An aid to the diagnosis of pneumoperitoneum from supine abdominal films.

Abstract

Aradiolucent Stripe under the diaphragm, seen on films of the abdomen made in upright position, is the classical roentgen sign of intraperitoneal gas. This finding is present in about 80 per cent of gastrointestinal perforations. Sometimes, however, only films made in supine position are available for study. On these, the diagnosis may still be made by detection of the visible contour of the outer (serosal) surface of a segment of bowel. The outline of the serosal surface of the bowel by contrast with intraperitoneal gas was described in 1941 by Rigler (3), but there has been little mention of the sign in the subsequent literature. Both Rigler and Frimann-Dahl (1) consider the finding pathognomonic of pneumoperitoneum. Although it cannot be detected as frequently as subdiaphragmatic gas on upright films, the visible outer bowel surface on supine films is not a rarity with pneumoperitoneum. Study of the films of patients with spontaneous pneumoperitoneum at this hospital revealed that the outline of the outer bowel wall was visible in over one-third of the cases. An example is shown in Figure 1. In each of the patients with this finding a moderate to large amount of free gas was present. In most instances a large quantity of free fluid (over 1,000 c.c.) was found in the abdomen at operation. The sign was most commonly associated with perforated gastric ulcer. The cases support Rigler's original impression that the visible outer bowel surface is usually evident only in the presence of relatively large amounts of peritoneal gas and fluid. To test the importance of abdominal fluid in the production of the roentgen sign, pneumoperitoneum of increasing increments was induced in 2 mongrel dogs of comparable size. In the first dog, 1,500 c.c. of air were necessary to produce a visible outline of the outer bowel surface on supine films. In the second dog, 400 c.c. of saline were instilled into the abdominal cavity before air was introduced. The outer bowel surface could then be defined with the addition of only 400 c.c, of air. On films of both patients and dogs it was noted that it was the outer walls of gasfilled loops of bowel which were almost always demonstrated. This fact and consideration of the physical factors suggest why the presence of peritoneal fluid brings out the sign on supine films. With peritoneal gas alone, the bowel loops fall dorsad by the force of gravity, gathering together, with the result that the outer surface of one segment is adjacent to that of another. The interface between the free gas and the more ventral loops is perpendicular or oblique to the roentgen rays, so that no clear shadow is produced on the film (Fig. 2, A). If both fluid and gas are present, however, any gas-filled segments of bowel float to the surface of the fluid, which tends to separate individual loops.