What finding is typically observed on plain abdominal films for diverticulitis?

In the context of diverticulitis, the finding typically observed on plain abdominal films is free air, which indicates the presence of pneumoperitoneum. This occurs when there is a perforation or rupture of the diverticulum that allows air to escape into the peritoneal cavity. In cases of diverticulitis, especially if the condition has progressed to complications such as perforation, the identification of free air on imaging is a key indicator of a potentially serious situation requiring urgent intervention.

While mass lesions and localized bowel obstruction can be seen in diverticulitis, they are not as definitive or characteristic as free air. Mass lesions could represent inflammatory changes or complications but do not specifically point to diverticulitis. Localized bowel obstruction may occur due to inflammation and edema from diverticulitis; however, it typically does not provide the immediate indication of perforation that free air does. Adhesions can develop as a consequence of prior abdominal surgeries or intra-abdominal inflammation, but straightforward diverticulitis does not typically present with this finding on a plain abdominal film. Therefore, the presence of free air is critical in assessing the severity of diverticulitis and determining the appropriate clinical management.