There are two types of small ovarian cysts which can be considered “normal”. During the first half of the menstrual month (“follicular phase”) estrogen stimulates the growth of a dominant follicle. This follicle fills with fluid which is spilled out when the ready egg (“oocyte”) is ejected (“ovulation“). After the egg is released, its former follicle closes off and becomes the “corpus luteum” which produces progesterone during the following two weeks (“luteal phase”).
If, in either of these phases, larger than normal amounts of fluid collect, one can develop ovarian cysts that will cause pain or menstrual bleeding changes. A normal ovary is about 2 x 3 cm (almond sized). A follicular ovarian cyst, if the egg is not ejected and the amount of fluid continues to increase, can reach sizes of up to 10 cm. Fortunately most follicular cysts are smaller and will resolve within one to three months. If the size is large (eg greater than 8 cm) the heavy cyst can prompt the ovary to twist on itself like a heavy flower on a too fragile stalk. This twisting (“ovarian torsion”) causes intense pain as it cuts off the blood supply to the ovary. While follicular cysts are the most common type of ovarian cysts, torsion is uncommon.
In another condition, polycystic ovaries (“polycystic ovarian syndrome/PCOS“), the ovary will contain multiple small follicular cysts. Unlike the cysts described above, PCOS cysts will usually stay small. Yet, like other follicular cysts the egg is not ejected. This lack of ovulations contributes to the fertility problems seen in PCOS.
Normally after ovulation a corpus luteum of less than 3 cm resolves within two weeks. This type of cyst will be maintained, if conception occurs, to produce hormones needed in early pregnancy. If excessive amounts of fluid collect, a corpus luteum cyst can also get large enough to cause pain—or very rarely, ovarian torsion. Occasionally, this type of cyst will have a small blood vessel which continues to bleed into a corpus luteum cyst. This is called a “hemorrhagic ovarian cyst”. A cyst of this type can either leak small amounts of blood, or it can rupture, spilling blood into the abdomen. This hemorrhagic ovarian cyst can be linked to prolonged pain, and merits closer follow up.
Each of the cysts described above can start with a normal process and become a medically significant cyst. They are all described as benign cysts. By contrast there are ovarian cysts which are not related to variations in normal processes. Endometriomas are cysts filled with old blood. This gave rise to the nickname “chocolate cysts” as the cyst fluid looked like chocolate syrup. Endometriomas can grow to 6-8 cm. They are formed when bits of uterine lining tissue (“endometriosis”) attach to pelvic organs such as ovaries. Dermoid cysts (“cystic teratomas”) can contain bits of hair, teeth, or other body tissues. It is still not known why demoid cysts form. At an incidence of 66%, dermoids are most common kind of benign tumors of the ovary. Cystadenomas (“serous cystadenomas”) are formed from epithelial cells on the covering of the ovary. These cysts are filled with a fluid or a gel like material. Cystadenomas comprise 20% of benign tumors. The concept of benign tumors sounds like a contradiction in terms. It means that there is a very small chance of this type of ovarian cyst to become cancerous. For example, in one study (Scully, 1973) less than 2% of dermoid cysts showed evidence of malignancy.
What If My Ultrasound Does Not Say What Type of Cyst I Have?
Often, when women get copies of their pelvic ultrasounds there is no definite diagnosis. The ovarian mass may only be described by location, size, and other attributes. The importance of size has been discussed above. The descriptors used can give an indication of the type of cyst that might be present. A cyst described as fluid filled with regular borders is often a simple follicular cyst. The ultrasound term anechoic (no echos) may be used to describe fluid, either cyst fluid or fresh blood.
A complex ovarian cyst generates more concern. A cyst that is a mixture of solid and fluid elements, or is solid, is not a simple follicular cyst. The presence of irregular borders, or septations (internal walls dividing the cyst into separate spaces) are more concerning features found in complex cysts. Other terms which may be linked to complex cysts are: mural nodule, fluid-debris level, retracting blood clot, or a mix of anechoic to hyperechoic appearances.
How Reliable is Ultrasound?
While simple ovarian cysts can usually be diagnosed by vaginal ultrasound, the question arises “How reliable is ultrasound when the cyst is complex?” One well done study (Jermy, 2001), looked at the reliability of ultrasound to make a correct diagnosis for possible endometriosis or dermoid types of complex ovarian cysts. After the mass was removed it was found that ultrasound was successful in predicting 96% of endometriosis cysts and 97% of dermoids. There were no ovarian cancers found.
What Should I Expect for Treatment?
If a simple cyst is suspected, the only treatment may be a repeat ultrasound in six to eight weeks to be sure that it is resolving. If the cyst is very large, and ovarian torsion is a concern, then more frequent ultrasounds may be performed.
Previously, birth control pills (BCPs) were commonly prescribed in an attempt to treat simple ovarian cysts. Studies comparing the use of BCPs to “expectant treatment” (Turan, 1994) began to suggest that “watch and wait” was as effective as treating with BCPs. More recently (Sanersak, 2006) found that low dose monophasic pills were not statistically better at treating functional ovarian cysts than following women with routine ultrasound screening.
In terms of prevention of ovarian cysts, several studies have examined the role for birth control pills. In an older study (Vessey, 1987) there was a 78% reduction in corpus luteum cysts and a 49% reduction in follicular cysts among women who had taken high dose birth control pills within the previous six months. A later study (Lanes, 1992) compared older, high dose mono-phasic pills to lower dose mono-phasic pills, and lower dose tri-phasic pills. This group found that the lower dose pills conferred less protection for functional cysts than did the older types of birth control pills.