Perforation of a sigmoid diverticulum with collection of extraluminal stool at the site of perforation. Small amount of stool mixed with ascites in the pelvis. Small bowel is thickened with mucosal and serosal hyperenhancement sandwiching submucosal edema, with some loops showing more diffuse hyperenhancement. This is due to peritonitis from perforation. 

The key to identifying the perforation in this case is noticing where the majority of the free air and extraluminal stool is - in the pelvis, and about the sigmoid colon.