A closed, sac-like pocket of tissue that can form anywhere in the body. It may be filled with fluid, air, pus, or other material. Most cysts are benign (not cancer).

Summary

• Cysts are abnormal sacs of fluid that can form anywhere in the body.
• If left untreated, benign cysts can lead to a range of serious complications, including blood poisoning.
• Surgical removal is the most common treatment.

A cyst is an abnormal pocket of fluid, like a blister, that can form in many different areas of the body including the skin, genitals and internal organs. A cyst can vary in size from a tiny sac right up to a heavy bag containing litres of fluid. The common symptom is swelling around the area, but a cyst may or may not be painful. Sometimes, depending on the cause and location, a cyst contains semi-solid or solid material.

The typical treatment for any cyst is removal by surgery and a routine test for cancer, even though most cysts are benign. All unusual lumps need to be investigated by a qualified health professional.

Most cysts form for no apparent reason. Some of the known causes of cysts include:

• Blocked ducts, which cause a build-up of fluid
• A defect in the cells
• An impact injury that pops a blood vessel
• A parasite.

Some of the different types of cysts include:

• Arachnoid cyst – the arachnoid membrane covers the brain. A baby may be born with an arachnoid cyst. It is caused by the arachnoid membrane doubling up or splitting to form an abnormal pocket of cerebrospinal fluid. This can be treated by surgical drainage if necessary.
• Bartholin’s cyst – the Bartholin glands are situated inside the vagina. A cyst occurs if the ducts become blocked. Treatment includes surgery and antibiotics.
• Breast cyst – these cysts are usually painful and need to be drained with a needle. There is some evidence that breast cysts might indicate an increased risk of breast cancer.
• Cystic hygroma – occasionally, a baby is born with a small cyst or bursa. This birth defect can be corrected with surgery.
• Hydatid disease – a small tapeworm forms cysts in the liver or lungs. The tapeworm eggs are spread by contact with infected dogs, their faeces (poo) or anything contaminated with faeces such as soil. Treatment includes surgery and drugs.
• Ovarian cyst – most are benign, but can grow to such a size that the woman looks pregnant. Cysts less than 5cm are a common part of normal egg formation in the reproductive years. Sometimes, bleeding occurs into these cysts (this is called a haemorrhagic cyst). In some cases, the cysts are cancerous. Treatment includes surgery.
• Pilonidal disease – a cyst forms in the skin of the lower back, sometimes containing an ingrown hair. Pilonidal cysts can grow in clusters and sometimes create a hole or cavity in the skin. Treatment includes draining the cyst or surgical removal.
• Sebaceous cyst – the skin is lubricated by sebaceous fluid. This fluid can build up inside a pore or hair follicle and form a hard lump filled with thick, greasy matter. When squeezed, a small dome-shaped projection will appear (the punctum), representing the opening of the cyst. This may allow material to be expressed (squeezed out). Treatment includes drugs, draining the cyst with a small needle, or removal by surgery. Sebaceous cysts are common on the face, back, scalp and scrotum.

All unusual lumps need to be investigated. Some cysts are cancerous and early treatment is vital. If left untreated, benign cysts can cause serious complications including:

• Infection – the cyst fills with bacteria and pus, and becomes an abscess. If the abscess bursts inside the body, there is a risk of blood poisoning (septicaemia).
• Peritonitis – if an internal cyst bursts, there is a risk of peritonitis, which is inflammation of the membrane lining the abdominal wall.

If a cyst is cancerous, treatment will depend on its size and location and on whether or not cancer cells have spread to other parts of the body. The cyst will be surgically removed along with surrounding tissue. Further treatment might include radiotherapy (using x-rays to kill cancer cells) or chemotherapy (drugs).

• Cysts are abnormal sacs of fluid that can form anywhere in the body.
• If left untreated, benign cysts can lead to a range of serious complications, including blood poisoning.
• Surgical removal is the most common treatment.