Cysts are closed capsule or sac-like structures, typically filled with liquid, semisolid, or gaseous material, very much like a blister. In this article, we will describe the various types.

Cysts occur within tissue and can affect any part of the body. They vary in size from microscopic to the size of some team-sport balls. Very large cysts can displace internal organs.

In anatomy, a cyst can also refer to any normal bag or sac in the body, such as the bladder. In this article, cyst refers to an abnormal sac or pocket in the body that contains liquid, gaseous, or semisolid substances.

A cyst is not a normal part of the tissue where it is located. It has a distinct membrane and is separated from nearby tissue — the outer (capsular) portion of a cyst is called the cyst wall. If the sac is filled with pus it is not a cyst; it is an abscess.

Fast facts on cysts

Here are some key points about cysts. More detail and supporting information is in the main article.

  • Cysts are usually noncancerous and have a sac-like structure that can contain fluid, pus, or gas.
  • Cysts are common and can occur anywhere on the body.
  • Cysts are often caused by infection, clogging of sebaceous glands, or around earrings.
  • It is unusual for cysts to cause pain unless they rupture, become infected, or inflamed.
  • Breast cysts are often painful and may be noticeable during a breast examination.

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Cysts can affect any part of the body.

Common causes of cysts include:

  • tumors
  • genetic conditions
  • infections
  • a fault in an organ of a developing embryo
  • a defect in the cells
  • chronic inflammatory conditions
  • blockages of ducts in the body that cause fluids to build up
  • a parasite
  • an injury that breaks a vessel

Benign and malignant cysts

Most cysts are benign and are caused by blockages in the body's natural drainage systems. However, some cysts may be tumors that form inside tumors — these can potentially be malignant. Examples include keratocysts and dermoid cysts.

Signs and symptoms vary enormously depending on what type of cyst it is. In many cases, a person becomes aware of an abnormal lump, particularly in cases with cysts of the skin or when a cyst is just below the skin. A person may notice a cyst in their breasts when they examine them by touching them. Breast cysts are often painful.

Some cysts in the brain can cause headaches, as well as other symptoms.

Many internal cysts, such as those in the kidneys or the liver, may not have any symptoms and go unnoticed until an imaging scan (MRI scan, CAT scan, or ultrasound) detects them.

Some of the most common types of cysts are listed below:

Acne cysts

Cystic, or nodulocystic, acne is a severe type of acne in which the pores in the skin become blocked, leading to infection and inflammation. You can read all about acne cysts in our other article: What is cystic acne?

Arachnoid cysts

The arachnoid membrane covers the brain. During fetal development the arachnoid membrane doubles up or splits to form an abnormal pocket of cerebrospinal fluid. In some cases, doctors need to drain the cyst. Arachnoid cysts may affect newborn babies.

Baker's cysts

Baker's cysts are also called popliteal cysts. A person with a Baker's cyst often experiences a bulge and a feeling of tightness behind the knee. Pain gets worse when extending the knee or during physical activity. Baker's cysts are usually caused by a problem with the knee joint, such as arthritis or a cartilage tear.

Bartholin's cysts

These may occur if the ducts of the Bartholin glands (situated inside the vagina) become blocked. Women may undergo surgery and/or be prescribed antibiotics.

Breast cysts

Breast cysts are often painful and usually need to be drained. Some studies have indicated that breast cysts may point to a raised breast cancer risk.

Chalazion cysts

Very small eyelid glands (meibomian glands) make a lubricant that comes out of tiny openings in the edges of the eyelids. Cysts can form if the ducts are blocked.

Colloid cysts

These are cysts that contain gelatinous material in the brain. In most cases, the recommended treatment is surgical removal of the cyst.

Dentigerous cysts

These are cysts surrounding the crown of an unerupted tooth.

Dermoid cysts

Dermoid cysts are a type of cyst that include mature skin, hair follicles, sweat glands, clumps of long hair, as well as fat, bone, cartilage, and thyroid tissue.

Epididymal cysts

These are cysts (spermatocele) that form in the vessels attached to the testes. This type of cyst is estimated to affect 20-40 percent of American males and does not typically impair fertility or require treatment. If it causes discomfort a doctor may suggest surgery.

Ganglion cysts

You can read more about these in our dedicated article: What is a ganglion cyst?

Hydatid cysts

A relatively small tapeworm forms cysts in the lungs or liver. Treatment includes surgery and medication.

Ovarian cysts

The majority of ovarian cysts are benign. Some can become so large that the woman looks pregnant. Ovarian cysts 5 centimeters (cm) long or less are common during a woman's reproductive years. Up to 18 percent of females will be diagnosed with an ovarian cyst or tumor at some time in their life, and a small percentage of them will be diagnosed with ovarian cancer.

Pancreatic cysts

Most pancreatic cysts are not regarded as true cysts. They are referred to as pseudocysts as they do not contain the type of cells found in true cysts. They can include cells normally found in other organs, such as the stomach or intestines.

Periapical cysts

These are also known as radicular cysts. They are the most common odontogenic (relating to the formation and development of teeth) cyst and are usually caused by inflammation of the pulp, pulp death, or dental caries.

Pilar cysts

These are also known as trichilemmal cysts. They are fluid-filled cysts that form from a hair follicle and are most commonly found in the scalp.

Pilonidal cysts

These cysts form in the skin near the tailbone (lower back), and can sometimes contain ingrown hair. This type of cyst can grow in clusters, which sometimes create a hole or cavity in the skin.

Renal cysts (kidneys)

Several types of cysts can develop in the kidneys. Solitary cysts contain fluids and may sometimes include blood. Some are present at birth; others may be caused by tubular blockages. People with kidney vascular diseases may have cysts formed by the dilatation of blood vessels.

Pineal gland cysts

These are benign cysts that form in the pineal gland in the brain. According to autopsy records, pineal gland cysts are fairly common.

Sebaceous cysts

People often use the term sebaceous cyst to describe a type of cyst that occurs on the skin of the face, back, scalp, or scrotum. Cysts that occur in these locations may be epidermoid or pilar cysts, although doctors can only tell the difference after removing and analyzing the cyst.

Tarlov cysts

These are also known as perineural/perineurial cysts, as well as sacral nerve root cysts. The cysts are located at the base of the spine and are filled with cerebrospinal fluid.

Vocal fold cysts

There are two types of vocal fold cysts - mucus retention cysts and epidermoid cysts. Vocal fold cysts can interfere with the quality of the person's speech, sometimes causing vocal cords to produce multiple tones simultaneously (diplophonia), or hoarseness and breathy speech (dysphonia).

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A large cyst may need to be removed surgically.

Treatment for a cyst will depend on various factors, including the type of cyst, where it is, its size, and the degree of discomfort it is causing.

A very large cyst that causes symptoms can be surgically removed. Sometimes, the doctors may decide to drain or aspirate the cyst by inserting a needle or catheter into the cavity. If the cyst is not easily accessible, drainage or aspiration is often done with the help of radiologic imaging so that the doctor can accurately guide the needle/catheter into the target area.

Sometimes, doctors examine the aspirated liquid under a microscope to determine whether cancerous cells are present.

If doctors suspect the cyst might be cancerous, it may be removed surgically, or they may order a biopsy of the capsule (cyst wall).

Many cysts arise as a result of a chronic or underlying medical condition, as may be the case with fibrocystic breast disease or polycystic ovary syndrome - in such cases, the focus of treatment is on the medical condition.