Development and Anatomy: Disorders of Development

Abstract

An overview of the complex embryological development of the lower female genital tract, some of which remains incompletely understood, is useful for the understanding of many neoplastic and nonneoplastic vulvovaginal lesions. The Fallopian tubes, uterus, and cervix develop from the paramesonephric (Mullerian) ducts. The vagina has a dual origin with the upper portion, including the vaginal fornices, arising from the paramesonephric ducts and the lower portion from the urogenital sinus. The development of the mesoderm surrounding the female genital tract in humans is incompletely understood. Experimental studies demonstrate that complex stromal epithelial interactions are crucial for site-specific epithelial differentiation, especially for development of glandular epithelia. Development of external genitalia occurs under the influence of sex hormones through proliferation of the mesoderm and ectoderm lateral and ventral to the cloaca. The area bounded by the vaginal orifice and the urogenital sinus enlarges to form the vestibule and is of endodermal origin. This is morphologically and functionally distinct from the rest of vulval tissues which are mesodermally and ectodermally derived. This difference in origin is reflected in differences in responses to sex hormones and other stimuli. A variety of abnormalities in development can therefore occur as a result of structural and hormonal disturbances, including external influences such as in utero exposure to diethylstilbestrol.