Müllerian Duct Anomalies
Synonyms/Description
Congenital uterine anomalies
Etiology
Congenital anomalies of uterine shape occur in 3% to 4% of all women. The prevalence in women with infertility and early miscarriage is up to 10%, and as high as 25% in those with midtrimester pregnancy losses. Patients with uterine shape abnormalities have an increased incidence of congenital renal anomalies such as unilateral renal agenesis. The American Society for Reproductive Medicine has developed the following classification of uterine anomalies.
Class I: Agenesis of the Uterus, Cervix, and/or Upper Vagina
Includes women with Mayer-Rokitansky-Küster-Hauser syndrome (incidence 1/5000). Patients with this condition are born with no uterus, cervix, or upper vagina.
Class II: Unicornuate Uterus (20% of Uterine Anomalies)
This anomaly results from a lack of or incomplete development of one of the two Müllerian tubercles. This gives rise to only one complete horn of the uterus with either total absence or hypoplasia of the contralateral horn (rudimentary horn). In 35% of cases, the unicornuate uterus is isolated, but most are associated with variable development of a contralateral rudimentary uterine horn. Thirty-three percent of women with a unicornuate uterus have a noncavitary rudimentary horn (without endometrium), whereas 32% have a rudimentary horn with endometrium present. This rudimentary horn may or may not communicate with the “normal” hemiuterus.
Unicornuate uteri are associated with an early pregnancy loss rate of 41% to 62%, especially when a rudimentary horn is present. They are also associated with preterm delivery.
Class III: Didelphic Uterus (5% of Uterine Anomalies)
These patients have a complete lack of fusion of the bilateral Müllerian ducts, resulting in two totally separate uterine horns, each with its own endometrial cavity and cervix. The vagina also contains a septum in 75% of cases. Uterine didelphys is associated with spontaneous miscarriage rates of 32% to 52% and premature birth rates of 20% to 45%.
Class IV: Bicornuate Uterus (10% of Uterine Anomalies)
Incomplete fusion of the two Müllerian ducts leads to a concave dip in the serosal surface of the uterine fundus as well as a division of the endometrial cavity into two horns that connect near the cervix. Bicornuate uteri are associated with spontaneous abortion rates of 28% to 35% and premature birth rates of 14% to 23%.
Class V: Septate Uterus (55% of Uterine Anomalies)
When there is absence of normal resorption of the uterine septum after the two Müllerian ducts have fused, the uterine cavity will be septate. The septum may be complete or partial (more common), but the serosal surface of the uterus remains normal. A uterine septum is associated with spontaneous abortion rates ranging from 26% to 94% and premature birth rates ranging from 9% to 33%.
Ultrasound Findings
Before 3-D ultrasound, 2-D ultrasound was the first imaging modality to suspect a Müllerian duct anomaly; however, MRI was needed to display the coronal view of the uterine cavity to make the correct diagnosis. Although the hysterosalpingogram accurately depicts the shape of the uterine cavity, it provides no information about the outer contour of the uterus. A hysterosalpingogram cannot distinguish between a septate and a bicornuate uterus.
Currently, 3-D ultrasound can easily provide a reconstructed coronal view of the uterus, demonstrating both the shape of the endometrial cavity and the outer serosal/myometrial contour of the uterus. MRI is no longer necessary to diagnose the vast majority of uterine malformations. The accuracy of both 3-D ultrasound and MRI for diagnosing specific uterine malformations is 90% to 95%.
Once a 3-D image of the coronal view of the uterine cavity is obtained, the anatomy of the uterus can be observed easily. The uterus is septate if the septum extends 10 mm or more into the cavity from the midcornual line and the serosal surface is normal. A septum that is shallow and extends less than 10 mm caudally defines an arcuate uterus. A bicornuate uterus has a serosal indentation extending 10 mm or more caudally from the normal serosal surface, thus creating two horns. The bicornuate uterus also has an obligatory septum or partial septum, called a subseptum. Patients with Müllerian duct anomalies may have two cervices (bicollis), which are visible using 3-D reconstruction of the cervix. A uterine didelphys has two completely separate uterine horns that are located at opposite sides of the pelvis. These two horns are typically hard to image simultaneously because of their distance from each other.
Differential Diagnosis
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