Diseases of the peritoneum are common, and given the considerable overlap in their imaging appearances and the resultant potential for misinterpretation, they can present a diagnostic challenge. Computed tomography and magnetic resonance imaging substantially aid in the identification of peritoneal disease. However, radiologists must be familiar with the anatomy of the peritoneal spaces and ligaments to provide an accurate interpretation of the findings.
Intraabdominal structures may be categorized according to their location with regard to the peritoneum: those surrounded by the peritoneal membrane are described as intraperitoneal, whereas those that are outside the membrane are described as extraperitoneal. Parietal peritoneum reflected over the abdominal organs forms supporting ligaments, mesenteries, and omenta. The peritoneal reflections carry vessels, nerves, and lymphatics from the extraperitoneal space to the intraperitoneal organs, providing natural connections between the extraperitoneal space and the peritoneal cavity and, thus, pathways for the dissemination of intraabdominal disease.
The dissemination of a primary peritoneal malignancy (eg, peritoneal mesothelioma, serous papillary peritoneal adenocarcinoma, and peritoneal carcinoma with a polyclonal multifocal origin) or secondary disease (eg, disseminated colon cancer and pseudomyxoma peritonei) may result in a condition known as peritoneal carcinomatosis. The imaging manifestations of this condition may resemble those seen in the presence of benign conditions such as peritoneal thickening due to active Crohn disease, diverticulitis, appendagitis, omental infarction, and severe pancreatitis, making differential diagnosis difficult. Accurate differentiation between these benign and malignant conditions is of crucial importance for selecting the most appropriate method of treatment. In the presence of peritoneal carcinomatosis, the radiologist’s precise localization and accurate description of all affected sites provide important guidance to oncologists and surgeons and may lead to a better prognosis. Sites where disease implants may be overlooked at staging laparotomy and where surgical access is difficult must be carefully evaluated by the radiologist to avoid incomplete resection; such sites include the subphrenic space and hepatic dome, mesentery root, serosal surface of the intestine, porta hepatis, intersegmental fissure, gastrohepatic ligament, and gastrosplenic ligament.