A 32-year-old woman, gravida 4 para 0, comes to the office for evaluation of recurrent pregnancy loss. She has had 4 consecutive spontaneous abortions with the same partner. The patient has menstrual cycles approximately 28 days apart, with light bleeding for 2-3 days. She has no chronic medical conditions and takes no daily medications. The patient does not use tobacco, alcohol, or illicit drugs. Results of her hysterosalpingogram are shown in the exhibit. Failure of which of the following processes is the most likely underlying mechanism of this patient's condition?
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Female reproductive tract development involves the lateral/vertical fusion and involution of the paramesonephric ducts (eg, Müllerian ducts), which give rise to the fallopian tubes, uterus, cervix, and upper vagina. Development of the renal system is closely linked; therefore, congenital uterine anomalies often coexist with renal anomalies (eg, unilateral renal agenesis).
During development, the paramesonephric ducts fuse laterally with each other and vertically with the urogenital sinus; failed fusion in either direction can lead to structural anomalies. Incomplete lateral fusion of the upper Müllerian duct segments causes a bicornuate uterus, whereas complete lack of lateral fusion can lead to uterine didelphys (ie, double uterus and cervix). Once fused, the ducts undergo involution; failure of involution results in a longitudinal uterine septum. In contrast, failed vertical fusion of the paramesonephric ducts with the urogenital sinus results in a transverse vaginal septum, which can cause primary amenorrhea and cyclic pelvic pain due to menses retained in the uterus (Choice E).
When a patient has difficulty conceiving or has recurrent pregnancy loss, structural genital tract anomalies are evaluated by hysterosalpingography (HSG), which involves contrast injection through the cervix into the uterus with a concurrent pelvic x-ray. This patient's HSG reveals 2 unfused uterine horns with a central filling defect, which likely represents a bicornuate uterus due to failed lateral fusion of the paramesonephric ducts.
(Choice A) Complete absence or hypoplastic development of the paramesonephric ducts leads to Müllerian agenesis (ie, Mayer-Rokitansky-Küster-Hauser syndrome). These patients have a lower vagina, which originates from the urogenital sinus, and an absent or rudimentary uterus. HSG would not reveal distinct uterine horns.
(Choice B) The mesonephric tubules arise with the mesonephric duct (eg, wolffian duct) to form the mesonephros. In females, the mesonephric tubules and mesonephric duct degenerate, not differentiate, to form Gartner ducts. In males, they form the epididymis, ductus deferens, seminal vesicles, and ejaculatory ducts.
(Choice C) The mesonephric (Wolffian) ducts do not fuse during embryonic development.
Educational objective:
In females, the paramesonephric (Müllerian) ducts fuse to form the fallopian tubes, uterus, cervix, and upper vagina. Disruptions in this process can lead to various Müllerian duct anomalies (eg, bicornuate uterus, uterine didelphys). Renal anomalies are a common comorbidity.