Physiological gut herniation is a natural phenomenon that occurs in early pregnancy. It usually occurs from around 6-8 weeks up until 12-13 weeks in-utero, after which the bowel returns to the abdominal cavity.

Physiology

It occurs as a result of the bowel (particularly ileum) growing faster than the abdominal cavity during the early gestational period. In the physiological situation, the intestine elongates and moves outside of the embryonic abdomen herniating into the base of the umbilical cord. This occurs at ~8 weeks gestational age and is due to a number of factors including rapid growth of the cranial end of the midgut (which will form the small intestine), and the large size of the developing liver and kidneys. While the bowel is within the umbilical cord, the midgut rotates 90 degrees counter-clockwise (facing the embryo). At approximately 10-11 weeks the abdomen enlarges and the intestines return to the abdominal cavity. The midgut then rotates an additional 180 degrees counter-clockwise, fixing to the posterior retroperitoneum.

Radiographic features

Antenatal ultrasound

presence of fetal bowel outside the anterior abdominal wall, at the base of the umbilical cord.

it should not be seen after 12-13 weeks gestational age.

it should never contain herniation of other organs, such as the liver

the extent of herniation is comparatively small (often <7 mm)

frequency: according to one study, this may be seen in 4 around 65% of the cases at 8 weeks 100% during 9-10 weeks around 25% at 11 weeks



Differential diagnosis

For ultrasound imaging appearances, consider: