MRI of the Female and Male Pelvis

© Springer International Publishing Switzerland 2015

Riccardo Manfredi and Roberto Pozzi Mucelli (eds.)MRI of the Female and Male Pelvis10.1007/978-3-319-09659-9_1

1. Magnetic Resonance Imaging of Congenital Malformation of the Uterus

Valerio Di Paola¹  , Eugenio Oliboni¹, Daniela Avolio¹, Riccardo Manfredi¹ and Roberto Pozzi Mucelli¹

(1)

Department of Radiology, University of Verona, Piazzale Scuro, Verona, Italy

Valerio Di Paola

Email: [email protected]

1.1 Introduction

Female genital tract anomalies are common deviations from normal anatomy with an estimated prevalence of 1–3 % in the general population and even higher in selected populations such as recurrent aborters [1, 2].

Their occurrence could be associated with a variety of clinical presentations ranging between life-threatening complications, severe health problems in the adolescence, and reproductive problems, although in most of them they are asymptomatic [1–3].

Due to their high prevalence and possible impact on the reproductive health of women, congenital uterine malformations of the female genital tract are a challenge for the therapeutic decision-making process.

The diagnosis of Mullerian duct anomalies (MDA) is based upon the clinical presentation, physical examination, and subsequent imaging work-up with different imaging methods available, namely, sonography and magnetic resonance (MR) imaging, among them MR imaging takes a leading role, especially in complex uterine malformation [1–4].

1.2 Epidemiology

Congenital malformations of the uterus frequency vary widely owing to different patient populations, non-standardized classification systems, and differences in diagnostic data acquisition. Because normal pregnancies can occur in women with MDA and the anomalies are discovered in most cases of patients presenting with infertility, the reported prevalence of MDA in the general population is probably underestimated. The overall published data suggest a prevalence range of uterovaginal anomalies of 1–3 % in the general population, among women with normal and abnormal fertility [5–7].

While conceiving is a minor problem for the majority of women with MDA, the risk of pregnancy loss is truly associated with MDA, and its prevalence in women with repeated miscarriage is considered to be in the order of 3 %. No racial predilection is reported in the literature [5, 8, 9].

1.3 Clinical Presentation

MDA may become clinically evident at different ages depending on their specific characteristics and associated disorders. In the newborn/infant age, an initial presentation of a palpable abdominal or pelvic mass due to a utero and/or vaginal obstruction causing intraluminal fluid retention can be discovered.

In adolescent age group a delayed menarche or primary amenorrhea with/without a fluid retention in the uterus (hematometra) and/or vagina (hematocolpos) may present as a painful intra-abdominal tumor. Some patients also have cyclical pain.

In childbearing age, MDA can present with various problems of infertility, repeated spontaneous abortions, premature delivery, fetal intrauterine growth retardation, and difficulties during delivery. The defective embryological development can also be associated with congenital malformations of other organ systems. Most frequently, renal malformations like renal agenesis or ectopia can occur. Much less frequent are bony malformations – most of them occur in a complex of varying symptoms – like abnormal scapula, supernumerary or fused ribs, vertebral malsegmentation, fusion of the vertebral column (i.e., Klippel-Feil syndrome), and radiocarpal hypoplasia.

Other malformations such as cardiac defects have been described, but it remains unclear if some of the associated malformations are caused in the same development field or if early exposure to teratogenic agents was causative [7, 9].

The literature does not show increased mortality for patients carrying an MDA compared to the general population, whereas the morbidity may be increased in some specific types of MDA causing obstructed Mullerian systems with the presence of hematosalpinx (retention of blood in the fallopian tubes), hematocolpos (retention of blood in the vagina), and retrograde menses causing the potential problem of endometriosis [5].

1.4 Embryology

The understanding of the embryogenesis of the urogenital female tract is of paramount importance to understand the pathogenesis of the different types of MDA.

The female reproductive system develops from the two-paired Mullerian ducts (synonym: paramesonephric duct) that start off in the embryonal mesoderm lateral to each Wolffian duct (synonym: mesonephric duct). The paired Mullerian ducts develop in medial and caudal directions, and the cranial part remains non-fused and forms the fallopian tubes. The caudal part fuses to a single canal forming the uterus and the upper two thirds of the vagina. This is called lateral fusion.

In a process called vertical fusion, the intervening midline septum of both ducts undergoes regression. The caudal part of the vagina arises from the sinovaginal bulb and fuses with the lower fused Mullerian ducts.

The ovaries originate from the gonadal ridge, a completely different tissue than the mesoderm, forming both the urinary and genital systems. Hence, associated malformations of the kidney, but not of the ovaries, are frequently observed together with MDA.

Pathogenesis of MDA can be basically classified into the presence of agenesis, hypoplasia, and defects in vertical and lateral fusion of the paired ducts [5].

1.5 Classes of Mullerian Duct Anomalies (MDA)

The first attempt to classify female congenital anomalies goes back to the beginning of the nineteenth century; Strassmann described septate and bicornuate uterus and some subgroups of the disorders in 1907. However, the first classification system for categorization of congenital uterine malformations was that of the American Fertility Society (AFS) published in 1988, mostly based on the previous work of Buttram and Gibbons [3, 4].

Then other classification systems followed, but the AFS classification is still the most broadly used, widely accepted among specialists.

The American Fertility Society introduced a classification system that stratifies MDA into seven different classes of uterine anomalies (Fig. 1.1).

Fig. 1.1

Classification system of Mullerian duct anomalies by the American Fertility Society

1.5.1 Class I Anomalies: Dysgenesis

Dysgenesis (segmental agenesis and variable hypoplasia) of the Mullerian ducts (uterus and upper 2/3 of the vagina) (Fig. 1.1). Mayer-Rokitansky-Küster-Hauser syndrome is the most common form of Class I anomaly and includes agenesis of uterus and vagina [5, 9, 10].

1.5.2 Class II Anomalies: Unicornuate Uterus

Unicornuate uterus is the result of partial or complete hypoplasia of one Mullerian duct (Fig. 1.1) [11]. Unicornuate uterus may be isolated (35 %) or associated with a contralateral rudimentary horn. The rudimentary horn presents with or without communication to the endometrial cavity and may be associated with or without endometrium, which is also called no cavity rudimentary horn. In patients with cavity non-communicating rudimentary horn, dysmenorrhea and hematometra may occur. Surgical resection either to relieve symptomatic pain or to reduce the risk of potential ectopic pregnancy is justified. As with every obstructed system, the risk of endometriosis is also increased with a non-communicating rudimentary horn. Renal malformations are common with unicornuate uterus and occur mostly on the same side as the rudimentary horn could be found [5].

1.5.3 Class III Anomalies: Uterus Didelphys

Uterus didelphys is a result of complete non-fusion of the Mullerian ducts forming a complete uterine duplication with no communication between each other (Fig. 1.1).

Uterus didelphys may be associated with a longitudinal (75 %) or, more rarely, with a transverse vaginal septum, the latter causing obstructive hematometrocolpos.

Endometriosis as a result of retrograde menstruation may also occur in these conditions. A nonobstructive uterus didelphys is usually asymptomatic [5].

1.5.4 Class IV Anomalies: Bicornuate Uterus

Bicornuate uterus is the result of incomplete fusion of the cranial parts of the Mullerian ducts (Fig. 1.1) [5–9, 12]. Two uterine cavities with normal zonal anatomy can be depicted. The leading imaging feature is a fundal cleft greater than 1 cm of the external uterine contour that helps to distinguish bicornuate uterus from septate uterus.

Extension of the intervening fundal cleft to the internal cervical os characterizes the complete bicornuate uterus with a single cervix (bicornuate, unicollis uterus), whereas variants of partial bicornuate uterus exist if the cleft is of variable length. Bicornuate uterus may be associated with a duplicated cervix (bicornuate bicollis uterus), as well as with a longitudinal vaginal septum that coexists in up to 25 % of bicornuate uterus. Nevertheless, a degree of communication is always present between both uterine cavities.

Still controversial is the need for surgical intervention and this is probably only necessary in specific cases.

A higher rate of cervical incompetence seems to be associated with bicornuate uterus [13].

1.5.5 Class V Anomalies: Septate Uterus

Septate uterus is a result of partial or complete non-regression or the midline uterovaginal septum (Fig. 1.1) [12, 13]. The main imaging feature is that the external contour of the uterine fundus may be either convex or mildly concave (<1 cm) and not with a cleft greater than 1 cm, the latter defining a bicornuate or didelphic uterus.

Septate uterus is the most common Mullerian duct anomaly and is unfortunately associated with the poorest reproductive outcome. Because of different treatment options, septate uterus must be differentiated from bicornuate and didelphic uterus. A widely accepted definition – empirically established during laparoscopy procedures – states that a uterus is septate if the outer contour of the uterine fundus is only mildly concave in the presence of a septum. The cutoff of concavity is 1 cm; deeper concavity is associated with bicornuate uterus and uterus didelphys.

In a complete septate uterus, the septum extends to the external cervical os. In 25 % of septate uteri, the septum extends even further into the upper part of the vagina.

Obstetric outcome seems not to be correlated with the length of the septum. The septum may be composed of muscle or fibrous tissue and is not a reliable means of distinguishing septate and bicornuate uteri.

Resection of the septum by hysteroscopic metroplasty is indicated and may improve the reproductive outcome significantly [5].

1.5.6 Class VI Anomalies: Arcuate Uterus

Arcuate uterus is the result of a near-complete regression of the uterovaginal septum forming a mild and broad saddle-shaped indentation of the fundal endometrium (Fig. 1.1).

Differentiation from bicornuate uterus is based on the complete fundal unification; however, a broad-based septate uterus is difficult to distinguish from an arcuate uterus. There is much controversy as to whether an arcuate uterus should be considered a real anomaly or an anatomic variant. MRI may detect this abnormality, but, typically, it is not clinically significant because arcuate uterus has no significant negative effects on pregnancy outcome [5].

1.5.7 Class VII Anomalies

DES-exposed uterus (Fig. 1.1). DES (synthetic estrogen, diethylstilbestrol, 1948–1971) may induce abnormal myometrial hypertrophy in the fetal uterus forming small T-shaped endometrial cavities, as well as increase the risk of developing a clear cell carcinoma of the vagina.

The characteristic uterine abnormalities must be categorized in the group of complex uterine anomalies and may occur with or without the exposure of DES [5–10, 12–14].

1.6 Diagnosis of Uterine Anomalies

Diagnosis of uterine anomalies should be based on diagnostic modalities that could determine the anatomical status of the female genital tract on an objective way.

The ideal diagnostic method should provide objective and measurable information on the anatomical status of the uterus in a noninvasive way [1–10, 12–15].

The available diagnostic methods that can be used in the investigation of the patient are as follows.

1.6.1 Gynecological Examination

It should be noticed that gynecological examination is very important in the diagnostic work-up of the patients with congenital malformations.

Vaginal malformations (aplasia, septum) and some cervical malformations could be diagnosed objectively mainly with inspection. Furthermore, palpation through the vagina and/or the rectum (in cases of vaginal aplasia) could provide useful but not always objective information [1].

1.6.2 Two-Dimensional Ultrasound (2D US)

This approach provides objective and, importantly, measurable information for the cervix, the uterine cavity, the uterine wall, and the external contour of the uterus. It is very popular and accessible, noninvasive, but its accuracy highly depends on the experience of the examiner and on the examination methodology followed.

Endovaginal US has the advantage of improved spatial resolution [1–10, 12–16].

1.6.3 Sonohysterography (SHG)

Compared to 2D US, this method has the additional advantage of offering a better imaging of the uterine cavity, thus enhancing the accuracy in identifying the anatomy of the female genital tract and especially that of the uterus.

With infusion of saline into the endometrial canal, sonohysterography provides improved delineation of the endometrium and internal uterine morphology; however, it shares limitations similar to those of conventional endovaginal US and can only help evaluate patent endometrial canal [17].

1.6.4 Hysterosalpingography (HSG)

HSG is indicated in the early stages of evaluation of the infertile couple. The examination provides a morphologic assessment of the endometrial and endocervical canal and supplies important information regarding tubal patency.

Characterization of uterine anomalies can be difficult; however, there can be considerable overlap in findings, notably with regard to differentiation of a septate from a bicornuate uterus.

The major limitations of the procedure are the ability to characterize only patent canals and the inability to evaluate the external uterine contour adequately.

HSG also entails exposure to ionizing radiation in these typically young women [12, 16–18].

1.6.5 Three-Dimensional Ultrasound (3D US)

3D US provides an ideal, objective, and measurable representation of the examined organs. It provides information on the cervix, the uterine cavity, the uterine wall, the external contour of the uterus, and the other structures with the exception of tubes. Theoretically, it seems to be an ideal method for the diagnostic approach of the uterus [19–21], but has limited application in clinical practice.

1.6.6 Magnetic Resonance Imaging (MR)

MR imaging has a reported accuracy of up to 100 % in the evaluation of Mullerian duct anomalies.

It is a very useful diagnostic tool, since it can provide clear delineation of internal and external uterine anatomy in multiple imaging planes and, most importantly, reliable depiction of the external uterine contour. Complex anomalies and secondary diagnoses such as endometriosis can often be optimally characterized noninvasively.

Although it is more expensive than US, its greater accuracy makes it more trusted by many gynecologists [12, 17–22].

1.6.7 Hysteroscopy (HYS)

Hysteroscopy is the gold standard for the examination of the cervical canal and the uterine cavity. However, as it does not provide information on the myometrial layer, hysteroscopy alone could not be used for the differential diagnosis between different groups.

Nowadays, with the use of normal saline as distension medium and the miniaturization of the rigid scopes, hysteroscopy has become a minimally invasive screening tool, well tolerated by the patients and feasible for gynecologists [1].

1.6.8 Laparoscopy and Hysteroscopy (Lap/Hys)

The combined application of these endoscopic techniques is thought to be the gold standard in the investigation of women with congenital malformations and especially the uterine ones.

However, the diagnosis is mainly based on the subjective impression of the clinician performing them, and this is thought to be a limitation in the objective estimation of the anomaly [1].

1.7 Imaging Findings in MDA

Once an MDA is suggested based on evidence from the patient history and physical examination, the next diagnostic step includes different imaging work-ups in order to detect and specify MDA and to guide further treatment options.

Before US and MRI were capable of visualizing MDA with a high accuracy, imaging of MDA was limited to hysterosalpingography (HSG). Since the diagnostic imaging properties of MDA include mainly the configuration of the endometrial cavity and the external uterine contour, HSG is able to depict only certain types of MDA, whereas it fails in other cases and stays nonspecific for precise diagnosis, the latter mainly due to the lack of the visualization of the outer uterine contour. Because of this drawback, HSG did not provide diagnoses with high degrees of confidence, and US and MRI soon began to play a larger role in assessment and treatment of patients. As HSG provides, besides the morphological, also the functional information of tubal patency, it is still used in the primary imaging work-up in case of infertility clarification.

Nowadays, the first imaging modalities in the MDA assessment include pelvic US – transabdominal US (performed with a 2.5- to 5-MHz probe, for evaluation of the entire abdomen, especially for associated renal malformations) and transvaginal US (performed with a 5- to 8-MHz endovaginal probe, for better delineation of the uterus, vagina, and ovaries) – and MRI. Newer techniques, such as 3D US, even further improved the imaging diagnostics by giving better information about the external contour of the uterus and its volume [5, 16, 17].

1.8 Magnetic Resonance Imaging (MRI)

Magnetic resonance imaging (MRI) is today considered standard in the evaluation of MDA and accepted as the leading imaging modality for further surgical planning. MRI provides high-resolution images of the entire uterine anatomy (internal and external contour), as well as of secondary findings like renal malformations.

Among the three major imaging methods, MRI has the best accuracy in the evaluation of uterine anomalies (up to 100 % has been reported) [5, 8, 16, 17, 23, 24].

1.8.1 MRI Technique [11, 17, 25]

Patients should be scheduled to undergo RM examination possibly in the second half of the menstrual cycle, during the follicular and secretory phase when the thickness of the endometrium is increased, thus permitting to better depict the normal zonal anatomy of the uterus. No specific patient preparation is necessary but patients should have an empty urinary bladder; an intramuscular antispasmodic drug could be administered some minutes prior the examination in order to reduce the motion artifacts related to the bowel peristalsis.

At moment, the gold standard for MR imaging of pelvic region is a high-field magnet such as a 1.5 T magnet with a phased array surface coil, but 3 T magnets could be used too [26, 27]. Standard pelvic MR imaging protocols include axial T1-weighted and T2-weighted images. T2-weighted imaging is essential for evaluation of uterine anatomy.

T2 RARE sequences have the best spatial resolution and are those to prefer in order to evaluate the presence of MDA, even if the acquisition time is longer than T2-weighted half-Fourier sequences.

Sagittal sections are best suited to image the uterus point for proper assessment of the uterine fundal contour. In addition it is mandatory to perform axial or coronal oblique sections, depending on uterine lie, parallel to the endometrial cavity resulting in a long-axis view of the uterus.

An additional oblique sequence obtained perpendicular to the cervical results in a short-axis view and allows accurate assessment of the cervix, demonstrating, if present, duplication or septation.

Because this series is pivotal in the evaluation of MDA, it is best performed earlier in the examination, prior to bladder filling, which often displaces consequently the uterus.

A coronal T2-weighted sequence, with a large field of view to enable assessment of the kidneys should be performed in addiction [12, 17].

T1-weighted sequences are mainly helpful to evaluate the presence of any associated pathologies such as ovarian disease; they should be obtained both without and with fat saturation in order to better demonstrate the presence of hemorrhage within the endometrial cavity (hematometra) and/or vagina (hematocolpos).

3D T2-weighted sequences are quick and provide submillimeter section thickness allowing multiplanar reconstruction, thus could be used in pediatric patients to significantly reduce imaging time.

Contrast material is not necessary to evaluate the presence and type of MDA and is not used in standard examination; Gadolinium-enhanced imaging is reserved for assessment of incidentally discovered additional disease.

1.8.2 Specific MRI Findings

1.8.2.1 Class I: Mullerian Agenesis and Hypoplasia

Variable degrees of early failure to form the Mullerian ducts prior to fusion occur in approximately 10 % of uterine congenital anomalies. Complete vaginal agenesis is the common presentation (Mayer-Rokitansky-Küster- Hauser syndrome) (Figs. 1.1 and 1.2) [11, 24–29].

Fig. 1.2

Vaginal agenesis (Ia). Fast spin-echo T2-weighted images on coronal (TR/TE 3310/94) (a) and sagittal plane (TR/TE 4070/94) (b) show normal uterus with cervix and no vaginal cavity (arrow in b)

Ninety percent of patients have associated uterine agenesis, and 10 % have a small rudimentary uterus (Fig. 1.3). Uterine agenesis manifests as lack of visualization of a discernible uterus on MRI.

Fig. 1.3

Uterine hypoplasia (I). Fast spin-echo T2-weighted images on axial (TR/TE 3000/108) (a) and sagittal plane (TR/TE 3310/94) (b) show uterine hypoplasia. Small uterine remnant demonstrating lack of normal zonal anatomy. The vagina is normal in configuration with normal vaginal tissue between urethra and rectum (arrow in a)

Hypoplastic uteri are small, low-signal-intensity, soft-tissue remnants on T2-weighted images with diminished zonal anatomy even if an endometrial segment is present (Fig. 1.3).

Vaginal agenesis is best characterized on the axial plane with no normal vaginal tissue insinuated between the urethra and rectum (Fig. 1.2) [24].

1.8.2.2 Class II: Unicornuate Uterus

Failure of one Mullerian duct to elongate while the other develops normally results in the unicornuate uterus and accounts for approximately 20 % of Mullerian duct anomalies (Fig. 1.1). A unicornuate uterus may be isolated, manifesting in 35 % of patients, although it is usually associated with variable degrees of a rudimentary uterine horn (Figs. 1.4 and 1.5) [17].

Fig. 1.4

Non-communicating unicornuate uterus (II b). Fast spin-echo T2-weighted images on axial (TR/TE 3000/108) (a) and coronal plane (TR/TE 3310/94) (b, c); fast spin-echo T1-weighted images on axial (TR/TE 550/12) (d) show unicornuate uterus with non-communicating rudimentary horn that contains endometrium. No communication with the cavity of normal left uterine horn. This cavity communicates with a normal cervix; the image (b) shows Naboth cyst of the cervix uteri. A large area of hematometra within the non-communicating horn is seen (arrow in d)

Fig. 1.5

Unicornuate communicating uterus (IIa). Fast spin-echo T2-weighted images on axial (TR/TE 2800/110) (a) and coronal plane (TR/TE 3310/93) (b) show unicornuate uterus with a communicating rudimentary left uterine horn (arrow in b). Hysterosalpingography images (c, d) demonstrated the filling of only the main uterine cavity; however, the lack of hematometra at MRI imaging allows excluding non-communicating uterus

A noncavitary rudimentary horn without associated endometrium is seen in 33 % of cases, and that with an endometrial segment is seen in 32 %. A cavitary rudimentary horn is designated communicating if there is communication with the endometrium of the contralateral horn (10 % of cases) and non-communicating if there is no such communication (22 % of cases) (Figs. 1.4 and 1.5) [22].

As with uterus didelphys, the manifestation is usually incidental unless a non-communicating rudimentary horn is present. Dysmenorrhea with hematometra may manifest at menarche in this subgroup.

In addition, the incidence of endometriosis is increased in this subgroup, similar to the case in an obstructed uterus didelphys [30].

Resection of the non-communicating horn is indicated, not only for symptomatic relief but also because ectopic pregnancy may occur in the rudimentary horn.

Resection of a communicating horn is also a consideration, because pregnancies that develop in the rudimentary horn rarely yield viable offspring.

Surgical intervention in a rudimentary horn without associated endometrium is rarely indicated.

Renal abnormalities are more commonly associated with unicornuate uterus than with other Mullerian duct anomalies and have been reported in 40 % of these patients. The anomaly is always ipsilateral to the rudimentary horn.

Renal agenesis is the most commonly reported abnormality, occurring in 67 % of cases.

Ectopic kidney, horseshoe kidney, cystic renal dysplasia, and duplicated collecting systems have also been described.

On MR images, the unicornuate uterus appears curved and elongated, with the external uterine contour assuming a banana shape. Uterine volume is reduced, and the configuration of the uterus is asymmetric. Normal myometrial zonal anatomy is maintained. The endometrium may be uniformly narrow or may assume a bullet shape, tapering at the apex. The endometrial-to-myometrial width and ratio are reported to be normal.

The appearance of the rudimentary horn is variable. When the endometrium is absent, the horn is of low signal intensity, with loss of normal zonal anatomy [31]. When the endometrium is present, zonal anatomy may be preserved [12, 17–24].

1.8.2.3 Class III: Uterus Didelphys

Uterus didelphys, which constitutes approximately 5 % of Mullerian duct anomalies, is the result of nearly complete failure of fusion of the Mullerian ducts (Fig. 1.1). Each Mullerian duct develops its own hemiuterus and cervix and demonstrates normal zonal anatomy with a minor degree of fusion at the level of the cervices. No communication is present between the duplicated endometrial cavities (Figs. 1.6, 1.7, and 1.8).

Fig. 1.6

Didelphys uterus (III). Fast spin-echo T2-weighted images on sagittal (TR/TE 4530/90) (a) and coronal plane (TR/TE 3310/93) (b) show two separate cervices and two divergent uterine horns (arrows in b) and duplication of the proximal vagina well defined by presence of fluid (arrowheads in b)

Fig. 1.7

Didelphys uterus (III). Fast spin-echo T2-weighted images on axial (TR/TE 2800/110) (a, c, d) and coronal plane (TR/TE 4070/94) (b) show two divergent horns with duplicated cervices in close apposition but no evidence of fusion. It is appreciable wide divergence of uterine horns without communication of endometrial cavities and presence of septum (arrow in b). No longitudinal septum is seen in the vagina (c)

Fig. 1.8

Didelphys uterus (III). Fast spin-echo T2-weighted images on axial (TR/TE 4070/94) (a) and coronal plane (TR/TE 3310/93) (b) show complete duplication of uterine horns, which result non-communicating. (c) US examination demonstrated the associated agenesis of the right kidney

A longitudinal vaginal septum is associated in 75 % of these anomalies.

Longitudinal vaginal septa may be complicated by defects in vertical fusion that result in a transverse vaginal septum and subsequent hematometrocolpos.

Nonobstructive uterus didelphys is usually asymptomatic, while uterus didelphys with unilateral vaginal obstruction may become symptomatic at menarche and manifest as dysmenorrhea.

Endometriosis and pelvic adhesions have an increased prevalence and are reported to be secondary to retrograde menstrual flow in the subset of patients with obstruction. MR imaging demonstrates two separate uteri with widely divergent apices, two separate cervices, and usually an upper vaginal longitudinal septum (Figs. 1.6, 1.7, and 1.8). In each uterus, the endometrial-to-myometrial width and ratio are preserved, as is normal uterine zonal anatomy.

An obstructed unilateral vaginal septum may cause apparent marked deformity of the uterus according to the degree of associated hematometrocolpos [17, 24, 32].

1.8.2.4 Class IV: Bicornuate Uterus

The bicornuate uterus results from incomplete fusion of the uterovaginal horns at the level of the fundus and accounts for approximately 10 % of Mullerian duct anomalies (Fig. 1.1). Patients with a bicornuate uterus and no extrauterine infertility issues usually have little difficulty conceiving.

A bicornuate uterus consists of two symmetric cornua that are fused caudally, with communication of the endometrial cavities – most often at the level of the uterine isthmus (Figs. 1.9 and 1.10).

Fig. 1.9

Partial bicornuate uterus (IV). Fast spin-echo T2-weighted images on sagittal plane (TR/TE 4530/90) (a) and on axial plane (TR/TE 4070/94) (b) show a unique uterine cavity with abnormal uterine contour (arrow)

Fig. 1.10

Partial bicornuate uterus (IV b). Fast spin-echo T2-weighted images on axial (TR/TE 4070/94) (a) and coronal plane (TR/TE 3300/108) (b) show large notch between two separate uterine horns and the communication with a solitary cervix (arrow). Hysterosalpingography (HSG) image of the same patients (c) shows normal opacization only of the left horn

The intervening cleft of the complete bicornuate uterus extends to the internal cervical os (bicornuate unicollis) (Figs. 1.9 and 1.10), while the cleft of a partial bicornuate configuration is of variable length (Figs. 1.11 and 1.12).

Fig. 1.11

Complete bicornuate uterus (IVa). Fast spin-echo T2-weighted images on coronal (TR/TE 4070/94) (a) and axial plane (TR/TE 3070/108) (b, c) demonstrate wide divergence of uterine horns, with communication of endometrial cavities in the cervix (arrow in c)

Fig. 1.12

Complete bicornuate uterus (IVa). Fast spin-echo T2-weighted images on axial (TR 2800/TE 110) (a) and coronal plane (TR/TE 4070/94) (b) demonstrate two uterine horns with communication of endometrial cavities within the lower uterine body (arrow in b) and two duplicated cervices

A bicornuate bicollis uterus is associated with a duplicated cervix, although a degree of communication is maintained between the two horns. At least six variations of the bicornuate uterus have been described in the literature. Longitudinal upper vaginal septa are reported to coexist in 25 % of bicornuate uteri.

On MR images, the bicornuate uterus demonstrates a cleft of at least 1.0 cm of the external fundal uterine contour. The horns demonstrate normal uterine zonal anatomy. The endometrial-to-myometrial ratio and width are normal in appearance. Superimposed leiomyomas and adenomyosis are well demonstrated [12, 17–24].

1.8.2.5 Class V: Septate Uterus

The septate uterus is the most common Mullerian duct anomaly (Fig. 1.1). This anomaly composes approximately 55 % of Mullerian duct anomalies and is associated with some of the poorest reproductive outcomes.

On MR images, the septate uterus is generally normal in size. The endometrial cavities appear smaller than in uteri with a normal configuration (Figs. 1.13 and 1.14). The external uterine contour is united and may be convex, flat, or mildly concave.

Fig. 1.13

Complete septate uterus (Va). Fast spin-echo T2-weighted images on axial (TR 2820/TE110) (a) and coronal plane (b) (TR/TE 4070/94) show a normal-sized uterus with the presence of a low-signal-intensity complete fibrous septum (arrows in a and b)

Fig. 1.14

Partial septate uterus (Vb). Fast spin-echo T2-weighted images on axial (TR 2820/TE 110) (a) and coronal plane (b) (TR/TE 4000/94) show the septum dividing the uterine cavity is of uniform low signal intensity, consistent with fibrous tissue surrounded by myometrium (arrow in a). The septum does not extend onto the cervical os

The fundal segment of the septum is isointense to myometrium in all septa, partial or complete (Figs. 1.13 and 1.14). In complete septa, the inferior segment of the septum is usually a low-signal linear band on T2-weighted images, corresponding to the more fibrous component. This band more often is absent in partial septa, which are uniformly isointense to myometrium.

The presence of leiomyomas and adenomyosis that can arise in the septum corroborates the myometrial composition of the septum [12, 17–24].

1.8.2.6 Class VI: Arcuate Uterus

The arcuate uterus is characterized by a mild indentation of the endometrium at the uterine fundus as a result of near-complete resorption of the uterovaginal septum (Fig. 1.1). Classification has been problematic, because it remains unclear whether this variant should be classified as a true anomaly or as an anatomic variant of normal. On revision of the classification by the American Fertility Society, a separate class was designated because the arcuate uterus can be distinguished from a bicornuate uterus on the basis of its complete fundal unification (Fig. 1.15).

Fig. 1.15

Arcuate uterus (VI). Fast spin-echo T2-weighted image on axial plane (TR/TE 4070/94) (a, b) in two different patients shows a mild indentation of uterine profile (arrows), with the normal myometrial signal intensity. The lack of low signal intensity allows to exclude the presence of fibrous septum and then of a septate uterus

Data regarding the reproductive outcomes of patients with an arcuate uterus are extremely limited and widely disparate.

On MR images, the normal external uterine contour is maintained. The myometrial fundal indentation is smooth and broad, and the signal intensity of this region is isointense to normal myometrium. No low-signal-intensity fibrous component is appreciated (Fig. 1.15) [12, 17–24]. A defining depth to differentiate a prominent arcuate from a mild septum has not been established.

1.8.2.7 Class VII: DES-Exposed Uterus

DES is a synthetic estrogen that was introduced in 1948 and prescribed for women experiencing recurrent spontaneous abortions, premature deliveries, and other pregnancy complications. By increasing the synthesis of placental steroidal hormones, DES was thought to decrease the frequency of pregnancy loss.

In utero exposure to DES was shown to be associated with clear cell carcinoma of the vagina, and use of the drug was abruptly discontinued in 1971.

Structural anomalies of the uterine corpus, cervix, and vagina were subsequently described and shown to affect reproductive potential. DES has been shown to interfere with embryologic development of the mesenchyme of the genital tract.

However, it should be noted that not all women exposed to DES have reproductive problems.

The amount of the drug ingested, as well as when the drug was taken during the gestation, has clinical implications. If the drug was taken very early in the first trimester or after 22 weeks gestation, structural abnormalities are not likely to occur [14–17].

Moreover, the characteristic spectrum of uterine abnormalities associated with DES exposure has been reported in women without a history of exposure to the medication. As such, the morphologic changes may represent a rare Mullerian anomaly of the uterus that may be expressed because of or induced by exposure to DES.

A T-shaped configuration of the endometrial cavity is the most commonly associated abnormality, seen in 31 % of exposed women (Fig. 1.1). Other uterine corpus anomalies include a small hypoplastic uterus, constriction bands, a widened lower uterine segment, a narrowed fundal segment of