THE RADIOLOGIC SIGNS OF DISEASE IN THE LESSER PERITONEAL SAC

Abstract

The contour of the lesser peritoneal sac is readily identified on supine and erect plain films of the abdomen if the cavity contains moderate or large amounts of gas. Small amounts of gas or loculated collections cannot be identified as being in the lesser peritoneal sac without lateral views of the abdomen after opacification of the stomach. Almost always, midline subdiaphragmatic gas collections will be shown to be intraperitoneal. Fluid collections in the lesser sac displace the stomach anteriorly, upward and to the right. Typically there is a large left-sided soft tissue density with an oblique lower border that runs laterally and downward. Abscesses originating in the pancreas may fill the lesser sac with multiple small gas collections or, if coalescent, with long retrogastric air-fluid levels. The distal ileum or right side of the colon may herniate through the foramen of Winslow into the lesser peritoneal sac. The small intestine proximally shows the signs of mechanical obstruction. The herniated segment usually undergoes obstruction of the closed-loop type. Often a characteristic extrinsic obstruction of the distal limb of the hepatic flexure is produced when the herniating loop of small intestine crosses the colon on its way to the epiploic foramen.