ABSTRACT
The variation in abdominal organ appearance with recumbency is most notable in the GI tract. Luminal contents within the stomach and small intestine often contain some degree of fluid and gas. Because patients are positioned in recumbency (rather than standing) and views are obtained with a vertical beam (rather than horizontal beam), the classic appearance of a combination of contents in the GI tract is a summation of opacities created by both gas and fluid that changes with positioning (Figure 13.1). The redistribution of gas within the GI tract (without administration of additional contrast agents) by obtaining a left lateral view has been used to diagnose pyloric outflow obstructions, locate obstructions within small intestines, highlight intussusceptions, distinguish colon from dilated small intestine, rule out gastric malpositioning, and definitively locate the pylorus, among other applications.
