PURPOSE: To evaluate the usefulness of the periportal free air (PPFA) sign on 
computed tomography (CT) to distinguish upper from lower gastrointestinal (GI) 
tract perforation.
MATERIALS AND METHODS: During a 30-month period, we retrospectively analyzed 
abdominal CT images of 53 consecutive patients with surgically proven GI tract 
perforation. We divided the patients into two groups, i.e. upper and lower GI 
tract perforation groups. According to the distribution of free air, we divided 
the peritoneal cavity into supramesocolic compartment and inframesocolic 
compartment. We observed the presence or absence of free air in each compartment 
in each group. When there was free air in the periportal area, it was defined as 
periportal free air (PPFA) and the sign was positive. To evaluate the usefulness 
of the PPFA sign, we compared the PPFA sign with the falciform ligament sign and 
the ligamentum teres sign, both of which are well-known CT signs of 
pneumoperitoneum. Statistical analyses were performed with univariate and 
multivariate analyses using SPSS version 11.5 for significant findings among the 
CT signs.
RESULTS: Free air was seen in supramesocolic compartment in 29 of 30 (97%) 
patients in the upper GI perforation group and in 17 of 23 (74%) in the lower GI 
perforation group. Free air in inframesocolic compartment did not show 
significant difference in either group (p=.16). The PPFA sign was seen in 28 of 
30 (93%) patients with upper GI tract perforation, but in only 8 of 23 (35%) 
patients with lower GI tract perforation (p<.0001). The falciform ligament sign 
was seen in 24 of 30 (80%) patients with upper GI tract perforation and in 10 of 
23 (43%) patients with lower GI tract perforation (p=.020). The ligamentum teres 
sign was seen in 16 of 30 (53%) patients with upper GI tract perforation and in 
2 of 23 (8%) patients with lower GI tract perforation (p=.008). Multivariate 
logistic regression analysis showed that the PPFA sign was the only variable, 
which adjusted odds ratio of 15.5 (p=.002).
CONCLUSION: The PPFA sign is a useful finding which can help to distinguish 
upper from lower GI tract perforation. When this sign is present, upper GI tract 
perforation is strongly suggested.