PURPOSE: The purpose of this retrospective study was to determine what gives 
rise to the periportal free air, and ligamentum teres and falciform ligament 
signs on CT in patients with gastrointestinal (GI) tract perforation, and 
whether these specific air distributions can play a clinically meaningful role 
in the diagnosis of gastroduodenal perforation.
MATERIAL AND METHODS: Ninety-three patients who underwent a diagnostic CT scan 
before laparotomy for a GI tract perforation were included. The readers assessed 
the presence of specific air distributions on CT (periportal free air, and 
ligamentum teres and falciform ligament signs). The readers also assessed the 
presence of strong predictors of gastroduodenal perforation (focal defects in 
the stomach and duodenal bulb wall, concentrated extraluminal air bubbles in 
close proximity to the stomach and duodenal bulb, and wall thickening at the 
stomach and duodenal bulb). The specific air distributions were assessed 
according to perforation sites, and the elapsed time and amount of free air, and 
then compared with the strong predictors of gastroduodenal perforation by using 
statistical analysis.
RESULTS: All specific air distributions were more frequently present in patients 
with gastroduodenal perforation than lower GI tract perforation, but only the 
falciform ligament sign was statistically significant (p<0.05). The presence of 
all three specific air distributions was demonstrated in only 13 (20.6%) of 63 
patients with gastroduodenal perforation. Regardless of the perforation sites, 
the falciform ligament sign was present significantly more frequently with an 
increase in the amount of free air on multiple logistic regression analysis 
(adjusted odds ratio, 1.29; p<0.001). The sensitivity, specificity, accuracy, 
and positive predictive and negative predictive values of each strong predictor 
for the diagnosis of gastroduodenal perforation were higher than those of 
specific air distributions. The focal wall thickening (accuracy, 95.7%) was the 
most useful parameter for the diagnosis of gastroduodenal perforation.
CONCLUSION: The prediction of the perforation site of the GI tract on CT should 
be based on the presence of strong predictors of the site of bowel perforation, 
and the specific free air distribution should be regarded as complementary 
predictors.