Uterine fibroids or uterine leiomyomas are benign (non-cancerous) tumors (growths) that commonly arise in the muscle wall (myometrium) of the uterus.

They are usually firm to hard in consistency, though larger tumors may be softer. They usually appear tan in color, and have a whorled pattern to their growth.

Larger fibroids often have multiple lobules within them much like a jar containing small balls. Their blood supply is largely peripheral, ie, they are surrounded on their exterior by a plexus of blood vessels. Only a few feeder vessels penetrate into the core of the fibroid.

Fibroids are usually multiple, though about 10% of uteri with fibroids will have only one. They grow anywhere in the uterus that there is myometrium or muscle cells.

That means that they may arise lower near the cervix, in any wall (right, left, anterior, posterior, or top (fundus), or even in the ligaments that connect to the uterus. Fibroids may rarely develop a blood supply from other structures nearby such as the ovary, fallopian tube or intestine.

They may then completely detach from the uterus and become separate and independent from the uterus (parasitic myomas).

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Uterine fibroids are important because:

  • They are extremely common in women (the most common tumor of reproductive age women)
  • They may cause symptoms that require medical treatment

Uterine fibroids are found at autopsy in 80% of all women. Fortunately, most women who have fibroids are not affected by them. However, 20% to 25% of women with fibroids will suffer from symptoms that can be very severe, causing hospitalization and even requiring surgical treatment.

Based on 2010 U.S. Census data and the known frequency of uterine fibroids in African-American and Caucasian women, 45.6 million U.S. women have fibroids and 9.1 to 11.4 million suffer from fibroid symptoms.

A recent study put the annual direct cost of uterine fibroids at $4.1 to 9.4 billion. Including the cost of obstetrical complications from fibroids and lost work hours, the cost was $5.1 to 34.4 billion.

This was a conservative estimate, since the authors included data only from cases of new diagnoses of fibroids. This data was published in the American Journal of Obstetrics and Gynecology in 2012 and was reported on Fox news and other media outlets.

At $34.4 billion, uterine fibroids cost as much as breast cancer, colon cancer, and ovarian cancer combined.

Uterine fibroids cause heavy menstrual bleeding (heavy bleeding that occurs during the normal time of menstruation), menstrual pain (pain that is more severe than “normal” menstrual cramps), urinary frequency and retention (having the urge to void often and being unable to effectively empty the bladder), pain during sexual intercourse, abdominal enlargement and distension, and back and abdominal pain.

These symptoms may also result in difficulty sleeping, fatigue, and feelings of self-consciousness and loss of control.

Large fibroids may also internally compress nerves causing leg and hip pain, making even normal walking difficult. They may also compress the ureters (the tubes that carry urine from the kidneys to the bladder) causing swelling (hydronephrosis).

Uterine fibroids cause symptoms in 20% to 25% of women who have them.

Uterine fibroids arise as early as the early 20s. This early occurrence is more common in African -American women, in whom fibroids arise earlier in age and in whom fibroids are more aggressive and cause more symptoms.

Uterine fibroids will slowly shrink over years after menopause occurs. New uterine fibroids do not usually arise after menopause.

It is likely that there are multiple triggers that cause a pluripotential cell or stem cell to develop into a leiomyoma cell instead of a normal muscle cell. That trigger may be lack of oxygen (hypoxia) or some other event. Once the leiomyoma cell is formed, it is independent of the normal regularly mechanisms that control cell growth. They grow and grow, creating a tumor.

Each fibroid tumor arises from a single genetic error or mutation. One fibroid does not directly cause another to appear. Different fibroids grow at different rates and at different times. They seem to behave independently, but similarly.

Some fibroid will tend to cause heavy bleeding, likely by affecting the uterus’ ability to contract effectively during menstruation.

They may also secrete bioactive chemicals that affect the growth of blood vessels in the uterine lining. Others will tend to grow rapidly and become very large, apply pressure to surrounding organs and creating pressure symptoms. Still other will grow to a certain size and then top growing.

Fibroids do not grow continuously and at a constant rate. Instead, fibroids actually grow in spurts. Then the grow very little or cease to grow for a period of time, then begin to grow again.

Fibroids also vary in shape and of course, size. Fibroids initially are spherical or nearly spherical when very small, but may become eliptical or even pancake-like in shape. Interestingly, fibroids closer to the outer surface are much flatter than those deeper in the wall. This is significant as physicians must be aware of the irregularity in shape in order to completely ablate the tumor.

Fibroids, like most tumors, can outgrow their blood supply or experience traumatic events that may cause parts of them to die. The entire myoma could also be affected. When that happens, the fibroid may stop growing, become softer or actually firmer, degenerate into a more liquid state, and demonstrate pockets of fluid.

Over time, calcium may become deposited in small specks throughout the tumor or in a shell-like pattern on the periphery if blood supply has been compromised. Some shrinkage may gradually occur, but rapid shrinkage is unusual.

After menopause, hormone stimulation to fibroids ceases so generally they stop growing and new fibroids do not form. The shrinkage of fibroids after menopause is a slow process and requires quite a few years.

Often, women develop one or more of the symptoms of fibroids and consult with their physicians. Physicians may detect a uterus that is enlarged by fibroids on physical exam, and then order a pelvic ultrasound examination for confirmation.

Uterine fibroids are visible on ultrasound and are thereby commonly detected by this method. They are also visible on MRI and CT scan evaluations.

Uterine fibroids require treatment when they become symptomatic (cause symptoms in patients) and when the symptoms are severe enough to warrant treatment. Often the early symptoms of fibroids are mild, but become progressively more severe over time.

For example, in women with heavy menstrual bleeding due to fibroids, initially only a few menstrual periods per year may be heavier and/or longer. But over time, more and more menstrual periods become abnormally heavy or long until finally most all menstrual periods are very heavy and/or long.

In this case, anemia often develops as the monthly blood loss exceeds the ability of the body to manufacture new blood, resulting in a deficit or low blood count. In this case, patients need to take oral iron to stimulate blood production and may need to have iron infusions or frequent blood transfusions.

Each uterine fibroid arises from a single abnormal cell in the uterine wall. Normally, cells only duplicate when they need to, replacing lost or dying cells, keeping the body healthy.

Tumors in general occur because cells replicate even when the body does not need them to. They grow independently and are not controlled by the body’s normal regulatory mechanisms. Think of them as “rogue” cells. As they continually and rapidly duplicate themselves, they become larger and larger, expanding the size of the uterus.

Uterine fibroids have been known to become massive if not removed or treated. In June, 2015, surgeons in India removed a fibroid tumor that weighed 30 pounds and was 21 inches in diameter.

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