Congenital anatomic disorders of the female reproductive tract develop frequently and result from insults at critical embryonic stages. Influences include genetic mutation, epigenetic factors, developmental arrest, or abnormal hormonal exposures. Disorders range from congenital absence of the vagina and uterus, to lateral or vertical fusion defects of the müllerian ducts, to external genitalia that are ambiguous. Sexual differentiation is complex and requires both hormonal pathways and morphologic development to be normal and correctly integrated. Thus, neonates with genital anomalies not surprisingly often have multiple other malformations. Associated urinary tract defects are especially frequent and are linked to the concurrent embryonic development of both reproductive and urinary tracts (Hutson, 2014).
The urogenital tract is functionally divided into the urinary system and genital system. The urinary organs include the kidney, ureters, bladder, and urethra. The reproductive organs are the gonads, ductal system, and external genitalia. Like most organ systems, the female urogenital tract develops from multiple cell types that undergo important spatial growth and differentiation. These develop during relatively narrow time windows and are governed by time-linked patterns of gene expression (Park, 2005).
Both the urinary and genital systems develop from intermediate mesoderm, which extends along the entire embryo length. During initial embryo folding, a longitudinal ridge of this intermediate mesoderm develops along each side of the primitive abdominal aorta and is called the urogenital ridge. Subsequently, the urogenital ridge divides into the nephrogenic ridge and the genital ridge, also called the gonadal ridge (Fig. 19-1).
Early development of the embryonic genitourinary tract. A. In the developing embryo, the urogenital ridge forms from coelomic mesenchyme lateral to the primitive aorta. B. Cross section through the embryo shows division of the urogenital ridges into the genital ridge (future gonad) and nephrogenic ridge, which contains the mesonephros and mesonephric (wolffian) ducts. The mesonephros is the primitive kidney and is connected by the mesonephric ducts to the cloaca. Primordial germ cells migrate along the dorsal mesentery of the hindgut to reach the genital ridge. Paramesonephric (müllerian) ducts develop lateral to the mesonephric ducts. (Reproduced with permission from Kim Hoggatt-Krumwiede, MA.)
At approximately 60 days of gestation, the nephrogenic ridges develop into the mesonephric kidneys and paired mesonephric ducts, also termed wolffian ducts. These mesonephric ducts connect the mesonephric kidneys (destined for resorption) to the cloaca, which is a common opening into which the embryonic urinary, genital, and alimentary tracts join (Fig. 19-2A). Recall that evolution of the renal system passes sequentially through the pronephric and mesonephric stages to reach the permanent metanephric system. The ureteric bud arises from the mesonephric duct at approximately the fifth week of fetal life. It lengthens to become the metanephric duct (ureter) and induces differentiation ...