A specific sign of pneumoperitoneum on sonography: enhancement of the peritoneal stripe

OBJECTIVE

Failure to reveal pneumoperitoneum is a recognized weakness of abdominal sonography. Our objective is to describe a reliable and reproducible sign of pneumoperitoneum that was first identified in an animal model and then confirmed in patients who had undergone laparoscopy.

SUBJECTS AND METHODS

We injected 300 ml of degassed water into the peritoneal cavity of a 15-kg anesthetized pig. Sonographic images were obtained of the anterior peritoneal area after intraperitoneal injection of a single bubble, a series of bubbles, and, subsequently, a 10-ml bolus of air. Later, abdominal sonography was performed in nine patients who had undergone laparoscopy. Close attention was paid to the anterior peritoneal area and signs of free air observed in the animal model. Ten healthy volunteers functioned as a control group.

RESULTS

In the pig, minute amounts of intraperitoneal air showed on sonography as enhancement of the peritoneal stripe. Larger volumes of intraperitoneal air showed as enhancement of the peritoneal stripe associated with dirty shadowing or distal multiple reflection artifacts. The stripe enhanced each time it appeared in the reflection artifact. Intraluminal gas was associated with a normal thin peritoneal stripe, superficial and distinct from the underlying gas artifact. The patients who had undergone laparoscopy showed findings suggestive of small and large pockets of free air, as we saw in the pig model. The control group showed findings consistent with intraluminal gas only.

CONCLUSION

On sonography, enhancement of the peritoneal stripe alone or with reflection artifacts involving the peritoneal stripe is an accurate sign of pneumoperitoneum.

Improved retroperitoneal and gastrointestinal sonography using oral contrast agents in a porcine model

OBJECTIVE

Abdominal sonography can be compromised by the presence of air within the scanning field. Gas-displacing oral contrast agents have the potential to improve the diagnostic yield of routine abdominal sonography. The purpose of this study was to investigate two oral contrast agents and water and to compare their ability to improve abdominal sonography with an unenhanced baseline study and each other in a porcine model.

MATERIALS AND METHODS

The acoustic properties of agent 1 (Oralex; Molecular Biosystems, San Diego, CA), a suspension of polydextrose in purified water; agent 2, a homemade agent (named BMW), a suspension of polysaccharide particles in water; and water were assessed in finger phantoms under laboratory conditions. Each solution was subsequently evaluated in 10 pigs, for a total of 30 animals. The bolus character, gas artifact, abdominal viscera, vessels, and gut wall were graded from 1 (nondiagnostic) to 5 (excellent) in the unenhanced and postcontrast states. Postcontrast grades were compared with unenhanced baseline grades using the Wilcoxon signed-rank correlation. Agents were compared with each other using the Mann-Whitney U test (Wilcoxon rank sum test).

RESULTS

All three solutions were hypoechoic, were homogeneous, and showed minimal attenuation and backscatter. Both oral contrast agents had excellent bolus characteristics (agent 1, grade 5.0 +/- 0; agent 2, grade 4.6 +/- 0.5), displaced gas from the scanning field, and significantly improved visibility in all categories, particularly the gut. No difference in performance was found between agents 1 and agent 2. Water had poor bolus characteristics (grade 1.3 +/- 0.48) and did not improve visibility over baseline.

CONCLUSION

The acoustic in vitro properties of agent 1 and agent 2 approach that of an ideal sonographic contrast agent. Both agents are superior to water in their improvement of direct visualization of the retroperitoneum and the gut in abdominal sonography in a porcine model.