CONGENITAL ANOMALIES OF THE CERVIX
The cervix develops from bilateral paramesonephric (müllerian) ducts in the sixth week of embryologic development. The midline fusion and subsequent canalization of the 2 müllerian ducts give rise to the uterine corpus, cervix, and upper vagina (Fig. 41–1). It has been estimated that a prevalence of the müllerian duct anomalies is about 7% in the general population.
Fusion of müllerian ducts to form cervix and corpus uteri.
There are 3 stages of müllerian duct development. During the first stage, the superior part of each müllerian duct develops into the left and right fallopian tubes, and the caudal portions of each duct develop into the left and right uterus, cervix, and upper two-thirds of the vagina. The lower one-third of the vagina develops from the urogenital sinus. During the second stage, the midline fusion of the separate left and right uterus, cervix, and upper vagina occurs. The resorption of the midline fused segments in the uterus, cervix, and upper vagina takes place during the third stage of development.
Müllerian anomalies result from defective lateral or vertical fusion, canalization (resorption) failure, or simply nondevelopment. The various ways the paired paramesonephric ducts can misalign during fusion enables a spectrum of müllerian anomalies. The most common type of müllerian fusion defect is a lateral fusion defect in which the paramesonephric ducts do not merge in the midline, resulting in either symmetrical or asymmetrical halves. If the part of the duct forming the uterine corpus does not connect with the cervix, 1 or both halves may be obstructed. When they connect with the cervix, they are usually unobstructed. If the 2 ducts remain independent of each other, duplication of the entire tract can result. Duplicated cervices (bicollis) are frequently associated with a longitudinal vaginal septum and are an example of lack of lateral fusion.
Vertical fusion refers to the fusion of the müllerian ducts with the more caudad urogenital sinus. Alternatively, with resorption failure, a single hemicervix or septate cervix (composed of single muscular septum extending from the lower uterine segment or vaginal septum) may be seen. The most profound defect is complete agenesis, or nondevelopment, of the paired ducts, resulting in absence of the uterus, cervix, and upper vagina.
It is important to note that as the reproductive organs are derived from the urogenital sinus, approximately 20–30% of women with müllerian duct anomalies have associated urinary tract abnormalities. In contrast, the ovaries are derived separately from the gonadal ridge. As a result, the ovaries are often normal appearing and produce normal hormone levels regardless of the presence of müllerian duct anomaly.
Isolated cervical agenesis is rare; but cases of an absent uterine cervix with a normal uterine corpus and normal vagina ...