What Is a Mullerian Duct?
The Müllerian duct (MD), which develops into the female reproductive system later, is an embryonic structure.
It has a different fate in male and female fetuses-
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Females - The fallopian tube, uterus, cervix, and the upper two-thirds of the vagina are the structures that make up the female reproductive tract. These tissues grow from a pair of Müllerian ducts. Different germ cells that migrate from the primitive yolk sac and the sinovaginal bulb give rise to the ovaries and the lower portion of the vagina, which have distinct embryological beginnings.
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Males - Males need mesenchymal-to-epithelial signaling to mediate Müllerian duct regression, which stops the development of Müllerian-derived organs. The Müllerian ducts are initially generated independent of genotypic sex. The preservation of female reproductive system organs in males is caused by anomalies in Müllerian duct regression, which have been described in a number of human syndromes.
Three phases must be completed for the Müllerian ducts to mature normally-
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Organogenesis - The establishment of both Müllerian ducts is a characteristic of organogenesis. Uterine agenesis, hypoplasia, or a unicornuate uterus arise from the failure of this step.
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Fusion - The ducts fusing together to create the uterus is known as fusion. A bicornuate or didelphys uterus is the result of the failure of this step.
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Septal Resorption - After the ducts have merged, septal resorption refers to the resorption of the central septum. A septate or arcuate uterus is the outcome of defects at this stage.
Although the formation of the Müllerian duct is crucial for human health, the underlying molecular pathways are still largely unknown.
What Are Mullerian Duct Anomalies?
Müllerian duct abnormalities (MDAs) are congenital conditions in which the Müllerian (paramesonephric) ducts fail to develop, have a deficient vertical or lateral fusion, or fail to resorb. MDAs are very common, and the majority of them are asymptomatic. The Müllerian duct abnormality classification system categorizes them based on clinical symptoms, prognosis, and treatment options. As the treatment differs depending on the type of deformity, an accurate diagnosis also plays a crucial role.
The types of Müllerian duct abnormalities (MDAs) are as follows-
1. Class I: Hypoplasia or Agenesis
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The uterus, proximal vagina, and, in some cases, the fallopian tubes are all absent or hypoplastic in vaginal agenesis.
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Partial or total Müllerian aplasia can occur. A normal uterus and a small vaginal pouch distal to the cervix characterize partial Müllerian aplasia, which is more uncommon.
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The most common variation is complete Müllerian aplasia present in Mayer-Rokitansky-Küster-Hauser (MRKH) syndrome. It is characterized by the absence of the vaginal and uterine canals at birth. The ovaries exhibit normal endocrine and oocyte function, and the fallopian tubes are normal.
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Congenital abnormalities of the urinary system and bones are common in people with Müllerian agenesis.
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Women with Müllerian agenesis who are sexually active should be aware that they are at a higher risk for sexually transmitted infections (STIs).
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Patients with Müllerian agenesis are typically discovered when they are assessed for primary amenorrhea and otherwise normal growth and pubertal development.
Treatment- In most patients, primary vaginal elongation by dilation should be the first line of treatment. It is safer, more patient-controlled, and less expensive than surgery. Surgery should be reserved for the rare patient who has failed to respond to primary dilator therapy or prefers surgery after receiving full disclosure.
2. Class II: Unicornuate Uterus (UU)
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When one Müllerian duct fails to elongate entirely or partially while the other usually develops, the unicornuate uterus is formed.
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A banana-shaped half-uterus is generated when one Müllerian duct is undeveloped or does not develop. This asymmetric anomaly is more likely than other Müllerian malformations to have a missing kidney or other renal issues.
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Although normal pregnancies can occur in this population, obstetric outcomes are often poor. Among all Müllerian defects, the unicornuate uterus is linked to the lowest fetal survival rate.
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This subtype is linked to higher rates of morbidity and mortality. Several difficulties, such as hematometra, can arise when the auxiliary horn becomes clogged. There is also a higher chance of getting endometriosis, which normally goes away after the horn is removed if diagnosed early.
Treatment - An accessory horn is removed with a laparoscopic hemihysterectomy. After laparoscopic removal of the accessory horn, successful pregnancy in the primary horn has been documented.
This is an extremely rare condition. It has four subtypes-
a. Non-communicating, Cavitary Horn - Since it is linked to dysmenorrhoea, hematometra, endometriosis, and ectopic pregnancy, it is always surgically removed.
b. Non-communicating, Non-cavitary Horn - Currently, surgery is not advised. Because there is no endometrium, there are no endometriosis or other issues.
c. Communicating, Cavitary Horn - Pregnancy that implants in the rudimentary horn is rarely viable, so it is also surgically removed.
d. No Horn - No treatment is required. It is possible to reach reproductive potential.
3. Class III: Didelphys
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Didelphys uterus develops when the Müllerian ducts' midline fusion is arrested, either totally or partially. Renal agenesis is more likely to develop in conjunction with uterine didelphys than with any other Müllerian defect.
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Ovarian malposition is also a possibility. It is possible for the vagina to be single or double. The double vagina appears as a longitudinal (horizontal) septum that runs from the cervices to the introitus, either entirely (complete septum) or partially (partial septum).
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Unless there is a blockage, patients with uterine didelphys are usually asymptomatic. Hematometrocolpos, hematometra, and hematosalpinx may arise in such instances.
Treatment - The obstructed unilateral vagina is an indication that the vaginal septum should be resected. Surgery is required to maintain the reproductive capacity and prevent damage to the uterine tubes. Metroplasty may be beneficial for patients who have a history of recurrent spontaneous abortions or premature births.
4. Class IV: Bicornuate
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When the Müllerian ducts partially fuse at the level of the uterine fundus, the uterus becomes bicornuate. The lower uterus and cervix are entirely united in this condition, resulting in two distinct but interconnected endometrial chambers, a single-chamber cervix and vagina.
Treatment - Surgical intervention is rarely required; metroplasty may be considered.
5. Class V: Septate
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Among all Müllerian duct anomalies, the septate uterus is the most prevalent structural anomaly. It is caused by incomplete resorption of the medial septum after the Müllerian ducts have fused completely.
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The ‘Robert uterus’ is a rare septate uterine variation. A full septum and noncommunicating hemiuteri with a blind horn describe this condition.
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The fertility of patients with a septate uterus does not appear to be significantly harmed. Despite this, of all the Müllerian duct anomalies, it is linked to the poorest reproductive outcomes.
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Sub-septate - A subseptate uterus is a moderate form of congenital uterine abnormality (frequently mistaken for a normal variety) in which the uterus has a partial septum.
Treatment - Transvaginal hysteroscopic septum resection is frequently used to treat this condition. Two months following surgery, conception is possible.
6. Class VI: Arcuate Uterus
It develops from near-complete resorption of the uterovaginal septum. Despite an occasional association with adverse obstetric results, the arcuate uterus is clinically benign and may not impair reproductive outcomes compared to other Müllerian abnormalities.
How Are Mullerian Duct Anomalies Diagnosed?
Mostly the cases are diagnosed based on their symptoms of primary amenorrhea, recurrent abortions, or ectopic pregnancies. The radiographic evaluation shows the following features-
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Ultrasound - Two-dimensional (2D) ultrasound imaging can occasionally aid in identifying the kind of MDA by confirming any structural abnormalities of the genital tract. 3D (three-dimensional) coronal transvaginal imaging is a highly accurate diagnostic tool that should be used during the secretory phase of the menstrual cycle.
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MRI (Magnetic Resonance Imaging) - It is a non-invasive technique. It aids in assessing female pelvic anatomy and provides accurate MDA classification.
Conclusion:
Müllerian abnormalities are a group of developmental disorders that affect the internal female reproductive tract and are morphologically variable. In order to plan treatment and management measures, a correct diagnosis is required. The surgical procedure for correcting Müllerian duct defects varies depending on the malformation type and the patient group. The patient's capacity to have healthy sexual interactions and achieve satisfactory reproductive results after surgery is a vital test of the procedure's value for most surgical operations.
