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“Cyst” comes from kustis, which means “pouch”, so ovarian cysts are fluid-filled
sacs on or in the ovaries.
They are very common in females of reproductive age, but can affect females of any age.
The ovaries are a pair of white-ish organs about the size of walnuts.
They’re held in place, slightly above and on either side of the uterus and fallopian
tubes by ligaments.
Specifically, there’s the broad ligament, the ovarian ligament, and the suspensory ligament.
And the suspensory ligament is particularly important because the ovarian artery, ovarian
vein, and ovarian nerve plexus pass through it to reach the ovary.
If you slice the ovary open and look at it (don’t try this at home) there’s an inner
layer called the medulla, which contains most of the blood vessels and nerves and an outer
layer called the cortex, which has ovarian follicles scattered throughout it.
Each follicle is initially made up of an immature sex cell, or primary oocyte, which is the
female sex cell, and layers of theca and granulosa cells surrounding the oocyte.
Now, there’s actually loads going on with the ovaries throughout the menstrual cycle,
which is controlled by the hypothalamus and the pituitary up in the brain.
The hypothalamus secretes gonadotropin-releasing hormone, or GnRH, which makes the nearby anterior
pituitary gland release follicle-stimulating hormone, or FSH, and luteinizing hormone,
In the first two weeks of an average 28-day cycle, the ovaries go through the follicular
phase, meaning that out of the many follicles scattered throughout the ovaries, a couple
of them enter a race to become the dominant follicle, that will be released at ovulation,
while the rest regress and die off.
All the developing follicles secrete loads of estrogen, which negatively inhibits pituitary
FSH, and they also make a few androgens like testosterone.
At ovulation, the oocyte is released into the fallopian tube, and the luteal phase begins
- which lasts for the last 2 weeks of an average 28-day cycle.
During the luteal phase, the remnant of the ovarian follicle, called the corpus luteum,
makes progesterone, which negatively inhibits pituitary LH.
If fertilization occurs then the corpus luteum continues making progesterone until the placenta
If fertilization doesn’t happen, then the corpus luteum stops making hormones after
approximately 10 days, becomes fibrotic, and is called the corpus albicans.
So as far as ovarian cysts go, there are 2 broad categories.
First, there are functional cysts, which result when the normal, cyclic development of the
ovarian follicles is disrupted.
One type of functional cyst that can form before ovulation is a follicular cyst, which
is a dominant follicle that fails to rupture and keeps growing.
This can happen, if say, the normal surge of LH that causes ovulation just doesn’t
happen during a given menstrual cycle.
A condition where you might have multiple follicular cysts is polycystic ovary syndrome,
which is caused by a dysfunction in the hypothalamic-pituitary-ovarian axis that causes chronic anovulation, which
may lead to amenorrhea, or absent menstruation, and excess androgen production.
Alternatively, if the dominant follicle ruptures but then closes up again after ovulation,
this is called a corpus luteal cyst.
In this case, the corpus luteum doesn’t dissolve but instead continues to grow.
As it grows, the arteries nourishing it can rupture and hemorrhage into the cyst, which
is why corpus luteal cysts are also called hemorrhagic cysts.
Both follicular and corpus luteal cysts are usually around 2 to 3 centimeters, but they
can get as big as 10 cm in diameter, they contain a clear serous liquid, and have a
smooth internal lining - so they are referred to as “simple cysts”.
The last kind of functional cysts are theca lutein cysts.
These are caused by overstimulation by human chorionic gonadotropin or hCG, a hormone that’s
produced by the placenta, so they’re only seen in pregnancy.
hCG stimulates growth of the follicular theca cells, so these cysts are usually bilateral,
since resting follicles can be found on both ovaries.
Theca lutein cysts are more likely to develop when there’s more hCG than usual, like when
there are multiple fetuses, or with gestational trophoblastic disease, where tumours made
up of placental cells causes higher than normal hCG levels.
Ok, now, the second category of cysts are neoplastic cysts - which is not to say all
of them are cancer, but rather that they’re caused by the abnormal reproduction of cells
on or in the ovaries, which can result in a benign or malignant mass.
Broadly speaking, neoplastic cysts are usually complex, meaning that they’re larger than
10 centimeters, have irregular borders, and have internal septations creating a multilocular
The fluid inside these cysts tends to be heterogeneous, meaning there’s something other than fluid
Benign neoplastic cysts include endometriomas, which occur in endometriosis, and it’s where
endometrial tissue from the uterus grows on the ovary.
Because they’re functionally the same as the endometrium inside the uterus, endometriomas
respond to hormones just like the uterus would.
Because of this, endometriomas tend to bleed within the cyst cavity during menstruation,
and over time, they fill up with old, dark blood and shed tissue - hence why they’re
sometimes also called “chocolate cysts”.
Endometriomas also release proinflammatory factors which cause inflammation, which leads
to cyst growth.
When they get too large, they can rupture and spill their contents inside the peritoneal
Ok, now let’s switch gears and look at ovarian tumors - since they also have cystic characteristics,
they’re also included under the umbrella term of neoplastic cysts.
First, there’s benign tumors.
Some originate from surface ovarian epithelium, such as serous cystadenomas, which are often
bilateral and filled with a watery fluid, and mucinous cystadenomas, which tend to be
multilocular and contain a mucus-like fluid.
Some originate from ovarian germ cells, such as mature cystic teratomas, also called dermoid
Mature cystic teratomas are the most common ovarian tumors in young women and usually
contain a heterogeneous mix of mature tissues that come from two or three of the germ cell
So they can contain fat, muscle, teeth, nails, hair - they’re pretty much the Frankenstein’s
monster of tumors.
Finally, the last category of neoplastic cysts include malignant ovarian tumours, like serous
or mucinous cystadenocarcinomas, which develop from surface ovarian epithelium, just like
their benign counterparts.
Now, there are three important complications of ovarian cysts.
First, some cysts can become hemorrhagic, meaning there is bleeding inside the cyst.
This is more common with follicular and corpus luteal cysts.
Second, some cysts can rupture, which will release their contents into the peritoneal
That can be pretty irritating for the peritoneal cavity.
Think for example of a dermoid cyst, with its mixture of tissues like hair and sebaceous
fluid: that’s not something the peritoneal cavity is meant to handle!
Rupture can happen spontaneously but more frequently it happens after sexual intercourse.
A third complication is ovarian torsion, where the ovary twists around the suspensory ligament.
Since this ligament suspends the ovary and contains the ovarian blood vessels within
it, torsion can cut off the blood supply to the ovary.
A risk factor for this is when the ovary is 5 centimeters or larger, which can happen
with all kinds of ovarian cysts.
Now, many ovarian cysts are asymptomatic.
When there are symptoms they include a dull aching lower abdominal pain around the location
of the cyst, dyspareunia, or pain during sexual intercourse, and a feeling of pressure in
the lower abdomen which can also cause frequent urination and bowel movements.
If the abdominal pain is sudden, sharp, and severe, that might indicate ovarian torsion,
or a hemorrhagic or ruptured cyst.
With a ruptured cyst, there may also be low blood pressure or a fast heart rate, and if
the blood makes it to the subphrenic space of the peritoneal cavity, which is right below
the diaphragm, it may cause upper abdominal or shoulder pain.
If the cysts are the result of polycystic ovary syndrome, you might also see amenorrhea
and hirsutism, or excessive hair growth on the chin and upper lip, chest, and back.
Endometriomas can also cause dysmenorrhea, or painful menstruation, and are associated
with fertility issues.
Finally, with ovarian torsion, there might also be nausea, vomiting, and a low-grade
Diagnosing an ovarian cyst starts with an abdominal ultrasound.
If diagnosis is uncertain, an MRI can be done for more information.
A blood test for cancer antigen 125 might be done to rule out a malignant ovarian tumor.
Ultimately, histologic analysis is the only way to get a definitive diagnosis of the type
of cyst, and this is usually achieved by collecting some cyst cells via ultrasound-guided aspiration,
or following removal of the cyst.
Treatment for ovarian cysts varies based on type and size.
Many simple cysts will get better on their own.
Broadly speaking, if the cyst is under five centimeters, observation is usually the mainstay
This applies to both functional cysts and benign neoplasms like endometriomas, as well
as serous and mucinous adenomas.
With uncomplicated cyst rupture where the person is hemodynamically stable, “expectant
management” is also used.
They might only be given NSAIDs for pain.
If the cyst is over five centimeters, it’s usually removed by laparoscopy.
Surgery is also done for benign tumors that cause symptoms on a regular basis, for malignant
tumors, if a cyst is hemorrhaging severely and it’s affecting blood pressure and heart
rate, or if there is ovarian torsion since lack of blood flow can damage the ovaries.
All right, as a quick recap…
Ovarian cysts are fluid-filled sacs on or in the ovaries.
They can broadly be grouped as functional and neoplastic cysts.
Functional cysts result from a disruption of the normal cyclic activity of the ovaries,
and they include follicular cysts, which occur when the follicle fails to rupture before
ovulation, and luteal cysts, which is when the follicle ruptured but then closed back
Particular types of functional cysts are those associated with PCOS, which happen because
of chronic anovulation, and theca-lutein cysts, which are only seen during pregnancy, when
there’s too much HCG.
On the other hand, neoplastic cysts include endometriomas, serous and mucinous cystadenomas,
and mature cystic teratomas, as well as malignant ovarian tumors.
Many ovarian cysts are asymptomatic, but when it’s symptomatic, a dull, aching pelvic
pain is common.
A sharp, sudden pain could be a sign of one of three potential complications of ovarian
cysts: rupture, hemorrhage, and ovarian torsion.
Small cysts can be expectantly managed, whereas cysts over 5 centimeters, who cause complications,
or those who appear malignant should be surgically removed.