An ultrasound scan is the most common investigation for an ovarian cyst. The scan shows some of the characteristics of the cyst and points to the likely type of cyst. An abdominal scan may be performed first, and is useful if the cyst is large. An abdominal scan also allows other structures in the abdomen to be visualised. A full bladder improves visualisation of the pelvic structures as the fluid in the bladder makes a kind of “window” to the pelvis. A transvaginal scan brings the ultrasound probe much closer to the pelvic organs and usually gives better detail of the ovaries, fallopian tubes and uterus. This scan should not cause any discomfort and does not require a full bladder.
Ultrasound characteristics of ovarian cysts:
- Thickness of the outer wall of the cyst. A simple cyst has a thin outer wall.
- Irregularities in the cyst wall. A simple cyst has a smooth wall whereas a complex cyst may have some irregular nodules or thickening of the wall.
- Internal divisions or “septae” are found only in complex cysts. These may be thin or thick and may also contain irregularities.
- Solid areas are seen in some complex cysts.
- The nature of the “fluid” filling the cysts varies and ultrasound can give some insight into this. Blood often looks very different to the thin fluid of a follicular cyst.
- If similar cysts are present on both ovaries this may be significant.
- Blood flow through various parts of the cyst can be measured by Doppler scanning and helps determine the nature of the cyst.
All the above characteristics are taken into account by the ultrasonographer who may be able to form a judgement on the type of cyst present. Such judgements are never 100% accurate and are sometimes very difficult. However they may give some guidance as to how to manage the cyst.
The information gained by an ultrasound examination is very dependent on the skill of the person performing the scan. Most radiologists have areas of the body they are particularly interested in and develop skills in those areas specifically. Choice of the right person to perform a scan is important, particularly if the diagnosis is difficult.
If a cyst appears simple, the ultrasound scan may be repeated at an interval of 4 to 6 weeks to see whether the cyst has resolved or increased in size.
This blood test measures the presence of a tumour antigen. The CA125 level may be elevated in ovarian cancer, although in 30% of early cancers it is not elevated at all. It is also elevated in many other circumstances including endometriosis. The CA125 level changes with the normal menstrual cycle and is therefore more useful after the menopause.
Magnetic Resonance Imaging is an alternative method of scanning the ovaries. It provides information that complements the ultrasound findings. The MR image differentiates between different tissue types by imaging the molecular characteristics of tissue. It can identify fat, blood and other tissues. If the cyst is complex MRI may be useful in helping to determine what type of cyst is present.
Treatment of ovarian cysts
The treatment of an ovarian cyst depends on what type of cyst is present. Unfortunately, even with the very best imaging and assessment it is not possible to be certain about the nature of an ovarian cyst. The treatment has to be decided on the basis of probability of various cyst types rather than certainty. One of the key issues is the possibility that the cyst is cancerous. With most simple cysts this is very unlikely, but often this possibility cannot be completely excluded.A simple “Risk of Malignancy Index” has been developed which takes into account the CA125 level, menopausal status and ultrasound findings. This is a guide that can be useful in raising suspicion of malignancy in some cases, although it is not very helpful with endometriosis as the ultrasound appearances are often complex and CA125 may be raised significantly. Other risk scores have been developed which perform better than the RMI.
With most ovarian cysts diagnosed, the suspicion of malignancy is very low and the women can be reassured.