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What are ovarian cysts?

An ovarian cyst is a growth or swelling on, or inside, the ovary. It may be solid, or filled with fluid. If yours is solid you might hear it called a tumour. This can be frightening because it immediately brings cancer to mind, but tumour is just the medical term for any swelling. The vast majority of ovarian growths are not cancerous.

Cysts may grow inside the ovary or they may be attached by a stem to the outside. (The stem is sometimes called a pedicle).

Types of ovarian cysts

Functional cysts

These are the most common type of cysts. They occur as a variation of the normal function of the ovaries.

During your monthly cycle one of the follicles may not release its egg, or it may not shrink after ovulation. The follicle enlarges and fills with fluid. Follicular cysts can last for four to six weeks and grow to 5 to 6 cm in diameter. They usually go away by themselves.

A less common type of functional cyst can form in the corpus luteum. Corpus luteum cysts form when the corpus luteum fills with fluid instead of breaking down as it should. Corpus luteum cysts can become larger than follicular cysts and so may cause pelvic discomfort. Usually corpus luteum cysts go away over two or three menstrual cycles, but occasionally bleeding in the cyst can cause a strong abdominal pain similar to that of an ectopic pregnancy.

Dermoid cysts

Dermoid cysts originate in the ovarian cells that form into different tissues as the fertilised egg develops. These cysts can grow quite large — up to 15 cm in diameter — and may contain hair, bone, teeth and cartilage. In about 12% of cases dermoid cysts may be present on both ovaries. They occur most commonly in young women and can occur in pregnancy. Large cysts are more prone to torsion, where the cyst twists on its stem, cutting off the blood supply and causing intense pain. Dermoid cysts should be removed surgically.

Serous and mucinous cystadenomas

These can grow to be very big and heavy, and may even weigh several stone. Serous cystadenomas are filled with a watery liquid, and the mucinous ones with a thicker sticky fluid. Both types often grow outside the ovary, attached by stems. They are not always benign and should be removed as quickly as possible.

Endometriomas

Up to 60% of women with endometriosis have endometriomas. These are cysts lined with endometrial cells similar to those lining the womb. These cells bleed during menstruation. The old blood in the cyst gives them a 'chocolate' appearance. They should be removed surgically.

Solid Ovarian Tumours

• Functional tumours (Ovarian stromal tumours)
  Functional tumours are completely different and much rarer than functional cysts. They are called either masculinising or feminising because they produce either male or female hormones. Masculinising tumours tend to occur to women in their 20s and 30s. Feminising tumours can occur at any age, even before puberty. They are usually benign, but need to be removed surgically because of the small risk that they are not benign.
  
  
• Fibromas
  These ovarian cysts are usually solid although they sometimes have fluid parts and may contain some bone. In some women they produce oestrogen. They should be removed surgically.
  
  
• Brenner tumours
  These are rare, solid ovarian cysts that are most commonly found in women over 40. They are usually quite small and always benign.

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Originally written by Jenny Tricker. This edition revised by Women's Health (2000).

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