Uterus didelphys is one of a spectrum of congenital uterine anomalies that occur due to mullerian duct abnormalities. According to most authors, the incidence of mullerian duct abnormalities is about 0.5 -1% [a range from 0.04 -12% has been reported]. These anomalies are important to recognize as some of these may have a grave implication on future obstetric outcome.
Embryologically the uterus, fallopian tubes, cervix and upper 2/3 of the vagina develop from the paired mullerian ducts. The remainder of the female reproductive system [lower 1/3 of vagina and the ovaries] develop separately. The normal developmental course follows the pattern of -
•Development of the ducts [and the initial phase of the organs]
•Fusion of the ducts [resulting in the normal anatomic configuration of the organs] and
•Resorption of the median septum resulting in a single uterine cavity.
An arrest in any of the above mentioned stages would result in a congenital anomaly affecting the uterus and /or other reproductive structures.
Classification: There are many different schemes that attempt to classify the various anomalies. One such widely used classification that incorporates most of the criteria is the one suggested by Buttram and Gibbons.
• Class I- this is very rare and includes uterine and cervical agenesis or hypoplasia.
• Class II- unicornuate uterus. It is due to arrested development of one of the mullerian ducts.
• Class III- uterus didelphys. This anomaly occurs due to complete failure of fusion of the two mullerian ducts resulting in a complete duplication anomaly.
• Class IV- bicornuate uterus. this occurs due to varying degrees of non-fusion of the mullerian ducts. This may result in a uterus with two uterine horns and a single cervix [bicornis unicollis] or a uterus with two uterine horns and two cervices [bicornis bicollis]. In both the cases, a single vaginal cavity is present.
• Class V- septate or sub-septate uterus. This anomaly occurs due to the partial or complete failure of resorption of the median septum that normally separates the two uterine horns during development.
• Class VI- arcuate uterus. This type has a single uterine body and a single endometrial cavity and is considered by many as a variant of the normal anatomy.
• Class VII- these are abnormalities of the uterus and the rest of the female reproductive tract that occur due to exposure to diethylstilbesterol. These may include abnormalities of the uterine size and the shape of the endometrial cavity as well as increased incidence of vaginal tumors.
Clinical presentation and complications: As noted earlier, it is important to diagnose the type of uterine anomaly, as some of these are associated with difficulty in conceiving and increased incidence of pregnancy loss. This is especially true of the septate uterus.
If the duplicated system contains functional endometrium with associated outflow tract obstruction, the patient may present with hematometra, hematocolpos and hematosalpinx. These patients also have an increased predisposition to developing endometriosis.
Associations of the disease process: The most important association is that of unilateral renal agenesis and ectopia, especially seen in conjunction with uterine didelphys. The renal agenesis is usually seen on the side of the rudimentary uterine cavity with the obstructed outflow tract [i.e. on the side of the hematometrocolpos].
Imaging findings: The modalities that may be used to diagnose congenital anomalies of the uterus include 2D and 3D ultrasound, conventional and Sono-hysterosalpingography and MRI. A combination of the two modalities is usually conclusive enough to make a definitive diagnosis. As most of these patients present with infertility, conventional hysterosalpingography and CT are usually to be avoided due to the added hazards of radiation.
Ultrasound findings: Ultrasound diagnosis of the anomalies is based on the external outline of the uterus, the transverse diameter of the uterus and the anatomy of the endometrial echo complex. The following findings are seen in each type.
1. Hypoplasia or agenesis [Class I] - in agenesis, there is absence of identifiable uterine or cervical tissue. in hypoplasia, the endometrial echo complex is small with reduced intercornual distance ( less than 2 cm).
2. Unicornuate uterus [Class II] - difficult to identify on ultrasound. The uterus may sometimes appear normal and more laterally placed; although the absence of the normal rounded fundal contour may be noted. A rudimentary horn, if present, can be visualized easily by its endometrium. If the endometrium is functional and the horn is obstructed, a cystic mass due to hematometra may be visualized. This is associated with a higher incidence of pregnancy loss.
3. Didelphys uterus [Class III] - this anomaly [as in our case here] shows two distinct normal-sized uterine cavities that are widely separated. There are also two cervices. If one of the cavities is non-communicating, a hematometrocolpos and hematosalpinx may result. Usually a vaginal septum is present as well, which is very difficult to visualize on ultrasound. This anomaly is also associated with high incidence of unilateral renal agenesis. This anomaly does not significantly affect the obstetric outcome.
4. Bicornuate uterus [Class IV] - it is very important to distinguish this anomaly from a septate uterus, as a bicornuate uterus causes minimal obstetric complications. Bicornuate uterus shows two uterine cavities with either two or one cervix. The characteristic finding is the presence of a fundal notch or a cleft greater than 1 cm. The fundus is concave. There is also increased intercornual distance [greater than 4 cm], so the endometrial cavities appear wide apart. The septum separating the two uterine cavities may or may not be adequately visualized on ultrasound, as this septum usually has the same echogenicity as the myometrium or may be partly fibrous.
5. Septate uterus [Class V] [click to view]- it is very important to distinguish this anomaly from bicornuate uterus, as a septate uterus is associated with poor obstetric outcome. A septate or subseptate uterus shows two uterine cavities with a normal or a divided cervix. The characteristic finding is a convex or flattened fundal contour, with no cleft [contrast bicornuate]. The intercornual distance may be normal or decreased [ less than 4 cm], so the two endometrial cavities appear closer together. The septum may or may not be visualized.
6. Arcuate uterus [Class VI] - this shows a single uterine cavity with a single endometrial complex. A small fundal cleft is noted.
7. DES- related abnormalities [Class VII] [click to view] – a diffuse small sized uterus or an irregular t-shaped endometrial cavity may be seen in the uterus. These patients have an increased predisposition to vaginal adenosis and clear cell carcinoma.
The management depends on the kind of anomaly that is discovered on imaging. Obstructed systems with rudimentary horns and a resultant hematometrocolpos would require drainage of the collected blood and release of the obstruction [septoplasty or dilatation of the stenosis]. Septate uterus can be treated with hysteroscopic resection of the septum. In contrast, the correction of a bicornuate uterus would require transabdominal surgery, because each of the two uterine cavities have a full thickness myometrium and endometrial complex and are separated by a thick muscular septum.Arcuate uterus requires no treatment.