Sebaceous cyst
Specialty	Skin

A sebaceous cyst (a form of trichilemmal cyst) also known as a "wen", is a closed sac or cyst below the surface of the skin that has a lining that resembles the uppermost part (infundibulum) of a hair follicle and fills with a fatty white, semi-solid material called sebum. Sebum is produced by sebaceous glands of the epidermis.

Terminology

It is sometimes (but not always) considered to be equivalent to epidermoid cyst, or similar enough to be addressed as a single entity.^[1]

Some sources state that a sebaceous cyst is defined not by the contents of the cyst (sebum) but by the origin (sebaceous glands). Because an epidermoid cyst originates in the epidermis, and a pilar cyst originates from hair follicles, neither type of cyst would be considered a sebaceous cyst by this definition.^[2] However, in practice, the terms are often used interchangeably.

"True" sebaceous cysts are relatively rare.^[3]

Presentation

The scalp, ears, back, face, and upper arm, are common sites for sebaceous cysts, though they may occur anywhere on the body except the palms of the hands and soles of the feet. In males a common place for them to develop is the scrotum and chest. They are more common in hairier areas, where in cases of long duration they could result in hair loss on the skin surface immediately above the cyst. They are smooth to the touch, vary in size, and are generally round in shape.

They are generally mobile masses that can consist of:

• Fibrous tissues and fluids
• A fatty, (keratinous), substance that resembles cottage cheese, in which case the cyst may be called "keratin cyst" This material has a characteristic "cheesy" or "foot odor" smell.
• A somewhat viscous, serosanguineous fluid (containing purulent and bloody material)

The nature of the contents of a sebaceous cyst, and of its surrounding capsule, will be determined by whether the cyst has ever been infected.

With surgery, a cyst can usually be excised in its entirety. Poor surgical technique or previous infection leading to scarring and tethering of the cyst to the surrounding tissue may lead to rupture during excision and removal. A completely removed cyst will not recur, though if the patient has a predisposition to cyst formation, further cysts may develop in the same general area.

Causes

Blocked sebaceous glands, swollen hair follicles,^[4] and excessive testosterone production will cause such cysts.^[5]

A case has been reported of sebaceous cyst being caused by Dermatobia hominis.^[6]

Hereditary causes of sebaceous cysts include Gardner's syndrome, and basal cell nevus syndrome.

Treatment

Sebaceous cysts generally do not require medical treatment. However, if they continue to grow, they may become unsightly, painful, infected, or all of the above.

Surgical

Surgical excision of a sebaceous cyst is a simple procedure to completely remove the sac and its contents.^[7]

There are three general approaches used: traditional wide excision, minimal excision, and punch biopsy excision.^[8]

The typical outpatient surgical procedure for cyst removal is to numb the area around the cyst with a local anaesthetic, then to use a scalpel to open the lesion with either a single cut down the center of the swelling, or an oval cut on both sides of the centerpoint. If the cyst is small, it may be lanced instead. The person performing the surgery will squeeze out the keratin (the semi-solid material consisting principally of sebum and dead skin cells) surrounding the cyst, then use blunt-headed scissors or another instrument to hold the incision wide open while using fingers or forceps to try to remove the cyst intact. If the cyst can be removed in one piece, the "cure rate" is 100%.^{[citation needed]} If, however, it is fragmented and cannot be entirely recovered, the operator may use curettage (scraping) to remove the remaining exposed fragments, then burn them with an electro-cauterization tool, in an effort to destroy them in place. In such cases the cyst may or may not recur. In either case, the incision is then disinfected and, if necessary, the skin is stitched back together over it. A scar will most likely result. In some cases where "cure rate" is not 100% the resulting hole is filled with an antiseptic ribbon after washing it with an iodine based solution. This is then covered with a field dressing. The ribbon and the dressing are to be changed once or twice daily for 7–10 days after which the incision is sewn up or allowed to close by secondary intention, i.e. by forming granulation tissue and healing "from the bottom up."

An infected cyst may require oral antibiotics or other treatment before and/or after excision.

An approach involving incision, rather than excision, has also been proposed.^[9]

Non-surgical

Another common and effective method of treatment involves placement of a heating pad directly on the cyst for about fifteen minutes, twice daily, for about 10 days (depending on size and location of the cyst).^{[10][failed verification]} There is some anecdotal evidence however that this home remedy can lead to infection in a previously uninfected cyst. This may be caused by an over-heated or non-sterile heat pad.

This method works by bringing the wax-like material inside of the cyst to a temperature at which it melts, and can be reabsorbed and processed by the body, as a small amount of oily fluid^{[citation needed]}. This method is preferred over surgery both for reasons of associated costs and risks of surgery.^{[by whom?]} This methodology is not applicable for non-sebaceous cysts, however, as other varieties of cysts do not contain the same hardened sebum deposits, and therefore do not melt to be reabsorbed by the body.

Gallery

• A small sebaceous cyst, located in the front of the ear lobe.
  A small sebaceous cyst, located in the front of the ear lobe.
• 
  An uninfected sebaceous cyst located on the calf of the right leg.
• 
  An infected sebaceous cyst located on the left shoulder.
• 
  The sebaceous cyst from the calf that has been surgically removed.

References

External links

• Overview at University of Maryland Medical Center
• Epidermal Inclusion Cyst at eMedicine