Ovarian cysts are swellings in the ovary that are typically filled with fluid or semi-fluid material. Thankfully, the vast majority are not cancerous and most resolve spontaneously without needing any intervention.
What causes an ovarian cyst?
There are many different types of ovarian cysts.
A largest proportion of cysts in premenopausal women are “functional”, meaning that they are derived from the follicles that normally make up the ovary. Each follicle is made up of an egg surrounded by layers of cells. During a normal menstrual cycle, one follicle develops a collection of fluid thereby forming a “cyst” that grows to a size of around 2 cm. These “cysts” that form during every menstrual cycle are actually normal pre-ovulatory follicles that rupture to release eggs (ovulation). For more information on ovarian follicles and follicle development during the menstrual cycle, see my section on The Menstrual Cycle and Ovulation Cycle Tracking.
Sometimes these large follicles that are part of the normal menstrual cycle don’t disappear as they should. Instead, they persist and can become larger than 2-3 cm. These persistent and enlarged follicular cysts are called functional cysts. Functional cysts are common in women of reproductive age and 70-80% will resolve without any intervention.
Endometriomas or “Chocolate cysts”:
Endometriotic deposits on the ovary sometimes lead to the ovary becoming stuck to the pelvic side-wall through scarring. The deposit then becomes sandwiched between the ovary and pelvic wall and if it undergoes repeated episodes of bleeding, blood can accumulate in this space to form a cyst. After time, the altered blood takes on a chocolate-like appearance hence the name “chocolate cyst”. For more information, see my section on Endometriosis.
Neoplastic cysts are tumours derived from overgrowth of particular populations of cells in the ovary. They can be benign or cancerous (malignant). The commonest benign neoplastic cysts are the serous and mucinous cystadenomas. Cancerous ovarian cysts, or ovarian carcinomas, are relatively rare and occur at the rate of around 15 cases per 100,000 women per year.
Dermoid cysts (Teratomas):
Dermoid cysts are benign and account for more than 10% of non-cancerous ovarian tumours. These are very unusual cysts that often contain different types of tissue such as hair and teeth.
What are the symptoms of an ovarian cyst?
Ovarian cysts often cause no symptoms and come to light when an ultrasound scan is performed for another reason.
The commonest symptom is lower abdominal pain or discomfort. Sometimes acute pain arises when the cyst causes the ovary to twist on its pedicle thereby cutting off blood supply to the ovary. This is called ovarian torsion and is a medical emergency. Torsion occurs in association with around 15% of cysts larger than 4 cm. If not treated quickly, torsion will lead to irreparable damage to the ovary. Pain associated with a cyst can also be due to bleeding into the cyst cavity or to cyst rupture leading to spillage of its contents into the pelvic cavity.
If a cyst becomes very large it can cause the tummy to become swollen and may place pressure on surrounding structures such as the bladder and bowel.
How are ovarian cysts identified?
Ultrasound scan is the commonest way of diagnosing ovarian cysts. They are often discovered as an incidental finding during an ultrasound scan performed for another reason.
Functional cysts typically appear as a single uniform sac of fluid. Features that raise suspicion about malignancy are large size, multiple compartments within the cyst rather than a single cavity and solid components. The risk of malignancy for a cyst can be estimated by combining the features of the cyst identified on scan with the woman’s age and the levels of a tumour marker known as CA-125.
How are ovarian cysts treated?
For functional cysts <5 cm, watchful waiting is usually sufficient as around 80% will resolve on their own. A repeat scan in 6-12 weeks will usually confirm that the cyst has disappeared. Cysts that are larger than 10 cm, or those that are persistent, or causing symptoms such as pain often require surgery. Surgery can usually be performed using laparoscopy during which, the cyst is separated from the remainder of the ovary and removed through very tiny incisions.
Endometriomas can be separated from the remainder of the ovary and removed using laparoscopy; this is the preferred treatment. They can also be opened and drained, followed by burning of the cyst walls using electrical energy to try to prevent the cyst from recurring.
Ovarian torsion is a medical emergency and requires immediate surgery. This can be performed via laparoscopy which allows the ovary to be untwisted thereby re-establishing blood flow to the ovary. The cyst that caused torsion to occur can then be removed. Laparoscopic untwisting (or detorsion) is effective in salvaging the ovary in around 90% of cases.
In some cases when cysts are very large, or in women who have already entered the menopause, treatment may involve removing the entire ovary along with the contained cyst.
If there is a high suspicion that a cyst may be malignant, urgent referral to a specialist in gynaecological cancer is advisable.