me so much in our weekly meetings to review vulval pathology. Dr Ágnes Pekár‐Lukacs has scanned most of the new histology slides to provide excellent‐quality images, and her contribution to this book has been enormous.
The staff at Wiley have provided great support, especially Rajalaxmi Rajendra Singh, who took on the administration of this edition with great skill. Jennifer Seward, the Managing Editor at Wiley, has been a constant help and guide and has tolerated my many queries with great patience. For this, I thank her.
Lastly, enormous thanks to my brother, Jeff Lewis, for ongoing help with grammar and spelling, and for being a good opinion in my attempts to make things understandable!
About the Companion Website
This book is accompanied by a companion website.
www.wiley.com/go/thevulva4e
This website includes:
Downloadable PDFs of the complete reference lists from the book.
Downloadable PowerPoint slides of over 100 extra figures.
1 Vulval Embryology and Developmental Abnormalities
Fiona M. Lewis
CHAPTER MENU
Vulval embryology Sexual determination and differentiation Early female embryogenesis (weeks 1–8) Carnegie stage 1–3 Carnegie stages 4–6 Carnegie stage 8 Carnegie stage 9 Carnegie stage 11 Carnegie stages 13 and 14 Carnegie stages 15 and 16 Carnegie stage 19 Carnegie stages 20–23 End of the female embryonic period and further development (week 8 onwards) Development of the epithelia
Disorders of Sexual Development Sex Chromosome DSD Turner’s syndrome Mosaicism 46,XX DSD Foetal androgen excess Maternal androgen excess Exogenous androgen excess 46,XY DSD Disorders of gonadal development Complete or partial gonadal dysgenesis Ovotesticular disorder
Structural developmental defects Vagina Vaginal agenesis (Müllerian agenesis) Vaginal atresia Vaginal septa Imperforate hymen Vaginal cysts
Vulval and urinary system abnormalities Kidney Ureter Bladder Urethra
Vulval and intestinal abnormalities
A basic knowledge of the normal embryogenesis and organogenesis of the female genital tract is important in order to understand the developmental abnormalities that may arise. The embryogenesis of the female genital tract is closely linked to that of the urinary tract and the terminal portion of the gastrointestinal tract, which explains why developmental abnormalities of the female genital tract are often seen in association with anomalies of these systems.
Vulval embryology
Sexual determination and differentiation
Sexual determination is the process whereby cells commit to a certain course of development. The genetic sex of an individual is established at fertilisation, and so can be regarded as the point of determination. However, the gonads and external genitalia remain sexually indeterminate for the first 6 weeks.
Sexual differentiation describes how the cells achieve sexual development as determined at fertilisation. The differentiating processes are regulated by at least 30 specific genes located on sex chromosomes or autosomes that act through a variety of mechanisms. The presence of the Y chromosome determines whether the undifferentiated gonad will develop into a testis or ovary and is an extremely important factor in testicular differentiation. It contains a region known as SRY (sex‐determining region of the Y chromosome). The testis‐determining factor is a 3.5 kilobase pair sequence located on the Yp11.31 sub‐band. If the SRY is absent or altered, the undifferentiated gonad will develop into an ovary. However, the SRY gene has been detected in some cases of Turner’s syndrome where there is no Y chromosome in their karyotype. This finding demonstrates that the presence of a single dominant Y chromosomal gene alone is not enough to determine testicular differentiation [1], and other genes are involved. These include WT1 Wilms’ tumour suppressor gene, which regulates SRY expression, DAX1 on the X chromosome,
