Medical Radiology / Diagnostic Imaging Imaging of Gynecological Disorders in Infants and Children Bearbeitet von Gurdeep S. Mann, Joanne C. Blair, Anne S. Garden 1. Auflage 2012. Buch. XII, 255 S. Hardcover ISBN 978 3 540 85601 6 Format (B x L): 19,3 x 26 cm Gewicht: 780 g Weitere Fachgebiete > Medizin > Sonstige Medizinische Fachgebiete > Radiologie, Bildgebende Verfahren Zu Inhaltsverzeichnis schnell und portofrei erhältlich bei Die Online-Fachbuchhandlung beck-shop.de ist spezialisiert auf Fachbücher, insbesondere Recht, Steuern und Wirtschaft. Im Sortiment finden Sie alle Medien (Bücher, Zeitschriften, CDs, eBooks, etc.) aller Verlage. Ergänzt wird das Programm durch Services wie Neuerscheinungsdienst oder Zusammenstellungen von Büchern zu Sonderpreisen. Der Shop führt mehr als 8 Millionen Produkte. Embryology of the Female Reproductive Tract Andrew Healey Contents Abstract The development of the normal female reproduc- 1 Introduction.............................................................. 21 tive tract is a complex process. The indifferent 2 Embryology of the Female gonad differentiates to the ovary. The mesonephros, Genitourinary Tract................................................ 22 Wolffian and Müllerian ducts differentiate in an 2.1 Development of the Gonads ..................................... 22 orchestrated manner to form the uterus, vagina and 2.2 Relationship Between the Early Fetal Genital lower urinary tract. Disordered differentiation can and Urinary Systems ................................................. 25 2.3 Development of the Fallopian Tubes Uterus, Cervix result in congenital abnormalities affecting the and Vagina................................................................. 26 female reproductive tracts, renal tract and lower 2.4 Development of the Lower Genital Tract ................ 28 intestines. A number of rudimentary structures can 2.5 Development of the External Genitalia.................... 28 persist and be encountered in clinical practice, most 2.6 Development of the Female Genital Accessory Glands ........................................................................ 30 commonly these are derived from the Wolffian 2.7 Embryological Vestigial Structures (Wollfian ducts. This chapter provides an overview of the Vestiges) .................................................................... 30 embryology of the female genital tract relevant to 3 Conclusion ................................................................ 30 the multidisciplinary team caring for young females presenting with illnesses related to the References.......................................................................... 30 reproductive system. Abbreviations AMH Anti-Müllerian hormone UGS Urogenital sinus 1 Introduction The development of the human reproductive tract, urinary system and distal gastrointestinal tract is intertwined sharing a close temporal and spatial relationship. Knowledge of the normal development and anatomy of the gynaecological tract is critical to & A. Healey ( ) the understanding of the timing and nature of a variety Department of Paediatric Radiology, Alder Hey NHS Foundation Trust, Liverpool, L12 2AP, UK of paediatric gynaecological conditions. Malforma- e-mail: [email protected] tions of the gynaecological tract are associated with G. Mann et al. (eds.), Imaging of Gynecological Disorders in Infants and Children, Medical Radiology. 21 Diagnostic Imaging, DOI: 10.1007/174_2010_128, Ó Springer-Verlag Berlin Heidelberg 2012 22 A. Healey disorders of the renal tract and lower intestines. Table 1 Summary of key phases of fetal genital tract Rudimentary structures from the immature genito- development urinary tract may persist and be encountered in clin- Phase of genital development Time (weeks of gestation) ical practice particularly those from the mesonephric Indifferent gonadal phase 4–6 (Wolffian) ducts. Gonadal differentiation 7 This chapter provides an overview of the embryol- Ductal differentiation 9–11 ogy of the female genital tract relevant to the multi- External genitalia 10–12 disciplinary team caring for young females presenting differentiation with illnesses related to the reproductive system. 2 Embryology of the Female germ cells are evident from around the fourth fetal Genitourinary Tract week and migrate from the yolk sac of the embryo along the dorsal mesentery of the hindgut to the mesenchyme of the gonadal ridges by the sixth week In females the genital organs comprise of gonads, and incorporate into the primary sex cords (Fig. 1b). reproductive ducts and external genitalia. Gonadal The primary sex cords are not well developed in the differentiation occurs before the end of the embryonic female embryo but do extend to the medulla of the period. Both the reproductive ducts and external future ovary and form the rete ovarii, a transient genitalia differentiate before the end of the first tri- structure. The primary sex cords regress by the eighth mester. Development of the female genital tract week. continues in utero. The gonads descend in utero in The genotype and chromosomal sex of a fetus is girls. The main events critical to the in utero devel- determined at conception. The mammalian fetus opment of the female gynaecological tract are sum- begins life with an undifferentiated gonad referred to marised in Table 1. Maturation of the genital tract is as the indifferent gonad. The indifferent gonad com- continuous during childhood through to puberty. The prises an inner medulla and outer cortex. The cortex postnatal development of the reproductive tract is contains the precursors of the ovarian parenchyma discussed in Normal Pubertal Development and and the medulla the ovarian stroma. The presence of Growth. primitive germ cells is critical to normal ovarian development. Absence of the primitive germ cells 2.1 Development of the Gonads will yield sterile gonads lacking follicles which will contain only stroma. 2.1.1 Indifferent Gonadal Phase The gonads develop from primitive germ cells, the 2.1.2 Gonadal Sexual Differentiation mesothelium of the posterior abdominal wall and The fetus has bipotential sexual development for the adjacent mesenchyme. Gonadal development begins first 3 months of life. The phenotype depends on the in the fifth fetal week. The mesothelium medial to the presence of sex chromosomes and the prevailing mesonephros of the developing kidneys thickens, biochemical and hormonal milieu. The default sex yielding the paired gonadal (urogenital) ridges phenotype is female in the presence of two X-chro- (Fig. 1a). Transient epithelial finger-like structures, mosomes. Under the influence of two X-chromo- referred to as the primary sex cords, form and extend somes the cortex of the indifferent gonad is much into the supporting mesenchyme. The gonadal ridges better developed in the female embryo than the male. remain similar in both male and female fetuses until The cortex gives rise to the secondary sex cords the seventh week. The indifferent (undifferentiated) (cortical cords) which extend from the surface epi- gonads are located inside the Wolffian body on the thelium to the mesenchyme (Fig. 1c). The secondary medial aspect of the urogenital ridge, either side of the sex cords sustain and regulate ovarian cortical fol- spine. licular development. The undifferentiated gonads The primitive or primordial germ cells are the persist until around the tenth week, at which time the precursors of oocytes or spermatozoa. The primitive ovaries first become identifiable. A male fetus will Embryology of the Female Reproductive Tract 23 Fig. 1 Development of the ovaries from the undifferentiated follicles develop in the yolk sac and migrate to the gonadal (indifferent) gonads: a The indifferent gonads appear as ridge and are sustained by the primary sex cords. c The primary primitive longitudinal streaks in the intermediate mesoderm cords are transitory and regress by 8 weeks. The cortical adjacent to the mesonephros. b Magnified view of the (secondary cords) maintain ovarian follicular development. The undifferentiated gonad during 5–6 fetal weeks. The primordial ovaries are identifiable by 10 weeks. develop in the presence of a Y-chromosome which In addition to the SRY protein and androgens a third encodes the SRY protein. The SRY protein enables factor is required for male development, anti-Mülle- testicular differentiation and the production of rian hormone (AMH). AMH prevents female genital androgens including testosterone. The medulla of the ductal differentiation. An immature female will indifferent gonad in males differentiates into the testis, develop in the absence of these three factors. Further the cortex involutes giving rise to vestigial remnants. maturation of the immature female is contingent upon 24 A. Healey Fig. 2 Pelvic descent of the ovary. The fetal abdominal ovary above the pelvic brim. Rarely the ovary may be located in the usually descends into the pelvis as depicted (left side of pelvis) inguinal canal or more inferiorly at the labium majorum (right lying in close approximation to the fimbrial portion of the hand side of pelvis). The canal of Nuck is a potential space lateral aspect of the paramesonephric duct (future fallopian which results from a patent evagination of the peritoneum to the tube). Maldescent of the ovary occurs when the ovary lies labium majorum the influence of oestrogens. Disorders of sexual dif- to as meiotic arrest (first phase of meiosis). First ferentiation are discussed further in Disorders of Sex meiosis will