In a female fetus, the mesonephric ducts regress in the absence of testosterone, and the paramesonephric (Müllerian) ducts continue to develop due to both the absence of anti-Müllerian hormone and stimulation from maternal and placental hormones. The Müllerian ducts form the basis of the uterine body, fallopian tubes, cervix, and at least the upper two-thirds of the vagina. Fusion of the Müllerian ducts also creates the broad ligament (i.e., the peritoneal fold that attaches the lateral aspects of the uterus to the pelvic side walls) and forms the vesicouterine and rectouterine spaces.

Fig 1: Hysterosalpingography. Anteroposterior image showing a normal uterine cavity (red star) with bilateral tuve patency (red arrows). Department of Radiology, University Clinical Hospital of Valladolid.

The caudal fused portion of the Müllerian ducts forms the uterovaginal primordium, which eventually makes contact with the urogenital sinus and promotes vaginal formation.

The ovaries develop from mesothelial, mesenchymal, and primordial germ cells and become identifiable by approximately the 10th week of gestation. In patients with Müllerian hypoplasia, ovarian function is typically normal, reflecting their separate embryologic origins. The ovaries may be located superior to their expected location due to failure of descent [2].

CMFGT include not only uterine malformations but also vaginal and cervical abnormalities, adnexal malformations, and anomalies in other organ systems, such as the kidneys and skeleton.

Despite their prevalence, most anomalies are asymptomatic. However, obstruction of the Müllerian duct may occur, leading to an abdominal mass and dysmenorrhea. Delayed treatment can have severe consequences, including potential infertility. Patients may also present with recurrent miscarriages and infertility.

Two-dimensional transabdominal and endovaginal ultrasound (US) are the first-line modalities for evaluating the female reproductive tract, including malformations involving the uterus, cervix, and vagina. Three-dimensional (3D) US is particularly helpful for assessing the external uterine fundal contour and the internal indentation of the endometrial cavity, best visualized in the mid-coronal plane. MRI is indicated for complex anomalies or cases with anatomic distortion due to deep pelvic endometriosis, prior surgery, or trauma. T2-weighted fast spin-echo MRI sequences in orthogonal planes to the uterus and cervix allow for precise classification of anomalies and provide additional information about the adnexa and ovaries. Volumetric 3D T2-weighted MRI allows for curved planar reconstructions. Targeted axial or coronal T2-weighted MRI of the abdomen enables assessment of associated urinary tract anomalies. Fat-saturated T1-weighted sequences can identify blood products in hematometrocolpos or glandular components of deep infiltrative endometriosis. Hysterosalpingography (HSG) remains the gold standard for evaluating fallopian tube patency in infertility patients and may prompt further assessment for suspected müllerian duct anomalies [2].

Fig 2: Axial T2-weighted image showing a normal endometrial cavity (red drawing). There ir also a intramural mioma in the right wall of the uterus (red star). Department of Radiology, University Clinical Hospital of Valladolid.

Main Developmental Anomalies of the Female Genital Tract [3]:

- Uterine agenesis (~10%): Complete absence of uterine tissue above the vagina. When the upper two-thirds of the vagina are also absent, it is termed Mayer-Rokitansky-Küster-Hauser syndrome, characterized by primary amenorrhea with normal hormonal levels due to fully functional gonads. It is sometimes associated with renal malformations, warranting a full urinary tract evaluation upon diagnosis.

Fig 3: 11 year-old girl. T2-weighted images in sagital (A) and coronal (B) planes showing uterine agenesis with no tissue above the vagina (red star). Note the normal configuration of the ovaries in the coronal plane (red arrows). Department of Radiology, University Clinical Hospital of Valladolid.

- Arcuate uterus (~7%): Mild indentation of the endometrium at the uterine fundus. It is the least commonly associated anomaly with reproductive failure and is sometimes considered a normal anatomical variation (ASRM system – see below).

Fig 4: T2-weighted axial image (A) showing an arcuate uterus (red arrow). Hysterosalpingography (B) demonstrates the shape of the uterine cavity (red arrow) with patent tubes in the same patient. Department of Radiology, University Clinical Hospital of Valladolid.

- Unicornuate uterus (~15%): Failure of one Müllerian duct to elongate while the other develops normally, resulting in a single-horned (banana-shaped) uterus draining into a single fallopian tube. It causes primary infertility in ~13% of cases and cryptomenorrhea when a non-communicating rudimentary horn contains functional endometrium.

Fig 5: Unicornuate uterus. A: Hysterosalpingography demonstrates the filling of only the right horn of the uterine cavity, showing the “banana-shape” sign. B: T2-weighted axial image confirms the diagnosis of unicornuate uterus. A small remnant of the left horn can be seen (red arrow). Department of Radiology, University Clinical Hospital of Valladolid.

- Uterine duplication anomalies:

  - Uterus didelphys (~7.5%): Complete duplication of the uterine horns and cervices, with no communication between them. Pregnancy outcomes are poor, with a term pregnancy rate of only 20%, one-third of pregnancies ending in miscarriage, and over half resulting in preterm deliveries.

Fig 6: Uterus dydelphys. A: Hysterosalpingography with double cannulation showing two independent uterine cavities with tubal patency. Axial T2-weighted image confirms the diagnosis of uterus dydelphus, with a significant cleft between the horns. Department of Radiology, University Clinical Hospital of Valladolid.

  - Bicornuate uterus (~25%): Failure of paramesonephric duct fusion, leading to a divided uterus. It is commonly associated with early pregnancy loss and cervical incompetence. MRI shows a deep (>1 cm) fundal cleft and an intercornual distance >4 cm.

Fig 7: Bicornuate uterus. Axial T2-weighted image showing a 12 mm indentation of the fundus. Department of Radiology, University Clinical Hospital of Valladolid.

  - Septate uterus (~45%): The most common congenital uterine anomaly, linked to subfertility, preterm labor, and reproductive failure. There are several classification systems for imaging differentiation from arcuate and bicornuate uterus (see below).

Fig 8: A: Hysterosalingography demonstrates a bifurcated uterine cavity (red arrow) with tubal patency but gives no information of the uterine wall morphology. B: Axial T2-weighted image shows a normal outer surface of the uterus (orange arrow), without any indentations, confirming the diagnosis of septate uterus. Department of Radiology, University Clinical Hospital of Valladolid.

Four classification systems have been proposed:

• The American Society of Reproductive Medicine (ASRM) [4]: This classification is an update of the American Fertility Society (AFS) system and includes seven classes of anomalies. It has criteria for defining a normal/arcuate uterus, septate uterus and bicornuate uterus.
• The European Society of Human Reproduction and Embryology/European Society for Gynaecological Endoscopy (ESHRE/ESGE) published a comprehensive classification system for congenital anomalies of the female genital tract, which encompassed not only uterine anomalies but also clinically significant cervical and vaginal anomalies [5].
• The embryological-clinical classification system of genito-urinary malformations [6]: This system describes the malformations from an embryological point of view. Although this includes changes in the vagina, adnexa, and renal system in addition to those in the uterus, it is extremely complex for use in clinical practice, and assignment to specific classes is difficult.
• The Vagina, Cervix, Uterus, Adnexae and associated Malformations (VCUAM) system, based on the tumor, nodes, metastases (TNM) principle in oncology [1]. Developed with a purely anatomical descriptive approach, it is a very comprehensive classification that allows for the inclusion of multiple combinations of anomalies.

The ASRM and ESHRE/ESGE classifications are the most commonly used, but they differ in criteria for septate uterus diagnosis. The ASRM considers a uterus as septate when there is both an indentation depth >15 mm and an indentation angle <90º, while a normal/arcuate uterus should have both an indentation depth <10 mm and an indentation angle >90º and a uterus that does not fit these criteria would be left in an unclassifiable “grey zone”. The ESHRE/ESGE recommend using an indentation-to-wall-thickness (I:WT) ratio >50% to diagnose septate uterus. ESHRE/ESGE overestimates, whereas ASRM underestimates its prevalence. The 2017 CUME classification sought to refine criteria, setting an internal indentation depth of ≤10 mm for septate uterus diagnosis [7]. All systems have limitations in terms of effective categorization, clinical utility, simplicity, and reproducibility, prompting further subclassifications [2,8].