As an early embryo, the fallopian tubes, uterus, cervix and upper vagina, develop from two separate tubes, known as mullerian or paramesonephric ducts. The mesonephric ducts develop into the internal male structures, but remnants can occur in the female and are known as paratubal cysts, or cysts that grow next to the fallopian tubes. Sometimes, they enlarge and have to be surgically removed. Developmental anomalies (abnormalities) of the mullerian duct system represent some of the most fascinating disorders in reproductive medicine.
The mullerian ducts differentiate to form the fallopian tubes, uterus, the uterine cervix, and the upper 1/3 of the vagina. The two mullerian tubes come together in the midline, the upper part of the two tubes spread apart to form each fallopian tube, the inner walls of the mid-portion of the tubes disintegrate, forming a hollow cavity or uterus, and the inner walls of the lower part of the mullerian ducts also disintegrate to form the cervix and upper vagina.
The lower 2/3 of the vagina develops from a completely different embryologic structure, known as the urogenital sinus. A wide variety of uterine malformations can occur when this morphogenesis (development) is disrupted. They range from uterine and vaginal agenesis (absence or failure to develop) to complete duplication of the uterus and vagina, to malformations of only the uterus, to minor uterine cavity abnormalities.
Since the renal (kidney) system and future parts of the axial skeletal system develop in close proximity to the uterine, or mullerian system, during embryonic development, mullerian malformations are frequently associated with abnormalities of the renal and skeletal system. Any patient that is found to have mullerian (uterine) anomalies should have a complete evaluation of their renal (kidney) system, including an intravenous pyelography (IVP) and renal sonography to exclude urinary tract anomalies.
Mullerian duct anomalies (MDA) are associated with functioning ovaries and age-appropriate external genitalia. These abnormalities are often recognized after the onset of puberty, when a young woman fails to menstruate (agenesis or absence of the uterus) or has very painful periods (non-communicating functional uterus). In the reproductive years, it is found on routine ultra sound, or when she has difficulty with getting pregnant or has repeated pregnancy loss. In the prepubertal period, normal development of external genitalia and age-appropriate developmental sexual milestones (like breast and pubic hair) often mask abnormalities of the internal reproductive organs.
The actual incidence and prevalence of all mullerian anomalies, both major and minor, in the general population are unknown, but is estimated at 1 in 300 (one reported range was 0.1 to 3.5%). Women with repeated pregnancy loss have a reported incidence of 5-10%, with the highest incidence of major mullerian defects occurring in patients having first trimester, late second or early third-trimester losses. The most commonly reported mullerian duct anomalies are as follows:
There are a number of ways to make the diagnosis of a mullerian duct anomaly:
The most common mullerian duct malformations (defects) can separately involve the uterus, vagina, a combination of both, less so the cervix and rarely the fallopian tubes unless in conjunction with anomalies of other reproductive organs. The most common parts of mullerian duct defects are the following:
Slight indentation in the fundus or top of the uterus. Does not have any reproductive consequences and is a "normal" variation and does not require surgical repair.
Only one of the mullerian ducts develops, thus, the uterine cavity is half the size of a normal cavity. No surgery can be done and this malformation can increase the risk of late 2nd and early 3rd trimester loss because the uterus will "run out of room" and trigger premature labor.
Partial or complete lack of disintegration of the inner wall of the mullerian tubes. The remaining partial or complete mullerian duct becomes a septum or band of connective tissue down the middle of the uterine cavity. The outside top or fundus of the uterus is normal. This connective tissue has poor blood supply and when an embryo attaches to it, the uterus cannot supply adequate blood flow and nutrients resulting in a first trimester loss generally between 8-12 weeks pregnant. A septate uterus can be corrected with surgery, resulting in a unified uterine cavity, allowing the pregnancy to go close to term or full term.
Partial or complete lack of disintegration of the inner wall of each mullerian tube. The remaining partial or complete mullerian duct becomes a septum but has normal endometrial or uterine lining. The outside top or fundus of the uterus is indented or "heart-shaped". The difference between a septate and a bicornuate uterus is either made visually, at laparoscopy, or on MRI, where you can distinguish between a heart-shaped uterus and a normal shaped uterus. The embryo attaches and continues to develop because it has adequate blood flow but results in premature labor generally around 22-26 weeks because the pregnancy "runs out of room" to grow, because technically, it is only growing in "half a uterus". A bicornuate uterus can be corrected with surgery, resulting in a unified uterine cavity, with very god pregnancy outcomes.
Underdevelopment of one side of the mullerian duct resulting in a much smaller but normal functioning uterus or "uterine horn"; that is either communicating with the other uterus, and hence no initial problems. There is an increased risk of prematurity and premature labor because it is basically a unicornuate uterus and a communicating very small "second uterus" or "uterine horn". Generally, if there is a history of pregnancy loss or the woman does not want to take the risk, the decision is to ablate or "burn" the endometrial lining or surgically removing the communicating horn because it is so small and cannot support a viable pregnancy, whereas the other side may be able to. A non-communicating horn poses a much greater problem because there is normal menstruation in that non-communicating "horn" but the menstrual blood has nowhere to go and continues to build up (hematometra or blood filled uterus), eventually causing considerable pain and the increased risk of endometriosis because of the back-flow of menstrual blood into the pelvic cavity (it has nowhere else to go). It will require surgery to remove the non-communicating horn.
Complete duplication of the entire reproductive system; with a fallopian tube on each side, a double uterus, a double cervix and a double vagina. This is due to the failure of any disintegration of either mullerian duct thus causing "duplication" all the way down the reproductive tract. Diagnosis is usually made on routine examination when either two vaginas or two cervices are found. Although, there is an increase in late 2nd and early 3rd trimester loss because the baby is "growing" in half of a uterus, statistically, surgical unification does not seem to improve pregnancy outcome.
Complete absence of the mullerian system (fallopian tubes, uterus, cervix and upper vagina) and the vaginal system (the lower 2/3 of the vagina). It presents in a young woman who has normal onset of secondary sexual characteristics but fails to begin menstruation. Pelvic examination only reveals a "dimple" where the vagina would normally be. Surgically this involves reconstructing a "new" vagina at the appropriate time so that the woman can have sexual intercourse. She will need to use a gestational carrier to achieve pregnancy. Psychological support and counseling are essential components of the pre-operative evaluation and care. In addition to not being able to have sexual intercourse, these young women will be infertile, resulting in possible psychological pain and self-esteem issues.
Absence of the fallopian tubes, uterus and upper vagina. First diagnosed in young woman who have normal development of secondary sexual characteristics but fail to begin menstruation. US and/or MRI shows the absence of the uterus and cervix and the vagina is shortened in ends in a blind pouch. No surgery is needed, the woman can have intercourse and pregnancy can be achieved by using a gestational carrier.
The shape of the uterine cavity is literally T-shaped. It is due to maternal exposure to DES, a drug used in the 50-60's to help prevent miscarriages. One consequence of maternal DES exposure was a T-shaped (or hypoplastic or underdeveloped) uterus in female offspring. This lead to an increased risk of miscarriages, because of the decreased uterine size, when these female offspring attempted pregnancy. It cannot be repaired by surgery and if a woman continues to have reproductive failure, she may have to consider a gestational carrier.
Once the diagnosis is made, surgical correction depends on the underlying symptoms (extremely painful periods, no menstruation, cannot have intercourse), early diagnosis (have not attempted pregnancy but does not want to take the risk of pregnancy loss) or a history of either first or second trimester loss. Most mullerian tract malformations are initially seen by the young woman's primary care physician or by her gynecologist. Reproductive endocrinologists generally see women with mullerian tract defects because of a history of repeated pregnancy loss and/or premature labor in the late second trimester; however, reproductive medical specialists are occasionally the first to make the diagnosis of a mullerian abnormality because the young woman comes in with her parents. All mullerian tract malformation surgery requires a significant amount of experience and expertise in order to get the desired result and preserve uterine integrity and safe future childbearing potential. Arizona Center for Fertility Studies has a vast amount of experience in surgical correction of all types of mullerian malformations, except those requiring vaginal reconstruction, in which case, the woman is referred to a surgeon who does numerous sex change procedures.
Surgery can be accomplished by several different techniques, but the end result, is a unification procedure of the uterus or removal of a compromised horn.
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