introduced a classification system in 1988 (1988) that stratifies MDA into seven different classes of uterine anomalies (Fig. 1). It is based on a previous classification system introduced by Buttram et al. (Buttram and Gibbons 1979). Other classification systems followed and included broader collections of anomalies in order to avoid conflicting observations and oversimplicity (Rock 2000; Grimbizis et al. 2013). With all classification systems, one must emphasize that with the overlap of associated cervical and vaginal anomalies, the classifications describe primarily the uterine defects, whereas cervicovaginal defects as well as associated malformations must be added separately in the form of a subset. The distribution among the different classes of MDA and their clinical presentations is summarized in Table 1. The diagnosis of MDA is based upon the clinical presentation, physical examination, and subsequent imaging workup with different imaging methods available, of which magnetic resonance imaging (MRI) takes a leading role, especially in complex uterine malformation (Minto et al. 2001; Olpin and Heilbrun 2009). For the following descriptions of the specific pathologies, we use the ASRM classification system and provide definitions of the different types of MDA in the imaging section.

2\ Imaging

2.1\ Technique

Once an MDA is suggested based on evidence from patient history and physical examination, the next diagnostic step includes different imaging workups in order to detect and specify MDA and to guide further treatment options. Before ultrasound (US) and MRI were capable of visualizing MDA with a high accuracy, imaging of MDA was limited to hysterosalpingography (HSG) (Krysiewicz 1992), a fluoroscopic spot film technique in combination with endoluminal filling of the uterine cavity with radiopaque contrast agent. 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 may still be used in the primary imaging workup in case of infertility clarification. A newer technique using MR for the visualization of the tubal patency, the so-called 3D MR-HSG, avoids exposure of the ovaries to ionizing radiation and has been found to be a reliable imaging alternative to conventional HSG in a couple of smaller studies (Winter et al. 2010; Ma et al. 2012). Nevertheless, it is not widely used due to the better availability of saline contrast hysterosonography (see below).

Nowadays, the first imaging modality in the MDA assessment includes pelvic US (Byrne et al. 2000; Goldberg et al. 1997) – (1) transabdominal US (performed with a 2.5- to 5-Mhz probe) for evaluation of the entire abdomen, especially for associated renal malformations, and (2) transvaginal US (performed with a 5- to 8-Mhz endovaginal probe) for better delineation of the uterus, vagina, and ovaries. Hysterosonography, a technique consisting of transvaginal US with prior infusion of saline or ultrasound contrast agent into the endometrial canal, further increases the delineation of the endometrial cavity. It is performed only for selected indications, i.e., in patients with a history of infertility. US is highly accurate for the ­detection of MDA (Pellerito et al. 1992). Newer techniques, such as 3D US

(Wu et al. 1997; Bermejo et al. 2010), even further improved the imaging diagnostics by giving better information about the external contour of the uterus and its volume.

Magnetic resonance imaging (MRI) is today considered standard in the evaluation of MDA and accepted as the leading imaging modality for further surgical planning (Behr et al. 2012; Steinkeler et al. 2009; Robbins et al. 2012). 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 and accuracies of up to 100% have been reported (Pellerito et al. 1992; Carrington et al. 1990).

According to the author’s institution’s imaging protocol (Siemens Magnetom Aera, 1.5-Tesla MR unit, Siemens Medical; Erlangen, Germany) for the assessment of congenital uterine anomalies, MRI of the uterus includes six basic native sequences without intravenous contrast using a bodyflex phased-array MR surface coil as shown in Table 2.

If possible, patients should be scheduled in the second half of the menstrual cycle, since the thickness of the endometrial stripe increases

­during the follicular and secretory phase and thus the normal zonal anatomy of the uterus can be better appreciated. No specific patient preparation is necessary. It may be debated if the application of a tampon by the patient or endovaginal administration of sterile gel prior to the examination might be helpful to delineate the vaginal lumen in selected cases. Intravenous injection of antiperistaltic agents like glucagon or scopolamine butylbromide (Buscopan®) can be performed to reduce artifacts caused by intestinal motion.

Native axial T1-weighted sequences are standard techniques for the assessment of the female pelvis. In this patient population with suspected MDA, they are mainly performed in order not to miss any associated pathologies, e.g., ovarian disease or peritoneal implants in endometriosis. In addition, the demonstration of hemorrhage within the endometrial cavity (hematometra) and/or vagina (hematocolpos) benefits from T1-weighted imaging. Highresolution T2-weighted images are most important for the assessment of the uterus. Sagittal sections are best suited to image the uterus and its zonal anatomy. Additional oblique sections parallel to the endometrial cavity results in a

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long-axis view, which is most helpful for imaging the fundal contour. An oblique sequence obtained perpendicular to the cervical canal results in a short-axis view and allows accurate assessment of the cervix, i.e., the diagnosis of duplication or septation. The protocol further includes fast sequences of the upper abdomen in axial and coronal orientation to diagnose or exclude renal pathology.

2.2\ Classes of Müllerian Duct

Anomalies (MDA)

The percentage distribution of the different MDA classes and their influence on reproductive and obstetric outcome, as well as their major associations, are summarized in Table 1.

2.2.1\ Class I Anomalies: Dysgenesis

Definition: Dysgenesis (segmental agenesis and variable hypoplasia) of the Müllerian ducts (uterus and upper two thirds of the vagina) (Pittock et al. 2005; Strübbe et al. 1993) (Fig. 2). Mayer–Rokitansky–Küster syndrome is the most common form of Class I anomaly and includes agenesis of uterus and vagina.

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2.2.2\ Class II Anomalies: Unicornuate Uterus

Definition: Unicornuate uterus is the result of partial or complete hypoplasia of one Müllerian duct (Brody et al. 1998) (Fig. 3).

Unicornuate uterus may be isolated (35%) or associated with a contralateral rudimentary horn. These rudimentary horns present with or without communication to the endometrial cavity and may or may not contain endometrium, the latter variant being also called no cavity rudimentary horn. In patients with cavity noncommunicating rudimentary horn, dysmenorrhea and hematometra may occur. Surgical resection to either 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 noncommunicating rudimentary horn. Renal malformations are common with unicornuate uterus and occur mostly on the same side as the rudimentary horn is found.

2.2.3\ Class III Anomalies: Uterus Didelphys

Definition: Uterus didelphys is the result of complete nonfusion of the Müllerian ducts forming a complete uterine duplication with no communication­

between each other (Carrington et al. 1990; Fedele et al. 1989; Fedele et al. 1988) (Fig. 4).

Uterus didelphys may be associated with a longitudinal (75%) or, more rarely, a transverse vaginal septum, the latter causing obstructive hematometrocolpos of one uterine horn. Renal agenesis might occur in these patients and are usually located on the same side as the septum. Endometriosis, as a result of retrograde menstruation, may also be an issue in these conditions. A nonobstructive uterus didelphys is usually asymptomatic.

2.2.4\ Class IV Anomalies: Bicornuate Uterus

Definition: Bicornuate uterus is the result of incomplete fusion of the cranial parts of the Müllerian ducts (Pellerito et al. 1992; Toaff et al. 1984) (Fig. 5).

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.

Bicornuate uterus occurs with wide variability. Extension of the intervening fundal cleft to the internal cervical os characterizes the complete bicornuate uterus with a single cervix (bicornuate,

Fig.3  (a–d) A 28-year-old female patient with infertility. HSG (a) shows a fusiform “banana-shaped” configuration of one small endometrial cavity (arrows) that is deviated to the right and drains into one fallopian tube. Note the absence of the normal triangular appearance of the fundal cavity. This configuration is highly suggestive of the presence of a unicornuate uterus. Iatrogenic filling defects in the uterine cavity by air bubbles. Oblique T2-weighted

MR images (b, c) and coronal T2-weighted MR image (d) confirm the diagnosis of a unicornuate uterus with the presence of a small elongated uterus that shows normal zonal anatomy (arrows). A rudimentary horn with low signal intensity and no zonal anatomy – thus corresponding to a rudimentary horn with no endometrium – can be depicted on the right side (arrowheads). No surgical resection is needed in this case

Fig.4  (a, b) A 14-year-old female patient with abdominal pain. MRI shows uterine fusion anomaly with two separate cavities, the right one markedly dilated (asterisk) due to retention of blood caused by an obstructing septum ((a): axial T1-weighted image with fat suppression; (b, c): axial

and coronal T2-weighted images); the left cavity shows a normal zonal anatomy (arrow). Coronal TRUFISP shows associated agenesis of the right kidney (d). Schematic drawing shows uterus didelphys with an obstructing septum on the right side (medical illustrator: W. Herzig) (e)

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Fig. 4  (continued)

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J. Roos et al.

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 it is probably only necessary in ­specific cases. A higher rate of cervical incompetence seems to be associated with bicornuate uterus.

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