This is pneumatosis intestinalis involving the colon. Note the subserosal gas bubbles grossly and the submucosal air-filled spaces microscopically. These air spaces appear as small dark holes on the abdominal CT scan. Pneumatosis is an uncommon and obscure condition that arises with inflammation and ulceration of gastrointestinal mucosa allowing escape of air into the bowel wall. Infections, ischemia, and ulcerative disorders can precede the appearance of pneumatosis. The gas bubbles may rupture, as in this case, to produce pneumoperitoneum, seen on the CT scan as the large dark area. If the underlying cause for the problem is not severe, the gas is eventually resorbed.