A Mullerian anomaly is a congenital difference affecting the development of the female reproductive system. These malformations arise during embryonic development when the structures that form the uterus, fallopian tubes, cervix, and upper vagina do not develop as expected, resulting in a variation in their shape or structure. These conditions originate very early in fetal development, and their specific causes are not fully understood. Most cases appear to happen sporadically, without a clear family history, although genetic and environmental factors may play a role.
Development of the Female Reproductive Tract
The female reproductive tract originates from two tube-like structures known as the Müllerian ducts. These paired ducts are destined to become the fallopian tubes, uterus, cervix, and the upper portion of the vagina. The formation of these organs occurs through a three-stage process: the ducts’ growth, their fusion, and the resorption of the central wall where they join.
The two ducts first form, then migrate toward the center of the embryo and fuse to create what will become the uterus. The final step involves the breakdown of the partition between the fused ducts, creating a single uterine cavity and cervix.
A Mullerian anomaly is the result of a disruption at any point in this sequence. For instance, if the ducts fail to develop properly, it can lead to an absent uterus. If they do not fuse correctly, a double uterus might form, and incomplete resorption of the dividing wall results in a divided uterus.
Types of Mullerian Anomalies
Mullerian anomalies are classified based on how development was altered. Uterine agenesis or hypoplasia is when the uterus is completely absent or severely underdeveloped. This is the primary feature of Mayer-Rokitansky-Küster-Hauser (MRKH) syndrome, where the vagina is also often absent or underdeveloped, though the ovaries remain functional.
A unicornuate uterus occurs when only one Müllerian duct develops, resulting in a smaller, banana-shaped uterus with one fallopian tube. A non-functional horn may remain from the undeveloped duct, which can sometimes contain uterine lining and cause pain if blood becomes trapped.
Uterus didelphys, or a double uterus, results when the two Müllerian ducts develop but fail to fuse. Individuals with this anomaly have two separate uterine cavities, each with its own cervix and sometimes a double vagina. A bicornuate uterus is when the ducts fuse partially at the bottom but remain separate at the top, creating a heart-shaped uterus.
A septate uterus occurs when the ducts fuse but the dividing wall, or septum, fails to dissolve, leaving a band of tissue that divides the uterine cavity. A less pronounced version is the arcuate uterus, which has only a slight indentation at the top of the uterine cavity.
Symptoms and Diagnosis
Many individuals with Mullerian anomalies have no symptoms and may only discover the condition incidentally during a pelvic exam or imaging test. Others become aware of an anomaly after puberty begins, often due to menstrual problems like painful periods (dysmenorrhea) or the complete absence of menstruation (primary amenorrhea). Other indicators include pain during sexual intercourse, difficulty using tampons, or cyclical pelvic pain if an obstructed uterine horn or blocked vagina traps menstrual blood. Recurrent pregnancy loss can also be the first sign that leads to an investigation.
Diagnosis begins with a physical examination and is followed by imaging studies. An ultrasound is often the first step, and a 3D ultrasound can provide a more detailed view of the uterine shape. Magnetic Resonance Imaging (MRI) is used for a definitive diagnosis, as it offers a clear and detailed picture of the soft tissue anatomy for precise classification. A hysterosalpingogram (HSG), a procedure using dye, can also be used to outline the uterine cavity and assess the fallopian tubes.
Impact on Fertility and Pregnancy
The effect of a Mullerian anomaly on the ability to conceive and carry a pregnancy varies by the specific type. While many can have successful pregnancies without intervention, certain anomalies are associated with challenges like difficulty conceiving, an increased rate of miscarriage, and premature birth.
The uterine structure influences pregnancy outcomes. For example, a septate uterus may interfere with embryo implantation, while the smaller size of a unicornuate uterus can restrict fetal growth and increase the risk of preterm labor or an abnormal fetal position for delivery.
Uterine agenesis, the absence of a uterus, makes carrying a pregnancy impossible. However, since the ovaries are functional, individuals with this condition can have biological children through gestational surrogacy. For other anomalies, careful monitoring during pregnancy can help manage potential complications and improve outcomes.
Medical Management and Treatment
Managing a Mullerian anomaly is individualized based on the type, symptoms, and a person’s reproductive goals. Not all anomalies require treatment; an arcuate uterus requires no intervention, and a double uterus may only need observation.
When symptoms are present, management focuses on relief. Painful periods or cyclical pain from an obstructed uterine horn can be managed with pain medication. In cases where menstrual flow is blocked, surgery may be needed to create a pathway for the blood to exit.
Surgical treatment is reserved for cases where an anomaly causes significant symptoms or contributes to infertility or recurrent pregnancy loss. A common corrective surgery is a hysteroscopic metroplasty, a minimally invasive procedure used to resect a uterine septum. This surgery aims to create a more spacious uterine cavity to improve the chances of a successful full-term pregnancy.