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Uterine fibroids, are also called leiomyomas.
Leio- means smooth, myo- means muscle, and
-oma means tumor, so these are benign smooth
muscle tumors of the uterus.
In fact, fibroids are the most common type
of tumor in females.
The uterus is a hollow organ that sits behind
the urinary bladder and in front of the rectum.
The top of the uterus above the openings of
the fallopian tubes is called the fundus,
and the region below the openings is called
the uterine body.
The uterus tapers down into the uterine isthmus
and finally the cervix, which protrudes into
Zooming into the cervix, there are two openings,
a superior opening up top, and an inferior
opening down below, both of which have mucus
plugs to keep the uterus closed off except
during menstruation, and right before ovulation.
The uterus is anchored to the sacrum by utero-sacral
ligaments, to the anterior body wall by round
ligaments, and it’s supported laterally
by cardinal ligaments as well as the mesometrium,
which is part of the broad ligament.
The wall of the uterus has three layers: the
perimetrium, which is a layer continuous with
the lining of the peritoneal cavity, the myometrium,
which is made of smooth muscle that contracts
during childbirth to help push the baby out,
and the endometrium, a mucosal layer, that
undergoes monthly cyclic changes.
Now, uterine fibroids are smooth muscle tumors,
and they’re monoclonal, meaning that they
arise from a single cell of the myometrium
that starts dividing uncontrollably.
Overall, fibroids most commonly affect women
of African descent.
They’re sometimes linked to a genetic mutation,
with the most common being a somatic mutation
with the mediator complex subunit 12 or MED12
Mediator complex subunit 12 is part of a group
of proteins that control gene activity by
regulating how transcription factors bind
to RNA polymerase II.
Another factor in fibroid development is steroid
Fibroids have a love affair with estrogen
Fibroids upregulate their receptors for these
two hormones and also produce a lot of aromatase,
an enzyme that converts androgens into estrogen.
When these hormones bind to the myometrium
cells, it has a mitogenic effect, meaning
it promotes mitosis.
Estrogen specifically upregulates growth factors,
like IGF- 1, EGFR, and TGF- beta1, and progesterone
upregulates EGF, TGF- beta1, and TGF- beta3.
So, the more estrogen and progesterone available,
the more a fibroid is likely to grow.
This is why fibroids typically affect pre-
menopausal females and why they grow rapidly
during pregnancy – when there’s a lot of
Another risk factor for developing a fibroid
is never having a pregnancy and breastfeeding,
and having many menstrual cycles – each with
a wave of hormones.
Finally, a historical risk factor that is
less relevant now, was exposure to diethylstilbestrol,
an estrogen medication that used to be given
to pregnant women.
Finally, in rare cases, fibroids are linked
to a hereditary condition called hereditary
leiomyomatosis and renal cell carcinoma syndrome,
also called Reed’s syndrome, which causes
skin and uterine fibroids and an aggressive
form of papillary renal cell cancer.
Fibroids can be described based on where they
are located in the uterus.
The most common type are intramural fibroids,
and they develops within the wall of the uterus.
Subserosal fibroids come from myometrial cells
at the perimetrium, and they can actually
detach from the uterus and get their blood
supply from another nearby organ.
Submucosal fibroids come from myometrial cells
just below the endometrium and they can grow
into the cavity of the uterus and change its
When that happens, they’re called pedunculated
Lastly, cervical fibroids grow in the wall
of the cervix.
Uterine fibroids are round, firm, and grayish-white
in color and they can range from barely visible
lumps to large tumors that can be felt on
the outside of the body.
Sometimes they are solitary, but they can
also develop in groups.
They’re benign, so they don’t invade neighboring
tissue or spread to other parts of the body.
Fibroids are usually small and asymptomatic,
but their location, number, and size can sometimes
lead to symptoms, like abnormal uterine bleeding,
which takes the form of heavy or long menstrual
Over time this can lead to iron deficiency
Fibroids can also cause abdominal pain, because
the fibroids put pressure on pelvic organs.
Submucosal and intramural fibroids, in particular,
are also associated with infertility and a
higher risk of miscarriage.
In pregnancy, fibroids can also cause issues
such as fetal malpresentation, preterm labor,
and postpartum hemorrhage.
Diagnosis of uterine fibroids is done with
a pelvic exam and ultrasound.
Rarely, a biopsy of the mass is done to rule
out that it’s not a cancerous tumor, called
a uterine sarcoma.
If it’s a fibroid, the biopsy will show
a whorled pattern of smooth muscles bundles
– like a wave in the ocean – with well- defined
Treatment of uterine fibroids varies: asymptomatic
uterine fibroids are usually left untreated.
Symptomatic fibroids can be treated with surgery,
either a myomectomy or a hysterectomy, if
the woman is no longer interested in childbearing.
Another, non- invasive option is uterine artery
embolization, where a catheter is used to
reduce blood flow to the fibroids and causes
them to shrink.
Medications aren’t typically used for treatment,
except gonadotropin- releasing hormone analogues
which help shrink fibroids before surgery.
All right, as a quick recap, uterine fibroids,
or leiomyomas, are benign smooth muscle tumors
of the uterus, and occur most commonly in
women of African descent.
They’re sometimes linked to genetic mutations
in smooth muscle cells like in the MED12 gene,
but estrogen and progesterone also play a
role in their development.
Most fibroids are asymptomatic, but some cause
abnormal uterine bleeding, pain, and fertility
What is a uterine fibroid? uterine fibroids, or leiomyomas, are benign smooth muscle tumors of the uterus.
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