bubble_chart Overview

Congenital uterine developmental anomalies are the most common type of reproductive organ malformations and hold significant clinical importance. During the evolution of the bilateral paramesonephric ducts, certain factors may influence and interfere with their development, causing them to cease at various stages and leading to different types of uterine developmental abnormalities.

bubble_chart Clinical Manifestations

I. Several Types of Uterine Developmental Abnormalities

(1) Congenital Absence of Uterus and Uterine Hypoplasia: The latter refers to the uterus remaining at various immature stages from the fetal period to pre-puberty.

1. Congenital Absence of Uterus: If the bilateral paramesonephric ducts fail to extend and meet at the midline, no uterus forms. Congenital absence of the uterus is often accompanied by congenital absence of the vagina, but normal fallopian tubes and ovaries may be present. On rectal examination, no uterus is palpable at the expected location of the cervix or uterine body; only peritoneal folds can be felt.

2. Primordial Uterus: If the bilateral paramesonephric ducts stop developing shortly after meeting at the midline, the uterus remains very small, often lacking a uterine cavity or having a cavity without endometrial growth, resulting in no menstruation.

3. Infantile Uterus: If uterine development halts at any stage from late pregnancy to pre-puberty, varying degrees of uterine hypoplasia may occur. The cervix of such a uterus is relatively long, often conical with a small external os, while the uterine body is smaller than normal and may exhibit extreme anteflexion or retroflexion. Anteflexion is often associated with underdevelopment of the anterior uterine wall, and retroflexion with underdevelopment of the posterior wall. An infantile uterus can cause dysmenorrhea, hypomenorrhea, amenorrhea, or infertility.

(2) Obstruction of Bilateral Paramesonephric Duct Fusion: This is the most common type and has significant clinical implications. Depending on the timing and extent of the obstruction, the following manifestations may occur:

1. Unicornuate Uterus: One paramesonephric duct develops normally, forming a functional unicornuate uterus with a normal fallopian tube, while the other duct fails to develop. A unicornuate uterus may function normally, and pregnancy and childbirth may proceed without issues, though it can also lead to late miscarriage or difficult labor.

2. Rudimentary Horn Uterus: One paramesonephric duct develops normally, while the other exhibits arrested development, forming a rudimentary horn of varying degrees. Most are connected to the unicornuate uterus by a fibrous band. If the endometrium is nonfunctional, symptoms are usually absent. If functional, cyclic lower abdominal pain due to hematometra may occur after puberty. If a narrow channel connects it to the contralateral uterus, pregnancy in the rudimentary horn can occur, resembling an interstitial tubal pregnancy, often rupturing at 3–4 months with severe internal bleeding.

3. Blind Horn Uterus: Both paramesonephric ducts develop well, but one uterine horn does not communicate with the vagina, forming a blind horn uterus. After puberty, menstruation causes cyclic lower abdominal pain that worsens over time. Hematometra may lead to uterine or tubal blood accumulation, or even intraperitoneal bleeding via the fimbriated end. A growing mass may be palpable in the lower abdomen. Some blind horn uteri have an underdeveloped vagina that does not connect to the normal vagina, potentially being misdiagnosed as a vaginal cyst. Treatment involves surgical correction to connect the blind horn to the contralateral uterine or vaginal cavity.

4. Double Uterus and Duplex Uterus (Symmetrical Type): These anomalies are very similar. The former results from complete non-fusion of the paramesonephric ducts, with two sets of fallopian tubes, uteri, cervices, and vaginas, which is rare. The latter, also called bicornuate bicollis uterus, involves complete fusion of the ducts but failure of the septum to resorb. The distinction lies in the wider gap between the uteri in the former. A double uterus may or may not have a vaginal septum.

5. Bicornuate Uterus: The caudal ends of the paramesonephric ducts mostly fuse, with the distal septum resorbed, resulting in one cervix and one vagina. However, incomplete fusion at the fundus causes two prominent uterine horns. Milder forms include a saddle-shaped, heart-shaped, or arcuate uterus, which may lead to late miscarriage or abnormal fetal positioning during pregnancy.

6. Septate uterus: After the fusion of the bilateral paramesonephric ducts, the septum is not absorbed, dividing the uterine body into two halves, but the external shape of the uterus remains completely normal. Sometimes the septum is incomplete, resulting in two separate uteri with a small passage between the cervixes, hence called a communicating uterus. It is often accompanied by a vaginal septum, with the passage usually located at the isthmus of the uterus. Occasionally, one side of the vagina is partially obstructed, and the retained menstrual blood can slowly drain through the isthmic passage to the opposite patent vagina. As a result, the patient may seek medical attention due to frequent discharge of old bloody secretions from the vagina.

7. Saddle-shaped uterus: The fundus of the uterus is depressed, with varying degrees of severity.

(3) Non-canalization of the fused paramesonephric ducts: The portion of the uterus formed by the fusion of the paramesonephric ducts may partially or completely fail to canalize, resulting in a solid uterus without an endometrial lining. Apart from being smaller in size, this type of uterus appears normal externally but does not menstruate.

(4) Congenital uterine malposition: The uterus or one of the duplicated uteri may, like the ovaries or fallopian tubes, be displaced into an inguinal hernia. The uterus may also remain in a higher embryonic position without descending into the pelvic cavity.

Uterine prolapse can occasionally occur at any time after birth, often coexisting with spina bifida and frequently accompanied by poor development of the pelvic floor muscles.

(5) Iatrogenic congenital uterine anomalies: Congenital uterine anomalies can occur in cases of abnormal paramesonephric duct development, such as in patients with diethylstilbestrol (DES) syndrome. Exposure to DES during intrauterine development can lead to DES syndrome or changes in vaginal epithelium. In 82% of these cases, hysterosalpingography reveals abnormalities. These anomalies include uterine hypoplasia or enlargement, T-shaped or arcuate uterus, fibrous-muscular constriction bands or uterine horns within the uterine cavity, constrictions at any part of the uterus or a relatively wide lower uterine segment, irregular uterine cavity margins or polypoid lesions, and intrauterine adhesions.

II. Clinical manifestations of uterine developmental anomalies Some patients with uterine malformations may exhibit no subjective symptoms, with normal menstruation, sexual activity, pregnancy, and childbirth, so the condition may go undetected throughout their lives or be discovered incidentally during physical examinations. However, some patients may experience varying degrees of impact on their reproductive system function, with symptoms appearing only at sexual maturity, after marriage, or during pregnancy or childbirth.

(1) Menstrual abnormalities: Patients with congenital absence of the uterus or a rudimentary uterus experience no menstruation. Those with an infantile uterus may have no menstruation or may exhibit hypomenorrhea, delayed onset, dysmenorrhea, or irregular menstrual cycles. Patients with a double uterus or bicornuate uterus often experience excessive menstrual flow and prolonged duration of menstruation.

(2) Infertility: Poor uterine development, such as absence of the uterus, rudimentary uterus, or infantile uterus, is often a major cause of infertility.

(3) Pathological pregnancy: A developmentally abnormal uterus often leads to late miscarriage, premature labor, or abnormal fetal positions after pregnancy. Spontaneous uterine rupture during pregnancy may occasionally occur. If the fallopian tube is patent in a rudimentary horn uterus, the fertilized egg may implant in the rudimentary horn, but due to poor development of the uterine muscle layer, rupture often occurs during pregnancy, with symptoms similar to ectopic pregnancy.

(4) Intrapartum and postpartum pathology: A malformed uterus is often accompanied by poor development of the uterine muscle layer. During childbirth, abnormal labor forces or difficulty in cervical dilation can lead to difficult delivery or even uterine rupture. Vaginal delivery may result in retained placenta, postpartum metrorrhagia, or postpartum infection. In patients with a double uterus, the pregnant uterus develops and grows, while the non-pregnant uterus, if located in the rectouterine pouch, can cause obstructive difficult delivery during childbirth. Patients with a double uterus, bicornuate uterus, or septate uterus may experience bleeding postpartum due to the shedding of decidua from the non-pregnant uterine cavity.

bubble_chart Diagnosis

If the patient has a history of primary amenorrhea, dysmenorrhea, infertility, habitual late abortion, abnormal fetal position in every pregnancy, or difficult delivery, the possibility of uterine malformation should first be considered. A detailed medical history and gynecological examination should be conducted. If necessary, use a probe to measure the size and direction of the uterine cavity or perform a hysterosalpingography to confirm the diagnosis. Malformations of the reproductive organs are often associated with urinary system malformations or lower gastrointestinal tract malformations. If needed, intravenous pyelography or barium enema examination can be performed. When urinary tract or lower gastrointestinal tract malformations are detected, a thorough examination for reproductive organ malformations, including uterine malformations, should also be conducted.

bubble_chart Treatment Measures

Abnormal development of the uterus, if it does not cause clinical symptoms, may not require treatment. If uterine hypoplasia leads to amenorrhea, dysmenorrhea, infertility, or habitual late abortion, endocrine therapy may be attempted. Detailed treatment methods can be found in the relevant chapters. For cases where medication fails to alleviate the patient's suffering, surgery may be considered. For dysmenorrhea, surgical removal of the malformed uterus may also be an option. If uterine malformation causes late abortion or premature labor, appropriate surgical interventions can be performed based on the specific type of malformation.

The most common and effective indication for uterine malformation repair surgery is symmetrical bicornuate uterus. Patients with recurrent late abortions should undergo this procedure as early as possible. The procedure involves making a transverse incision from one uterine horn to the opposite horn, splitting the muscular wall in half, and suturing the incised surfaces together. Postoperative live birth rates can reach 60–85%. If a rudimentary uterus contains accumulated blood causing clinical symptoms, it may be excised. For pregnancies following surgical correction of uterine malformations, precautions should be taken to prevent late abortion, and close monitoring is necessary to avoid spontaneous uterine rupture. The mode of childbirth should be selected based on fetal position and labor progress. Since the uterine incision scar is significantly larger than that of a previous cesarean section, the indications for cesarean delivery should be considerably relaxed. Postpartum hemorrhage and puerperal infection should be prevented, and retained placenta should be guarded against during vaginal delivery.

Since the advent of hysteroscopy, uterine septa can be resected under laparoscopic guidance. During the procedure, the laparoscopic light is dimmed to allow the assistant to observe the hysteroscopic light transmitted through the uterine fundus, guiding the surgery. The surgeon first examines the uterine cavity and the shape of the septum via hysteroscopy, then begins sharp dissection from the midline at the lowest point of the septum until the conical portion of the uterine tube is visible. The incision must remain midline to avoid perforation. Once the septum is fully separated, a symmetrical uterine cavity can be seen at the internal cervical os. To assess whether the septal incision is sufficiently wide, the laparoscopic light can be turned off during the procedure to check for any interruption in the hysteroscopic light from one uterine horn to the other. Postoperatively, two cycles of estrogen and progesterone therapy are administered. After discontinuation, hysterosalpingography is performed to evaluate the surgical outcome and uterine cavity morphology. This method is simpler than abdominal uterine reconstructive surgery, with lower postoperative morbidity, no intrauterine adhesions, and no need for intrauterine device placement. Pregnancy can be attempted after two cycles of hormone therapy, with favorable outcomes and low cesarean rates, making it the preferred treatment for uterine septa. Later, CO₂ was proposed as a distension medium, providing a larger and clearer field of view compared to liquid media. Additionally, injecting pitocin (20 units of posterior pituitary hormone in 50 ml saline, 6–8 ml per side) into the paracervical area (via the lateral fornix) during surgery reduces bleeding and expands the scope of hysteroscopic procedures. However, this method is unsuitable for thick septa or small uteri.