Introduction

Müllerian ducts are a pair of tubular structures that give rise to uterus, cervix, fallopian tubes and upper two-thirds of vagina. Disruption or failure of normal development can result in occurrence of Müllerian duct anomalies (MDAs). These are commonly associated with other congenital anomalies of urinary tract and ovaries due to the close relationship between the development of mesonephric and paramesonephric ducts; few patients also have associated skeletal system anomalies.

Clinical features

Most of the patients with MDAs are asymptomatic and found incidentally on imaging for any other gynaecological problems, in evaluation of a patient with renal, skeletal or abdominal wall abnormalities. In symptomatic women, complains are related to the type, severity, obstructive anomaly or nonobstructive anomaly. The symptoms can be obstetric or gynaecological related, includes recurrent spontaneous abortions, infertility, preterm labour, intrauterine growth restriction and abnormal foetal lie. Few adolescent girls may present with primary amenorrhoea, hypomenorrhoea, abnormal vaginal bleeding, cyclical pain and mass. Rarely they can present with pelvic inflammatory disease with abnormal vaginal discharge, dyspareunia and urinary tract infections.

Embryogenesis

The female reproductive system develops from a pair of Müllerian or paramesonephric ducts, urogenital sinus and vaginal plate. The ovaries develop separately from the primordial ridge.

It is of great importance to understand the normal stages of development, as failure or interruption of any of these stages can lead to a simple to complex spectrum of anomalies.

The three stages of Müllerian duct development include:

At 6–10 weeks of gestation age, two paired Müllerian ducts and Wolffian ducts formation occurs. When Y chromosome factor (testicular determining factor) is absent, the Wolffian ducts undergo degeneration. The Müllerian ducts further elongate caudally and cross the Wolffian ducts to fuse in the midline.

At 10–13 weeks of gestation age, caudal and lateral fusion of the two Müllerian ducts forms primitive uterovaginal canal, which is possessed of solid tissue initially located side by side and further internal canalization leads to the formation of two channels/canals divided by a septum. At this stage, there is reabsorption of the caudal septum and forms single cervical canal and vagina lumen.

In around 15–20 weeks of gestation age, complete resorption of the septum takes place in a caudocranial direction from the isthmus to fundus and development of single endometrial cavity results. The fused caudal part of Müllerian ducts gives rise to the uterus, cervix and upper two-thirds of vagina; the unfused cranial part forms the fallopian tubes (Fig. 11.14.1.1).

The lower vagina develops from the urogenital sinus, which is separated from the rectum by urorectal septum around 7 weeks of gestation age. The primitive uterovaginal canal embeds into the dorsal wall of urogenital sinus and forms Muller’s tubercle. Around 13 weeks of gestation, two solid masses known as sinovaginal bulbs originate from the upper part of the Muller’s tubercle, further proliferate into the caudal end of the uterovaginal canal to become a solid vaginal plate. Later canalization or degeneration of the central cells of the vaginal plate forms the lower vagina, which is usually completed by 20 weeks’ gestation. The vertical fusion of the upper and lower vagina occurs with resorption of tissue in between and forms single vaginal cavity (Fig. 11.14.1.2).

The vaginal lumen is separated from the urogenital sinus by the hymenal membrane. Just before birth, the hymen normally ruptures due to retrogression of the central epithelial cells. However, a thin fold of mucous membrane persists around the vaginal introitus.

The ovaries develop separately from migration of primordial germ cells to the genital ridge. Ureteric buds develop separately and concurrently. So renal anomalies are most commonly associated with MDAs with an association of 30%–50%.

Key points to remember

Classification

Various classification systems have been proposed over the past several decades to describe MDAs. Ideally, same classification system needs to be followed by a gynaecologist, surgeon and radiologist for better communication.

Buttram and Gibbons classification

Buttram and Gibbons classification was suggested in 1979, and it was based upon the level of failure in normal development and segregate the anomalies into groups with similar clinical manifestations, treatment, and prognosis for foetal salvage. According to Buttram and Gibbons, the uterine anomalies were classified into six classes as described in Table 11.14.1.1. The drawback is the lack of classification of vaginal and other anomalies separately.

American society for reproductive medicine (ASRM) system for Müllerian duct anomalies

The ASRM (previously the American Fertility Society – AFS) classification system is the most widely accepted classification worldwide over the past years and was introduced in 1988. According to this classification, MDAs are classified into seven classes (class I to class VII) as mentioned in Table 11.14.1.2. However, several limitations have been described by Grimbizis and Campo in 2010 (Fig. 11.14.1.3).

The drawbacks of the ASRM classification system are as follows:

Hence in 2016, an updated classification of uterine septum, that is ASRM-2016 was proposed and officially approved morphometric criteria are given for distinguishing between septate, normal/arcuate and bicornuate uteri (Table 11.14.1.3).

The vagina cervix uterus adnexa–associated malformation (VCUAM) classification

The VCUAM classification was proposed in the year 2005. The main concern is to provide a simple, systematic, clinical classification in addition to providing a precise reflection of the entire malformation. The female genital organs were divided into the following subgroups in accordance with the anatomy: vagina (V), cervix (C), uterus (U) and adnexa (A). Associated malformations were assigned to a subgroup (M) relative to each specific organ. The disadvantage is due to its inherent complexity, and more than 56,700 individual combinations of anomalies are possible.

European society of human reproduction and embryology (ESHRE) and European society of gynaecological endoscopy (ESGE) classification

ESHRE and ESGE established a common working group named CONgenital UTerine Anomalies (CONUTA) in order to devise an improved classification system (Table 11.14.1.4). It was published in 2013. Anatomy is the basis for systemic categorization of the MDAs. The subclasses are divided by the different degrees of uterine deformity and their clinical significance (Fig. 11.14.1.4). Cervical and vaginal anomalies are classified into independent supplementary subclasses (Figs. 11.14.1.5–11.14.1.6). For most of the clinicians, it helped as starting point for the development of guidelines for their diagnosis and treatment. The malformations are graded according to severity, U0–U5, C0–C4 and V0–V4, with U5, C4 and V4 being more severe. Class U3 incorporates bicorporeal fusion defects (didelphys and bicornuate) as this was considered as a more functional mode of classification. Arcuate uterus was not included separately, but this is categorized under normal variant into class U1c. Recent studies have demonstrated that the ESHRE/ESGE system provides an effective and comprehensive classification for almost all the currently known MDAs and overcomes the limits of previous classifications. However, there is a relative overdiagnosis of septate uterus with the application of ESHRE–ESGE criteria has been reported and which potentially might lead to unnecessary surgical overtreatment.

ESHRE guidelines for classification of Müllerian duct anomalies

Hysterosalpingography

HSG was the most recognized imaging modality, earlier to the development of the ultrasonography (USG) and MRI. It is an invasive fluoroscopic-guided procedure for uterine and tubal assessment, and is performed during the midproliferative phase of the cycle, ideally between days 7 and 10 of the cycle when endometrium is thin. Fluoroscopic spot images obtained to evaluate uterine configuration, uterine filling defects and fallopian tube patency. HSG allows evaluation of only the component of the uterine cavity that communicates with the cervix. The anatomic information about myometrium and external fundal contour will not be provided by HSG. The diagnostic criteria used to diagnose MDAs on HSG include:

1. a) Intercornual distance: Distance between the distal ends of horns. Normal 2–4 cm.
   
2. b) Intercornual angle: Angle formed between the most medial aspects of two uterine hemicavities.

HSG findings of different MDAs are described in Table 11.14.1.5 and Fig. 11.14.1.10.

TABLE 11.14.1.5

HSG Findings in Various Müllerian Anomalies

Arcuate Uterus	Septate Uterus	Bicornuate Uterus	Didelphys Uterus	Unicornuate Uterus	DES Exposure
Single uterine cavity with a broad saddle-shaped indentation at the uterine fundus	Two cavities with intercornual angle of less than 75 degrees	Two cavities with intercornual angle of more than 105 degrees	Two separate, oblong endometrial cavities with contrast opacification of fallopian tubes	Off-midline fusiform cavity deviated to one side with opacification of the single fallopian tube	T-shaped appearance with shortened upper uterine segment

Ultrasonography (2D and 3D)

Transabdominal pelvic ultrasound can diagnose uterine anomalies with accuracy rate of 47%.

Two-dimensional transvaginal ultrasound (TVUS) has high sensitivity and specificity than transabdominal study and provided some information about external and internal fundal contours. The detection rate is high if the scan is performed in secretory phase due to better visualization of endometrium.

Three-dimensional USG shows great accuracy than 2D USG in evaluation of the uterine morphology. The technique of 3D USG varies with different vendors. It displays both the external and internal fundal contours and lower uterine segment by acquisition of single coronal view of uterus (c-view) (Fig. 11.14.1.11). The only disadvantage is that it is transvaginal study and shall not be done in paediatric age group and sexually inactive women. Three-dimensional TVUS has become the first line of screening tool in most of the infertility clinics as it is noninvasive, faster, repeatable, allows storage of volume data and has multiplanar capability for systematic evaluation of the uterine and cervical cavities.

The salient features of various Müllerian anomalies on 3D USG are described in Table 11.14.1.6 with images.

TABLE 11.14.1.6

3D USG Images and Characteristic Features of Different Müllerian Duct Anomalies

3D Sonography of Uterus	Müllerian Duct Anomaly	Salient Features
	Normal uterus ESHRE classification: Class U0	Normal uterine outline Normal shape of the cavity
	Dysmorphic uterus ESHRE classification: Class U1a ASRM classification: Class VII	Normal uterine outline Abnormal shape of the uterine cavity excluding septa Thickened lateral walls Normal two-thirds of uterus and one-third of cervix
	Dysmorphic uterus with normal cervix Arcuate uterus ESHRE classification: Class U1c ASRM classification: Class VI	External fundal contour – convex/flat Internal fundal contour – dip I:WT ratio: Less than 50% Lower uterine cavity is normal
	Partial septate uterus ESHRE classification: Class U2a ASRM classification: Class V	External fundal contour – convex/flat Internal fundal contour – dip I:WT ratio: More than 50% Lower uterine cavity is partially divided above the level of the internal os
	Complete septate uterus and cervix ESHRE classification: Class U2bC1 ASRM classification: Class V	External fundal contour – convex/flat Internal fundal contour – deep dip I:WT ratio: More than 50% Lower uterine cavity completely divided by the septum up to the internal os Septum further extends to the cervix
	Bicorporeal uterus ESHRE classification: Class U3b ASRM classification: Class III	External fundal contour – deep indentation Internal fundal contour – dip Lower uterine cavity completely divided by the fundal indentation up to the internal os
	Hemiuterus ESHRE classification: Class U4b ASRM classification: Class II	Banana-shaped/fusiform uterus deviated to one side No rudimentary cavity on right side
	Hemiuterus ESHRE classification: Class U4a ASRM classification: Class II	Unilateral developed left uterus with noncommunicating right rudimentary cavity

MRI

MRI is a universally accepted imaging modality in the documentation of MDAs and accuracy rate of 100% have been reported. MRI provides excellent delineation of both the internal and external uterine anatomies. T2-weighted (T2W) images are the mainstay of pelvic imaging and are performed without fat suppression. T1-weighted (T1W) images are mainly for the haemorrhagic content. The disadvantages of MRI include time-consuming procedure, not cost-effective, large body habitus, pacemakers, recent surgical history and claustrophobia.

MRI protocol

The current and proposed MRI protocol given by the European Society of Urology (ESUR-MRI protocol) intends a dedicated evaluation of MDAs as mentioned below (Fig. 11.14.1.12):

1. 1. Two-dimensional T2W high-resolution Turbospinecho (TSE)/Fast pin echo (FSE) sequences:
   
   
   

   
   
   • • Sagittal T2W images of pelvis with a slice thickness of 4 mm, high matrix (512 × 512) and a small field of view (FOV).
     
   • • True coronal and true axial sections of uterus are obtained (uterus oriented sequences) along the long axis and short axis of the uterine body to delineate the external uterine morphology and the cavity shape.
   
   
2. 2. T2 shot axis view of the cervix is an optional sequence, obtained perpendicular to the cervical canal.
   
3. 3. Coronal SSFSE T2W sequence with large FOV for the abdomen: Evaluate the kidneys for associated anomalies. It is also useful for the detection of the ectopic location of ovaries.
   
4. 4. Axial T1W sequence of uterus: For presence of haematometra, haematocolpos or endometriosis.
   
5. 5. Three-dimensional T2W sequence: Gives better image quality and 3D reconstructions. The images will be reformatted in any plane, to obtain the coronal and axial sections of the uterus. The 3D T2W sequences have different vendor names: CUBE (GE), VISTA (Philips), SPACE (Siemens), among others.

Vaginal anomalies can be accurately diagnosed with the prior administration of the ultrasound gel, to distend vagina (Fig. 11.14.1.13). It will help in better diagnosis of complex vaginal anomalies, like vaginal septations or vaginal duplication.

The normal MRI appearance of uterocervical canal and vagina are shown in Fig. 11.14.1.14.

Imaging features of Müllerian duct anomalies

Uterine aplasia/dysplasia/agenesis

Uterine aplasia/hypoplasia/agenesis is class 1 MDA according to ASRM classification and U5 uterine anomaly according to ESHRE classification. It is a formation defect of the paramesonephric ducts with complete or segmental agenesis of uterus and vagina. The incidence rate is around 10%–15% of all MDAs and considered as the most severe form of uterine anomaly. Most of them have complete uterovaginal agenesis with no single completely developed uterine cavity and are associated with Mayer–Rokitansky–Küster–Hauser syndrome (MRKHS). Two types of this syndrome are depicted. The typical form or type A represents the absence or remnants of the uterus, cervix, upper two-thirds of vagina with normal ovaries and fallopian tube (Fig. 11.14.1.15). The atypical form or type B is associated with the abnormalities of the ovaries, fallopian tubes and genitourinary system (Fig. 11.14.1.16). In a few cases (approximately 10%), unilateral or bilateral uterine remnants and with or without endometrial cavity will be seen (Fig. 11.14.1.17).

Unicornuate uterus

Unicornuate uterus or hemiuterus is defined as the unilateral uterine development and the contralateral Müllerian duct could be either partially formed or absent. It is a formation defect and the necessity to classify it in a different class than that of uterine agenesis, which is also a formation defect, is due to the existence of a fully developed functional uterine hemicavity.

It is considered as class II anomaly according to ASRM classification and class U4 according to ESHRE classification. The frequency rate is around 20% of MDAs. Renal anomalies most often occur in association with unicornuate uterus and usually on the same side of uterine agenesis.

Further unicornuate uterus is divided into two subclasses depending on the presence or absence of a functional rudimentary cavity in ESHRE classification:

In ASRM classification, unicornuate uterus is divided into four subcategories:

Imaging appearances

On imaging, unicornuate uterus is seen as tubular and fusiform or banana-shaped structure at paramedian location, the endometrium is narrow and tapers to the apex with normal myometrial anatomy and reduced uterine volume. The rudimentary cavity or remnants are better depicted on 3D USG (Fig. 11.14.1.18) and MRI. However, MRI is superior to USG due to its high soft tissue resolution. The rudimentary cavity can communicate with main cavity or connected by fibrous band. The nonfunctioning cavity will be seen as T2 hypointense structure with loss of zonal anatomy (Figs 11.14.1.19 and 11.14.1.20), whereas the functioning cavity will show the deformed zonal anatomy (Fig. 11.14.1.21), and its complications like haematometra as T1/T2 hyperintense endometrial collection.

Clinical symptoms

Uterine didelphys is usually asymptomatic and diagnosed incidentally on pelvic examination or caesarean section. The uterine didelphys with obstructed vagina (Fig. 11.14.1.22) will present at adolescence as dysmenorrhoea, haematometrocolpos and haematosalpinx. Sometimes retrograde menstrual flow can cause endometriosis and pelvic adhesions. Obstetric-related complications include abortion/foetal growth restriction and poor pregnancy outcome.

The uterine didelphys with obstructed hemivagina due to transverse vaginal septum and associated ipsilateral renal agenesis are the manifestations of the syndrome called obstructed hemivagina and ipsilateral renal agenesis anomaly/Herlyn–Werner–Wunderlich (HWW) syndrome (Fig. 11.14.1.23).

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