Follicles are a normal part of the ovaries. Each follicle houses an egg, and in women ovulating regularly, a follicle will burst each month (mid-cycle), releasing an egg. The egg may be picked up by the fallopian tube. If a woman has had unprotected sex, a sperm may reach and fertilise the egg in the tube. It then develops for a further 3-5 days in the tube before reaching the uterus.

The outside of a follicle contains cells which produce estrogen and progesterone. These hormones regulate the menstrual cycle and prepare the inside lining of the uterus (endometrium) for pregnancy. A woman’s ovaries actually contain many thousands of follicles. Each month a handful are potentially available for ovulation. 1-2 follicles may develop from 2-6mm diameter to 20-24mm diameter before they burst. Some woman are aware of ovulation, which may be a sharp or dull pain in the lower part of the abdomen, often on one side or the other. This may be termed ‘mid-cycle’ pain, or ‘Mittelshmerz’

These are most common in reproductive age women. They are filled with clear fluid. This fluid has a classic ‘black’ appearance on ultrasound scan. Simple cysts will normally resolve without intervention, but are occasionally removed if large, do not resolve or are causing symptoms such as pain.  They are often left over from an episode of ovulation.

These cysts most commonly originate from recent ovulation as well. When a developed follicle bursts, some bleeding commonly occurs in the cyst remnant. This cyst remnant (the corpus luteum) actually has a very important function, producing hormones (estrogen and progesterone) in very large amounts to support an egg if it is fertilized by a sperm.  The progesterone stops the period from starting, preventing loss of the pregnancy.

Some women will have more bleeding than usual, which may collect in the cyst capsule. It is essentially a ‘bruise’ on the ovary. Generally this will simply resolve over the next few weeks, but in rare cases they may cause substantial bleeding requiring emergency surgery.

These are corpus luteum cysts that continue to produce hormones (estrogen and progesterone) instead of breaking down. They may cause irregular or prolonged vaginal bleeding, and affect the regularity of a woman’s menstrual cycles until they resolve. Most will resolve spontaneously.

These are sometimes referred to as ‘chocolate cysts’. They are called this as the material inside the cyst has the consistency of melted chocolate. It is in fact blood, caused by bleeding from endometriosis tissue within or beside the ovary. In most cases, endometriomas  are indicative of moderate to severe endometriosis. If an endometrioma is present, it is highly likely endometriosis is present elsewhere in the pelvis.

These are a common benign cysts of the ovary and are the most common ovarian tumour of women in their 20s and 30s. Dermoid cysts are ‘mature’ meaning they may contain many different elements such as hair, sebaceous fluid, teeth and skin.  Occasionally they can contain a cancerous area, more commonly in very young women, or women approaching or after menopause.

Borderline tumours are a more concerning type of cyst.  On scan they usually look quite abnormal, with some solid and some cystic areas; they look different to the simple, dermoid or endometrioma cysts mentioned above.  We would recommend surgical removal if a cyst looks suspicious, although we often won’t know exactly what kind of cyst it is until it has been examined in the laboratory.  Other factors such as age and wishes to keep the ovaries for pregnancy will come into the decision around whether the whole ovary should be removed, or just the cyst.

Borderline tumours have some features of cancer, but don’t spread in the same way or as aggressively as ovarian cancers (see below).  If they are diagnosed, the usual recommendation is to remove the whole ovary, and then take the other ovary out once a woman has completed her family.  Sometimes additional surgery (such as removal of the appendix) may be suggested.

Ovarian cancer is more common in women in the menopause. The diagnosis is made through examination of the cyst in the laboratory, however ultrasound and blood tests are helpful to determine the likelihood of cancer. Often there are little or no symptoms. Some patients may present with abdominal swelling, weight loss, nausea or lethargy.

Younger women may also develop ovarian cancer, however the chance is far lower.  We are more concerned if the cyst has solid areas or is growing rapidly.