Congenital Anomaly

TARGET AUDIENCE: Clinical diagnostic radiologists including residents and fellows OBJECTIVES – To discuss the embryology and key imaging findings of congenital Müllerian duct anomalies (MDA) and their mimics to differentiate MDA subtypes. Introduction Müllerian duct anomalies (MDAs) include a wide spectrum of developmental abnormalities. They are related with various gynecologic and obstetric complications such as primary amenorrhea, infertility, and endometriosis. Its incidence has been estimated 2%–3% and about 15% of these women suffering from recurrent miscarriage 1. MDAs frequently accompany congenital anomalies in renal and vertebral systems, with the reported prevalence of 30%–50% for renal anomalies because close relationship between the paramesonephric and mesonephric duct 1 and 29% for vertebral anomalies 2. The Role of Imaging Hysterosalpingography (HSG) is typically indicated as an initial examination evaluating infertility. It allow assessment of uterine cavity and association with tube and other cavities. However, HSG does not provide important diagnostic feature about external uterine contour and also needs radiation exposure with a catheter placement into the cervical canal 3. Ultrasound and MRI can provide detailed anatomy of the uterus to diagnose MDA and also enable to assess concomitant renal anomalies. US is rapid and has easy accessibility, and 3D US of the uterus has reported improved detection of external uterine contour 4,5. However, evaluation of uterine remnant or vaginal septum may not be always fully demonstrated by US because of limited acoustic window 6. MR imaging is ideal modality for characterizing MDAs providing clear anatomic detail of both the internal uterine cavity and the external contour by its excellent soft-tissue resolution 7,8. Oblique coronal T2-weighted images of the uterus are useful for proper assessment of the uterine fundal and internal contour. Recently 3D-T2-weighted sequences can provide thin slice images along with multiplanar reformatting (MPR) capability 3. Classification of MDA and Image findings Classification system proposed by American Society for Reproductive Medicine has prevailed for systematically categorizing the MDA, that was revised system from Buttram and Gibbons 9,10. Embryologically, Müllerian duct development consists of three stages, those are ductal development, ductal fusion and septal resorption by Robbins et al. and most of the problem happens during the 8th week of development11. MDA corresponds the arrest of each stage of development. MDA class I (Müllerian agenesis and hypoplasia) and II (unicornuate uterus) are failure of ductal development, class III (uterine didelphys) and IV (bicornuate uterus) are fusion anomaly and class V (septate uterus) and VI (arcuate uterus) are resorption anomaly. MDA class I (Müllerian agenesis and hypoplasia) include variable degree of uterovagianl hypoplasia, then the symptom is also different depending on the presence of uterine remnant. Mayer–Rokitansky–Küster–Hauser (MRKH) syndrome is a complete agenesis of the Müllerian duct derivatives, the most extreme type of MDA. Radiologically, detecting normal ovaries and rudimental genital structures is a key to diagnosis. MDA class II (unicornuate uterus) consists simultaneous presence of normal development of one Müllerian duct and the structure of arrested development of the contralateral duct. Four subtypes are classified based on the degree of the developmental arrest in the contralateral duct. Since most of the symptoms occur due to retrograde flow of menses through the obstructed horn, the degree of symptom depend on the presence or absence of a non-communicating functional rudimentary horn12. Therefore, anatomical structure of arrested developed duct and the presence of communication with normal duct is required for imaging diagnosis. MDA class III (uterine didelphys) and class IV (bicornuate uterus) are included as a fusion anomaly. Complete failure of Müllerian duct fusion results in uterine didelphys and incomplete or partial fusion of the Müllerian ducts results in bicornuate uterus 2. MR imaging of uterine didelphys shows two widely divergent uterine horns with normal zonal anatomy and two separate cervices. Obstructed Hemivagina and ipsilateral renal agenesis (OHVIRA) syndrome, also known as Herlyn–Werner–Wunderlich (HWW) syndrome is correlated with uterine didelphys, defined as a uterus didelphys with hemivaginal obstruction and ipsilateral renal agenesis. As for bicornuate uterus, unlike in a uterus didelphys, there is soft tissue separating the two symmetric uterine cavities 2. There are two types according to the presence of accompanying cervical duplication. Bicornuate bicollis (complete type) has cervical duplication and bicornuate unicollis (partial type) does not. MRA class V (septate uterus) is complete or partial failure of resorption of the uterovaginal septum after normal Müllerian duct fusion 2. The septum is composed of fibromuscular tissue visualized as low signal intensity on T2-weighted image 13. It is the most common type of MDA over half of the MDA cases 2. Differentiation of a fibrous septum of septate uterus from a muscular septum of bicornuate uterus is clinically important in terms of surgical planning 14. MDA class VI (arcuate uterus) is mild form of resorption anomaly with near complete resorption of the uterovaginal septum, then it is considered to be normal uterine variant by researchers. There are many other anomalies including androgen insensitivity syndrome, vaginal anomalies such as transverse/longitudinal septum etc. CONCLUSION MDAs are broad spectrum of developmental anomalies and accurate classification of MDAs is important as surgical treatment may varies among MDA subtypes. MR images can provide useful information for those differentiation with concomitant problems.

Acknowledgements

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