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Uterine Anomalies
Incomplete fusion of the paramesonephric, aka, Müllerian ducts, creates uterine anomalies. These anomalies occur along a spectrum, and the risks of infertility increase with the severity of the anomaly.
Müllerian agenesis (aka vaginal agenesis, Müllerian aplasia) is often simply referred to by its most common variant, Mayer-Rokitanksy-Kuster Hauser syndrome.
MRKH occurs when the paramesonephric ducts do not develop, so the uterus and upper vagina are absent or severely hypoplastic; we show a ‘vaginal dimple’ where the vaginal canal did not form. Some patients with MRKH also have skeletal, auditory, cardiac, renal and digital anomalies.
Unicornuate uterus (single-horned anomalies are the result of an absent or incomplete development of one paramesonephric ducts (the unicornuate uterus is sometimes called a “banana-shaped” uterus).
It’s helpful to remember that “uni” means “one”, and “cornuate” means “horn”; the horn of the uterus is where the uterine tubes meet the uterine body, and there are typically two horns.
Variations of unicornuate uteri can present with different “rudimentary” horn development.
For our example, we show a uterus with a communicating hemi-uterus, which connects the primary uterine cavity with a cavity in the rudimentary horn. The non-communicating horn with a cavity can obstruct menstrual flow and cause abdominopelvic pain.
Other variants of the unicorunate uterus present without rudimentary horns and with and without non-communicating cavities.
Uterus didelphys, aka, double uterus; though not typical in humans, the double uterus is common in other animals, including cats and dogs.
We highlight where the two uteri open to the vagina via separate cervical openings; though it is possible to carry two fetuses to term, one in each uterus, this phenomenon is rare. In some cases, a septum divides the vaginal canal to form double vaginas.
A bicornuate (aka bicorporeal) uterus has two distinct horns separated by a cleft, thus, they appear “heart-shaped.” This anomaly is the result of incomplete fusion of the paramesonephric ducts; incidentally, the horns may be undeveloped.
Septal anomalies are the result of incomplete reabsorption of the paramesonephric duct septum, and may comprise fibrous or muscular tissue (this is relevant when deciding whether to undergo surgery).
in our example, the septum of the uterus arises from the inner wall of the fundus and extends towards the cervix.
Be careful not to confuse the septate uterus with the bicornuate uterus; notice that the septum divides the inner uterine cavity, but the cleft of the bicornuate uterus is visible on the external surface of the uterine fundus (the superior most region of the uterus).
This distinction is clinically important, as the septate uterus is more often associated with reproductive impairment than is the bicornuate uterus.