Small bowel perforation resulting from blunt abdominal trauma: interval change of radiological characteristics

We analyzed radiography and computed tomography (CT) findings of small bowel perforation due to blunt trauma to identify the keys to diagnosis. Twelve patients with surgically proven small bowel perforation were retrospectively studied. All patients underwent radiography and CT, and five underwent presurgical follow-up CT. Radiological findings were evaluated and correlated to the elapsed time from the onset of the trauma retrospectively. Radiography demonstrated free air in only 8% (1/12) and 25% (3/12) at the initial and follow-up examinations, respectively. In contrast, the initial and follow-up CT scans detected extraluminal air in 58% (7/12) and 92% (11/12), respectively. Mesenteric fat obliteration was seen in 58% (7/12) and 75% (9/12) at initial and follow-up CT, respectively. The incidence of both extraluminal air and mesenteric fat obliteration on CT increased as time elapsed, particularly after 8 h. High-density ascites was seen in 75% at initial CT, including two patients without extraluminal air, but was observed in all but one patient at follow-up CT. The chance of detecting extraluminal air increases as time elapses. High-density ascites may be seen without extraluminal air and might be an indirect or precedent sign of small bowel perforation. Radiologists need to be familiar with these radiological features.