Developmental changes in the retrorectal region of the human fetus.

A morphological study concerning the development and arrangement of the connective tissue in the retrorectal region was performed by investigating 300-700 micron thick sections through fetal pelves, plastinated with the epoxy resin E 12 and cut with a diamond wire-saw. In 9-20-week old fetuses several developmental processes take place simultaneously in the retrorectal region: In the 9-week old fetus there is a marked incongruity between the curvature of the rectal wall and that of the caudal elements of the vertebral column. However, by the 20th week this incongruity has disappeared and the curvatures of the two structures parallel each other. During this developmental process, the position of the rectum in relation to the caudal parts of the vertebral column is changed. Due to the changing position of the rectum, alterations of the connective tissue are found especially in the precoccygeal portion of the retrorectal region. In the mesenchyme of 9-week old fetuses a differentiation of the retrorectal space into compartments can already be seen. With increasing age of the fetuses, three different compartments can be distinguished between the rectum and the ventral surface of the sacrum and coccyx. By the 20th week of human development fasciae can be identified within the connective tissue. In comparison to the various fasciae that have been described in the retrorectal region of the adult, only the pelvic parietal fascia is to be found in 20-week old fetuses. Fibres of this fascia traverse the retrorectal space and divide it into a presacral and a precoccygeal portion.