Peritoneal metastasis is a known complication of advanced gastrointestinal, primary peritoneal (mesotheliomas), and genitourinary malignancies and brings a very poor prognosis. The clinical presentation is initially asymptomatic, but at some point, complaints of abdominal pain, weight loss, and ascites appear. The diagnosis is made through the use of imaging studies, such as computed tomography (CT), magnetic resonance imaging (MRI), and positron-emission tomography (PET).
Metastatic spread of malignant tumors into the peritoneum, a two-layered (parietal and visceral) mesothelial lining, is almost universally fatal within a short period of time, as only palliative therapeutic measures may be implemented at this stage of progression     . Neoplasms of the gastrointestinal system (particularly colorectal cancer) and the genitourinary tract, as well as hepatic, pancreatic, and primary peritoneal tumors (mesothelioma), are known for their propensity to metastasize into this anatomical landmark, and they are able to do so in several ways    . Proximal masses (eg. gastrointestinal or ovarian cancers) are able to directly penetrate into the peritoneum, whereas spread via the lymphatic or hematogenous routes (typical for more distant primary malignancies, such as melanoma, lung cancer, or breast cancer), as well as intraperitoneal dissemination of the tumor through ascitic fluid (a potential complication during surgical procedures), are other possible routes   . The clinical presentation of peritoneal metastasis is quite variable, and often depends on the location and the severity of tumor invasion, but in most cases, the initial course is asymptomatic . The majority of patients, however, develop symptoms of abdominal pain, distension, and discomfort (developing as a result of bowel obstruction), followed by weight loss, nausea, vomiting, and severe fatigue with cachexia   .
The clinical manifestation of peritoneal metastasis is nonspecific, but the observation of a newly formed ascites must raise suspicion toward a malignant etiology . For this reason, the physician must obtain a detailed patient history that will assess the duration of symptoms, their onset, as well as progression, whereas anamnestic data of malignant diseases is crucial for making a presumptive diagnosis. In fact, up to 50% of gastric cancers and 10-35% of colorectal cancers recur as peritoneal metastasis . After a thorough physical examination, imaging studies need to be employed. Abdominal ultrasonography, a common first-line procedure, provides little benefit when it comes to visualizing the metastatic deposits, but its use as a guide to obtain a viable sample of the ascitic fluid or of superficial tumors for histopathological testing is invaluable . Instead, more advanced methods - computed tomography and magnetic resonance imaging are the cornerstones for identifying peritoneal metastasis and tumor spread    . Typical findings range from multifocal nodules to aggressive infiltrating masses, whereas stellate lesions and calcifications might also be encountered  . MRI is particularly effective if used with gadolinium as a contrast, and images should be obtained 5-10 minutes after the agent is administered . The diagnosis can be further solidified through the use of fluorodeoxyglucose (FDG)-PET .