Computed tomographic analysis of colonic perforation: 'Dirty mass,' a new computed tomographic finding

The purpose of this study was to determine the potential of computed tomography (CT) for the diagnosis of colonic perforation. Abdominal CT and plain radiographic images in 29 cases of surgically proved colonic perforation were reviewed retrospectively. Three radiologists evaluated the presence of free air, the site of free air on CT, the finding of the focal collection of extraluminal fecal matter ('dirty mass'), and other CT findings. Plain radiographs depicted free air in 13 cases (44.8%); CT demonstrated free air in all cases except one (96.6%). The locations of free air on CT were as follows: peritoneal space only in 23 cases, pararenal space only in 2, both in 3, and no free air in 1. In 5 cases, pneumoperitoneum was demonstrated only in the lower abdomen. The finding of dirty mass was seen in 15 cases (51.7%). CT is particularly valuable for the diagnosis of colonic perforation.