Introduction

At the moment of birth, the gastrointestinal tract is gasless. The newborn infant will swallow air virtually from the first breath. The progressive aeration of the gut is, however, surprisingly rapid. Radiographs reveal gas in the stomach within a minute of birth, the proximal small bowel within an hour, the distal small bowel and cecum by about 6 hours, and the distal large bowel by 12–24 hours [1–4]. It is this gas, and knowledge of its normal appearance, that acts as a useful contrast medium, allowing the clinician to detect pathology. Only occasionally is barium or similar contrast medium needed to characterize the gastrointestinal tract.

Which views?

Where gastrointestinal disease is suspected in the newborn, a plain supine anteroposterior radiograph is normally the preferred initial imaging investigation. This provides the clinician with a lot of useful information in most circumstances. In many situations, the astute clinician will obtain enough information from this film so that further views are unnecessary.

Other views may occasionally be requested where the plain supine film provides inadequate information. The commonest, and probably most useful, of these other views is the lateral decubitus. This is usually requested where pneumoperitoneum is suspected but cannot be clearly seen on the plain supine film, but it can also reveal fluid levels within the bowel. The lateral decubitus film should be taken with the patient lying on the left side (a left lateral decubitus) so that the liver is uppermost.