Müllerian Duct Anomalies: Understanding Uterine Abnormalities and Their Treatment

In short: Congenital abnormalities of the uterus occur when the uterus does not form completely before birth, and affect about 1–5% of women. They can cause delay in conceiving, recurrent miscarriage and preterm birth. They are diagnosed by HSG, MRI or 3D ultrasound, and treatment depends on the type, sometimes by hysteroscopy or laparoscopy.

How the Female Genital Tract Develops

The female genital tract develops from three separate origins:

1. The ovaries form from germ cells that migrate from the yolk sac into the mesenchyme of the peritoneal cavity, later developing into the ova and their supporting cells.

2. The lower third of the vagina develops from the ascending Sino vaginal bulb.

3. The uterus, fallopian tubes, and upper two-thirds of the vagina develop from the fusion of two Müllerian ducts — and this is our main subject for discussion today.

Complete formation of the genital tract depends on three key stages being completed successfully.

• Organogenesis

If one of the ducts fails to develop, the result is a unicornuate uterus. If both ducts fail to develop, this can cause uterine agenesis or hypoplasia.

• Fusion

Two Kinds of Fusion

1. Lateral fusion is the process by which the two Müllerian ducts join together to form the uterus, tubes, and cervix. When this process doesn’t complete properly, it can result in a bicornuate or didelphys uterus.

2. Vertical fusion completes the formation of the vagina, joining the lower part of the Müllerian duct (which forms the upper two-thirds) with the ascending Sinovaginal bulb (which forms the lower third). Incomplete vertical fusion can lead to a transverse vaginal septum. An imperforate hymen is a related condition in which the thin membrane at the vaginal opening fails to open.

• Septal resorption

Normally, the median part of the fused Müllerian ducts forms a septum that is gradually resorbed to create a single uterine cavity. When this resorption doesn’t happen fully, it can lead to a septate uterus, either complete or partial.

How Common Are Müllerian Duct Abnormalities?

These abnormalities are found in about 5% of women in the general population, about 8% of women with infertility, and about 13% of women with miscarriage when modern imaging is used.

Signs and Symptoms of Müllerian Duct Abnormalities

Symptoms vary from patient to patient depending on the type of abnormality, but the most common presentations include:

• Infertility

• Recurrent miscarriage

• Preterm labor

• Intrauterine growth restriction

• Primary amenorrhea, in cases of imperforate hymen and haematocolpus

Diagnosing Müllerian Duct Abnormalities

Clinical history and physical examination alone rarely provide a clear diagnosis, so imaging techniques are the most reliable approach:

1. Hysterosalpingography (HSG)

This test has a false-positive rate of around 38% and a false-negative rate of around 28%. It also cannot assess the outer fundal contour of the uterus, making it difficult to tell the difference between a septate and a bicornuate uterus.

Specific criteria help confirm the diagnosis on HSG:

• a- Intercornual distance (distance between the distal ends of the horns):
• • Less than 2 cm suggests a septate uterus.
• More than 4 cm suggests a bicornuate uterus.
• Between 2 and 4 cm is indeterminate, and further imaging (3D ultrasound or MRI) is needed.

• Intercornual angle (formed by the most medial aspects of the two uterine hemi-cavities):

• • Less than 60° suggests a septate uterus.
• More than 60° suggests a bicornuate uterus.

• A T-shaped uterus may indicate prior DES exposure.

2. MRI

MRI allows imaging of the uterus in the coronal plane and can assess both the uterine cavity and the outer contour. However, it can be costly and often requires referral to a specialized imaging facility, which may delay diagnosis.

3. Three-dimensional ultrasound

3D ultrasound provides information that is comparable to, or even better than, MRI, while being less expensive and more widely available in most clinics — allowing for a faster diagnosis.

When combined with saline infusion, 3D ultrasound can yield information similar to that obtained through HSG.

When scanning a gynecology patient, especially when a uterine abnormality is found, it’s also important to check the kidneys, as related abnormalities can occur together.

Classification of Müllerian Duct Abnormalities and Surgical Treatment Options

Anatomically, Müllerian duct anomalies are most commonly categorized using the American Fertility Society (AFS) Classification Scheme (1988), which includes seven classes:

(This classic system is still widely known, but in 2021 the American Society for Reproductive Medicine published an updated classification (ASRM MAC 2021), and European specialists use the ESHRE/ESGE classification; the main categories described below remain the same.)

1- Class I (hypoplasia/agenesis): This class includes conditions such as uterine or cervical agenesis or hypoplasia. The most common form is Mayer-Rokitansky-Küster-Hauser syndrome, involving combined agenesis of the uterus, cervix, and upper vagina. Natural reproductive potential is generally absent, though options such as IVF with a gestational carrier may be considered in some cases; skeletal abnormalities may sometimes also be present.

Uterus transplantation, followed by IVF, is a newer option available in some specialised centres for women born without a uterus, with many healthy babies born worldwide since 2014.

Diagnosing Vaginal Agenesis

• Presents as primary amenorrhea
• Normal secondary sex characteristics are usually present
• Pelvic examination may reveal a patulous urethra
• The vagina may be completely absent, or a shallow vaginal pouch may be present
• The uterus cannot be felt on rectal examination
• Ultrasound typically shows an absent uterus, and sometimes reveals renal abnormalities
• Laparoscopy is generally not needed unless the diagnosis remains unclear from the above findings

Treatment Options for Vaginal Agenesis

1. Non-surgical treatment using graduated dilators is the recommended first choice; it succeeds in about 9 out of 10 motivated women, although it can take several months to create a functional vagina. Surgery is usually reserved for women in whom dilator treatment does not work or who prefer surgery after counselling.

2. Surgical treatment (vaginoplasty) aims to create a new vagina. It’s generally considered only when the patient wishes to become sexually active and is highly motivated to use a vaginal prosthesis for several months after surgery. There are several methods of vaginal reconstruction, including:

• Full thickness skin graft
• Transposition flaps

2- Class II (unicornuate uterus): A unicornuate uterus results from complete, or almost complete, arrest of development of one Müllerian duct. If the arrest is incomplete — as in about 90% of cases — a rudimentary horn (with or without functioning endometrium) may be present. If this rudimentary horn is obstructed, it may require surgical attention as it can present as an enlarging pelvic mass. If the healthy horn on the other side is well developed, a full-term pregnancy is generally considered possible (see didelphys uterus below).

• Surgical treatment

Women with a unicornuate uterus are not usually candidates for reconstructive metroplasty. The main surgical indication is the presence of functioning endometrium in the accessory horn, which can be removed by laparoscopic hemi-hysterectomy. Surgery is not indicated when the rudimentary horn lacks endometrium.

3- Class III (didelphys uterus): This anomaly results from complete non-union of both Müllerian ducts. Each horn is fully developed and close to normal size, and two cervices are always present. A longitudinal or transverse vaginal septum may also be present. Didelphys uteri are commonly associated with a longitudinal vaginal septum, which may block one side of the vagina (often with an absent kidney on the same side), though septa can appear in other anomalies too. Since each horn is nearly a fully formed uterus, many patients are able to carry a pregnancy to full term; treatment depends on the specific presentation.

a- Uterine didelphys with obstructed unilateral vagina: treated by full excision or marsupialization of the vaginal septum. Laparoscopy is often performed at the same time to treat any associated endometriosis or adhesions.

b- Uterus didelphys, non-obstructed: These patients are generally not candidates for surgical unification. Fortunately, they tend to have few associated problems, and fertility outcomes are generally good.

4- Class IV (bicornuate uterus): A bicornuate uterus results from partial non-union of the Müllerian ducts. The central myometrium may extend to the level of the internal cervical os (bicornuate unicollis) or the external cervical os (bicornuate bicollis). This differs from a didelphys uterus in that some fusion exists between the two horns, whereas in a true didelphys uterus, the horns and cervices are completely separate. The horns of a bicornuate uterus are also typically smaller than those of a didelphys uterus. Some patients may be candidates for metroplasty.

Surgery is rarely needed, because most women with a bicornuate or didelphys uterus can carry a pregnancy. In selected women with repeated late miscarriages or preterm births and no other cause, the Strassman procedure (fusing the two uterine fundi together) may be considered, although evidence of benefit is limited. If two cervices are present, their unification is not recommended.

Hysteroscopic resection is not recommended in this setting, as it can cause uterine perforation.

5- Class V (septate uterus): A septate uterus results from failure of resorption of the septum between the two uterine horns. The septum may be partial or complete (extending to the internal cervical os), and may be made of myometrium or fibrous tissue. The uterine fundus is typically convex but may sometimes be flat or slightly concave (with a fundal cleft of less than 1 cm). Women with a septate uterus have the highest reported incidence of reproductive complications among these anomalies. Distinguishing a septate uterus from a bicornuate uterus is important, since septate uteri are treated with transvaginal hysteroscopic resection of the septum, while surgery for a bicornuate uterus (if indicated) typically requires an abdominal approach for metroplasty.

Surgical Treatment of a Uterine Septum

The preferred treatment is transcervical resection of the uterine septum, usually combined with concurrent laparoscopy to help reduce the risk of uterine perforation during the procedure.

It is important to know that recent studies, including a randomised trial, have not shown that removing a septum improves the chance of a live birth in all women. The operation is therefore discussed individually, mainly for women with recurrent miscarriage or preterm birth, and is not routinely needed for a septum found by chance.

The procedure is performed hysteroscopically: an instrument is introduced through the cervix, the septum is divided, and sometimes an IUD is placed temporarily (for at least 2 months) to help reduce the risk of intrauterine adhesions. Some specialists consider this step unnecessary, as it may cause local inflammation and potentially lead to adhesions itself.

Intrauterine septum as seen by hysteroscopy

Hysteroscopic Septum Resection Video Clips | Hysteroscopic Septum Photos

6- Class VI (arcuate uterus): An arcuate uterus has a single uterine cavity with a convex or flat fundus, showing only a small fundal impression (less than 1-1.5 cm deep). The outer contour of the uterus remains convex or flat. This variation is often considered a normal anatomical variant, since research has not shown a significant difference in reproductive outcomes compared with a normal uterus, and it usually does not require any treatment.

7- Class VII (diethylstilbestrol-related anomaly): Several million women were treated with diethylstilbestrol (DES), an estrogen-like medication once prescribed to help prevent miscarriage, between 1945 and 1971. The drug was withdrawn once its effects on the developing reproductive tracts of male and female fetuses became understood. Uterine anomalies have been observed in the female offspring of up to 15% of women exposed to DES during pregnancy. Affected women may show uterine hypoplasia and a T-shaped uterine cavity, along with abnormal transverse ridges, cervical hoods or stenosis, and vaginal adenosis, which carries an increased risk of a rare vaginal clear cell cancer. Imaging findings for this anomaly are typically very distinctive.

Conclusion

Not every type of uterine abnormality affects fertility, and not all of them can be corrected surgically. Uterine abnormalities (Müllerian duct anomalies) are a relatively common finding, and some types can contribute to infertility or pregnancy loss. Women with these anomalies may have a higher likelihood of infertility, repeated first-trimester miscarriage, fetal growth restriction, abnormal fetal position, preterm labor, and retained placenta. Imaging plays a key role in detecting, diagnosing, and distinguishing surgically correctable forms of these anomalies from those that are not operable, and in some cases, imaging findings help guide the surgical approach.

If you have concerns about a possible uterine abnormality or its impact on your fertility, our clinical team is here to help guide you through diagnosis and the options available.

Dr Najeeb Layyous F.R.C.O.G

Consultant Obstetrician, Gynecologist and Infertility Specialist