A radiological study of morphology and growth in the human fetal colon.

A radiological study has been made of the colon in 64 human fetuses between 11 and 20 weeks gestation (64-160 mm crown rump (CR) length). A dynamic picture of colon development was obtained from analysis of the radiographs. The findings challenge textbook descriptions, but can be interpreted in terms of the ultimate morphology of the colon. According to the morphology of the proximal (pre-splenic) part of the colon, there are three types of colon. In Type 1 it lies transversely, in Type 2 it is oblique in direction, and Type 3 has a postnatal form with ascending and transverse elements. Although the Type 1 predominates in smaller fetuses and the type 3 is most common in larger fetuses, there is some overlap in their distribution. The ileocaecal junction does not descend, but actually slightly ascends as the fetus grows. The splenic flexure grows in a distinctly cranial direction, and at almost three times the rate of the ileocaecal junction. Thus, as the fetus develops, the ileocaecal junction and splenic flexure grow further apart, and this determines the change from a Type 1 to a Type 2 colon. The divergence of the ileocaecal junction and splenic flexure appears to be related to different rates of growth in the colon, the distal (post-splenic) part growing almost half as fast again as the proximal (pre-splenic) part. The more mature (Type 3) form of colon appears to result from conversion of the Type 2 following early adhesion between the proximal colon and the second part of the duodenum.