Ovarian cyst

Functional cysts form as a normal part of the menstrual cycle. There are several types of functional cysts:

• Follicular cyst, the most common type of ovarian cyst. In menstruating women, a follicle containing the ovum, an unfertilized egg, will rupture during ovulation. If this does not occur, a follicular cyst of more than 2.5 cm diameter may result.[4]
• Corpus luteum cysts appear after ovulation. The corpus luteum is the remnant of the follicle after the ovum has moved to the fallopian tubes. This normally degrades within 5 to 9 days. A corpus luteum that is more than 3 cm is defined as cystic.[4]
• Theca lutein cysts occur within the thecal layer of cells surrounding developing oocytes. Under the influence of excessive hCG, thecal cells may proliferate and become cystic. This is usually on both ovaries.[4]

Non-functional cysts may include the following:

• An ovary with many cysts, which may be found in normal women, or within the setting of polycystic ovary syndrome
• Cysts caused by endometriosis, known as chocolate cysts
• Hemorrhagic ovarian cyst
• Dermoid cyst
• Ovarian serous cystadenoma
• Ovarian mucinous cystadenoma
• Paraovarian cyst
• Cystic adenofibroma
• Borderline tumoral cysts

• 
  Transvaginal ultrasonography of a hemorrhagic ovarian cyst, probably originating from a corpus luteum cyst. The coagulating blood gives the content a cobweb-like appearance.
• 
  Transvaginal ultrasonography showing a 67 x 40 mm endometrioma, with a somewhat grainy content.

Follow-up imaging in women of reproductive age for incidentally discovered simple cysts on ultrasound is not needed until 5 cm, as these are usually normal ovarian follicles. Simple cysts 5 to 7 cm in premenopausal females should be followed yearly. Simple cysts larger than 7 cm require further imaging with MRI or surgical assessment. Because they are large, they cannot be reliably assessed by ultrasound alone; it can be difficult to see posterior wall soft tissue nodularity or thickened septation due to limited ultrasound beam penetrance at this size and depth. For the corpus luteum, a dominant ovulating follicle that typically appears as a cyst with circumferentially thickened walls and crenulated inner margins, follow up is not needed if the cyst is less than 3 cm in diameter. In postmenopausal patients, any simple cyst greater than 1 cm but less than 7 cm needs yearly follow-up, while those greater than 7 cm need MRI or surgical evaluation, similar to reproductive age females.[11]

An Axial CT demonstrating a large hemorrhagic ovarian cyst. The cyst is delineated by the yellow bars with blood seen anteriorly.

For incidentally discovered dermoids, diagnosed on ultrasound by their pathognomonic echogenic fat, either surgical removal or yearly follow up is indicated, regardless of patient age. For peritoneal inclusion cysts, which have a crumpled tissue-paper appearance and tend to follow the contour of adjacent organs, follow up is based on clinical history. Hydrosalpinx, or fallopian tube dilation, can be mistaken for an ovarian cyst due to its anechoic appearance. Follow-up for this is also based on clinical presentation.[11]

For multiloculate cysts with thin septation less than 3 mm, surgical evaluation is recommended. The presence of multiloculation suggests a neoplasm, although the thin septation implies that the neoplasm is benign. For any thickened septation, nodularity, vascular flow on color doppler, or growth over several ultrasounds, surgical removal may be considered due to concern of cancer.[11]

There are several systems to assess risk of an ovarian cyst of being an ovarian cancer, including the RMI (risk of malignancy index), LR2 and SR (simple rules). Sensitivities and specificities of these systems are given in tables below:[12]

Ovarian cysts may be classified according to whether they are a variant of the normal menstrual cycle, referred to as a functional or follicular cyst.[4]

Ovarian cysts are considered large when they are over 5 cm and giant when they are over 15 cm. In children, ovarian cysts reaching above the level of the umbilicus are considered giant.

In juvenile hypothyroidism multicystic ovaries are present in about 75% of cases, while large ovarian cysts and elevated ovarian tumor marks are one of the symptoms of the Van Wyk and Grumbach syndrome.[13]

The CA-125 marker in children and adolescents can be frequently elevated even in absence of malignancy and conservative management should be considered.

Polycystic ovarian syndrome involves the development of multiple small cysts in both ovaries due to an elevated ratio of leutenizing hormone to follicle stimulating hormone, typically more than 25 cysts in each ovary, or an ovarian volume of greater than 10 mL.[14]

Larger bilateral cysts can develop as a result of fertility treatment due to elevated levels of HCG, as can be seen with the use of clomifene for follicular induction, in extreme cases resulting in a condition known as ovarian hyperstimulation syndrome.[15] Certain malignancies can mimic the effects of clomifene on the ovaries, also due to increased HCG, in particular gestational trophoblastic disease. Ovarian hyperstimulation occurs more often with invasive moles and choriocarcinoma than complete molar pregnancies.[16]

A widely recognised method of estimating the risk of malignant ovarian cancer based on initial workup is the risk of malignancy index (RMI).[17] It is recommended that women with an RMI score over 200 should be referred to a centre with experience in ovarian cancer surgery.[18]

The RMI is calculated as follows:[18]

RMI = ultrasound score × menopausal score × CA-125 level in U/ml.

There are two methods to determine the ultrasound score and menopausal score, with the resultant RMI being called RMI 1 and RMI 2, respectively, depending on what method is used:[18]

An RMI 2 of over 200 has been estimated to have a sensitivity of 74 to 80%, a specificity of 89 to 92% and a positive predictive value of around 80% of ovarian cancer.[18] RMI 2 is regarded as more sensitive than RMI 1.[18]

In case an ovarian cyst is surgically removed, a more definite diagnosis can be made by histopathology:

Type	Subtype	Typical microscopy findings	Image
Functional cyst	Follicular cyst	A variable inner layer of granulosa cells which are luteinized after puberty[19] An outer layer of usually luteinized theca interna[19]
	Corpus luteum cyst	A convoluted cyst lining of luteinized granulosa cells[20] A prominent inner layer of fibrous tissue[20] An outer layer of theca cells[20]
Cystadenoma	Serous cystadenoma	Cyst lining consisting of a simple epithelium, whose cells may be either:[21] columnar and tall and contain cilia, resembling normal tubal epithelium cuboidal and have no cilia, resembling ovarian surface epithelium
	Mucinous cystadenoma	Lined by a mucinous epithelium
Dermoid cyst		Well-differentiated components from at least two germ layers (ectoderm, mesoderm and/or endoderm).[22]
Endometriosis		At least two of the following three criteria:[23] Endometrial type stroma Endometrial epithelium with glands Evidence of chronic hemorrhage, mainly hemosiderin deposits
Borderline tumor		Atypical epithelial proliferation without stromal invasion.[24]
Ovarian cancer		Many different types, but generally severe dysplasia/atypia and invasion.	Serous carcinoma.
Simple squamous cyst		Simple squamous epithelium and not conforming to diagnoses above (a diagnosis of exclusion)

Pain associated with ovarian cysts may be treated in several ways:

• Pain relievers such as acetaminophen, nonsteroidal anti-inflammatory drugs,[1] or opioids.
• While hormonal birth control prevents the development of new cysts in those who frequently get them,[1] it is not useful for the treatment of current cysts.[2]

Although most cases of ovarian cysts involve monitoring, some cases require surgery.[30] This may involve removing the cyst, or one or both ovaries.[31] Technique is typically laparoscopic, unless the cyst is particularly large, or if pre-operative imaging suggests malignancy or complex anatomy.[32] In certain situations, the cyst is entirely removed, while with cysts with low recurrence risk, younger patients, or which are in anatomically eloquent areas of the pelvis, they can be drained.[33][34] Features that may indicate the need for surgery include:[10]

• Persistent complex ovarian cysts
• Persistent cysts that are causing symptoms
• Complex ovarian cysts larger than 5 cm
• Simple ovarian cysts larger 10 cm or larger than 5 cm in postmenopausal patients
• Women who are menopausal or perimenopausal