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The cervix develops from the 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. 40–1). Müllerian duct anomalies result from nondevelopment, defective lateral or vertical fusion, or resorption failure. The most common type of müllerian fusion defect is a lateral fusion defect in which the resulting defective organs can be either symmetrical or asymmetrical and can be obstructed or unobstructed. These fusion defects result from failure of fusion of the müllerian ducts, failure of formation of 1 müllerian duct, or absorption of the intervening septum. Defective resorption of the tissue between the fused müllerian ducts results in a uterine septum that can be partial or extend to the full length to the cervix. The most common lateral fusion defect is a septum. Vertical fusion refers to the fusion of the müllerian ducts with the urogenital sinus. The absence of müllerian development results in agenesis of the cervix and uterus. A double cervix is frequently associated with a longitudinal vaginal septum and is an example of lack of fusion. A single hemicervix or septate cervix composed of single muscular septum that can be an extension of a lower uterine segment or vaginal septum is seen with resorption failure. Approximately 20–30% of women with müllerian duct anomalies also have urinary tract abnormalities, a finding that warrants urinary tract imaging. Women with müllerian duct anomalies have normal ovaries and develop normal secondary sex characteristics.
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Isolated cervical agenesis is rare, but cases of an absent uterine cervix with a normal uterine corpus and normal vagina have been reported. These cases presumably result from either failure of müllerian duct canalization or abnormal epithelial proliferation after canalization. More common is absence of the cervix combined with absence of the uterine corpus and upper vagina, known as müllerian agenesis or Mayer-Rokitansky-Kuster-Hauser syndrome, which occurs in approximately 1 in 4000 female births. Because most of the vagina is derived from müllerian ducts, the vagina may be shortened in müllerian agenesis. Female offspring of women with müllerian agenesis have been studied to identify a possible genetic contribution to this disorder. Because no offspring with müllerian agenesis have been reported, this disorder is assumed to result from a polygenic multifactorial inheritance pattern.
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Cervical agenesis with a normal functioning uterine corpus must be differentiated from müllerian agenesis (Figs. 40–2 and 40–3). In the former, menstrual blood may accumulate within the uterus or result in retrograde flow and development of endometriosis. Thus cervical agenesis is usually diagnosed at menarche when patients present with primary amenorrhea and cyclic abdominopelvic pain. Suppression of menstruation with continuous combined estrogen/progesterone pills may improve the pain-related complaints. Ultrasonography, ...