The peritoneal cavity is lined by mesothelium that splits the cavity into parietal and visceral compartments. Box 64.1 lists peritoneal ligaments and mesenteries and Box 64.2 the retroperitoneal structures.

Diseases of the peritoneum include peritonitis, pseudomyxoma peritonei, and tuberculous peritonitis. Peritonitis, an inflammation of the peritoneal linings, requires surgical intervention. The abdomen can remain open if safe closure is not possible or for a planned reoperation, using a Bogata bag as illustrated in Figure 64.1. Peritonitis can develop secondary to a gossypiboma (such as a mass of cotton or a sponge left behind during surgery) or retained foreign object (RFO). Derived from the Latin gossypium for “cotton” and “oma” meaning tumor, gossypiboma develop if surgical materials remain in the abdomen postoperatively (Figures 64.2 and 64.3). Tuberculous peritonitis results from spread of infection from a primary focus, usually the lung, and occurs in approximately 1% of patients. A computed tomography (CT) scan may identify thickened bowel and ascites (Figure 64.4).

Peritoneal carcinomatosis (PC) is a metastatic manifestation of gastrointestinal and pelvic carcinomas. Figure 64.5 demonstrates PC secondary to metastatic ovarian cancer. Features include ascites, peritoneal studding, and bowel obstruction (Figure 64.5).

Primary peritoneal cancer (PPC) is a rare tumor of the peritoneal lining. PPC has diffuse involvement of the peritoneum by papillary carcinoma without a primary site and grossly normal ovaries. Figure 64.6 demonstrates calcifications throughout the omentum and peritoneal lining.

Pseudomyxoma peritonei is another rare condition that involves the peritoneal cavity and omentum. Characteristic CT findings include scalloping of the hepatic and intestinal margins caused by extrinsic compression of ascitic spaces containing gelatinous material (Figure 64.7). Given the inherent metastatic nature of the underlying primary cancer, the response to routine therapies (chemotherapy and/or radiation) is generally poor, with a median survival without treatment in the region of 5–8 months (in the case of colon cancer). Therefore, alternate treatments have been suggested, such as cytoreductive surgery (CRS) (including peritonectomy) combined with hyperthermic intraperitoneal chemotherapy (HIPEC). CRS‐HIPEC may be indicated for peritoneal metastases secondary to appendiceal, colorectal, ovarian, and, in rare instances, gastric cancers. Eligible patients who have limited peritoneal disease should be considered for this treatment strategy. Box 64.3 shows a peritoneal cancer index scoring to determine eligibility for HIPEC. For example, in colorectal carcinomatosis, a PCI of 10 or less was associated with a 50% 5‐year survival while a PCI of 11–20 was associated with a 20% 5‐year survival, and an index greater than 20 was associated with a 0% 5‐year survival.

The retroperitoneum is the space behind the abdominal cavity that extends from the diaphragm to the levator muscles of the pelvis. Retroperitoneal diseases include retroperitoneal hemorrhage, inflammation, fibrosis, and neoplasia. Rupture of an abdominal aortic aneurysm results in retroperitoneal hemorrhage and hypovolemic shock (Figure 64.8). Retroperitoneal infections are caused by diseases surrounding abdominal organs, urinary tract, or vertebral column. Figure 64.9 demonstrates a retroperitoneal abscess with gas and enhancing margins due to Crohn’s disease. Retroperitoneal fibrosis is an uncommon disease characterized by progressive nonspecific fibrosis of connective and adipose tissue in the retroperitoneal space (Figure 64.10). Retroperitoneal tumors arise from mesodermal, neuroectodermal, or embryonic remnants (Figure 64.11). Enlarged tumors cause hollow viscus obstruction by invasion and mass effect (Figure 64.12). Magnetic resonance imaging (MRI) has become an important diagnostic tool in the diagnosis and management of retroperitoneal neoplasms. It allows better definition between the mass and surrounding muscle groups and vascular structures compared to CT scanning (Figure 64.13).

The mesentery or omentum may become involved in a variety of disease processes, most of which originate in adjacent visceral organs. These include inflammatory and vascular processes, mesenteric/omental cysts, and tumors (benign, malignant, and metastatic) (Box 64.4). Fibromatous proliferation of the mesentery, or mesenteric desmoid, is a rare, noninflammatory condition. The majority of these cases are associated with Gardner syndrome, a form of familial adenomatous polyposis (FAP). These mesenteric lesions generally do not metastasize, but infiltrate surrounding structures and tend to recur locally when excised (Figure 64.14). The mesentery is sometimes the first site to manifest clinical symptoms related to systemic inflammatory diseases. Mesenteric amyloidosis is a very rare condition with symptoms that include abdominal pain and distension (Figure 64.15). An omental infarction results from vascular compromise of the greater omentum. Patients present with sudden onset of abdominal pain, absence of fever, and gastrointestinal symptoms. Healthy patients, such as marathoners, often present with this condition because of reduced omental blood flow. This condition has a nonspecific clinical presentation, and is managed nonoperatively (Figure 64.16).