: Rupture of the cyst often leads to infection.

Infection: Infection over the affected area leads to a severely painful condition. Antibiotics are suggested by doctors to treat infection and subside the pain.

Skin Cancer: Rarely the epidermal inclusion cyst may transform into cancer. Cyst with such malignant potential requires complete removal of the cyst to prevent its recurrence.

Is Epidermal Inclusion Cyst Contagious in Nature?

No, epidermal inclusion cysts are not contagious.

Conclusion:

Epidermal inclusion cysts are the most common cutaneous cyst. They are mostly benign and rarely transform into malignant. The cyst becomes painful once it gets infected. Your doctor might suggest treatments like surgery, incision and drainage, and medication to treat the cyst. Although this condition occurs spontaneously, certain preventive measures like avoiding trauma and injury to the skin and avoiding chronic sun exposure could possibly avoid the risk of developing the condition.