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Ultrasound_Scan_ND_152

Image: Ultrasound Scan. By: Dilmen Nevit. License: CC BY-SA 3.0


Introduction

The most common risk factors for uterine anomalies are the maternal use of thalidomide or diethylstilbestrol during pregnancy. Fortunately, awareness about the teratogenicity of these 2 medications has contributed significantly to lowering the incidence of Mullerian duct anomalies.

Embryogenesis and Abnormal Development of the Female Reproductive Tract

At 6 weeks of embryological development, the male or female fetus has 2 pairs of genital ducts, known as the Mullerian and Wolffian ducts. These ducts come from a common embryonic mesoderm that gives rise to the genital system in both females and males.

At this stage, the genitourinary systems are identical and cannot be differentiated. The Wolffian duct system initially grows faster than the Mullerian ducts, forming a pathway for growth of the latter. As well, the Wolffian ducts initially drain to the primitive mesonephric kidney; there is therefore a close association between Mullerian duct anomalies and urinary system anomalies.

Regression of the Wolffian duct system is based on the absence of the testosterone-induced SRY gene found on chromosome Y. The ducts elongate in week 9 to form 3 distinct regions:

  • The cranial vertical, which forms the fimbriae and fallopian tubes
  • The horizontal, which develops into the remaining structures of the fallopian tubes
  • The caudal vertical segment of each side, which fuse together at the midline of the future pelvis and form the uterovaginal primordium; later, this becomes the uterine and upper vaginal region

Abnormal development at any stage leads to abnormalities, including the following:

  • Bilateral deficient Mullerian duct development leads to an absent vagina, cervix, and uterus, in addition to absent fallopian tubes
  • Failure of the Mullerian ductal fusion is responsible for anomalies such as uterine didelphys, bicornuate uterus, and arcuate uterus
  • Failure of resorption of the medial walls of the vagina and uterus is the mechanism of formation of a complete or partial septate uterus
  • Abnormal hormone balance, which is linked to the maternal use of diethylstilbestrol, can cause a T-shaped uterus. The most common type of uterine anomalies is arcuate or hypoplastic. Unicornuate or bicornuate uteri are 2 common examples of an arcuate uterus.

Up to one-tenth of patients with congenital uterine malformations also have associated anomalies of the urinary tract, gastrointestinal tract, musculoskeletal system, or heart. Endometriosis is more common in malformed uteri compared with normally developed ones. Renal agenesis is very common in patients with uterus didelphys and unicornuate uterus.

Despite the association with other anomalies, the risk of neoplasms in patients with congenital uterine malformations appears to be equal to that of the general population.

Diagnostic Workup and Imaging Studies

Most patients with congenital uterine malformations present to the clinic because of a history of recurrent spontaneous abortions or amenorrhea. (Spontaneous abortions are most common with T-shaped, septate, and unicornuate uteri.)

Ultrasound and magnetic resonance imaging (MRI) are the most common imaging modalities used to diagnose Mullerian duct anomalies, as they indicate the type of the anomaly and the presence or absence of concomitant renal malformations with high accuracy, compared with other modalities. The diagnosis of a malformed uterus can be delayed due to operator dependency of ultrasonography, the first imaging modality used in the evaluation of structural uterine anomalies in a patient with recurrent abortions. The increased incidence of spontaneous abortions and infertility may be related to the direct effect of the abnormal uterus on the implantation of the uterus, or the co-presence of cervical incompetence. Cervical incompetence is found in up to one-third of women with congenital uterine malformations.

Ultrasonography

The accuracy of transvaginal ultrasound in the identification of congenital uterine malformations is excellent, at 82%–92%. Vaginal and cervical atresia in addition to uterus didelphys is reliably identified on ultrasound. However, septate uterus, unicornuate uterus, and other less common uterine malformations are poorly visualized and recognized with ultrasonography.

Another drawback of ultrasonography in the identification of congenital uterine malformations is operator dependency. Additionally, obese patients usually have ultrasound images of lower quality and the identification of uterine anomalies may therefore be problematic.

Magnetic Resonance Imaging

MRI studies have an estimated accuracy of 100% in identifying almost any type of uterine anomalies. MRIs can identify vaginal, cervical, and uterine anomalies reliably, including septate, unicornuate, and bicornuate uterine malformations. Additionally, MRI studies of the fallopian tubes, ovaries, and other pelvic structures makes it easy for the radiologist to identify endometriosis, even in its initial stages. Standard pelvic MRI protocols employed include T1-weighted, T2-weighted, and contrast-enhanced images.

The main disadvantage of ultrasonography and MRI studies is the fact that both are diagnostic, not therapeutic.

Laparoscopy

Direct visualization of the external contour of the uterus can be helpful in differentiating between bicornuate and septate uterus. Hysteroscopy is helpful in the identification of intrauterine adhesions and septa. These 2 techniques can be also used for adhesiolysis or other treatments.

Examples of Uterine Malformations and the Imaging of Malformations

The following table outlines some common congenital uterine malformations, the imaging modality of choice for the visualization of that malformation, and the main characteristics that can be seen for each.

Uterine Anomaly Imaging Modality of Choice Main Imaging Findings
Hypoplastic uterus MRI A small uterus with regular morphology and normal relationship to the uterus.
Hysterosalpingography can be also used, with good results.
Unicornuate uterus 3D ultrasonography or MRI Decreased uterine volume with asymmetry, and the presence of a rudimentary uterine horn. Ultrasonography results can be confusing, however, and some cases have been missed by conventional transvaginal ultrasound.
Uterine didelphys Ultrasonography or MRI Uterine didelphys can be easily diagnosed with either transvaginal ultrasound or MRI. Divergent uterine horns, fundal cleft, 2 services, and a vaginal septum are the most common findings on both imaging modalities.
Bicornuate uterus Ultrasonography, MRI, or hysterosalpingography As this uterine anomaly can be easily identified by all 3 imaging modalities, the most cost-effective method is advisable (ie, ultrasound). T2-weighted MRI images visualize the 2 uterine horns.
Septate uterus MRI or hysterosalpingography T2-weighted images can accurately identify the identification of the uterine septum. Hysterosalpingography is also helpful, as it can show a septum that is associated with uterine contraction. Although the septum appears hypoechoic on ultrasonography, it is missed in a significant number of patients.
T-shaped uterus Hysterosalpingography Unlike the other uterine anomalies, a T-shaped uterus is best visualized with hysterosalpingography. MRI and ultrasound are inferior in the identification of this anomaly. Suspicion of this anomaly is based on a maternal history of diethylstilbestrol use during pregnancy.
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