Intestinal nonrotation is a congenital anomaly of the intestines that results in the small bowel occupying the right side of the peritoneal cavity and the colon predominantly on the left.
It is sometimes thought of as a subtype of intestinal malrotation.
Nonrotation is estimated to occur in up to 1 in 500 live births.
Although nonrotation itself does not usually cause symptoms, it is thought to predispose to midgut volvulus and ischemia. Chronic abdominal pain, discomfort, and bilious vomiting have been described, possibly relating to intermittent volvulus .
The midgut develops between the 5-10 weeks in the fetus. During this time the midgut tube herniates outside the peritoneal cavity. It subsequently returns to the cavity a sequential manner that involves rotation of the midgut tube. However, in nonrotation, a large umbilical ring defect allows for the small bowel to descend altogether.
The result is that the small bowel occupies the right peritoneal cavity and the colon is displaced to the left.
Small bowel loops are seen confined to the right side of the abdomen and colon predominantly to the left of midline. This can be difficult to appreciate on plain radiographs and would be better demonstrated on a barium study or CT/MR.
On cross-sectional imaging, there is disruption of the normal SMA and SMV relationship, with the SMV seen to the left of the SMA.
Complicating obstruction, volvulus, and ischemia would be best demonstrated on CT.